tC!<;/oJ~'l,.. Extension Folder 191 Revised February 1956

CULTURAL AND CHEMICAL Weed Control IN MINNESOTA

1956

R. S. Dunham R. E. Nylund H. L. Hansen E. H. Jensen

The recommendations and discussions in this folder are based on the Recommendations ol the Research Committee ol the North Central Weed Control Conference for 1956. This com­ mittee is comprised of representatives of state universities throughout the area. Since the effectiveness of herbicides de­ pends on factors that vary from region to region, the recom­ mendations have been modified where necessary to make them fit Minnesota conditions. The use of chemicals suggested in this report is contingent upon registration by the United States Department of Agriculture and/ or establishment of residue tolerances, where necessary, by the United States Department of Health, Education, and Welfare. Chemicals should be used only as recommended on the label. Persons recommending uses beyond those on the lobel may be held liable.

,I UNIVERSITY OS: MINNESOTA A-{JA.icultUJLa.L Gx.te;suicn... t:Se11.oice... U. S. 0 E PA RT M ENT O S: A G R I C U L T U R E CONTENTS

Page Weed control in field crops 3 Corn 3 F~ 4 Forages-Alfalfa and clovers 5 Forages-Pastures and meadows 6 Peos 7 Small grains-Spring wheat, oats, barley . 7 Small grains-Winter wheat 8 Soybeans 8 Control of individual weeds 9 Canada thistle and Perennial sow thistle 9 Cockle burs 10 Field bindweed 10 Foxtails 11 Hoary cresses 12 leafy spurge 11 Perennial peppergrass 12 Perennial sow thistle 9 Quackgrass 13 Wild oats ...... 14 Weeds in horticultural crops 1 S Vegetable crops ...... 15 Fruits and ornamentals 18 Seedbeds and transplant beds 20 Established nursery stock 20 Turf 21 Undesirable woody plants 21 Common methods of treatment 22 Woody weeds in pastures 23 Woody weeds on roadsides, utility lines, and other rights-of-way 24 Woody weeds in forests, forest plantations, and farm woodlands 24 Poisonous and disease-carrying woody weeds 25 Soil sterilants 26 Farm sprayer calibration and adjustment . 28 Summary of recommendations for application of chemi- ~~ ~ Recommendations for spraying field crops 29 Recommendations for killing specific weeds 30 Spraying recommendations for specific areas .. 31 Recommendations for spraying horticultural crops.. 32 Description of herbicides 36

MEMBERS OF STAFF IN WEED CONTROL Agricultural Engineering-L. A. Liljedahl, USDA. Agricultural Extension-E. H. Jensen, extension agronomist· O. C. Turnquist, extension horticulturist; D. W. Bates, ex: tension engineer. Agronomy-R. S. Dunham, research; R. G. Robinson, research. Forestry-Henry Hansen, research. Horticulture-R. E. Nylund, research. Plant Pathology and Agricultural Botany-Thor Kommedahl, research. Cultural and Chemical Weed Control

WEED CONTROL IN FIELD CROPS Corn

WEED CONTROL in corn is based primarily on cultural practices which include seedbed preparation, establishment of an adequate stand, and timely and effective cultivations. The use of shallow cultivation implements, such as the rotary hoe, is highly recom­ mended for early cultivation. Postemergence treatment-Spray with 2, 4-D, amine, to give complete and early control of annual weeds. Use rates of¼ to ½ pound per acre. Use the ¼-pound rate whenever there is danger of injury or to control susceptible weeds, and the ½-pound rate for moder­ ately resistant kinds. One pound may be necessary for resistant weeds, but the corn will probably be injured. If spraying must be done when the corn is large enough to put the spray under the top leaves by means of drop nozzles, the chemical must strike the tops of the weeds to be most effective. When two nozzles are directed on one row, use a spray solution equivalent to no more than ¼ pound per acre. Some injury may result if the corn is sprayed with 2,4-D during the period from emergence to tasseling. Brittleness followed by bending or breaking of stalks is the most serious type of injury, and it may result in severe stand losses when followed by a storm or careless cultivation. Several factors influence the degree of injury re­ sulting from 2,4-D treatments. Corn growing rapidly is more susceptible than corn developing under less favorable growth conditions. At the rates of applica­ tion commonly used it is probable that the stage of growth at which treatment is made during the period from emergence to tasseling is less important than the effects of environmental factors. But during the period from two weeks before silking until the silks are dry, severe reduction in seed set may result from 2,4-D treatments regardless of growing conditions. Hybrids and varieties vary in their susceptibility to 2,4-D, but differences are not important at rates below ½ pound per acre. Inbred lines vary more widely and single-cross seed fields should not be sprayed except in an emergency or on inbreds of proved tolerance, and then at minimum rates. MCP has not proved less injurious to corn than 2,4-D. Stalk breakage increases with larger rates and with later applications. Where annual grasses are a problem, selective sprays of the DN type, such as Premerge and Sinox PE, have shown promise the past two seasons. Apply

3 4 pounds per acre in 20 to 40 gallons of water per acre. Treat while corn is in the coleoptile or spike stage. Later applications burn some corn leaves, but the injury does not always reduce yields. Later ap­ plications may not be as effective on the weeds. These low rates of application give no residual effect and can only be expected to kill the seedling grasses present at the time of spraying. The treatment substi­ tutes for the first cultivation and keeps the rows clean. Lay-by applications of 2 pounds per acre of amino triazole or 4 pounds per acre of Premerge or Sinox PE have shown promise this past season. Band applica­ tions are recommended to reduce cost. The chemicals should be applied with drop nozzles in order to wet not more than the lower 6 inches of stalk. Pre-emergence treatment-This treatment is not recommended. Flax Cultural pracl:ices-Weeds are generally more of a problem in flax than in small grain; therefore, grow­ ers should sow flax on relatively clean land. Practice early after-harvest tillage of small grain stubble to control perennial weeds, prevent weed seed produc­ tion, and stimulate annual weed seed germination in late summer and fall to prepare land for flax, except where after-harvest tillage results in serious wind erosion. Another desirable weed control practice is to pre­ vent weed seed production in the preceding corn, soybean, or other cultivated crop and prepare the seedbed for flax by shallow tillage. Delayed sowing of flax to permit spring tillage for wild oat control has been successful in some areas, although the delay is sometimes detrimental to the flax. For delayed sowing, use early-maturing varieties such as Marine. Herbicides-Flax should be sprayed with MCP or 2,4-D as soon as there is sufficient emergence of sus­ ceptible weeds to make spraying practical. Spraying may reduce yields of seed and straw unless weed competition is reduced sufficiently to offset injury from spraying. MCP is less likely to injure flax than 2,4-D. Use 2 to 3 ounces per acre of MCP or 2,4-D in sodium or amine formulations for susceptible weeds like wild mustard. Use 4 ounces for lambsquarters, red-root pigweed, stinkweed, cocklebur, marsh elder, and rag­ weed. Good kills of moderately resistant weeds seldom result but growth can be checked and seed produc­ tion largely prevented by using higher rates. Use 4 to 5 ounces for wild buckwheat or smartweed. Use MCP at 5 to 6 ounces per acre to prevent seed pro­ duction by Canada thistle and perennial sow thistle.

4 Use 2,4-D, ester, at 4 to 5 ounces per acre or MCP, ester, at 5 to 6 ounces to control Russian pigweed and Russian thistle--but expect damage to flax. Do not spray flax during the period between bud stage and when 90 per cent of the bolls have formed. Germination of the seed may be reduced by spray­ ing between full bloom and the stage when seeds are colored. Weeds controlled more easily by MCP than 2,4-D and vice versa are listed under SMALL GRAINS, page 8. TCA at 5 pounds per acre will kill green foxtail, yellow foxtail, giant foxtail, and barnyard grass in young flax. For best results the flax should be at least 2 inches tall and the weeds less than 3 inches. TCA can be applied in mixture with MCP or 2,4-D to kill susceptible grass weeds and susceptible non­ grass weeds with one application-but spraying must be done before early bud. When flax is used as a companion crop with alfalfa, red clover, alsike clover, ladino clover, timothy, meadow fescue, bromegrass, or crested wheat grass, broad-leaved weeds can be controlled with 2,4-D or MCP at 3 or 4 ounces per acre. However, MCP is preferred for the flax. The seedlings of alfalfa or clover should be at least 2 inches tall when sprayed. Sweetclover seedlings are likely to be killed by either MCP or 2,4-D. TCA can be used on flax sown with alfalfa or sweetclover. However, it will probably kill red clover, alsike clover, timothy, meadow fescue, or bromegrass.

