organic crop production

PArt 1, seCtIon 11

Organic Crop ProductionPest Management in Organic Systems ........................................135

Insects ...................................................................................135Weeds ....................................................................................138Diseases .................................................................................140

M. E. Barbercheck, professor of entomology, Department of EntomologyW.S.Curran, professor of weed science, Department of Plant ScienceJ. M. Dillon, senior extension associate, Department of Plant Science

tAbles

Table 1.11-1. Organic crop production foundation principles and practices. ........................................................................136

Table 1.11-2. Effect of Matran II (34 percent clove oil) applica-tion rate on annual weed control three and ten days after application. ...........................................................................140

Table 1.11-3. Herbicides listed by OMRI for use in organic production. ..........................................................................140

Part 1, Section 11 ❦ Organic Crop Production 135

organic farming became one of the fastest growing segments of agriculture during the 1990s, and

the demand for a wide range of organic products continues to grow. Some U.S. producers are turning to organic farm-ing systems as a potential way to lower input costs, decrease reliance on synthetic chemicals, capture high-value markets and premium prices, and boost farm income.

The Agricultural Marketing Service (AMS) of the U.S. Department of Agricul-ture (USDA) is the home to the National Organic Program (NOP), which devel-oped, implemented, and administers na-tional production, handling, and labeling standards for organic agricultural prod-ucts. The USDA standard defines organic production as “a production system that is managed in accordance with the Organic Foods Production Act and regulations in this part to respond to site-specific condi-tions by integrating cultural, biological, and mechanical practices that foster cycling of resources, promote ecological balance, and preserve biodiversity.” The national organic standards address the methods, practices, and substances used in producing and handling crops, live-stock, and processed agricultural prod-ucts. All agricultural products labeled or represented as organic must be in compli-ance with the regulations as of October 2002. Organic crops can be produced on land that has had no prohibited sub-stances applied to it for at least 3 years. The regulations require that organic producers and handlers be certified by a state or private agency accredited under the uniform standards developed by the USDA, unless the farmers and handlers sell less than $5,000 per year in organic agricultural products. For further infor-mation, visit the USDA’s Agricultural Mar-keting Service/National Organic Program website at www.ams.usda.gov/nop or call 1-202-720-3252. This site includes a list of accredited certifying agents, consumer information, state information, and NOP regulations and policies, information for producers, handlers, and processors.

Organic farming systems rely on ecolog-ically based practices, such as cultural and biological pest management, and virtually exclude the use of synthetic chemicals in crop production and prohibit the use of antibiotics and hormones in livestock production. Genetically modified crops are not allowed. Under organic farming systems, the fundamental components

and natural processes of ecosystems, such as soil organism activities, nutrient cycling, and species distribution and competition, are used directly and indirectly as farm management tools. For example, crops are rotated, planting and harvesting dates are carefully planned, and habitats that supply resources for beneficial organ-isms are provided. Soil fertility and crop nutrients are managed through tillage and cultivation practices, crop rotations, cover crops, and supplemented with ma-nure, composts, crop waste material, and allowed substances. Sewage sludge is not allowed. Lists of allowed substances are available from accredited certifiers; prod-ucts are reviewed by the Organic Materi-als Review Institute (OMRI), omri.org, phone: 541-343-7600.

Several sources of information on organic production are available. The Alternative Farming Systems Information Center (AFSIC) is one of several topic-ori-ented information centers at the National Agricultural Library (NAL). The AFSIC serves as a clearinghouse, specializing in locating and disseminating information related to alternative cropping systems including sustainable, organic, low-input, biodynamic, and regenerative agricul-ture. AFSIC’s staff and resources can be accessed at www.nal.usda.gov/afsic or by calling 301-504-6559.

The National Sustainable Agriculture Information Service is managed by the National Center for Appropriate Technol-ogy and provides information and other technical assistance to farmers, ranchers, extension agents, educators, and others involved in sustainable agriculture in the United States. Their technical publica-tions address current topics in sustain-able and organic agriculture and can be accessed at attra.ncat.org or by calling 1-800-346-9140.

Pest MAnAgeMent In orgAnIC systeMsInseCts

The term “organic” describes production systems that optimize natural processes. Certified organic growers use a wide range of IPM practices that comply with the standards of the USDA’s National Organic Program (NOP) (www.ams.usda.gov/nop, phone: 202-720-3252).

