6-1 Risk Management Guide for Organic Producers

Chapter 6 Weed Management Jeff Gunsolus Don Wyse Kristine Moncada Carmen Fernholz

n Chapter 5—Weed Biology, we discussed how weeds grow Iand compete with crops. While there inevitably will be a certain level of weeds, it is the grower’s task to make sure that the weeds present do not exceed damaging thresholds that limit crop yields. In this chapter, we will address prac- tical weed management techniques for the organic producer. Weed management for organic crop production falls into two categories: cultural weed control and mechanical weed control. A third type of weed control using chemicals is another option, but will not be discussed in this man- ual as organic herbicides are not commonly used on a large scale in agronomic crops.

John Deere John Figure 6-1. Row crop cultivator. 6-2 Risk Management Guide for Organic Producers

crops can prevent weeds from Cover crops and Cultural weed adapting to the planting regimen. smother crops control Competitive perennial crops Winter cover crops and smother such as alfalfa are especially ef- crops are two additions to rota- fective in reducing seed banks Cultural weed control includes tions that can have an effect on of annual grasses and broadleaf diversifying rotations, delaying weeds. Winter cover crops can weeds and in suppressing pe- planting, changing planting rate, occupy the niche that exists after rennial weeds like thistle. The timing of nutrient application, a summer crop is harvested and advantage of alfalfa is that it is and using cover crops (see Chap- before the next season’s crop is harvested three or four times dur- ter 13 for more information on planted. They can displace weeds ing the growing season which cover crops). Cultural methods that might otherwise germinate prevents annual weeds from are the first line of defense in in the fall or very early spring. flowering or producing seed and weed management. Winter rye and hairy vetch resi- depletes root reserves of peren- due also has been shown to have Rotation nials. In addition, its continuous allelopathic effects on some ger- Diversifying a rotation is the cover provides a habitat for ani- minating weeds, but this effect strongest tool against weeds. mals that consume weed seeds. is short-lived and lasts only until Over time, using similar planting Cover crops in rotations can also the residue decomposes. See dates, and cultivation timing will play a role in preventing weed Chapter 13 for more information select for weeds that are adapted infestations. on the benefits and risks of win- to these strategies. Varying crops Because rotation is so impor- ter cover crops. by different planting date (e.g. tant for organic farmers, we have A smother crop is a vigorous- wheat is planted several weeks devoted an entire chapter to the ly-growing crop that growers use before soybean) or growing a pe- topic in Chapter 2. to suppress weeds. Generally, a rennial crop in rotation with row smother crop is not harvested, but plowed down instead. Two examples of summer smother crops used in the Upper Midwest Crop seed size include buckwheat and sudan- Crop varieties vary in seed size and those with larger seed size of- grass (or sorghum-sudangrass). ten have increased competitiveness against weeds. Large seed mass Smother crops may suppress gives an initial head start to the crop at the time it is most critical. some perennial weeds, but a Small-seeded weeds are capable of fast initial growth, but are de- perennial crop such as alfalfa pendent on photosynthesis and outside nutrients. A large crop seed grown for two or more years has its own internal resources and can provide a jump start over generally will be a better choice weeds under the right conditions. Crop seed size is one of many to affect perennial weeds in the factors to consider in crop variety selection. long-term. The primary risk in 6-3 Risk Management Guide for Organic Producers

using smother crops is that their effectiveness in weed control may be inconsistent and unpre- dictable. Additionally, a smother crop such as buckwheat has po- tential to become a weed itself.

Delayed planting Delayed planting is an option in weed management, but it can reduce crop yields. However, for many organic farmers, delayed planting can be the correct choice Figure 6-2. Sorghum-sudangrass grown as a smother crop. in highly weed-infested fields. early in the season. Producers to decide if a delayed planting Delaying planting allows for need to monitor their fields and strategy is warranted. They also more mechanical weed control be constantly aware of which need to consider if a potential de- operations to be performed prior weed species (see Chapter 7 for crease in yield is justified. to crop planting with the prospect weed identification) are present of fewer weeds in the crop. Organic farmers in the Upper Producer profile Midwest balance the potential yield gains from improved weed Smother crops control against potential yield An organic producer from Wadena County uses buckwheat as a losses from delayed planting by smother crop to control Canada thistle and quackgrass. Buckwheat planting corn around May 15 and easily reseeds so he notes that control of buckwheat before it goes to planting soybean between June 1 seed is important to prevent volunteers. Oats are not a good choice and June 15. Cool-season crops to plant after buckwheat because of the danger of seed contamina- like small grains or field pea that tion by potential buckwheat volunteer plants in oats. Buckwheat can are planted early in the spring are be planted in June at a rate of up to 50 pounds/acre. not likely to benefit from delayed A farmer from McLeod County uses sorghum-sudangrass (Figure planting. 6-2) to suppress Canada thistle and quackgrass, but he finds that large-seeded broadleaf weeds like velvet leaf are not effectively Delayed planting can reduce controlled. He plants in the middle of June (no later than June 25th) populations of early-emerging to get a good stand. Sorghum-sudangrass will winter-kill so it can weed species (Figure 6-3). See be tilled in the fall or spring. Sorghum-sudangrass is a warm-season Table 5-11 from the previous crop planted when soils have warmed in June at a rate of 35 to 40 chapter for weeds that emerge pounds/acre if drilled or at 40 to 50 pounds/acre if broadcast. 6-4 Risk Management Guide for Organic Producers

100 90 80 70 60 50 become more competitive and

% contro l 40 30 subsequently compete for light and Mid-May 20 water resources. Examples where June 10 this most frequently occurs is with 0

n n n n small grains like wheat and barley, which is why applying manure

Cultivatio Cultivatio or compost before planting these

RH+cultivatio RH+cultivatio crops is not recommended. For Rotary hoe (RH) Rotary hoe (RH) Lambsquarters Pigweeds crops with high nutrient needs, Figure 6-3. Effect of delayed planting on control of lambsquarters and pig- providing proper levels of nutrients weeds in soybean, 1989-1991, Rosemount, MN. Soybeans were planted mid-May can lead to increased competitive- or early June and treated with the rotary hoe, cultivation or both. Delayed plant- ing usually led to increased weed control, particularly in lambsquarters which ness against weeds. emerges earlier than the pigweeds. Adapted from Buhler and Gunsolus, 1996. The timing of fertilizer ap- plication can be important. When Planting rate Nutrient application nutrients are applied too early for Increasing the planting rate is Just as nutrients nourish the crop, crop utilization, weeds may be fa- another common strategy for they can also nourish the weeds. vored. Producers may be tempted organic growers. Higher crop There are two issues with compost to delay fertilization. However, the densities can lead to greater and manure application – how the unpredictable release of nutrients competitiveness against weeds. nutrients affect growth of existing from organic fertilizers will make In addition, higher planting rates weeds in the field and the potential using nutrients to manage weeds a can compensate for crop losses introduction of new weed seeds. challenge. that occur during mechanical Compost application in the weed control operations. The spring can stimulate ger- bigger the weed problem, the mination of early-emerg- Table 6-1. Effect of nitrogen on weed growth. Increasing nitrogen levels more effective increasing plant ing weeds. The growth of can have a positive or negative ef- many weeds like foxtails, population will be. Less competi- fect on weed growth depending on tive crops like flax may show a pigweed and lambsquar- the species. Adapted from Davis, 2005. ters is stimulated by nu- greater yield increase. For guide- N increases N inhibits lines as to whether to increase trients such as nitrogen growth growth crop plant populations, producers that are intended for crops Velvetleaf Common ragweed should consult the chapters in (Table 6-1). When weeds Foxtail Canada thistle Redroot pigweed this manual for individual crops have a stronger response Lambsquarters to high fertility than the and with local extension person- Giant ragweed nel for optimum planting rates crop does, there will be a Pennsylvania smartweed for their area. negative effect on yield Eastern black nightshade because the weeds will Quackgrass 6-5 Risk Management Guide for Organic Producers