Forages-Alfalfa and Clovers Seedling legumes generally are poor competitors with weeds. Management practices in preceding crops such as use of intertilled crops and after-harvest till­ age to make the land as weed-free as possible for the legume seedlings are desirable. Clipping of seedling legumes (except sweetclover) when sown alone, mowing the stubble of companion crops, and patch mowing of perennials help to con­ trol weeds. A void the use of herbicides on seedling legumes unless the crop is seriously threatened by weeds. When weeds are a problem, spray seedling stands of ladino clover, alsike clover, red clover, and alfalfa with the sodium or amine salts of 2,4-D or MCP at rates of ¼ pound per acre or less. Sweetclover usually will not tolerate either 2,4-D or MCP. A complete canopy of companion crop or weeds will reduce the injury to the legumes. Use TCA at 5 to 7 pounds per acre to control an­ nual grasses in seedling stands of alfalfa, sweet­ clover, and birdsfoot trefoil, but it should not be used

5 when wheat, oats, or barley is the companion crop. TCA cannot be used on alsike and red clover, and to be effective grasses must be less than 3-4 inches tall. Dalapon also may be used to control annual grasses in seedling stands of alfalfa and birdsfoot trefoil, if the forage is not harvested the year of treatment. Apply 2 pounds per acre soon after emergence of the grasses. It may be used later in the season also. It cannot be used when the companion crop is wheat, oats, barley, or flax. In established legumes the use of 2,4-D or MCP is often hazardous. Either herbicide should be applied in the dormant stage of the legume-in late fall after killing frosts, or in very early spring. Serious yield losses and often stand losses may result from spray­ ing after growth has started. Treat established stands of alfalfa, sweetclover, and birdsfoot trefoil with TCA at 5 to 7 pounds per acre for control of many annual grasses (not wild oats) without permanent injury to the legumes. Do not treat ladino clover, alsike, and red clover with TCA. In legumes grown for seed the weed problem is dif­ ferent than where legumes are grown for forage since seed production of weeds cannot be controlled by grazing or mowing. Furthermore, the generally effec­ tive method of frequent mowing to control perennial weeds cannot be used in seed fields. Quackgrass has not been controlled satisfactorily by spraying an established alfalfa crop, but infested land can be cleaned in the fall with TCA or Dalapon. Use 22 pounds of TCA per acre on plowed ground. Use 12 to 15 pounds of Dalapon applied to the foliage. The following year alfalfa may be sown either alone or with a companion crop of flax or oats. It is not safe to sow red or alsike clover. Some damage to seed production has resulted from application of 4 ounces per acre of 2,4-D or MCP on alfalfa, red clover, and alsike clover in one year of trial. Red clover was the most sensitive. Yields on MCP-treated plots were three times those on 2,4-D­ treated plots. The untreated clover yielded about twice that of MCP-treated.

Forages-Pastures and Meadows Good management and controlled grazing are most important in any attempt at control in pasture land. In very weedy pastures where good perennial grasses are thin, reseeding may be the most important practice. To be successful, prepare a good, firm seed­ bed for any reseeding and add fertilizer if needed. Protect new seedlings from grazing until they are established and graze moderately thereafter. Plowing (or intensive surface tillage) and seeding to adapted

6 grasses, where practicable, will usually eliminate many of the perennial pasture weeds. Spraying with 2,4-D, 2,4,5-T, or a mixture of the two gives better control of more kinds of weeds by a single application than is obtained by a single mow­ ing treatment. Spray when the weeds are growing actively. Repeated treatment for two or more years is usually necessary. In general, these chemicals may be used at rates necessary for weed or brush control without appreciable injury to the grasses. While they may eliminate some legumes, other native and intro­ duced legumes have a relatively high tolerance to some of the growth regulators. Seedlings of perennial grasses may be treated with 2,4-D if broad-leaved weeds are a problem. Use up to ¾ pound per acre after the grass seedlings have reached the two- to four-leaf stage. Mowing is the recommended practice for controll­ ing many kinds of weeds if done at the right time and if repeated for two, three, or four years. In general, mow herbaceous weeds in the early bud to blossom stage. Brush control. (See page 23, WOODY WEEDS IN PASTURES.) Peas Weed control in canning peas is usually accom­ plished by thorough seedbed preparation prior to sowing, but annual broad-leaved weeds can be con­ trolled when in the two- to four-leaf stage by apply­ ing from ¾ to 1 pound per acre of DNBP as an amine salt in approximately 40 gallons of water. Broad-leaved annual weeds can also be controlled by applying 4 ounces per acre of MCP amine or sodi­ um salt to peas when they are 3 to 7 inches in height. Flower bud development of Canada thistle can be controlled by spraying with 4 to 6 ounces per acre of MCP. Use at least 15 gallons of spray per acre to avoid crop injury.

Small Grains-Spring Wheat, Oats, Barley Wheat and barley are less sensitive then oats to 2,4-D applications made during the growing season. Wheat is less sensitive than barley. All three crops are sensitive as seedlings-from emergence to the two-leaf stage. Wheat and barley are relatively toler­ ant from the time five full leaves appear until the early-boot stage. During this period ¼ to ½ pound of 2,4-D ester or ½ to % pound of 2,4-D amine can usually be used to control broad-leaved weeds with­ out injury to the crops.

7 Avoid spraying wheat and barley in the boot or shot-blade stage of development. Varietal differences in wheat have been unimportant and in barley have been small. Some injury to oats should be expected from spray­ ing any time from seedling to early-boot stages of growth, with the time of jointing apparently the most sensitive. However, weed control generally will more than offset losses resulting from 2,4-D injury. Oats are more tolerant of MCP than of 2,4-D, permitting the use of 1h pound per acre. At rates adequate for susceptible weeds like mus­ tard, the stage at application is not so important as it is when ½ pound and more of 2,4-D amine is used. Mindo and, to a lesser degree, Clinton and Andrew have been more susceptible to 2,4-D than Bonda, Ajax, and Branch. In general during seasons when growing conditions are poor due to drouth or cold weather, use the upper limits of the range of rates given. Likewise, when the growth rate of weeds and crops is rapid the lower rates can be used. Weeds more easily controlled by MCP than 2,4-D are hemp nettle, horse tail, buttercup, Tartary buck­ wheat, corn spurry, corn cockle, and perennial pepper­ grass. Those more easily controlled by 2,4-D than MCP are Russian thistle, false flax, wild buckwheat, velvet weed, Jimson weed, smartweed, redroot pig­ weed, ball mustard, tansy mustard, and wild hemp.

Small Grains-Winter Wheat Many annual broad-leaved weeds can be controlled in winter wheat by spraying with 2,4-D. Apply the ester at ¼ to ½ pound per acre or the amine at ½ to ¾ pound per acre in the spring after the wheat is fully tillered but before it is in the boot. Winter wheat should not be sprayed in the fall. Preharvest treatment applied when the wheat is in the milk to hard-dough stage should be considered an emergency measure and used only when weeds threaten to interfere seriously with harvesting. A rate of 1 pound per acre is usually required at this stage and may result in damage to the crop. Weed control is often unsatisfactory.

Soybeans Several cultural practices control annual weeds in soybeans. Early plowing and delayed sowing of the crop can kill many weeds. Postemergence cultivation with the rotary hoe is effective, if done when the weeds are small and soil conditions are favorable. The use of a companion crop of winter rye sown with soybeans drilled in 6-inch rows has a place--

8 where danger of erosion makes sowing the crop in rows to be cultivated undesirable, or where the land for other reasons cannot be cultivated. One bushel per acre is sown, either with the soybeans or immedi­ ately afterward. The rosette type of growth early in the season affords competition for the weeds. By August 1, the companion crop is dead and the beans largely recover from the early competition. Weed control in soybeans by either pre-emergence or postemergence applications of herbicides has not been dependable. The only postemergence spray rec­ ommended for soybeans is 2,4-D for cockleburs or mustard (see page 10).

CONTROL OF INDIVIDUAL WEEDS Canada Thistle and Perennial Sow Thistle

CANADA THISTLE and Perennial Sow Thistle can be controlled by cultural practices, chemical methods, and combinations of the two. Recommended cultural practices are: 1. Plow deep immediately before freeze-up. 2. Plow 4-6 inches deep in the fall or use a one-way disk. About two weeks after the thistles come up, cul­ tivate with a field cultivator equipped with wide over­ lapping duckfoot sweeps operated at a 4-inch depth. Several alternatives can be used following this treatment: a. Cultivate every three or four weeks until freeze­ up. b. Cultivate every three or four weeks until July 1 and sow sorgo, Sudangrass, or proso millet. Cut sorgo and Sudangrass for forage and millet for seed. Cultivate till freeze-up. The second year, repeat the treatment or sow oats and spray with 2,4-D amine at 8 ounces per acre when the thistles have sent up a flower stem. Spray again after harvest with 1 pound per acre of 2,4-D. c. Cultivate every three or four weeks until Sep­ tember and sow winter rye or winter wheat. Cultivate after harvest until freeze-up. 3. Sow alfalfa or an alfalfa-grass mixture on well drained soils or reed canary grass on wet soils and cut for hay over several years. Best results will fol­ low if the land is intensively cultivated the preceding season. Usually two or more applications of 2,4-D each year over a period of two or more years are necessary to eradicate these weeds. For the first application each year spray the thistles in a tolerant crop using the amount of chemical recommended for the crop and

9 spraying when the thistles are in early bud. In some seasons it may be necessary to spray earlier to avoid a sensitive stage of the crop. (See page 8.) After har­ vest is completed cultivate the land intensively until freeze-up. Or plow immediately and spray the thistles with 1 pound per acre when they are in the rosette stage. Sow thistle is somewhat easier to kill with 2,4-D or MCP than Canada thistle. For small patches of either thistle use soil sterilants (see page 26). Cockleburs Cockleburs are annual plants and can be controlled by preventing seed production. The bur contains two seeds, one of which germinates the year it is pro­ duced. The other germinates the next year or later. In the early stages cockleburs are very susceptible to 2,4-D or MCP. In the seedling stage, they can be killed with 2 ounces of the amine salt. This makes possible the spraying of soybeans. For least injury to the beans, spray when the plants are 3 to 5 inches tall. Up to about 6 inches tall, the cockleburs can be killed with 4 to 6 ounces per acre. Later they are stunted but seldom killed with 8 ounces. If cockleburs are in flax, spray when they are less than 6 inches tall with 4 ounces of MCP amine or sodium salt. If in small grain or corn, 8 ounces of 2,4-D amine can be used. (See pages 3, 7, and 8.)