In organic systems, the goal is to alter the production system so that pests do not find plants, are controlled by natural en-emies (biological control), or their damage

is kept to a minimum (Table 1.11-1). Vigor-ous, healthy plants are more able to with-stand damage caused by arthropods and disease. Therefore, healthy soil and plants are the foundation of organic production. Described here are general principles of insect pest management in organic pro-duction. More information on biologically based (biointensive) pest management, including information on suppliers of bio-logical control agents, can be found in the ATTRA publication Biointensive Integrated Pest Management available at attra.ncat.org or by calling 1-800-346-9140.

biological ControlBiological control is the use of living organisms to maintain pest populations below damaging levels. Natural enemies of arthropods fall into three major categories: predators, parasitoids, and pathogens. Predators catch and eat their prey. Some common predatory arthro-pods include ladybird beetles, lacewings, syrphid flies, carabid (ground) beetles, minute pirate bugs, nabid bugs, big-eyed bugs, and spiders.

Parasitoids (sometimes called parasites) do not usually eat their hosts directly. Adult parasitoids lay their eggs in, on, or near their host insect. When the eggs hatch, the immature parasitoids use the host as food. Many parasitoids are very small wasps and are not easily noticed. Tachinid flies are another group of para-sitoids. They look like large houseflies and deposit their white, oval eggs on the backs of caterpillars and other pests. The eggs hatch, enter the host, and kill it.

Pathogens are disease-causing organ-isms. Just as many other organisms get sick, so do insects. The main groups of in-sect disease-causing organisms are insect-parasitic bacteria, fungi, protozoa, viruses, and nematodes. Biological control us-ing pathogens is often called microbial control. One very well-known microbial control agent that is available commer-cially is the bacterium Bacillus thuringiensis (Bt). Because not all formulations of Bt are approved for use in organic systems, it is important to check with your certifier. Several insect-pathogenic fungi are used as microbial control agents, including Beauveria, Metarhizium, and Paecilomyces. These are most often used against foliar insect pests in greenhouses or other locations where humidity is relatively high. Nuclear polyhedrosis (NPV) and granulosis (GV) viruses are available to control some lepidopteran pests (moths

136 The Agronomy Guide 2013–14

and butterflies). Insect-parasitic (entomo-pathogenic or insecticidal) nematodes in the genera Steinernema and Heterorhabditis infect soil-dwelling insects and occur naturally or can be purchased. As with all biological control agents, it is especially important to match the correct microbial control agent with the correct pest in order for them to be effective.

Biological control can be applied (in-undation or augmentation of natural populations) or natural (conservation of natural enemies). Many biological and microbial control agents are commer-cially available for purchase. Information about rates and timing of release are avail-able from suppliers of beneficial organ-isms. The quality of commercially avail-able biocontrol agents is an important consideration. Biological and microbial control agents are living organisms, and, as such, must not be mishandled during shipping, storage, or application.

In many cases, purchasing biocontrol agents should not be necessary. Natural enemies are common and a grower just needs to know how to attract and keep the natural enemies in their system by providing environmental conditions conducive to their survival. “Farmscap-ing” describes the creation of habitat to enhance the chances for survival and reproduction of beneficial organisms. For example, many adult predators and parasitoids feed on nectar and pollen, so it is essential to have these resources nearby. Having several species of pollen- and nectar-producing plants in an area will provide resources more continuously than only having one species. Organic mulches and crop residue moderate fluctuations of temperature and moisture

and can provide hiding places for soil predators such as carabid and staphylinid beetles, spiders, and centipedes. Other habitats provided by farmscaping include water, alternative prey, perching sites, overwintering sites, and wind protection. The success of farmscaping efforts de-pends on knowledge of pests and benefi-cial organisms.

