Weeds Your Way: How Upstate New York Organic Farmers Manage Weeds

Introduction

Although organic farming differs from conventional agriculture in several key ways, one of the greatest differences is in the way farmers manage weeds. Organic weed management focuses on the integration of multiple practices to prevent increases in weed population over time, rather than the use of synthetic herbicides to kill already existing weeds. Organic farmers have identified weeds as a leading research priority and challenge to organic production (Baker and Mohler, 2014; Walz, 2004).

What is Weeds Your Way?

The objective of the project was to assist development of a farmer-driven approach to weed management. The premise of the project was that experienced organic farmers have valuable information about weed control. Our approach was to summarize the tactics used by the region's most experienced and successful farmers and make the information available to less experienced farmers and to professionals who work with farmers. Organic growers regularly adapt and share strategies and techniques for efficient weed management, and our intent was to facilitate that process. Also, researchers can benefit from a better understanding of existing farmer practices to examine and validate or refute their efficacy (DeDecker, et al. 2014; Jabbour, et al., 2014; Riemens, et al., 2010). The approach taken here was intended to complement rather than replace systematic, prescriptive extension publications on weed management like van der Schans and Bleeker (2006) and Davis et al. (2005). Long-term management of weeds in organic farming systems requires an understanding of how to disrupt the life cycles of various weed species and prevent them from becoming established through a variety of cultural practices. When weeds get established, tactics can be used to reduce weed density and still get a decent yield.

The information presented here is based on what we were told by organic farmers in interviews, a focus group and a field day (Baker and Mohler, 2014). The farmers interviewed were located throughout upstate New York, with one located in western Massachusetts near the New York border. These farmers were selected based on referrals from agricultural professionals, including Cooperative Extension and Integrated Pest Management specialists, and by other farmers based on their observed skills and expertise in managing weeds. The focus group was held just prior to the 2011 meeting of the Northeast Organic Farmers Association of New York. Farmers at the focus group identified to the authors the strategies and techniques that they found useful for managing weeds in field and vegetable crops, emerging weed management challenges for organic growers, and promising avenues for research. A field day was held in western New York at the end of August 2011, where farmers shared with one another strategies and practices that they used to manage weeds.

Table 1: Characteristics of farmers interviewed

The farmers participating tended to be more experienced and operating on a larger scale than the average New York farmer. In addition, the farmers were representative of a diverse range of farming systems and marketing channels.

In 2010 and 2011, 20 organic farmers were interviewed using a systematic questionnaire. The farmers included five with field crop systems, eight vegetable growers, two growers with both field crop and vegetable crop production, and two dairy farmers who grow both pasture and field crops, and two dairy farmers who raise pasture but did not produce any other crops at the time of the interview. These last two farmers were excluded from the results.

Important Weed Species

Farmers identified a small subset of the hundreds of weed species present in New York State as posing problems for crop production (Table 2).
 

Table 2: Weeds identified as important by two or more of the farmers interviewed

Source: Baker and Mohler 2014, reprinted by permission of Cambridge University Press.

Other weeds reported included burdock (Arctium spp.), curly dock (Rumex crispus L.), vetch (Vicia spp.), and wild garlic (Allium vineale L.). Farmers did not identify specific annual grasses. In additional to foxtail, annual grass species observed on the farms visited included annual bluegrass (Poa annua L.), cheatgrass (Bromus secalinus L.), and witchgrass (Panicum capillare L.), among others.

Problem weeds were a function of the cropping system. Weed species identified as important by growers who work with both vegetable and field crop systems included common lambsquarters, pigweed, foxtail, common ragweed, and quackgrass. Field bindweed and cocklebur were seen as problems only in field crop systems. Purslane and common chickweed were reported as problem weeds only by vegetable growers. Most who identified galinsoga as a significant problem were vegetable producers. Weed populations were also observed to shift over time and point in organic transition. Bindweed, quackgrass and yellow nutsedge were reported to decline on some farms following the introduction of organic practices. 

Weed Control Strategies
 

Table 3: Farmer control strategies and techniques for specific problem weeds

Source: Baker and Mohler 2014, reprinted by permission of Cambridge University Press.

Farmers use a variety of strategies to manage particular problem weeds. Several of these strategies are based on knowledge of a weed's life cycle or ecological characteristics. Four important weed management strategies were common among the farms studied: crop rotations, intercropping, cover cropping, and fertility management.