Field Bindweed Field bindweed can be controlled by cultural meth­ ods. They are the same as described for Canada Thistle, page 9. Grazing is also effective in controlling field bind­ weed. Sow winter rye in the fall; pasture with sheep the next spring until the crop begins to head. Turn the sheep on supplementary pasture, plow under the rye, and sow Sudangrass. Pasture the Sudangrass, plow, and sow winter rye. The next year, pasture or harvest the rye and cultivate until freeze-up. Applications of ½ to 1 pound of 2,4-D per acre in bud to bloom stage or in late fall are effective. Use ½ pound when spraying in a crop. On noncrop land, cultivate in the spring and spray the plants with 1 pound per acre when they are in the bud to bloom stage. In small areas and where the effect on the soil is not objectionable, apply 5-6 pounds per square rod of dry sodium chlorate and follow a year later with spot treatment of any remaining plants. CMU and boron compounds are also suitable. Use 80 pounds of CMU in a large volume of water per acre or 15 pounds of concentrated Borascu, 10 to 15

10 pounds of Polybor, or 8 to 10 pounds of Polybor chlorate per square rod. Any surviving plants should be treated again, beginning the second spring after the original treatment.

Foxtails There are three common kinds of foxtail in Minne­ sota-the yellow, the green (usually called pigeon grass), and the giant. The giant species frequently grows 6 feet or more tall with a dense growth that can smother a crop. It can be distinguished from the other two foxtails by its leaves. The giant foxtail leaf is covered with short hairs on the upper surface, the green foxtail leaves are hairless, and the yellow has long hairs on the upper surface near the leaf base. All three species can be controlled by use of one of the following practices: (1) Sow flax and spray with TCA at the rate of 5 pounds per acre when the weeds are less than 3 to 4 inches tall. Alfalfa may be established when this practice is used. (2) Plant corn and treat with DN-type sprays such as Premerge or Sinox PE while the corn is in the coleoptile or spike stage. An application of 4 pounds per acre in 20 to 40 gallons of water is suggested. (3) Checkrow corn, cultivate both ways, and apply 2 pounds per acre of amino triazole at layby. To pre­ vent injury to the corn, take care not to wet more than the 6 lower inches of the stalk. (4) Fallow after harvest of winter grains, early­ maturing oats, or peas. (5) Sow alfalfa with an early-maturing small grain and apply TCA at the rate of 5 pounds per acre after harvest. The herbicide will reduce the competition from the older foxtail and kill seedlings. This treat­ ment is practical when there is a heavy stand of an­ nual grassy weeds in alfalfa. Do not use it if alsike and red clover or grasses are included in the mixture. The action of TCA is slow. Weed plants may show little effect for two weeks; it may be longer before they die. Leafy Spurge For extensive infestations on arable land, intensive cultivation alternated with cropping will in time bring even the most persistent stands under control. Plow in the fall 4 to 6 inches deep; cultivate at two- to three-week intervals until freeze-up. In the spring start cultivations two weeks after spurge comes up and continue at two- to three-week intervals: 1. Until freeze-up.

11 2. Until winter rye or winter wheat is sown. Culti­ vate after harvest until time for sowing another crop of rye or wheat. Several years of this cropping and tillage are required to give complete elimination. 3. Until July 1. Sow Sudangrass and harvest for hay. Cultivate until freeze-up. Use a field cultivator with wide overlapping duckfoot sweeps. Grazing is an effective method of controlling leafy spurge. Sow winter rye at 2 bushels per acre in the fall and pasture in the spring with sheep until the crop begins to head. Turn the sheep on supplementary pasture, plow under the rye, and sow Sudangrass. Pasture the Sudangrass, plow, and sow winter rye. The next year pasture or harvest the rye and culti­ vate until freeze-up. Leafy spurge on untillable land can be controlled by grazing with sheep. Pasture early in the spring and continue all season. If sheep do not keep the vegetation down, cattle may be used ahead of them. Leafy spurge may be controlled with 2,4-D in con­ junction with tillage. Cultivate immediately after harvest until freeze-up. Apply 1 pound per acre of 2,4-D ester after spurge comes up in the spring. Culti­ vate four times when regrowth appears. Or cultivate intensively one season, then sow wheat or barley the next spring. Spray with ½ pound per acre of 2,4-D ester and cultivate after harvest until freeze-up. Re­ peat this cropping for four or five years. On rough or stony pasture, apply 2 pounds per acre of 2,4-D ester at the bud stage and treat again in the fall. Next spring, apply nitrogen fertilizer and graze. Soil sterilants can be used to eliminate small patches. Use borax herbicides at 5 to 6 pounds per square rod of boron trioxide (B,0,) equivalent after July 1. Or use similar rates of sodium chlorate or am­ monium sulfamate (Ammate) or equivalent amounts of borate-chlorate mixtures applied in the early fall. A 5-to-1 borate-2,4-D mixture applied at the rate of 3 ½ to 4 pounds per square rod in the fall is also recommended. CMU is not effective.

Perennial Peppergrass and Hoary Cresses Where soil type and topography permit, duckfoot cultivations at two-week intervals will prevent seed production and reduce the stand. Sowing winter wheat or rye and cultivating after harvest will also give satisfactory reductions after two to three years. Where possible, a control program should make use of the combined beneficial effects of crop competition and intensive cultivation. To control the top growth of these weeds in grow­ ing crops, apply ½ to 1 pound of 2,4-D per acre when

12 the weeds are in bud. Retreatment of fall rosettes at 1 to 2 pounds will give substantial stand reductions. Such a combination of treatments should give almost complete elimination after two or three seasons. Use soil sterilants to eliminate small patches or scattered plants that remain after the treatments recommended above have been given. Use sodium chlorate at 4 to 6 pounds per square rod, concentrated Borascu or Polybor at 10 to 15 pounds, or Polybor chlorate at 6 to 8 pounds. Use CMU at 40 pounds per acre. A fall or early spring application of 2,4-D at 10 pounds per acre is also effective. Seedlings can be controlled by applying 2,4-D to the leaves, by cultiva­ tion, or by seeding bromegrass.

Quackgrass Cultivation is the cheapest method of eradicating quackgrass on large areas if soil erosion is not a problem. Two methods are used: (1) the reduction of food reserves in the rootstocks to the point where the plant can no longer remain alive or (2) the drying of rootstocks and top growth to the point where the plant dies. Occasionally the weed may be killed by exposing the rootstocks to freezing. Weather in the spring usually does not favor kill­ ing quackgrass by drying. Therefore, cultivate when­ ever there is a leaf growth of 2 to 3 inches in order to exhaust the food reserves. Continue cultivations as late as possible before sowing a crop. A sharp disk or a duckfoot cultivator is satisfactory. During the summer the most effective control re­ sults from drying the rootstocks and roots by bringing them to the surface. Best results come from working up old hay fields and pastures. Ordinarily there is no advantage from plowing be­ fore cultivating, but close grazing prior to cultivation makes control easier. If hay is harvested, cultivate immediately after the first crop has been removed. If the field cannot be cultivated during early fall, some benefit will result from late-fall tillage. In either method cultivations must be frequent and continued over a long enough period to free the soil of all living quack material. If the quack is in scat­ tered patches, use a disk so rootstocks will not be dragged to clean parts of the field. In wet years or on poorly drained soils, cultivation is not very effective. Quackgrass can also be controlled with chemicals. Apply TCA at the rate of 22 pounds per acre in Sep­ tember or October on land that has recently been plowed or thoroughly cultivated. If the land is cropped the next year, make a second application of 18 pounds per acre or cultivate after harvest to eradicate the quack. Under these conditions better results have been obtained following flax than 13 following corn. TCA on land that has been cropped does not give as good a kill as on old sod. Normal growth of crops sown or planted in the spring following application of 22 pounds of TCA in the fall can be expected from flax, potatoes, sugar beets, oats, corn, and strawberries. Where it has been dry following the application of TCA, however, it is advisable not to plant corn the following spring. Dalapon gives results similar to those obtained with TCA except that it is more effective when applied to a good growth of foliage. Fall treatment of 12-15 pounds per acre followed in a week or two by plow­ ing or other similar soil preparation will give good control of quackgrass the following year. Repeated treatments will be necessary for eradication. Crops tolerant of TCA and sown in the spring on fall-treated areas will usually not be affected. Dalapon may also be applied to foliage in the spring. Application of 4 pounds per acre when the grass is from 4 to 10 inches tall is most satisfactory. This should be followed in about 2 weeks by plowing or some other form of soil preparation. Some hazard to crops follows the spring application; they should not be planted until four weeks after application. Corn, wheat, soybeans, and other types of beans are especially sensitive to small quantities of Dalapon remaining in the soil. Effective control for the season can be obtained by early-spring foliage applications of 4 pounds per acre of MH or amino triazole, followed in four to eight days by plowing. Best results occur on fertile soils or following fertilization of quackgrass with nitrogen. These chemicals do not leave a toxic residue in the soils; crops may be sown a few days after application. On non-agricultural land, or to eradicate patches of quackgrass, use sodium chlorate at 2 to 4 pounds per square rod, preferably in the fall. Or apply CMU in early spring or late fall. The minimum amount of CMU for a satisfactory kill of quackgrass is 20 pounds per acre. If a higher rate is used, normal development of crop plants is prevented for at least two years.