The method of manure appli- the minimum temperature for cation can also have an effect on composting is 131° F. Therefore, weeds. When manure is injected, some weed seeds will still sur- Mechanical nutrients are placed closer to where vive under common composting the crop (instead of weeds) can use situations, but the overall number Weed Control them. Broadcast manure applica- of weed seeds will be less than in tion can favor weeds that emerge raw manure. See Chapter 4 – Soil In addition to the use of cultural from shallow depths. If manure is Fertility for more information on methods to manage weeds, suc- broadcast applied, harrowing the composting. cessful organic producers must manure into the soil can help place master the art of mechanical weed nutrients closer to crop roots. Reducing risk: cultural control. Effective mechanical Manure application can in- weed control. Diversify weed control is more effective troduce new weed seeds. When crop rotations as part when using a diversity of equip- livestock consume weed seed, a of a weed management plan. ment that provides options to percentage of it survives diges- Avoid deep tillage in late spring eliminate weeds at different stages tion and remains in the manure. when using delayed planting; of crop growth. Lack of favorable Broadleaf weeds with large this can stimulate weed weather or soil conditions to per- seeds are more likely to survive germination at the same time form a mechanical weed control digestion than are grass or small- the crop germinates. Choose operation in a timely manner is seeded weed species. Addition- the correct crop planting rate one of the biggest reasons for fail- ally, livestock bedding such as and obtain good stands to ure; thus, the availability of differ- straw mixed in with manure can make the crop competitive and ent implements that allow opera- be a source of weed seed. To to compensate for stand loss tion under different conditions can minimize weed introductions due to mechanical weed control reduce risk. Some general guide- from manure, avoid using ma- operations. Time application of lines for mechanical weed control nure from livestock that graze on amendments to when the crop are shown in Table 6-2. weed-infested fields. (not the weeds) needs it most. Compost will generally have If manure is known to be Table 6-2. Mechanical weed fewer viable weed seeds than from a weedy source, do not control guidelines. manure. Composting manure at apply to “clean” fields with Adapted from Steel in the Field, 2001. temperatures above 140° F for low weed pressure; instead • Go as shallow as possible 2 weeks should kill most weed choose a weedy field if there • Do as infrequently as possible; every seed. Seed of weeds such as is no other option. Choose tillage pass reduces soil moisture • Control should be specific to weed issue velvetleaf and field bindweed composted manure over raw • Limit soil impact is not killed until temperatures manure to reduce weed seed • Know the weed growth stages that are reach 160-180° F. However, un- establishment. most vulnerable to control practices der National Organic Plan rules, • Get weeds when small 6-6 Risk Management Guide for Organic Producers

Mechanical weed control can for crop rows) before and after The unpredictability of the be divided into several catego- the crop has emerged or inter-row weather in the spring greatly af- ries —primary­ tillage, secondary cultivation between rows once fects the risk of not getting cultiva- tillage, and cultivation. Primary the crop is at the correct stage of tion accomplished in a timely man- tillage and secondary tillage (or growth. A common mechanical ner. It is essential to take advantage seed bed preparation) are per- weed control regime for an organ- of favorable weather and soil con- formed before the crop is planted. ic producer in the Upper Midwest ditions for mechanical weed con- Cultivation occurs after the crop in corn and soybean is tillage (fall trol operations. The consequences has been planted; examples in- or spring), seed bed preparation, are that weeds may become too clude pre-emergence and post- two rotary hoe or harrow opera- large to control with any type of emergence broadcast cultivation tions after planting and two culti- cultivation. (blind cultivation without regard vations when the crop is larger.

Total management effects on weeds In this chapter, we address distinct management experiment by Cardina et al.(2002) where weed options and how they individually affect weeds. seed banks under different conventional rotations In reality, every decision such as rotation or tillage (continuous corn, corn-soybean, and corn-oats- equipment choices made in the field has an interac- hay) and tillage systems (chisel and moldboard) tive effect on weeds. No matter which choices are were analyzed on a long-term research site in Ohio made, some weeds will be favored over others, (Table 6-3). Some of their other findings were: resulting in a field’s specific weed communities • Common chickweed and barnyardgrass seeds and weed seed bank. These interactions can ap- were lower in moldboard than in chisel. pear complex so that the effects of each individual • Large crabgrass, yellow foxtail, shepardspurse, choice can be difficult to discern from other ef- Pennsylvania smartweed, redroot pigweed seeds fects. Weed scientists are studying these factors in were higher in the corn-oats-hay rotation. combination with one another. An example is the • Giant foxtail seed decreased with more complex crop rotations and more tillage.

Table 6-3. Effect of tillage and rotation on weeds in the seed bank (up to 4-inch depths) in Wooster, Ohio, 1997-1999. Cardina, et al., 2002. Fall panicum Giant foxtail Lambsquarters total Weeds tillage rotation ------seeds/ft2 ------Chisel Continuous corn 15 20 351 527 Corn-soybean 12 77 566 870 Corn-oats-hay 43 57 41 957 Moldboard Continuous corn <1 2 144 219 Corn-soybean 9 20 144 246 Corn-oats-hay 45 22 59 545 6-7 Risk Management Guide for Organic Producers

R A producer from Waseca County who grows corn, soybean, alfalfa, and small grains found that mechanical weed control was one of the most challenging techniques to master when he transitioned to organic farming. Not only does one need to know when is the best time to perform an operation, one needs to account for how weather can prevent performing operations at the optimum time.