Crop Rotation

Rotations that incorporate crops that vary in growth habit, life cycle, planting date and harvest time, and associated tillage, cultivation and mowing practices can suppress weeds by disrupting their life cycles (Mohler and Johnson, 2009). Crop rotation is also an important tool in organic farming for fertility, disease, and insect pest management. Most of the vegetable crop growers described rotation strategies that were explicitly based on disease prevention (alternating crop families) or fertility management (alternating crops with heavy and light nutrient demands) rather than weed management. The rotations of three vegetable growers specified alternating non-vegetable crops—such as hay crops or small grain/legume cover crops—with row-planted vegetables. This practice maintains soil quality and suppresses weeds. Almost all field crop growers used rotations that alternated sod, row crops, and small grains. Several field crop farmers mentioned the importance of limiting the number of row crops in the rotation to prevent weed problems. As the farmers became more experienced they tended to use more diverse crop rotations.

Cover Crops

As with crop rotation, the use of cover crops can provide multiple benefits to the farming systems, including erosion prevention, improvement of soil quality, disease management, insect pest reduction, and weed suppression. Cover crops can suppress weeds by outcompeting them for needed resources and by impeding their growth through the secretion of toxic substances (allelopathy). The cover crops used varied with cropping system. Farmers explicitly noted the usefulness of several cover crops for weed suppression (Table 4).
 

Table 4: Cover crops identified by organic farmers as weed smother crops

Source: Baker and Mohler 2014, reprinted by permission of Cambridge University Press.

Figure 1 demonstrates the weed pressure that is associated with different planting densities of buckwheat. On the left is buckwheat broadcast sown at 60 lb/A and packed. On the right is buckwheat sown at 20 lb/A with gaps. Note the pigweed pressure in the gaps.  

Figure 1: Densely planted buckwheat on the left; Lightly planted buckwheat on the right. Photo credit: Brian Baker

Fertility Management

Fertility practices should favor crop growth over weed growth. High rates of fertilization can favor weeds over many crops. Manure is an important soil amendment on organic farms—and can be a significant source of weed seeds. Farmers believed that some weeds had been introduced or increased by the application of uncomposted manure. Composting manure is known to reduce or eliminate weed seeds, and some farmers exclusively use manure that has been composted. The NOP standards require that crops grown for human consumption must have an interval from manure application to harvest of 120 days for edible parts in contact with soil, and 90 days for other food products. Crops grown with composted manure do not have this requirement, which may be a more significant factor than weeds for using compost. Farmers explicitly acknowledged the benefits of composting for weed management. However, this benefit can be lost if weeds are allowed to go to seed in or around compost piles. Some farmers noted that crops grew better than certain specific weeds after compost was applied. Compost consistently improved soil structure in a way that helped tillage and cultivation.

Variety Selection

Most growers select varieties for reasons other than competitiveness against weeds. Even those who said that they planted varieties competitive with weeds indicated that weed management was never the only reason and seldom the primary reason for variety selection. Specific crops and traits that increase a crop's competitiveness with weeds include corn varieties that have early emergence and good early vigor. Klaas Martens of Penn Yan, NY noted that soybean varieties with bushy canopies are more competitive than those with open canopies. Similarly, forage oats with wide leaf blades will shade soil faster than varieties with narrow or average leaf blades.

Equipment for Tillage and Cultivation

Mechanical tillage and cultivation are important techniques for organic weed management. Most farms that are in intensive vegetable production till intensively and cultivate frequently. Although field crop producers work the soil less, they typically make several passes over the field with tillage or cultivation implements for each grain crop.

Figure 2: Front-mounted toolbar set up by Martin Stosiek of Hillsdale, NY. The front-mount enables the operator to see the rows being cultivated while looking forward, as opposed to looking behind with a rear-mounted cultivator or down for a belly-mount. Photo credit: Brian Baker

Farmers were asked what primary and secondary tillage tools they used. Then they were asked what equipment they used for cultivation (Table 5). 

Table 5: Tillage and cultivation equipment reported

Source: Baker and Mohler 2014, reprinted by permission of Cambridge University Press.

The scale of equipment varied proportionally with the size of the farm. The general rule of thumb is to use the smallest tractor needed to accomplish the task. The largest tractors (100-250 hp) were used only for primary tillage. Cultivating tractors tended to be in the 35-65 hp range.

Farmers sometimes used different names to refer to the same tool, so some adjustments were made to fit standard definitions (American Society of Agricultural Engineers, 2004). Most farmers had a basic complement of standard equipment that included a moldboard plow, disc harrow, and field cultivator. In addition to these rear-mounted tools, farmers often had more than one type of cultivator, usually attached as rear-, front-, or belly-mounted toolbars.

Tillage

For fields with heavy weed pressure, several farmers said that moldboard plowing is the most effective means of primary soil preparation. However, farmers avoided overuse of moldboard plows because of their potential negative effects. Moldboard plows can promote soil erosion. Deep plowing can bring weed seeds up to more a favorable position in the soil profile for germination.