Wild Oats There are two major reasons for the difficulty in controlling wild oats: (1) its habit of shattering its seed before most small grain crops are harvested, and (2) its delayed germination characteristic. Unless the crop in which wild oats occurs is cut for hay, enough seed is shattered to infest the soil for years. The ger­ mination of the seed and the length of time it can remain viable in the soil depend on several factors. Favorable temperature and moisture for germina­ tion are most common in fall and spring; very little seed germinates between June and September. Some

14 seeds require after-ripening, a period in which the seed coat becomes more permeable to oxygen, which is necessary for germination. Seeds which require this after-ripening germinate the next spring after they have been produced, or the following fall. Seeds kept under conditions favorable for germi­ nation have all grown in two or three years. How­ ever, when seeds are plowed under-or otherwise kept under conditions unfavorable for germination at the time natural dormancy has been completed­ they may remain dormant and viable for a long time. At this time, there are no chemical methods of control that can be recommended. Some promising results have been obtained with CIPC, TCA, and Dalapon-and even newer chemicals show possibil­ ities. However, consistently effective control, together with safe use of crops, has not been worked out to a practical basis as yet. At present only cultural methods can be recommended. 1. Do not plow under seeds that have shattered from the current crop of wild oats. They may remain alive for many years when buried. 2. Cultivate shallow in the spring to break the soil crust and cover seed. Cultivate later to kill the wild oats that have germinated, and to bring up other seed that is no longer dormant. Cultivate again when these seeds have germinated. About the middle of June sow a crop adapted to late sowing-such as early va­ rieties of flax, potatoes, corn, sugar beets, proso millet, buckwheat, Sudangrass, and soybeans. 3. Sow tame oats early and cut for hay before wild oats have formed seed. Plow immediately after the hay crop. 4. More than one year of early tillage, and delayed sowing or cutting of tame oats for hay, is necessary on badly infested fields. 5. Wild oats can regrow after cultivation. Avoid this by cultivating not earlier than the three-leaf stage, completely uprooting the plants.

WEEDS IN HORTICULTURAL CROPS

THE RATES of application of chemicals recom­ mended for use in garden crops are based on over-all coverage. If only a narrow strip over the row is sprayed, the amount of chemical should be reduced accordingly. Vegetable Crops Asparagus-After the early spring disking and be­ fore spears have emerged, apply 2 pounds of 2,4-D or 4 to 6 pounds of SES per acre to control most annual broad-leaved weeds in established asparagus 15 plantings. To control both broad-leaved weeds and grasses, add 5 to 8 pounds of TCA to the above spray mixtures. Or use 6 to 8 pounds of DNBP amine, 4 to 8 pounds of NP, or 1 to 2 pounds of CMU per acre. Use the lower rate of each of those chemicals on mineral soils; use the higher rate on muck soils. During the cutting season, weeds can be kept under control by using a wire weeder, or by applying granu­ lar calcium cyanamid at the rate of 300 to 400 pounds per acre immediately after a cutting and when the weeds are small. The dust form of calcium cyanamid applied at 75 to 100 pounds per acre is also effective if weeds are small and if there is enough dew to stick the dust on the foliage. Following the disking after harvest of an estab­ lished asparagus bed, apply the above rates of 2,4-D, SES, TCA, DNBP, NP, or CMU before any spears appear. If 2,4-D, TCA, or CMU have been applied earlier in the season, they should not be used again after harvest. To control weeds in asparagus seedbeds, use 80 to 100 gallons of Stoddard solvent, 1 pound of DNBP, or 1 pound of 2,4-D per acre as a pre-emergence spray. Beans-The use of pre-emergence sprays to control weeds in the row, together with cultivation between rows, has proved quite successful. The application of 6 to 9 pounds of DNBP amine per acre of actual sprayed area will control annual weeds for a con­ siderable period. The higher rate should be used when sprays are applied immediately after planting. When spraying is delayed until shortly before bean emer­ gence-at a time when many weeds have emerged­ the lower rate may be used with equal effectiveness. DNBP should not be applied to beans planted in light-colored sandy soils. Where weeds such as smartweed make up a large part of the weed population, apply CIPC at 4 to 8 pounds per acre as soon as possible after planting. Use the higher rate on heavy soils and on muck soils. CIPC will control many annual grasses and broad­ leaved weeds, but will not control lambsquarters and ragweed. Where many kinds of weeds are present in a field, mixtures of DNBP and CIPC have often given better results than either one alone. Beets-For the control of annual grasses, apply TCA at 8 to 10 pounds per acre at least two days be­ fore beet emergence. On muck soils, 4 pounds of sodium PCP may be added to the TCA spray to con­ trol annual broad-leaved weeds. If weather makes it impossible to spray before emergence of the crop, wait 10 days after emergence and apply 10 pounds of TCA. Since some beets will be stunted by the latter treatment, use it only as an emergency measure.

16 Cabbage, cauliflower, rutabaga, turnips, brussels sprouts, broccoli-When any of these crops is direct­ seeded, a pre-emergence spray of 4 to 6 pounds of TCA per acre, applied two to three days before crop emergence, may be used to control annual grasses. Carrots, celery, dill, parsnips, parsley-Small an­ nual weeds can be controlled by the application of 80 to 100 gallons of Stoddard solvent per acre, if the entire area is sprayed. Apply the spray when most of the first crop of weeds has emerged but before any of them is more than 2 inches tall. The oil is most effective, and often at lower rates, when it is applied at night when there is little air movement and humidity is high. Early-evening ap­ plications are best in areas where exceptionally heavy dews may cause run-off of the chemical if it is applied later at night. Do not spray carrots and parsnips after the tap root is more than one-fourth inch in diameter, or after five or more leaves are present. Apply Stoddard sol­ vent to celery only in the seedbed. Onions-For the control of weeds that have emerged before the onions, use 60 to 80 gallons of Stoddard solvent, 75 to 100 pounds of calcium cyanamid dust, or 3 to 5 per cent sulfuric acid at 100 gallons per acre as pre-emergence applications. Where smartweeds and purslane are the most troublesome weeds, apply CIPC at 4 to 6 pounds per acre on heavy mineral soils; apply at 8 pounds on muck soils. A combination of 8 pounds of CIPC in 50 gallons Stoddard solvent per acre will control most annual weeds on muck soils. Apply all of the above chemicals at least two to three days before onion emergence. For control of weeds in onions in the loop stage or after the first true leaf is at least 2 to 3 inches long, postemergence sprays of 6 to 8 pounds of CIPC or 12 to 16 pounds of potassium cyanate in 50 to 100 gallons of water per acre are recommended on muck soil. For the control of weeds in onions having three or more leaves, basal applications of 3 to 4 per cent sulfuric acid at 100 gallons per acre, 16 to 20 pounds of potassium cyanate, or 8 pounds of CIPC in 50 to 100 gallons of water are recommended. The CIPC treatment is particularly effective for the residual control of purslane (Portulaca oleracea). Apply all sprays so as to avoid hitting the tops of the onion plants. This can be done by using shields over the spray nozzles or over the onion row, or by using drop nozzles. Potatoes-While blind cultivation is generally pre­ ferred to control weeds, in wet weather chemical pre-emergence treatments may be valuable. Good re- 17 sults have been obtained by using DNBP amine at 5 to 10 pounds, or PCP at 15 to 30 pounds, applied two to six days before emergence. The higher rates are used on muck soil. Where annual grasses are a problem, TCA at 8 to 10 pounds per acre may be used as a pre-emergence spray-either alone or in com­ bination with one of the above herbicides. During wet weather, if broad-leaved weeds threaten to take over a potato field after emergence of the potato plants, you can use 2,4-D amine at 1 pound per acre to control the weeds. If this application is made when the tubers are setting, crop yields may be reduced as much as 25 per cent. Thus this treat­ ment should be used only as an emergency measure during that period. It should never be used in fields being grown for seed certification. Sweet corn-To control weeds by chemicals in sweet corn, follow the same recommendations given for field corn. (See page 3.) Vine crops-Weeds in cucumbers, muskmelons, and watermelons have been successfully controlled with NP. Apply it pre-emergence immediately after plant­ ing these crops, using 2 to 3 pounds per acre on sandy soils, 3 to 4 pounds on sandy loams, or 4 to 6 pounds on clay and silt loams. As a postemergence treat­ ment when these vine crops are grown from trans­ plants, do not use more than 4 pounds per acre. Because of danger of injury to the crop, NP should not be applied to extremely early plantings of vine crops when the soil is cold. Summer squash and pumpkins are less tolerant of NP than are winter squash, cucumbers, musk­ melons, and watermelons-thus should not be sprayed with NP. To be effective in controlling weeds, NP must be applied before weeds emerge since it kills germinat­ ing weed seeds only. It will not kill weeds which have already emerged.