Primary tillage Primary tillage is the initial step in seedbed preparation. It incorporates residues from the previous crop and can incorporate fertilizers. Primary tillage is performed with moldboard, chisel, and disk plows (Figure 6-4). Primary tillage can have a mixed effect on weeds. In the case of weed seeds, it buries some weed seeds so deeply they d eere j ohn Figure 6-4. Chisel plow (above) and disk harrow (below). cannot germinate, but it also brings other seeds to the surface allow- perennial weeds, but it also can tions in the spring/fall and soil type ing them greater opportunity for spread vegetative propagules of suitability for certain equipment. germination. For short-lived weed quackgrass and Canada thistle. The type of tillage equipment seeds (see Chapter 5), moldboard The timing of primary tillage used can also promote different tillage can bury the seeds and they will encourage different weed spe- weed species. Chisel plows will may die before they can emerge. cies to predominate (Table 6-4). not affect seeds that are below However, for some weed species, Fall tillage promotes winter annual four inches. With chisel plowing, such as velvetleaf and common and perennial weeds, while spring the majority of seeds will remain lambsquarters, deep burial increas- tillage promotes spring annual in the top two inches, while with es seed longevity due to reduced weeds. Often, producers will not moldboard plowing, the majority fungal and bacterial activity and have an option as to the best time of seeds will end up below two lower oxygen levels. For existing for primary tillage and what type of inches in depth. Chisel plowing weed plants, primary tillage can kill equipment they use; what will de- may favor weeds that germinate annual weeds and suppress some termine this instead are soil condi- from shallow soil depths. 6-8 Risk Management Guide for Organic Producers

Table 6-4. Species associated with fall and spring tillage. Weed species associated with spring tillage were usually early germinat- ing and C4 grasses. Weeds associated with fall tillage were late germinating forbs and C3 grasses. Adapted from Smith, 2006. Fall Spring Common ragweed Velvetleaf Mouse-ear cress Lambsquarters Marestail or Horseweed Redroot pigweed Quackgrass Common crabgrass Common plantain Stinkgrass Poa Fall panicum Prostrate knotweed Giant foxtail Red clover Green foxtail Deere. John Figure 6-5. Field cultivator.

for when different weed species as undisturbed as possible prior Reducing risk: primary germinate. Thus, early weeds can to crop planting so weed seeds tillage. Be aware of how be controlled by seed bed prepara- remain dormant. The goal here primary tillage affects tion, while later emerging weeds is to minimize germination by existing weeds and weed seed like pigweeds may have to be con- minimizing soil disturbance. Once banks. Avoid spreading vegeta- trolled at a later date with row crop the crop is planted, the weeds that tive propagules of perennial cultivation. do germinate can be controlled weeds with primary tillage. A fundamental aspect to con- through flaming (see later in this sider in seed bed preparation is Chapter) and in-row (inter-row) the concept of providing the crop cultivation once the crop is at Seed bed prep / with an “even start.” An even start the correct stage. Note that flame Secondary tillage means controlling weeds that ger- weeding is not specific to the stale Secondary tillage further breaks minate before the crop germinates. seedbed technique—it can also be up the soil to destroy weeds and Once seed bed preparation is com- used in combination with the false prepare the seedbed, and can also plete, the crop must be planted as seedbed technique or other weed work in amendments like compost soon as possible because if crop control regimens. and manure. Field cultivators, planting is delayed (even for a mat- The false seedbed is another disks, and harrows are used for ter of hours), weeds can germinate secondary tillage weed control secondary tillage (Figure 6-5). The and get a head start on the crop. strategy. With a false seedbed, timing of seed bed preparation af- This can provide a competitive ad- secondary tillage is used repeat- fects which weeds are destroyed. vantage for the weeds and have a edly to stimulate weed germina- Weeds that emerge early like com- larger impact on yields. tion and subsequently destroying mon lambsquarters are susceptible Secondary tillage weed control those seedlings in order to deplete to seed bed preparation. See Table techniques include stale and false the weed seed bank. Much of the 5-11 or Chapter 7—Weed Profiles seedbeds (Figure 6-6). A stale effectiveness of false seedbed

seedbed is when the soil is left practices is dependent on warm 6-9 Risk Management Guide for Organic Producers

after crop emergence will have less Carmen Fernholz. Carmen Figure 6-7. The rotary hoe has an operating depth of one inch or more. negative yield impact on yield, but still may contribute to the weed seedbed soil temperatures levels to Cultivation seed bank for problems in future promote a flush of weed seed ger- Row crop cultivating tillage is years. When it comes to weeds that mination. Secondary tillage depth performed after the crop is plant- emerge with the crop, it is best to should be shallow to prevent new ed. Cultivation kills weeds by be proactive, rather than reactive. weed seeds from being brought up digging them out, burying them, Waiting until weeds are noticeable to the surface. The false seedbed breaking them apart, or drying will limit the control options. technique is commonly used in them out. In addition to control- The types of cultivation are row crops on organic farms in the ling weeds, cultivation can break broadcast cultivation (blind or full- Upper Midwest. up soil crusting and thus can field cultivation without regard for increase crop emergence, water crop rows), inter-row cultivation Reducing risk: seed bed infiltration, mineralization of nu- (between crop rows), and intra- preparation. Prepare trients, and soil aeration. row cultivation (within crop rows). a good seed bed to assure A short window of time usually the success of subsequent me- exists for timely use of cultiva- Pre-emergence broadcast cul- chanical weed control opera- tion. Weeds that emerge before or tivation Broadcast cultivation tions. Plant as soon as possible with the crop are the most critical can be performed before or after after seed bed prep to ensure an to eliminate. Weeds that emerge the crop emerges. Pre-emergence “even start”. Use a false seed- bed approach to deplete seed stale seedbed banks. The effectiveness of the Delayed or no primary tillage—g early planting—g flame weeding—g cultivation false seedbed approach will be False seedbed reduced on soils with high levels Early primary tillage—g repeated shallow cultivation—g of crop residues that depress delayed planting—g rotary hoe or harrow 3-4 days post planting—g soil temperatures. In addition, second rotary hoe or harrow operation 3-4 days later—g cultivation excessive tillage on wet and cold Figure 6-6. A comparison of stale and false seedbed techniques. soils can cause soil compaction. False seedbed is the more common method for organic farmers in the Upper Midwest. Adapted from MSU, 2005. 6-10 Risk Management Guide for Organic Producers