Chisel plows are preferred when less disturbance of soil is desired or when weather does not permit moldboard plowing. More plant residue on the soil surface is left after chisel plowing, although some of this is usually incorporated by secondary tillage. Thor Oeschner of Newfield, NY equipped a chisel plow with 22 inch sweeps that overlap 6 inches that ensures no gaps in cultivation. The configuration cuts the tops from the roots and allows him to cover ground more quickly, saving time and fuel in the process. He follows this implement with a second pass using a field cultivator that mixes the severed weeds into the top 4 inches of soil.

Several farmers also used heavy disks as a primary tillage tool. When a field is cross-disked, the soil is disturbed to a greater degree than with chisel plowing, but to a lesser extent than with a moldboard plow. Disks are also used as secondary tillage, most often following a moldboard plow. Farmers who use raised beds consider bed shaping to be a tillage operation as well. If timing permits, weed seeds can be allowed to germinate in a false seed bed prior to planting. Once the weeds have emerged, the tops of the beds can be cultivated at a shallow depth to kill seedlings at an early stage.

Cultivation

Farmers usually relied on one or more cultivations after planting to enable their crops to outgrow weeds. Timing was universally considered essential for effective cultivation, but when describing how timing was important, farmers used different descriptors and had difficulty summarizing their rules of thumb. They agreed that for cultivation to be effective the soil must be dry and temperatures warm. Cultivation under wet conditions can cause soil compaction. Some weed species thrive in compacted soil, and consequently, cultivating wet soil can increase weed pressure. Cool, moist conditions give weeds a better chance to recover from cultivation.

Farmers used multiple cultivators, finding a combination to be more effective than relying on a single tool. Tine weeders are used at early stages of crop growth to kill very small weeds, including those in the crop row. Toolbars and row crop cultivator gangs can be fitted with various cultivation tools, including sweeps, shovels and knives. These penetrate the soil one to three inches and kill weeds that escape tine weeding. However, some farmers reported that close cultivation sometimes damaged roots when the mounted tools were not properly adjusted.

Farmers will set up their toolbar with combinations of sweeps, knives, disks and spiders to take advantage of multiple ways of killing weeds. Spiders are toothed wheels that substitute for cultivating disks or which are ganged to cover more of the inter-row area. Toolbar setup varies according to the size of the crop, skill of the operator, and crop susceptibility to root damage and burial. Farmers purchased shields or fabricated guards to protect young crops from soil thrown by the cultivator.

Farmers noted that the ability to switch toolbars rapidly during critical periods also led to more timely cultivation and lower weed pressure. Multiple toolbars can be set up early in the season rather than reconfigured for each operation. The labor saved and higher yields associated with timely cultivation quickly paid back the cost of the additional toolbars.

A vegetable grower mounted a seeder on a cultivator to undersow a relay cover crop during the final cultivation. The modification made it possible to cultivate and plant in a single pass. Rick Pederson of Seneca Castle, NY and Peter Martens of Dresden, NY reported looking at Geographical Positioning Systems (GPS) for more precision cultivation. With GPS, a record of the crop's row positions are made and the tractor and cultivator follow this record during cultivation.

Tine weeding is a popular technique among field crop growers (Figure 3) and is used in both row crops, such as soybeans and corn, and in small grains. Factors identified as important for tine weeding included shape of the tine, timing, depth, tractor speed, and the angle of the tines to the ground.

Tines of tine weeders can be straight or bent at various angles. Mike Thorpe of East Aurora, NY said that straight tines are used for earlier weeding because they are less aggressive. They are also used with crops that are more sensitive to physical damage. In corn, the initial tine weeding should be timed as close to weed emergence as possible, before more than just a few of the corn plants have emerged. At that stage, the depth is set shallow and tine angle is usually set low to disturb the surface soil without injuring germinating seeds or burying newly emerged crop plants. 

Figure 3: Einbock tine weeder, Thorpe's Family Farm. Photo credit: Brian Baker

As the crops grow larger, they are able to take more stress from the tine weeder. Bent tines are used for more mature crops. Faster speeds and more aggressive angles are needed as the weeds and the crops grow. However, at higher speeds, the tines can jump and miss weeds. Therefore, the tine angle is often increased and weight transferred from the tractor to the weeder so that the tines are working the soil at a greater depth.

Other Practices

Flame weeding can be an effective physical means for controlling weeds. Dick DeGraff of Pulaski, NY custom-built his own flame weeder. Not all crops are amenable to flame weeding, and flaming is most effective if applied before weeds reach the 4-leaf stage. Carrots pre-emergence, onions post-emergence, and corn both pre- and post-emergence were the most commonly and successfully flame weeded crops. Rick Pedersen of Seneca Castle, NY has experimented with flame weeding on some crops less commonly flame weeded, such as asparagus and corn. He has been able to improve the timing and positioning to get effective reduction of weeds with minimal crop damage.