Fruits and Ornamentals Apples-Poison ivy in apple orchards can be con­ trolled with ammonium sulfamate applied as a wet­ ting spray at ¾ pound per gallon. Also recommended are 2,4-D (amine, sodium salt, or low volatile ester) or 2,4,5-T (low volatile ester) at 2 pounds per 100 gallons of water. Avoid applying the latter two chemicals when fruit buds are forming in late June and July. Keep herbicidal sprays off the trunk and leaves of the trees. Grapes-Where weeds beneath the trellis cannot be controlled effectively with the hoe, use an oil emulsion containing 10 to 20 gallons of aromatic or fuel oil and 2 pounds DNBP, or 4 pounds PCP, per

18 100 gallons of spray. Use a suitable emulsifying agent and make certain the oil remains emulsified. Apply 40 to 50 gallons per acre in a strip 18 inches wide beneath the trellis, using a low-pressure sprayer. Keep the spray off foliage, and do not spray young vines which do not have a protective coating of loose bark. Both CMU at 2 pounds per acre and CIPC at 10 to 14 pounds per acre applied to weed-free soil or small weeds have shown considerable promise for use in mature vineyards. One application per season is usually adequate. Raspberries-Young weeds can be successfully con­ trolled by basal sprays of ½ pound of 2,4-D (amine or sodium salt) or 2 to 4 pounds of DNBP amine. Make the first application early in spring before new shoots have emerged. Delay the second application until the young canes are tall enough so that the basal spray will not hit the growing tips. Use DNBP at 2 pounds per acre for the second application. SES at 3 to 6 pounds per acre can be used at any season without injury to raspberry plants. However, to be effective SES must be applied before the weeds emerge. CIPC at 6 pounds per acre applied in late fall ap­ pears promising for the suppression of common chick­ weed and fall-germinating grasses. Strawberries-The use of 1 to 2 pounds of 2,4-D amine or 3 to 6 pounds of SES per acre is recom­ mended. In a new planting, 1 pound of 2,4-D can be applied during the period from three to four weeks after setting to September when fruit buds begin to form. Treatment at the time runners are beginning to form may inhibit their production. For the control of overwintering weeds, a late-fall application of 2,4-D at 1 ½ pounds per acre or DNBP amine at 3 pounds per acre will give excellent con­ trol of susceptible weeds. If overwintering weeds were not sprayed in the fall, apply 1 pound of 2,4-D when you remove the mulch in the spring. During the fruiting year 2,4-D can be used at 1 ½ to 2 pounds per acre, but should not be applied to strawberries in bloom. SES can be applied without injury at any time after plants are set out, and repeat applications may be made as needed. SES, however, must be applied before weed emergence and thus is not effective when applied to a weedy strawberry planting. On light sandy soils, rates of SES exceeding 2 to 3 pounds may cause some crop injury especially in hot, dry seasons. Gladiolus-When applied before the emergence of the gladioli, 2 pounds of 2,4-D, 8 pounds of DNBP amine, or 3 to 6 pounds of SES will control most an-

19 nual broad-leaved weeds. Where annual grasses are a problem, a pre-emergence spray containing 10 pounds of TCA is effective. Postemergence treatment using 1 pound of 2,4-D sodium salt when the gladioli are 6 inches tall, or before the leaf blades open, will control most of the weeds in the row. Injury may result if plants are treated with higher concentrations or at later stages of growth. SES at 3 to 6 pounds per acre can be used either as a pre-emergence or postemergence spray without injury. To be effective, SES must be applied prior to weed emergence. Although cormels grown for size-increase are more subject to injury from herbicides than flowering-size corms, SES can be applied at 3 to 4 pounds per acre before or immediately after leaf blades appear. Chrysanthemums-To control germinating seeds of annual weeds, apply SES at 3 to 4 pounds per acre in the nursery row two to three weeks after trans­ planting.

Seedbeds and Transplant Beds Weeds can be controlled successfully with steam sterilization or fumigation with methyl bromide, vapam, or chloropicrin. Weed seeds which are present in surface soil can also be killed by applying granular calcium cyanamid at the rate of 50 to 75 pounds per 1,000 square feet to a warm, moist soil; work it in to a depth of 2 to 3 inches. Wait 5 to 6 days before 1,eeding. Apply Stoddard solvent at 25 to 75 gallons per acre to control small, broad-leaved weeds and annual grasses in coniferous seedling and transplant beds.

Established Nursery Stock Considerable hand labor can be eliminated by planting lining-out stock on the square to permit cross cultivation. For coniferous transplants and deciduous stock in rows, aromatic oils fortified with PCP or DNBP may be used between rows. A low-pressure sprayer with a hooded boom should be used to prevent drift. Be­ cause of the oil in the mixture, avoid spraying the base of the stem. Weeds in established nursery stock can be con­ trolled by the application of SES at 3 to 5 pounds per acre. The soil must be weed-free when the SES is applied as it kills only germinating weed seeds. A combination spray containing 2 pounds each of CIPC and SES per acre, applied as a directed spray to woody lining-out stock, will control many annual 20 weeds. The treatment should be repeated two or three times during the growing season, preferably after a rain, for an effective control sequence. CIPC at 6 pounds per acre can be applied in late fall to control over-wintering weeds in established nursery stock. Turf Annual broad-leaved weeds in new turf can be con­ trolled by ordinary mowing and management prac­ tices which favor the development of turf grasses. Herbicidal sprays should not be applied until the turf is one year old. In established turf, perennial broad-leaved weeds can be controlled by 2,4-D applications when the weeds are in active growth. A concentration of 0.1 to 0.2 per cent of 2,4-D amine, applied at a volume of 1 gallon per 1,000 square feet, will control most weed species. For resistant weed species, better con­ trol is obtained when 2,4-D esters are used, but nearby ornamentals may be damaged more from drift. Crabgrass can be controlled by application of phenyl mercuric acetate (PMA) at 0.3 ounce, potas­ sium cyanate at 3 ounces, or disodium methyl arsonate at 4 ounces per 1,000 square feet. These should be applied as soon as you see crabgrass seedlings. Addi­ tional applications at 7- to 10-day intervals may be required. All of these treatments may cause severe temporary discoloration of turf grasses, especially if applied during hot dry weather.

UNDESIRABLE WOODY PLANTS

BoTH 2,4-D AND 2,4,5-T are useful in controlling undesirable woody plants, particularly where a selec­ tive control of certain species is desired. Ammonium sulfamate is also effective where killing all the vege­ tation is permissible. Amino triazole and 2,4,5-TP are also recommended for certain species. Soil treatments using sodium chlorate, sodium chloride, CMU, and borax formulations may be useful for spots where complete kill of all vegetation is required and where higher treatment costs are justified. The chemical 2,4,5-T will kill some plants not killed by 2,4-D and vice versa. For general treatment of mixed brush populations, mixtures of 2,4-D and 2,4,5-T are recommended. Applications of 2,4,5-T are especially effective in killing blackberry, wild rose, chokecherry, poison ivy, and some other species not as readily killed by 2,4-D. For most species and methods of treatment repeated applications during several years are necessary.