Weed management equipment In recent years, a resurgence of new and updated imple- R Soil moisture greatly ments for mechanical weed affects the success control has become available of rotary hoeing. An organic to organic farmers. Choosing producer in Lac Qui Parle new tools (if any) in which County says it is preferable to invest can be complicated. to rotary hoe early than to be Attending field days that dem- forced to wait until after a rain. onstrate new equipment and Rotary hoeing is less effective networking with other organic in wet soil. farmers about their experiences are some ways to learn. Below are some additional resources cultivation is done with chain har- available online that discuss rows, flex-tine harrows, spring- Carmen Fernholz. Fernholz. Carmen tooth harrows, spike-tooth harrows applications of both new and Figure 6-8. Shovel configuration on traditional weed management a chisel plow used for primary tillage. and rotary hoes and affects the top equipment. ½ - 1 ½ inches of the soil depend- ing on the equipment (Figure 6-7). Steel in the Field: A Farmers Guide to Weed Management Tools These tools are most effective un- This manual, published by Sustainable Agriculture Research and der hot and dry conditions so the Education, is an excellent resource for investigating the implements up-rooted weeds near the surface used for mechanical weed control. It provides in-depth descriptions will dry out. Pre-emergence cul- and uses of different equipment, as well as farmer’s experiences tivation is done three to five days and recommendations. The appendices include a comprehensive list after the crop has been planted. of manufacturers of weed management equipment. This publication Chain harrows are best for light is available for free at http://www.sare.org/publications/weeds.htm soils and before crop emergence. Spring-tooth and spike-tooth har- New Cultivation Tools for Mechanical Weed Control in Vegetables rows are aggressive and are best This factsheet from Cornell University is geared toward vegetable for pre-crop emergence rather than production, but has good descriptions of cultivation equipment and post-emergence. Flex-tine harrows includes the advantages and disadvantages of various harrows and and rotary hoes can be used either weeders. Also includes a list of manufacturers. Available at: http:// pre- or post-emergence (see next www.vegetables.cornell.edu/weeds/newcultivationmech.pdf section). Reducing risk: pre- Tillage equipment: Pocket identification guide emergence cultivation. This publication from the USDA-NRCS is intended as identifica- Perform when the soil tion for primary and secondary tillage equipment. Includes many is dry for maximum weed photos with general descriptions of the effects of the implements on control. Do not cultivate to a soils. http://www.mn.nrcs.usda.gov/technical/ecs/agron/Tillage%20 soil depth that is at or below pocket%20guide.pdf where the crop seed is located. 6-11 Risk Management Guide for Organic Producers

Post-emergence broadcast tion can be performed after the operation. The best-case scenario cultivation Post-emergence crop has emerged. However, for post-emergence cultivation cultivation is an important tool there are several factors to con- is when the crop is larger than to eliminate weeds that emerge sider such as the type of crop the weeds, which results in the around the same time as the crop. and crop maturity. This type of crop being more strongly/deeply Among the weeds that emerge cultivation has the greatest risk rooted and able to withstand the after planting, these will be the for crop damage and planting cultivation, and the weeds are ones that affect crop yield the rates may need to be increased to smaller and more easily uproot- most. Broadcast or blind cultiva- compensate for this type of field ed. Post-emergence broadcast

Table 6-5. Timing by growth stage for rotary hoe operations for individual crops. Adapted from NDSU. Crop Pre-emergence Post-emergence Amaranth Shallow, up to 3-5 days after germination Not recommended Buckwheat Up to 3-5 days after germination Not recommended Corn Up to and including emergence Emergence to 8 inches tall Dry Bean before crook stage 1-2 trifoliate stage Field Pea Epicotyl ½” or more below surface Emergence to 4 inches tall Flax Shallow, up to 3-5 days after germination Not recommended Lentil Epicotyl ½” or more below surface 1-4 inches tall, stand reduction will occur Oats Before coleoptile near soil surface Not recommended Pearl Millet Before coleoptile near soil surface 2-6 leaf stage Proso Millet Shallow, up to 3-5 days after germination Not recommended Sorghum Before coleoptile near soil surface Emergence to 8 inches tall Soybean Before crook stage 1-2 trifoliate stage Sunflower Before hypocotyl emergence 2-6 leaf stage Wheat, Barley Before coleoptile near soil surface 1-3 leaf stage

Table 6-6. Timing by growth stage for harrow operations for individual crops. Adapted from NDSU. Crop Pre-emergence Post-emergence Amaranth Shallow, up to 3-5 days after germination Not recommended Buckwheat Up to just before emerging Not recommended Corn Up to and including emergence Emergence to 8 inches tall Dry Bean before crook stage 1-2 trifoliate stage Field Pea Epicotyl ½” or more below surface Emergence to 4 inches tall Flax Shallow, up to 3-5 days after germination Not recommended Lentil Epicotyl ½” or more below surface 1-4 inches tall, stand reduction will occur Oats Before coleoptile near soil surface Not recommended Pearl Millet Before coleoptile near soil surface 2-6 leaf stage Proso Millet Shallow, up to 3-5 days after germination Not recommended Sorghum Before coleoptile near soil surface Emergence to 8 inches tall Soybean Before crook stage 1-2 trifoliate stage Sunflower Before hypocotyl emergence 4-6 leaf stage Wheat, Barley Before coleoptile near soil surface 1-3 leaf stage 6-12 Risk Management Guide for Organic Producers

post-emergence cultivation. Ro- tary hoes are more effective on crusted soils than are harrows or tine weeders. Rotary hoeing is less effective when the soil surface is rough. Tine weeders, harrows and rotary hoes are all hindered

Carmen Fernholz. Carmen by large amounts (greater than

Figure 6-9. Flex-tine weeder. This tool is becoming more prevalent among 30% coverage) of surface residue organic producers in the Upper Midwest. (Figure 6-10). Harrows and tine cultivation is performed with ro- velvetleaf, wild proso millet, wild weeders may be more effective on tary hoes and harrows. Timing of oat, and woolly cupgrass are not loamy soils than are rotary hoes. these operations is critical—see effectively controlled by rotary Tine weeders have different tines Tables 6-5 and 6-6 for the recom- hoes or harrows. Rotary hoes, tine varying in flexibility and thickness mended crop stages at which to weeders, and harrows are more that can be used depending on the rotary hoe and harrow. effective on warm, sunny, and heaviness of the soil. Rotary hoes The best time to rotary hoe windy days, which help dry out are operated at speeds of seven is when weeds are newly ger- small weed seedlings pulled out of to twelve miles per hour, while minated and have reached the the soil by these operations. harrows are usually operated at “white thread” stage (also called Soil type and condition may speeds between four to six miles the “white root” or “white sprout” determine which tool is best for per hour. stage). Weeds in the white thread stage have not emerged from the soil. The top inch of soil must be examined to determine if weeds are at the white thread stage. Grass weeds that are past the one-leaf stage or broadleaf weeds that have formed their first true leaves are too firmly-rooted to be controlled with the rotary hoe. However, harrows and tine weeders are more effective on weeds that are somewhat more mature than is the rotary hoe (Figure 6-9). Perennial weeds like Canada thistle, quack- grass, yellow nutsedge or deep-

Carmen Fernholz. Carmen germinating weeds like cocklebur, Figure 6-10. Large amounts of residue can interfere with flex tine weeders. 6-13 Risk Management Guide for Organic Producers

