Weed Control in MINNESOTA

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.

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