Vegetable farmers used a combination of plastic and straw mulches, sometimes in combination. Plastic mulches are better suited for beds, and straw mulch can be used on the drive alleys or on the beds instead of plastic. Straw mulch can also be a key part of permanent or rotational no-till systems. Jay Armour of Four Winds Farm was the only no-till grower interviewed in the study. Straw and compost mulches were vital to suppressing weeds in his system. Jody Bolluyt and Jean-Paul Courtens of Kinderhook, NY use a bale shredder to help create a more even distribution of mulch and increase the area covered per bale.

Transplants can be more competitive with weeds than direct seeding the same crop, particularly early in the season. Under wet, cold conditions seedling establishment can be poor, and transplanting can lead to more uniform and thus more competitive stands. Several of the farmers interviewed will hedge and start seedlings of some crops that are ordinarily direct seeded, like sweet corn and squash, and transplant them if conditions prevent direct seeding early in the season.

Hand weeding is economically worthwhile in high value crops such as vegetables and seed crops. However, field crops and lower value vegetable crops like potatoes will seldom be worth spending a lot of labor to hand weed. There are exceptions. Dairy farmers will rogue noxious perennial weeds from pasture and hay fields. Some cereal grains will be tainted in their flavor by wild garlic and ragweed, and producers will hand weed early in the season if time and conditions permits.

Several farmers mentioned that they occasionally tilled cash crops under before they were harvested to prevent weeds from going to seed. The management decision to lose an entire planting to avoid future weeds requires an assessment of the weed density, potential yield and price of the cash crop. If a crop is badly infested with weeds, allowing the weeds to go to seed can cost more than the net value of the crop. In other cases, crops originally intended for food or seed were harvested for forage to prevent massive weed seed production.

Conclusions

Experienced organic farmers have considerable information to share on weed management, particularly regarding the identification of essential equipment and mechanical cultivation techniques. However, most farmers had difficulty in identifying key components of their management system and explaining their practices in a step-by-step fashion that could be followed by other growers. Weed control requires balancing acceptable loss of crop yield to weeds with the loss of crop yield to cultivation.

References and Citations

• American Society of Agricultural Engineers. 2004. Terminology and definitions for agricultural tillage implements. St. Joseph, MO, ASAE.
• Baker, B. P., and C. L. Mohler. 2014. Weed management by upstate New York organic farmers: Strategies, techniques and research priorities. Renewable Agriculture and Food Systems, Cambridge Journals Online. (Available online at: http://dx.doi.org/10.1017/S1742170514000192) (verified 26 Apr 2015)
• Davis, A., K. Renner, C. Sprague, L. Dyer, and D. Mutch. 2005. Integrated weed management: One year's seeding. Michigan State University Extension Bulletin E-2931. East Lansing, MI.
• DeDecker, J. J, J. B. Masiunas, A. S. Davis, and C. G. Flint. 2014. Weed management practice selection among Midwest U.S. organic growers. Weed Science 62:520-531. (Available online at: http://dx.doi.org/10.1614/WS-D-13-00138.1) (verified 4 May 2015)
• Jabbour, R., E. R. Gallandt, S. Zwickle, R. S. Wilson, and D. Doohan. 2014. Organic farmer knowledge and perceptions are associated with on-farm weed seedbank densities in northern New England. Weed Science 62:338-349. (Available online at: http://dx.doi.org/10.1614/WS-D-13-00098.1) (verified 4 May 2015)
• Liebman, M., and A. S. Davis. 2009. Managing weeds in organic farming systems: An ecological approach. p. 173-196 In: C. A. Francis (ed.) Organic farming: The ecological system. American Society of Agronomy, Madison, WI.
• Mohler, C. L., and S. E. Johnson (eds). 2009. Crop rotation on organic farms: A planning manual. Natural Resource, Agriculture, and Engineering Service (NRAES) Cooperative Extension, Ithaca, NY. (Available online at: http://www.sare.org/Learning-Center/Books/Crop-Rotation-on-Organic-Farms) (verified 9 May 2015)
• Riemens, M. M., R.M.W. Groeneveld, M.J.J. Kropff, L.A.P. Lotz, R. J. Renes, W. Sukkel, and R. Y. van der Weide. 2010. Linking farmer weed management behavior with weed pressure: More than just technology. Weed Science 58:490-496. (Available online at: http://wssajournals.org/doi/abs/10.1614/WS-09-048.1) (verified 9 May 2015)
• van der Schans, D. A., and P. Bleeker (eds). 2006. Practical weed control in arable farming and outdoor vegetable cultivation without chemicals, Publication number 352. Applied Plant Research Wageningen, The Netherlands.
• Walz, E. 2004. Final results of the fourth national organic farmers' survey. Organic Farming Research Foundation, Santa Cruz, CA. (Available online at http://ofrf.org/sites/ofrf.org/files/docs/pdf/4thsurvey_results.pdf) (verified 9 May 2015)

 This article was written with support from the Organic Farming Research Foundation.