R An organic producer from McLeod County says timing is the key to Stand losses—post-emergence operations managing weeds in his corn Once the crop has started growing, any weed control operations and soybean crops. You must performed will have the potential to damage the crop. Crop stand get the first weed flush after losses due to post-emergence operations like harrowing or rotary the crop is planted with a hoeing will range from 1% to 25%. Establishing whether weed con- harrow or rotary hoe. The 1st trol operations are too aggressive is an important aspect to maxi- or 2nd cultivation between the mizing crop yields. To determine stand losses, producers should rows can be timed to last the take a crop stand count prior to and after post-emergent mechanical rest of the season. weed control. This can aid in planting rate decisions and can ensure that the control is not too aggressive. Frequency of weed control operations should be dependent on Rotary hoe versus harrow weed pressure. Two or three passes for post-emergence control is Organic producers will often usually sufficient and additional cultivations can adversely affect have a preference for a type of crop stand density in addition to adding to cost of production. Even tillage implement depending on though more weeds are killed with each successive pass, more of the field conditions. A producer from crop is also being killed. There is a tradeoff between the yield loss Waseca County prefers the rotary potential due to weeds and reduced crop stands. A reasonable loss hoe in his soybeans, although he of crop stand per operation should be less than 5%, but experienced notes that the rotary hoe is less ef- organic farmers say if a few crop plants are not being taken out, the fective on fields with loamy soils operation is not aggressive enough. Once the crop loss for mechani- and better tilth. Another organic cal weed control is estimated, it can be used as a factor to determine producer from Waseca County what planting rates should be used in subsequent years, assuming does not use the rotary hoe be- the number of weed control operations is similar. cause it misses spots due to his soil, which is highly variable and has an uneven surface. He har- Reducing risk: post- Inter-row cultivation Inter-row rows instead. He cautions that emergence cultivation. cultivation controls weeds that soybeans are more sensitive to Use the proper equipment grow between the rows, and harrowing because of their fragile for the soil conditions present. therefore is only used in row cotyledons at the crook stage. Yet Time operations to the correct crops (Figure 6-11). Row crop another organic producer from crop and weed growth stage— cultivation is secondary to the Lac Qui Parle County is moving see Tables 6-5 and 6-6. Do not weed control operations that away from the rotary hoe and has use post-emergence cultivation were performed earlier because not used it in 4 years. His reasons on soybean at the crook stage; the earlier emerging weeds are are that the rotary hoe requires it is too fragile. more critical to control due to the use of a big tractor, which can their greater potential to reduce cause soil compaction. He can crop yield. If the pre- and post- cover the same width with a har- emergence operations were ef- row and a smaller tractor. fective, there may be a lag before 6-14 Risk Management Guide for Organic Producers

R Organic farmers may need to prove they have effective weed and pest management in order to make an insurance claim. Your organic plan detailing your weed control operations will provide support. John Deere John Reducing risk: inter-

ourtesy o f ourtesy row cultivation. Do not

Photo c Photo cultivate too deeply or crop Figure 6-11. Row crop cultivators only affect weeds between these corn rows. roots can be damaged. Do not rely on inter-row cultivation as inter-row cultivations must be Cultivators can affect weeds up your primary method for weed done. Inter-row cultivation is to five inches tall as compared to control—use in conjunction done three to five weeks post a rotary hoe which only controls with pre- and post-emergence planting. Tools used for inter-row newly germinated weeds. Gener- operations. cultivation include cultivators, ally, cultivation is performed at rotary tillers, brush weeders, depths less than two inches so that rotary cultivators, rolling cultiva- crop roots are not damaged and Intra-row cultivation Intra-row tors, basket weeders, and rolling soil moisture is conserved. cultivation, also called in-row cul- harrows. If the young crop is in danger tivation, is accomplished through Inter-row cultivation is low of becoming buried by soil or the use of equipment that controls risk to the crop compared to post- weeds during cultivation, shields weeds within the crop row. This emergence broadcast operations. can be used on the cultivator. The type of cultivation is more com- Because cultivation is performed goal is to maximize the cultiva- monly used in horticultural crops, between the rows, the crop tion area between the crop rows but interest in controlling weeds should not be directly affected without damaging the crop. Inter- within a crop row is increasing for by the machinery. Cultivation is row cultivators also can have those who grow agronomic crops. generally performed when the modifications that allow soil to As mentioned previously, weeds crop is four inches tall and up to be ridged upon the crop row to that occur at the same time as the the height where equipment will control within-row weeds. Weeds crop can have a great effect on still clear the crop. are buried along with the crop yields and the ones within the crop Inter-row cultivation is most ef- so this method can only be per- row are difficult to impossible fective when weeds are not overly formed on certain crops such as to control after the crop is past a mature. Timing of inter-row culti- corn and only at certain stages of certain maturity. Equipment for vation is not as critical of an issue crop growth. intra-row cultivation is specialized as it is for broadcast cultivation. precision tools that include torsion 6-15 Risk Management Guide for Organic Producers

weeders, spring hoes, spyders, electronic guidance systems. One possibly not viable for large-scale and finger weeders. Intra-row drawback is that this equipment operations. For more information, cultivation operations must be must be operated slower than most consult the sources in the “Weed done precisely to avoid crop dam- other weed control equipment management equipment” Side- age and may require the use of and thus is time-consuming and bar.

Established perennials Perennial weeds such as quackgrass or Canada thistle are common weed problems in the Midwest and among the most difficult perennial weeds to manage with mechanical weed control because even small pieces of their rhizomes can generate new plants (Table 6-7). Perennials with deep rhizomes will not be affected greatly by typical weed control operations that are done in the spring. At the same time, peren- nials with shallow rhizomes will only be affected in the short term Table 6-7. Equipment effectiveness in managing different by typical seed bed preparation perennial weeds. Tillage for perennial weeds will be more effective when done prior to active growth or flowering to lower plant reserves. and cultivation and bulbs can typ- Adapted from Liebman et al, 2001. ically survive these operations. Weed Growth moldboard Chisel Field Quackgrass and field sowthis- species Habit plow plow cultivatoR tle are most susceptible to bury- Canada thistle deep rhizomes Fair Poor Fair Common milkweed deep rhizomes Fair Poor Fair ing when new shoots are at the Common plantain fibrous root Good Fair Fair three-to-four leaf stage in spring, Curly dock taproot Good Fair Fair followed with a second tillage op- Field bindweed deep rhizomes Fair Poor Fair eration. As a last resort, perennial Field sowthistle shallow Fair Poor Fair weeds can be controlled by fallow creeping roots cultivation. Most will respond Nutsedge bulb Fair Poor Fair negatively to repeated cultiva- Quackgrass shallow rhizomes Fair Poor Fair tion at two to four week intervals Table 6-8. Effects of repeated tillage on number of Canada (Table 6-8). Another alternative is thistle shoots after one year in Lamberton, MN, 2003 and including perennial crops in rota- 2004. Disking to a depth of four to six inches was initiated in May or June tions. Canada thistle can be con- and was repeated every three weeks until fall. Repeated tillage significantly trolled by growing alfalfa for three reduced the number of thistle shoots after one season in both 2003 and 2004. The number of shoots increased under the corn crop in both years. years. A taprooted perennial weed % thistle shoot change species may be impacted by being Treatment 2003 2004 buried, while a fibrous-rooted spe- Repeated tillage, May start -93 -87 cies can be chopped or buried dur- Repeated tillage, June start -96 -93 ing primary or secondary tillage. Corn, one rotary hoe, 2 cultivations 20 110 6-16 Risk Management Guide for Organic Producers