21 Common Methods of Treatment I. Foliage applications-These involve spraying the foliage in the active growing season. Such sprays are generally most effective when applied after the leaves have attained full size in the spring and before a re­ duction in activity takes place in late summer. Esters of 2,4-D, 2,4,5-T, brush-killer mixtures of these two chemicals, as well as 2,4,5-TP and amino triazole, are used in these applications. Water is the most com­ monly used diluent, but oil-water emulsions may be desirable in some situations. Low-volatile ester for­ mulations should be used when there is danger of fumes reaching sensitive vegetation. Where selec­ tivity is not required, ammonium sulfamate is also recommended with the addition of spreaders and stickers. 2. Basal-bark applications-Ester formulations of 2,4-D, 2,4,5-T, and brush-killer mixtures are effective on many species when applied to the base and ground­ line portions of trees and brush 6 inches in diameter or less. Such applications may be made either in the dormant or in the growing seasons. The chemicals should be diluted in oil. It is important to liberally spray the basal 1 to 2 feet plus the ground-line area. 3. Stump applications-Where the presence of dead standing trees is objectionable, the trees may be cut and the fresh stumps sprayed to a point of run-off so as to thoroughly wet the tops and sides as well as exposed roots. Chemicals recommended include 2,4,5-T and 2,4-D esters in oil, or ammate applied as crystals or in a concentrated water solution. 4. Cut-surface applications-Ammonium sulfamate and 2,4,5-T esters are recommended for application in "frills" or "girdles" cut to encircle basal portions of trees too large or too thick-barked to effectively kill by basal-bark treatments. For some species like cot­ tonwood and willow, 2,4-D esters are also suitable. These treatments applied to standing trees are usually more effective in preventing resprouting than are cut stump applications. The ammate is applied as crystals or in a concentrated water solution and the 2,4-D and 2,4,5-T in oil (dormant season) or water (grow­ ing season). 5. Aerial applications-Considerable variation in the effectiveness of aerial applications may be expected depending on the species treated and on conditions associated with the treatment. Several species have been effectively controlled using 1 to 3 pounds (acid equivalent) per acre of 2,4,5-T, 2,4,5-TP, or brush­ killer mixtures applied in 2 to 5 gallons of oil or oil-water emulsions. The higher volumes give better coverage and more uniform results. Such applications

22 should be made in the season of active growth for best results. These treatments are particularly useful where control rather than eradication is desired and on areas difficult of access by ground equipment. Repeat sprays may be required to give the necessary control.

Woody Weeds in Pastures (See also page 6. Pastures and Meadows.) The growth regulator herbicides (low-volatile esters preferred) and ammonium sulfamate will control many of the brush and tree species on land suitable for range and pasture development. However, their use should be accompanied by a management pro­ gram which will encourage the desirable grasses, thus reducing sprout regrowth. The methods com­ monly used to apply the herbicides are foliage sprays, basal-bark, and cut-surface treatments. Annual ap­ plication for two or in some cases three consecutive years may be needed. Foliage sprays-Woody plants sensitive to 2,4-D, 2,4,5-T, or 2,4,5-TP esters may be controlled with a solution consisting of 3 pounds of the acid in 100 gallons of water. The latter chemical is particularly effective on oak species. Ammonium sulfamate in a concentration of at least ¾ pound in 1 gallon of water with the addition of a spreader-sticker is effective on mixed brush-but it may cause considerable injury to nearby grasses. Buckbrush and hazel may usually be controlled by foliage applications using 3 pounds of 2,4-D ester per 100 gallons of water applied in the active growing season. Two or three annual applications are usually required to obtain good control. Basal-bark treatment-Basal-bark and ground-line treatments are good control measures on trees less than 6 inches in diameter. Concentrations ranging from 8 to 16 pounds of the low-volatile 2,4,5-T ester in 100 gallons of diesel fuel are recommended for most species. These treatments are particularly effective on prickly ash. However, cottonwood and willow may be controlled with the same quantity of 2,4-D ester. Cut-surface treatment-Generally, 16 pounds of 2,4,5-T ester in 100 gallons of diesel fuel make an effective spray to be applied in frills or cups on larger trees and those having thick bark. The same solution, when applied thoroughly on freshly cut stumps, pre­ vents sprouting. Regrowth on stumps may also be prevented by application of ammonium sulfamate in the crystal form or in a concentrated water solution (4 to 6 pounds per gallon).

23 Woody Weeds on Roadsides, Utility Lines, and Other Rights-of-Way Effective chemicals for the control of woody plants on rights-of-way are 2,4-D and 2,4,5-T-alone or in combination-and ammonium sulfamate. Mixtures of 2,4-D and 2,4,5-T are useful when mixed stands of woody plants are to be controlled. Foliage sprays-Woody plants sensitive to 2,4-D and 2,4,5-T should be treated using a wetting foliage spray containing at least 3 pounds of 2,4-D and 2,4,5-T per 100 gallons of water. Brush killers containing 2,4-D and 2,4,5-T are suggested where mixed species are encountered. Low-volatile esters are generally preferred. Ammonium sulfamate at a concentration of at least ¾ pound per gallon of water is effective as a foliage spray on mixed brush. Aerial spraying on utility rights-of-way and roadsides is still in the development stage. Basal sprays (dormant and active growth period)­ Basal sprays with 2,4-D and 2,4,5-T properly applied are usually more effective on the more resistant spe­ cies than are foliage sprays. Applications of 2,4,5-T or mixtures of 2,4-D and 2,4,5-T at rates of 8 to 16 pounds per 100 gallons of oil have proved effective. Thorough coverage is essential. Stump treatment-In areas recently cut-as in the case of new rights-of-way or where dead standing trees are objectionable as along highways-the cut plants may be effectively treated by using 2,4,5-T or mixtures of 2,4-D and 2,4,5-T at rates of 8 to 16 pounds of acid equivalent per 100 gallons of oil. Am­ monium sulfamate applied as crystal or as a concen­ trated water solution (4 to 6 pounds per gallon) is effective in preventing sprouting of stumps.

Control of Woody Weeds in Forests, Forest Plantations, and Farm Woodlands Chemicals may be useful in several ways in con­ nection with controlling undesirable woody plants on forest, plantation, and woodland areas. In many of these applications a goal of temporary control rather than permanent eradication of the woody weeds may be adequate in obtaining the desired objectives. Foli­ age sprays, cut-surface, and basal applications are all useful under certain conditions. For purposes of freeing coniferous regeneration from brush competition, foliage sprays containing 2 pounds of ester formulations of 2,4-D or 2,4,5-T per 100 gallons of spray are recommended. Where the

24 brush consists of hazel, willows, or alder, 2,4-D is adequate. For the control of blackberries, raspberries, cherry, thornapple, ash, osage-orange, basswood, and maple, 2,4,5-T is more effective. For mixed brush populations, mixtures of 2,4-D and 2,4,5-T are recom­ mended. Foliage applications should be made after the leaves have attained full size and before their activity has been reduced in late summer. Such ap­ plications, properly made, will usually be effective in reducing competition to coniferous seedlings for three to five years. Where control for a longer period is necessary, repeat sprayings are recommended. Where brush control is necessary preliminary to the planting of trees for forest plantations, foliage treat­ ments using 2,4-D, 2,4,5-T, or ammonium sulfamate can be used. Amino triazole and 2,4,5-TP may also be useful on certain species. If natural regeneration of conifers is present on the areas, 2,4-D or 2,4,5-T should be used exclusively to avoid killing the coni­ fers. Chemical treatment can be useful in releasing es­ tablished plantations from overhead competition and in eliminating poorly formed individual or inferior species from sapling or pole-sized forest stands. For this purpose cut-surface treatments in frills or cups as well as basal applications are recommended. Esters of 2,4,5-T in oil solutions at concentrations of 8 to 16 pounds of acid per 100 gallons of oil are recom­ mended for both cut-surface and basal types of ap­ plication. Ammonium sulfamate as a dry salt or as a concentrated water solution (4 to 6 pounds per gal­ lon of water) can be effectively applied to cut sur­ faces of stumps, frills, or cups to prevent resprouting of most species of woody plants. Addition of a sticker or spreader to such water solutions may be necessary. In some situations aerial sprays have been found to be a cheap and relatively effective method for re­ leasing conifers from an undesirable overstory or competition from brush. Rates of from 1 to 3 pounds per acre of 2,4-D or 2,4,5-T acids or their mixtures in 2 to 5 gallons of oil or oil-water emulsions have been found to be successful in some cases in controlling aspen, alder, oak (bur, northern red, and northern pin oak), and paper birch. Where oaks are to be con­ trolled, 2,4,5-TP is particularly effective. In general, spraying in desirable stands of conifers should be confined to the last half of the growing season to avoid damaging the succulent new growth.

Poisonous and Disease-Carrying Woody Weeds Barberry. the alternate host of stem rusts of wheat, oats, barley, and rye-European barberry (B. vul­ garis) can be killed by common salt liberally applied

25 around the base of the plant. However, ammonium sulfamate applied to the surface of cane stubs cut at the ground line, or basal sprays of MCP ester, or a combination of 2,4-D and 2,4,5-T esters (plus PCP using 14 pounds of acid per 100 gallons of oil) are also effective and easier to apply. Currants and gooseberries, the alternate hosts of white pine blister rust-Basal treatments with 2,4,5-T ester-or a combination of 2,4-D and 2,4,5-T esters­ at 8 to 14 pounds of acid per 10 gallons of oil kill most upland species. Ribes americanum can also be killed with a foliage spray of 2,4-D ester at ¾ to 2 pounds of acid per 100 gallons of water, or dormant-season treatments using 8 to 14 pounds acid per 100 gallons oil solution. Prostrate swamp species are usually more difficult to eradicate. Over-all sprays using oil solu­ tions of 2,4,5-T are effective. Buckthorn, the alternate host of crown rust of oats­ Eradication of buckthorn by mechanical uprooting, ammonium sulfamate applied to cut stems, or a mix­ ture of 2,4-D and 2,4,5-T (12-16 pounds acid per 100 gallons oil) in oil applied as a basal spray is recom­ mended. Red cedar, alternate host of apple rust-These trees may be killed with common salt (sodium chloride), sodium chlorate, and possibly other soil sterilants ap­ plied at the ground line. A foliage wetting spray of ¾ pound ammonium sulfamate per gallon of water is also effective. Poison ivy-A thorough foliage spray of 2,4,5-T ester-or a combination of 2,4-D and 2,4,5-T esters­ using 2 pounds of acid per 100 gallons of water is recommended. Amino triazole mixed at the rate of 6 pounds per 100 gallons of water is also effective. A dormant spray of 2,4,5-T at 12 pounds of acid per 100 gallons of oil may be used. Ammonium sulfamate, sodium chlorate, or borax formulations also have proved effective. Poison sumac-Due to the height of this shrub and danger of skin poisoning, treatment with either a growth regulator, ammonium sulfamate, or a soil­ sterilant type of herbicide is recommended in the dormant rather than in the foliage stage.