Flame weeding

Flame weeding is becoming more popular with organic farm- ers in Minnesota and the Upper Midwest. This technique uses flaming propane burners to rup- ture the cells of the weeds, which usually die within three days. In Figure 6-12. In-row flame weeding. row crops, flame weeding is used rows, as they usually have other There is no single recommended as a method of directed, within- mechanical options for broadcast setting; producers will need to row weed control (Figure 6-12). weeding that can be performed gauge their conditions and make However, it can also be used as a faster than flame weeding and adjustments accordingly. Gener- broadcast technique, usually prior may be cheaper to operate. ally, around seven gallons of pro- to crop emergence, which is most When used after the crop has pane is used per acre. suitable when using the stale emerged, flame weeding is timed Producers gauge effectiveness seedbed technique. Most organic when the crop is at the correct of each flame weeding operation row-crop farmers in the Upper stage so that minimal damage oc- by using the fingerprint method. Midwest use flame weeding to curs. The proper stage for flame Weeds are not burned to a crisp, control weeds within the crop weeding varies by crop—see but instead should show a water- next sections. Ideal conditions to mark immediately after the flame flame are when the crop is bigger weeding when a leaf is pressed Two organic growers R than the weeds. Flaming works (Figure 6-13). Corn will also in Waseca County best on dry, calm days. demonstrate the same effect (Fig- agree that lack of diverse weed Tractor speed and gas pressure ure 6-14). control equipment availability are two components that can be The age and type of weeds can be a risk factor in weed modified to optimize weed kill. determine flaming effectiveness. management. Having different The slower the speed and/or the Annual weeds are more vulner- equipment provides greater higher the gas pressure will in- able to flame weeding compared flexibility in timing operations. crease effectiveness, but potential to perennial or biennial weeds. The tools that they use for crop damage must also be taken Broadleaves are more suscep- their soybean and corn crops into consideration. Typical tractor tible than grasses and broadleaf include rotary hoes, harrows, speeds and propane pressures are weeds less than two inches tall flame weeding equipment, in the range of three to five mph are the most susceptible. Flam- and in-row cultivators. and 30 – 40 PSI, respectively. ing is more effective on lambs- 6-17 Risk Management Guide for Organic Producers

Thumbprint Markings

Figure 6-13. Using the thumbprint method to analyze damage, the weed above has Figure 6-14. Fingerprint Figure 6-15. This corn is at the proper stage for flam- been affected as is shown by the marking on corn leaf. ing. The fourth leaf has not yet developed. dark spot on leaf where a thumb was pressed. The grass is not vis- ibly burnt, but this indicates the flaming does not control grasses Flame weeding corn correct level of flaming. well, rotary hoeing or harrow- There are two options for flaming quarters, chickweed, velvetleaf, ing may be a better option for once corn has emerged. The first and pigweed than on mustards, fields where grasses predominate is when the growing point is still ragweeds, and grasses. Newly (Table 6-9). Producers should below the soil when corn is one to emerged grasses are not much also be aware that warming the two inches high (Figure 6-15). affected because their growing soil with flame weeding may At this stage, nutrients are still be- point may still be underground stimulate some weed seeds such ing obtained from the seed. Direct at the time of flame weeding. as pigweeds to germinate. flaming corn after the 4-leaf stage Weeds that have germinated, but Of the agronomic crops com- will likely lead to damage of the are not yet emerged, will also not monly grown in the Upper Mid- crop. If necessary, corn at later be affected by flame weeding. west, only corn and soybean are stages (greater than 10 inches) can Dust and dew on weed leaves flamed post-emergence. Flaming be flamed by directing the flame may protect weeds and limit in these crops is discussed below. under the leaves and protecting the flaming effectiveness. Because corn plants using shields. Corn is the crop least sus- Table 6-9. A comparison of rotary hoe and flame weeding. Both tools can be equally effective under the right conditions. Producers can ceptible to damage by flaming minimize risk by having as many weed control implements as possible at their because for several weeks after disposal. Adapted from Mutch et al., 2008. emergence the seed and growing Rotary hoe Flame weeding Soil type can limit effectiveness Soil type does not matter point remain below ground. How- Operation takes less time Operation takes more time ever, corn will have reduced yields Can be performed in more crops Few crops can withstand flaming if the timing of flaming is wrong, Disturbs soil structure Preserves soil structure the speed is too slow (e.g. 1 mph), Soil must be dry Soil can be wet or dry or if flaming is repeated multiple Effects may be longer lasting Little residual effect Cheaper More expensive; dependent on gas prices times. Corn will look damaged Timing of operation is critical Timing of operation is critical after flaming, but it generally has stimulates further weed Does not stimulate weed enough reserves to recover if the germination germination flaming was timed properly. Windiness increases effectiveness Windiness decreases effectiveness 6-18 Risk Management Guide for Organic Producers

Flame weeding soybean 6-16). Soybeans will be dam- Organic farmers conduct flame aged if they are flamed anytime weeding of soybean in Min- after the crook stage. It is im- nesota, but the practice is not portant to be aware that after the as established as it is for corn. crook stage, vegetative develop- Overall, flame weeding in soy- ment can occur quickly. Some- Figure 6-16. The soybean plant bean presents a high risk of dam- times it will only be a matter of on the left can survive flame weeding, but any growth stage where the age to the crop. If flame weed- hours before the growth stage cotyledons are no longer protecting ing is used, it is best before the progresses from safe to a high the first leaves as in the soybean on soybeans emerge or at the crook probability of damage. Flame the right is susceptible to injury from flame weeding. stage before leaves unfurl (Figure weeding of soybean is a high risk procedure and should be Producer profile considered an advanced tech- nique for those with an above- Flame weeding in Faribault County average level of flame weeding An organic grower in Faribault County has been flame weed- knowledge and expertise. ing successfully for over 30 years. He routinely flame weeds corn, but usually will not flame soybean. Reducing risk: flame this producer flame weeds corn when it is between 10 to weeding. Use flame 12 inches tall. When flaming corn at the 10-12" stage, the fire is weeding on a smooth and shot underneath the leaves to minimize corn damage. He culti- flat seedbed rather than an vates and flames at the same time with the same machine, but uneven and cloddy seedbed he notes that most people flame and cultivate separately. to lower risk for misdirected Cultivation and flame weeding is only possible for him flames. If weeds are noticeably because he flame weeds at a later crop stage. Flame weeding burnt immediately after and cultivating at the same time when corn is a few inches the operation, then the tall would result in the cultivation burying the crop seedlings. operation was excessive— He flames weeds at about 4 miles per hour at 30 to 35 PSI. He use the fingerprint method will do one round and gauge damage and then sometimes to determine if weeds are comes back and flames again a week later. damaged. Flame weeding of his biggest weed problems are pigweed, foxtail, and soybeans is extremely high risk Canada thistle. Due to the perennial nature of Canada thistle, compared to flame weeding he finds that while thistle will appear damaged after flaming, of corn. Flame weeding can it will grow back quickly. Foxtail will not be controlled unless be potentially dangerous to it is very small. The flame weeder is just one of many tools he human and animal health; uses for weed control. He also utilizes a harrow, cultivator, follow all safety precautions for cover crops, smother crops, and a diverse rotation. the use of flammable liquids. 6-19 Risk Management Guide for Organic Producers

R A producer from Waseca County says Rescue Scouting he is constantly scouting anytime he goes out. He recommends that transitioning operations The contribution of scouting in farmers scout often in order to weed management is often un- get a feel for when individual Inter-row cultivation is usually derappreciated. Fields should be weed species or weed flushes the final weed management step checked before mechanical weed occur to determine when for the season. However, when control operations begin to en- harrowing or rotary hoeing timely weed control operations sure that the correct implement is should be done. Otherwise, he were not able to be performed, chosen to control weeds at their says, you will always be playing as in cases where weather was proper growth stages. Once an catch-up. In organic farming uncooperative, weeds can escape. operation has been completed, when dealing with weeds, you If there are spots where weeds fields should be checked after need to be ahead of the game. were not adequately controlled, four or five days or sooner to de- producers can have day labor- termine if the procedure was suc- ers hand weed. Another option cessful and to decide if another Reducing risk: scouting. as a last resort is to till under the operation will be necessary. Write memos about portion of a field where weeds scouting activities. dominate. An organic producer Transitioning producers R should scout their fields often Reducing risk: rescue in Lac Qui Parle to determine patterns of weed operations. Make sure County has problems with emergence. Keep records on that rescue operations are sunflowers at the edge of one weed management practices worthwhile. Remove hand- of his fields. He will go in with a from year to year and note weeded plants from the field if hand pruner and cut the flower effectiveness of the various they have gone to seed so they heads off so the seeds do not mechanical weed control do not contribute to the seed remain on the field. Organic operations performed. Create bank. Organic farmers must farmers need to be sensitive weed maps for each field noting be prepared to forfeit part of a to the impact of adding to the location and relative density crop if weeds get out of control weed seed bank. for each weed species. to protect their fields from adding an excessive amount of weed seeds to the seed bank. 6-20 Risk Management Guide for Organic Producers

Conclusion

This chapter has emphasized the risk in not performing mechanical weed control operations at the optimum time. However, it is important to note that it is possible to perform too many operations. The risk in this is damage to soil structure, crop injury and lowered yields, or unnecessary time and labor spent on redundant operations. Producers should try to strike a balance between controlling weeds and maximizing crop yields. An indispensable component of weed management is scouting for weeds. This includes identifying your weeds and determining when those weeds emerge. Weed operations should be timed to coincide with emergence of your problem weeds. For help in weed identification and weed emergence times, see Chapter 7: Weed Profiles. John Deere John Figure 6-17. Disk harrow. 6-21 Risk Management Guide for Organic Producers

Quiz: Weed Management

Points Score Points Score 1. Which of the following is closest to 9. Which of the following do you primarily the rotation you follow? use to provide soil fertility? Two-year rotation with cover crop 0 Manure 1 Three-year rotation 1 Compost 2 Four-year rotation 3 Green manures 4 Five or more year rotation 5 Other amendments 2 2. Does your rotation include a perennial crop? A mix of above 2 Yes 5 10. Do you time your nutrient application to No 0 coincide with crops’ needs? 3. Does your rotation include a cover or Yes 3 smother crop? No 0 Yes 2 I don’t know 0 No 0 11. Do you apply nutrients only at amounts 4. Do you ensure that the seed you plant is at which the crops’ needs are met? clean and does not contain weed seed? Yes 3 Yes, always 3 No 0 Yes, most of the time 1 I don’t know 0 No, not really 0 12. How do you apply compost or manure? 5. Do you plant your crop as soon as possible Broadcast, no incorporation 0 after seed bed prep, giving the crop an even start? Broadcast, with incorporation 2 Yes, always 5 Injection (manure only) 3 Yes, most of the time 3 Not applicable 2 No, not really 0 13. Do you make an effort to ensure that the 6. Which of the following describes your view manure you apply has relatively few weed seeds? on delayed planting? Yes, always 2 I always plant at a later date Yes, most of the time 1 regardless of conditions 0 No, not really 0 I sometimes plant at a later date, 14. Can you identify the specific weeds that especially if weeds are heavy 3 occur in your fields? I usually do not plant at a later date 2 Yes 5 7. If you delay planting, do you know if you have Yes, most of the them 3 early-emerging weeds (the ones most affected No 0 by delayed planting)? 15. Do you know at which stage your weeds Yes, I have early-emerging weeds 3 are most vulnerable to control? No, I don’t know if I have Yes 5 early-emerging weeds 0 Yes, for most of them 3 I do not delay planting 1 No 0 8. Do you adjust your planting rate to 16. Are you attentive to the timing and density accommodate changes in the number of of weed emergence in your fields each year? mechanical weed control operations? Yes, always 5 Yes, always 3 Yes, most of the time 3 Yes, usually 1 No, not really 0 No, my planting rate is always the same 0

continued next page

6-22 Risk Management Guide for Organic Producers

Quiz: Weed Management

Points Score Points Score 17. Do you have a diversity of tools for 26. Are you prepared to perform rescue mechanical weed control? operations if weed escapees become dominant? Yes 5 Yes, always 3 No 0 Yes, most of the time 1 18. After performing a weed control operation, No, not really 0 do you gauge its effectiveness? 27. Do you keep records on your weed Yes, always 3 management practices and their effectiveness? Yes, most of the time 1 Yes 3 No, not really 0 No 0 19. Do you gauge how much crop loss is occurring 28. Do you scout your fields for weeds before with your mechanical weed control operations? and after weed control operations? Yes, always 3 Yes, always 3 Yes, most of the time 2 Yes, most of the time 1 No, not really 0 No, not really 0 20. Do you try to account for unpredictable 29. Do you feel confident that you are not weather conditions when planning mechanical doing too many mechanical weed control weed control operations for the season? operations? Yes, always 3 My operations are timed to control the Yes, most of the time 1 weed flushes I know occur in my fields 5 No, not really 0 I always do the same operations 21. Do you know when the best time to rotary regardless of weed pressure 2 hoe or harrow for each of the crops you grow? I am not sure 0 Yes 5 30. Which of the following mechanical weed Not sure 0 control strategies do you follow? 22. Do you try to time cultivation to warm, Give yourself 2 points for each strategy. dry conditions? Till or cultivate as shallowly as possible 2 Yes, always 3 Till or cultivate as infrequently as possible 2 Yes, most of the time 1 Each operation is geared toward No, not really 0 specific weed issue 2 23. Do you know how effective different Limit soil impact of weed control 2 equipment is on perennial weeds? Equipment used is appropriate for Yes 2 weed growth stage 2 No, not really 0 Weeds are targeted when small 2 24. If you use flame weeding, how do you 31. Which of the strategies do you plan gauge its effectiveness? on implementing in the future? Weeds show signs of visible burning 0 Give yourself 1 point for each strategy you plan to use from Weeds show watermark when the above list. pressed with finger 3 Do not check weeds after flame weeding 0 Do not flame weed 3 25. If you use flame weeding, do you flame weed soybean? If your score is: Your risk is: TOTAL Yes 0 76 or greater Low 36 to 75 moderate No 3 35 or less high Do not flame weed 3 6-23 Risk Management Guide for Organic Producers