SOIL STERILANTS

WEEDS in places where it is difficult to plow or mow or where complete vegetation control is desired can be controlled with herbicides, but the cost on an acre basis may be rather high. Larger dosages than those recommended will give better and more lasting

26 control. Larger dosages are generally more necessary on low ground than on high, dry locations. Lower dosages and less water or other carrier are needed if applications are made before growth be­ comes large and dense. For a temporary kill, 3 pints of DNAP or DNBP phenol in 3 or more gallons of diesel oil diluted with water to 40 gallons per acre gives a quick kill, but grass and perennial weeds quickly recover. For a quick kill of herbaceous vegetation ( except quackgrass) use a 5-to-l borate-2,4-D mixture, ap­ plied at 550 to 650 pounds per acre (3½ to 4 pounds per square rod). Or use concentrated borascu at 2,400 pounds per acre (15 pounds per square rod), or poly­ borchlorate at about 1,600 pounds per acre (10 pounds per square rod). These treatments should last for at least one season. Sodium chlorate applied at 480 to 800 pounds per acre (3 to 5 pounds per square rod) will give complete vegetation control. CMU at 40 or more pounds per acre applied in either fall or spring gives nearly complete vegetation control for at least one or two years. CMU is very slow acting and if applied in April it might take until July for all vegetation to be killed. Morning glory, Canada thistle, perennial sow thistle, dogbane, spurge, dandelion, and plantain are relatively tolerant of CMU and on some soils may require more than 40 pounds per acre for a kill.

27 FARM SPRAYER CALIBRATION AND ADJUSTMENT uNIFORM APPLICATION of spray chemicals is essential to control weeds. A small variation in the rate of application may fail to kill the weeds or may injure the crop, thereby causing a loss of time, effort, and money. A simple method for determining the amount of liquid a sprayer applies per acre is as follows: 1. Start with a full tank of clean water and have the pressure adjusted as you will use it in the field (usually 30 to 40 pounds). 2. Drive exactly 1/s of a mile (40 rods) in a field at the speed you will use when spraying-usually 4 to 5 miles per hour. Mark the notch the throttle is in and keep it in this notch when spraying. 3. Refill the tank, carefully measuring the amount of liquid required. 4. Calculate the application rate as follows: Number of gallons ~sed X 66 = gallons per acre. Boom coverage m feet Example: If 2½ gallons were used in ¼ mile and the width covered by the boom is 24 feet, multiply 2½ by 66 and divide by 24. The result is 6.9 gallons per acre.

2·5 X 66 = 165 = 6.9 gallons per acre. 24 24 Here is the way to determine the amount of herbi­ cide to be put in the tank. 1. Divide the number of gallons the tank will hold by the number of gallons your sprayer applies per acre. This will give you the number of acres one fill­ ing will spray. 2. Multiply the number of acres the tank will spray by the amount of herbicide to be used per acre. This will give the amount of herbicide to be used per tank. Example: If the tank hold 55 gallons and the sprayer applies 6.9 gallons per acre, one tank will spray 8.0 acres (55 divide by 6.9 equals 8.0). If 1 pint of spray material is required per acre, 8.0 pints would be required for each tankful. That is, 1 pint per acre X 8.0 acres = 8.0 pints per tankful.

28 SUMMARY OF RECOMMENDATIONS FOR APPLICATION OF CHEMICALS Recommendations for Spraying Field Crops

Crops Chemicals Rate per acre (pounds) Time Remarks Wheat or 1 2,4-D amine or 1/., 5th leaf to early-boot Amine less injurious to crop. barley \ 2,4-D ester % 5th leaf to early-boot Oats 2,4-D amine ½ 6th leaf to early-boot MCP for susceptible varieties (see page 8). MCP amine or sodium ½ 6th leaf to early-boot Flax MCP amine or sodium ¼ Before bud MCP less injurious to crop. 2,4-D amine ¼ Before bud Mixture of MCP or 2,4-D and TCA for broad­ TCA 5 Weeds 1 to 3 inches leaved and grassy weeds. Corn 2,4-D amine ½ l O days after emergence Corn most susceptible during rapid growth. to tasseling Early spring best. Premerge 4 At emergence Use drop nozzles (see page 3). Premerge (repeat) 4 After lay-by Amino triazole 2 After lay-by Use drop nozzles. Alfa /fa and clover } 2,4-D amine ¼ Not before 2 inches tall Sweetclover injured. in small grains MCP amine or sodium % Not before 2 inches toll Canopy of crop or weeds reduces injury. Alfa /fa in flax TCA 5 Weeds l to 3 inches TCA on alfalfa and flax only. Peas DNBP amine Weeds 2 to 4 leaves Use 40 gallons of water per acre. MCP amine or sodium 3/e Peas 3 to 7 inches Soybeans 2,4-D amine ¼ Beans 3 to 5 inches For cockleburs or mustard in seedling MCP amine or sodiu_m___ 'la______B_e_a_ns_3_t_o_5_in_c_h_es ______st_a""'g_e_o_n_ly._. ______~ Recommendations for Killing Specific Weeds

Crops Chemicals Rate per acre (pounds) Time Remarks Quackgrass TCA 22 Fall Apply on plowed ground. TCA 18 Next fall after harvest Follow up with cultivation or second treatment if land was cropped. Dalapon 12 ta 15 Fall Apply on foliage. MH, Dalapon, or Amino triazole 4 (of one used) Spring Apply on foliage before seedbed preparation. Leafy spurge: On noncrop land 2,4-D ester 2 lo 3 Bud Treat again in fall. On crop land 2,4-D amine ½ Bud Spray in crop of wheat or barley. Cultivate after harvest until freeze-up. Field bindweed: On noncrop land 2,4-D ester Bud lo bloom or late fall Cultivate land before spraying. On crop land 2,4-D amine ½ Bud lo bloom Canada and l 2,4-D amine ½ Approximate bud Spray in tolerant crop. sow thistle ( 2,4-D ester 1 Fall rosette Treat again in fall on new growth. Sodium chlorate 3 lo 5 per square rod Spring or fall Spot spraying Concentrated borascu 15 per square rod Spring or fall Poor control of grasses. perennial weeds Polybor chlorate 8 lo 10 per square rod Spring or fall CMU 30 to 80 Spring or fall Poor control of thistles and spurge. 5:1 borate-2,4-D mixture 3½ to 4 per square rod Spring or fall Poor control of grasses. Spraying Recommendations for Specific Areas ======------Crops Chemical, Rote per acre (pounds) Time Remarlcs Fence lines CMU 30 to 40* Spring or fall Complete vegetation control for 2 to 3 years. Brush When leaves are full size in For mixed brush use mixture of 2,4-D and 2,4-D ester J Not less than 3 pounds por 2,4,.5-T ester or spring and before slow 2,4,.5-T. Use 2,4,.5-T for brambles where no 100 gollons of woter mixture of bot growth of summer selectivity is needed. Ammate ¾ pound per gallon of water Brush 2,4,.5-T ester } 16 pounds per 100 Apply In frills or girdles on Use 2,4-D for cottonwood or willow. All treat­ 2,4-D ester gallons of oil large trees at any time of ments prevent stump regrowth. year Ammate 4 to 6 pounds per gollon of water Brush Either dormant or active. Use 2,4-D for cottonwood or willow. Spray 2,4,.5-D ester } B to 16 pounds per 2,4-D ester or Spray basal 1 to 2 feet till it runs off. 100 gallons of oil mixture of both and ground-line area Brush 2,4,.5-T ester or mix-} Freshly cut stumps Wet top and sides to ground level until it runs 8 to 16 pounds per lure of 2,4-D and off. Also spray roots. 100 gallons of oil 2,4,.5-T esters Ammate 4 to 6 pounds per gallons of water • Morning glory, Canada thistle, perennial sow thistle, dogbane, spurge, dandelion, and plantain ore relatively tolerant and may require larger amounts or an application of 2,4-0. Recommendations for Spraying Horticultural Crops

Crops Chemicals Rate per acre (pounds) Time Remarks Asparagus Stoddard solvent 80-100 (gal.) Pre-emergence (seedbeds) DNBP l Pre-emergence 2,4-D amine l Pre-emergence Asparagus 2,4-D amine 2 After spring disking and 2,4-D plus SES for broad-leaved weed control (established beds) SES 4-6 before spears emerge TCA added to 2,4-D or SES for grass plus TCA 5-8 broad-leaved weeds. DNBP amine 6-8 DNBP, NP, and CMU for both grass and NP 4-8 broad-leaved weeds. CMU 1-2 Higher rates for muck soils. Beans DNBP amine 6-9 Pre-emergence Lower rate for delayed pre-emergence. Do not use DNBP on light sandy soils. CIPC 4-8 Pre-emergence Use where smartweed and purslane serious problem. Higher rate on muck and heavy soils.