For More References Cloutier, D.C., R.Y. van Katovich, J., Becker, R. Information der Weide, A. Peruzzi, and Doll, J. 2005. Weed Alexandrou, A. 2004. and M.L. Leblanc. 2007. Seed Survival in Livestock Organic Weed Control Evaluation of in-row Chapter 8: Mechanical Systems. University of Cultural and Mechanical weed cultivators in or- Weed Management in Non- Minnesota Extension Service Methods by Mary-Howell ganic soybeans and corn. chemical Weed Management: and University of Wisconsin and Klaas Martens. ACRES, A project report submit- Principles, Concepts and Extension. August 2002, Vol. 32, No. ted to the Organic Farming Technology by Upadhyaya, 8 http://www.acresusa.com/ Research Foundation. http:// M.K. and R.E. Blackshaw. LeBlanc, M.L. and D.C. toolbox/reprints/Organic%20 ofrf.org/funded/reports/ CABI Publishing. Cloutier. 2001. Susceptibility weed%20control_aug02.pdf alexandrou_02s24.pdf of row-planted soybean Davis, A. from Chapter 2. (Glycine max) to the rotary Weedsoft Yield Loss Buhler, D.D., and J.L. Soil Properties in Integrated hoe. Journal of Sustainable Calculator – Producers can Gunsolus. 1996. Effect of Weed Management: One Agriculture 18(4):53-61. enter in their crop and weed date of preplant tillage and year’s seeding, February data and the calculator with planting on weed populations 2005, Michigan State Liebman, M., C.L. Mohler figure out the yield losses. and mechanical weed control University Extension and C.P. Staver (eds.). 2001. http://driftwood.unl.edu/ in soybean (Glycine max). Bulletin E-2931. Ecological Management weedsoft/YieldLossCalc/ Weed Science 44:373-379. of Agricultural Weeds. YieldLossOne.php Endres, G., D. Berglund, Cambridge, U.K.: Cambridge Canadian Organic Growers. A. Dexter, and R. Zollinger. University Press. Steel in the Field: a farmer’s 2001. Organic Field Crop August 1999. Mechanical guide to weed management Handbook, 2nd edition. Weed Control with a Harrow Liebman, M. and A.S. Davis. tools. http://www.sare.org/ Canadian Organic Growers. or Rotary Hoe. NDSU 2000. Integration of soil, publications/weeds.htm Extension Service. W-1134. crop and weed management Cardina, J., C.P. Herms, and in low-external-input farm- Principles of Sustainable D.J. Doohan. 2002. Crop Fernholz, C.M. 1995. ing systems. Weed Research Weed Management for rotation and tillage system Sustainable Management 40:27-47. Croplands from ATTRA. effects on weed seedbanks. Practices for the 21st http://attra.ncat.org/attra-pub/ Weed Science 50:448-460. Century. 2nd edition. Lovely, W.G., C.R. Weber, weed.html A-Frame Press: Madison, and D.W. Staniforth. 1958. Cisneros, J.J. and B.H. MN. Effectiveness of the rotary Weed Management, eXten- Zandstra. 2008. Flame weed- hoe for weed control in soy- sion. http://www.extension. ing effects on several weed Forcella, F., K. Eradat- beans. Agronomy Journal org/article/19642 species. Weed Technology Oskoui, and S.W. Wagner. 50:621-625. 22:290-295. 1993. Application of weed seedbank ecology to low- Martens, K. and M. Martens. Clark, A. (editor). 2007. input crop management. 2005. Look, Ma! No Weeds: Managing Cover Crops Ecological Application Early Season Weed Control. Profitably. Third edition. 3(1):74-83. Part 1: The basics of ef- Handbook Series Book 9. fective tillage techniques. Published by the Sustainable Gunsolus, J.L. 1990. The New Farm. January 27, Agriculture Network, Mechanical and cultural 2005. Beltsville, MD. http://www. weed control in corn and sare.org/publications/cover- soybeans. American Journal Martens, K. and M. Martens. crops/covercrops.pdf of Alternative Agriculture 2005. Look, Ma! No Weeds: 5(3):114-119. Early Season Weed Control. Part 2: Blind cultivation. The New Farm. February 10, 2005. 6-24 Risk Management Guide for Organic Producers

Martens, K. and M. Martens. Schonbeck, M. 2010. An or- 2005. Look, Ma! No Weeds: ganic weed control toolbox. Early Season Weed Control. eXtension.org and eOrganic. Part 3: In-row cultivation. org. http://www.extension. The New Farm. March 17, org/article/18532 2005. Smith, R.G. 2006. Timing Mohler, C.L. 2001. of tillage is an important fil- Enhancing the competitive ter on the assembly of weed ability of crops. Pp. 269- communities. Weed Science 321 in M. Liebman, C.L. 54:705-712. Mohler and C.P. Staver (eds.) Ecological Management Sustainable Agriculture of Agricultural Weeds. Network. 2001. Steel in the Cambridge, U.K.: Cambridge Field: a farmer’s guide to University Press. weed management tools. Edited by Greg Bowman. Mohler, C.L., J.C. Frisch, Sustainable Agriculture and C.E. McCulloch. 2006. Research and Education, Vertical movement of weed United States Department of seed surrogates by tillage Agriculture. implements and natural processes. Soil and Tillage Taylor, E., K. Renner, and Research 86:110-122. C. Sprague. 2008. Integrated weed management: Fine tun- Mutch, D.R., S.A. Thalmann, ing the system. Michigan T.E. Martin, and D.G. Baas. State University Extension. 2008. Flaming as a method of weed control in organic farming systems. Michigan State University Extension Bulletin E-3038.

Renner, K.A. 2000. Weed pest ecology and manage- ment, in Michigan Field Crop Pest Ecology and Management. Michigan State University Extension Bulletin E-2704, January 2000.

Schonbeck, M. 2009. Knock weeds out at critical times. eXtension.org and eOrganic. org. http://www.extension. org/article/18882