Beets TCA 8-10 2 days before emergence For annual grass control. PCP 4 2 days before emergence Add lo TCA for grass and broad-leaved weeds on muck soils. Cabbage and TCA 4-6 2 days before emergence For annual grass control in direct-seeded crops. related crops Carrots and Stoddard solvent 80-100 (gal.) Weeds less than 2 inches tall Carrots and parsnips to 5-leaf stage. Celery related crops in seedbed only. Spraying Horticultural Crops (continued)

Crops Chemicals Rate per acre (pounds) Time Remarks Onions Stoddard solvent 60-80 (gal.)} Use when weeds emerge first. Calcium cyanamid (dust) 75-100 Use when weeds emerge first. At least 2 days before Sulphuric acid (3-5%) 100 (gal.) Use when weeds emerge first. emergence CIPC 4-6 Heavy mineral soil CIPC 8 Muck soil. Can mix with 50 gallons Stoddard solvent on muck. CIPC 6-8 } "Loop" to 2- lo 3-inch stage Use on muck soil. Potassium cyanate 12-16 Sulphuric acid (3-4%) 100 (gal.)} Potassium cyanate 16-20 Onions with 3 leaves or more Use directed basal sprays. CIPC 8 Potatoes DNBP amine 5-10 2 days before emergence Controls broad-leaved weeds mostly PCP 15-30 2 days before emergence Controls broad-leaved weeds mostly TCA 8-10 2 days before emergence Contra Is grasses. Can mix with the DN8P or PCP. 2,4-D Postemergence Emergency measure only. Delay until tubers set. Sweet Corn (see Corn under "Spraying Field Crops") Vine crops NP 2-3 (sandy soil) Pre-emergence Do not use on summer squash and pumpkins. 3-4 (sandy loam) Pre-emergence Do not use on early plantings in cold soil. 4-6 (clay and silt) Pre-emergence 4 (all soils) Postemergence Apply before weed emergence. Apples (Poison Ivy control) Ammate ¾ per gallon water Any time except late June Spray to dripping. Avoid tree trunks and 2,4-D amine or ester 2 per l 00 gallons water and July leaves. 2,4,5-T ester 2 per l 00 gallons water Spraying Horticultural Crops (continued)

Crops Chemicals Rate per acre (pounds) Time Remarks Gropes Aromatic oil plus 10-20 (gal.) } Apply at 40-50 gallons per acre on 18-inch DNBP or 2 per 100 gallons spray When weeds small { strip in the row. PCP 4 per 100 gallons spray Avoid grape foliage and young vines. CMU 2 When weeds small One application per season. CIPC 10-14 When weeds small Raspberries 2,4-D amine ½ Early spring and again when Use directed basal spray. DNBP amine 2-4 new canes tall enough For 2nd application, use only 2 pounds DNBP. SES 3-6 SES before weeds emerge. Strawberries: In new planting 2,4-D amine from 3 to 4 weeks after Avoid spraying during runner formation. setting to September SES 3-6 Anytime Apply before weeds emerge. Not over 3 pounds on sandy soil. In fruiting planting 2,4-D amine 1½-2 Anytime except at blooming DNBP amine 3 Late fall for overwintering weeds (can use 2,4-D also). SES 3-6 Anytime Not over 3 pounds on sandy soil. Gladiolus 2,4-D 2 Pre-emergence for broad-leaved weeds. DNBP amine 8 Pre-emergence for broad-leaved weeds and grasses. SES 3-6 Pre-emergence and post- For broad-leaved weeds and grasses. emergence TCA 10 Pre-emergence For grasses. 2,4-D 1 Postemergence Apply before leaf blades open. Spraying Horticultural Crops (continued)

Crops Chemicals Rate per acre (pounds) Time Remarks Chrysanthemums SES 3-4 2 to 3 weeks after Ira ns­ Apply before weeds emerge. pla nti ng Seedbeds and transplant beds: a) Sterilization Steam Soil temperature must be raised to 180° F. and held there ½ hour. Calcium cyanamid 50-75 pounds per 1,000 square feet-work to depth of 2-3 inches in moist, warm soil. Wait 5-6 days be­ (granulor) fore seeding. b) Fumigation Methyl bromide} Vapam Follow manufacturers' directions closely in using these fumigants. Chloropicrin c) Weed control after seeding or transplanting Stoddard solvent 25-75 gallons In coniferous seedlings or transplant beds. Established nursery stock SES 3-5 Anytime Directed spray to stem base. CIPC plus SES 2 pounds each Anytime Repeat 2-3 times. Basal spray. CIPC 6 Late fall Kills overwintering weeds. Turf: a) Broad-leaved weeds 2,4-0 amine or low­ 0.1-0.2% at 1 gallon When weeds growing actively Will control most broad-leaved species. volatile esters per 1,000 square feet b) Crabgrass PMA 0.3 ounces per 1,000 l square feet Potassium cyanate 3 ounces per 1,000 L As soon as crabgrass is visible Repeat at 7- to 10-day intervals for 3 to 5 square feet r applications. Disodium methyl arsenate 4 ounces per 1,000 j square feet DESCRIPTION OF HERBICIDES All rates of 2,4-D, 2,4,5-T, MCP, Dalapon, TCA, and Amino triazole refer to acid equivalent; rates of PCP, DNBP, and DNAP refer to phenol equivalent; and rates of PMA, IPC, CIPC, CMU, MH, SES, NP, and KOCN refer to active ingredient. Avoid direct contact with skin and eyes-specially repeated or prolonged contact with all chemicals.

Amino triazole--3-amino-1,2,4-triazole Ammonium sulfamate--Ammate Calcium cyanamid-Aera Cyanamid, special grade or granular CMU-Karmex W 3(p-chlorophenyl)-l, l dimethylurea Karmex DW 3(3,4-dichlorophenyl)-l, 1-dimethylurea Karmex FW 3(phenyl)-l, 1-dimethylurea Concentrated 8orascu-contains 61.5 per cent 8,0, Dalapon-sodium salt of 2,2-dichloropropionic acid DNAP-4,6-dinitro-o-sec-amyl phenol, Sinox General DNBP-4,6-dinitro-o-sec-butyl phenol, Dow General, contains 5 pound of active ingredient per gallon DNBP ammonium salt-Sinox W and Dow Selective, contains pound of active ingredient per gallon DNBP amine salt-Premerge, Sinox PE contains 3 pounds active ingredient per gallon Endothal-disodium 3,6-endoxohexahdrophthalate IPC and CIPC-isopropyl-N-phenyl carbamate and isopropyl-N-(3- chlorophenyl) carbamate MCP-sodium or amine salt of 2-methyl-4-chlorophenoxyacetic acid Methyl-bromide-bromomethane, soil fumigant MH-sodium salt of maleic hydrazide NP-N-1-naphthylphthalamic acid; Alanap is the sodium salt, con- taining 2 pounds active ingredient per gallon PCP-sodium salt of pentachlorophenol, water soluble PMA-phenyl mercuric acetate, 10 per cent active ingredient Polybor-contains 66.6 per cent 820, Polybor chlorate-contains 50 per cent 820, and 25 per cent sodium chlorate Potassium cyanate--contains 91 per cent active ingredient SES---2,4-dichlorophenoxyethyl sulfate, Crag Herbicide Sodium chloride-common salt Sodium chlorate-highly flammable when mixed with organic ma­ terials Stoddard solvent-petroleum distillate, contains 15 to 18 per cent aromatics TCA-sodium salt of trichloroacetic acid 2,4-D-2,4-dichlorophenoxyacetic acid, formulated as sodium and amine salts and esters 2,4,5-T-2,4,5-trichlorophenoxyacetic acid, formulated as sodium and amine salts and esters 2,4,5-TP-2-(2,4,5-trichlorophenoxy) propionic acid Vapam-Sodium N-methyl dithiocarbamate dihydrate

UNIVERSITY OF MINNESOTA, INSTITUTE OF AGRICULTURE ST. PAUL 1, MINNESOTA Cooperative Extension Work In Agriculture and Home Eco­ nomics, University of Minnesota, Agricultural Extension Service and United ~tates n,martment of AP"ricnlture Cooperating, Skull Agricultural Exten- UNIVERSITY OF MINNESOTA 20M-l-56

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