In field crop systems, there are sev-eral well functioning biological control systems. A major successful biological control program was the release of parasitoid wasps to control alfalfa wee-vil populations. There are six primary wasp species helping to regulate weevil populations, with three being most com-mon. These parasitoid wasps, along with a fungal pathogen, have successfully reduced the percentage of fields sprayed in Pennsylvania from nearly 100 percent in the 1960s and early 1970s to less than 5 percent in most years. Organic growers have the option of managing their forages to encourage maximum effectiveness of the wasps, thus eliminating the need for pesticides. Another example of success-ful introduction of a beneficial organism is in the population regulation of cereal leaf beetles in cereal crops (wheat, barley, oats, rye, triticale, etc.). These wasps have again significantly reduced the number of fields sprayed to control the pest. Again, organic producers can manage to opti-mize the effectiveness of these parasitoids. A third example of effective biological control is that of the European corn borer. Although, this insect is still a major concern in vegetable and field corn pro-duction and significant acreage is planted to new transgenic Bt corn hybrids (not allowed in organic production), its popu-

lations receive considerable regulation from beneficial organisms. During the 1930s, 1940s, and 1950s, the USDA im-ported and release at least 25 beneficial parasitoids in an attempt to regulate the species populations. Smaller re-releases occurred during the 1960s through 1990s. Several of these parasitoid species have become established and contribute to the regulation of corn borer populations. In the early years after introduction of the European corn borer into the United States, open-pollinated varieties were commonly infested with ten or more larvae per plant, and yields were com-pletely eliminated. Today, with beneficial organisms and improved crop resistance (traditional, not transgenic methods), it is uncommon to see more than an aver-age of three or four larvae per plant. In fact, the large majority of fields have less than one larva per plant. Research has shown that infestations below one larva per plant seldom cause measurable yield reductions. All crop producers should recognize, whether organic or other, that only 1 to 5 percent of the population of the majority of insects survive from the egg to the damaging stage. This tells us that nature, either through effects of weather conditions or natural enemies, is doing a lot to keep pest numbers down. In field crops, many times, we can tolerate infestations of a pest with out significant economic loss.

Given the great help we receive from nature, we are fortunate in field crops to have very few major insect pests that con-sistently cause economic losses. Excep-tions are potato leafhopper in alfalfa and corn rootworm in corn. All other pests tend to be cyclic and only hit a few fields each year. Knowing about the life require-ments of these pests can be a great help in designing effective organic production systems. table 1.11-1. organic crop production foundation principles and practices.

Biodiversity

Diversification and integration of enterprises Sustainability

Natural plant nutrition

Natural pest management Integration

Rotation Rotation Rotation Rotation Rotation Rotation

Green manure Animal manure Green manure Green manure Green manure Records

Cover crops Composting Cover crops Animal manure Cover crops

Animal manure Intercropping Biocontrol Composting Composting

Composting Farmscaping Farmscaping Natural fertilizers Intercropping

Intercropping Mulching Animal manure Foliar fertilizers Biocontol

Biocontrol Composting Farmscaping

Farmscaping Mulching Sanitation

Buffers Buffers Tillage

Fire

Natural pesticides


Cultural ControlMany organic cultural practices are also carried out as best management practices that are applicable to all types of crop management systems and are discussed elsewhere in this guide. Some examples of cultural controls are crop rotation, sanitation, cover crops, resistant varieties, maintenance of biological diversity, ap-propriate planting dates, and plant spac-ing. As a general rule in field corn, early plantings have fewer losses to insect pests. Timing of cutting in alfalfa can be an effective management tool against potato leafhopper. Because the life cycle of the pest is about 28 to 30 days, cutting sched-ules of less than 30 days can reduce dam-age from leafhoppers. Although leafhop-pers may reduce the quantity of forage harvest, increased protein content of the hay may partly offset this. Crop rotation is an effective method of eliminating corn rootworm injury in corn. Corn rotated annually to another crop will not have corn rootworm infestations. Continuous corn production in a field allows eggs to be laid in the field that will hatch the fol-lowing year and result in larval feeding on corn roots.

When designing cultural controls for a production system, crop rotation and cover crops can lead to specific insect and other invertebrate pest problems. Slug populations can build up in sods and hay fields and then cause problems in field corn and soybean fields in the following years. The cover crop provides an ideal environment for slugs since they need shelter from the sun, which will cause them to desiccate. Tillage between crops, when slugs are present, can help reduce population before planting into the field. Other pests of field corn that can increase in frequency with cover crops and abun-dant residue include sod webworm, black cutworm, true armyworm, stalk borer, white grub, seed corn maggot, and wire-worm. Plowing under residues at least 10 to 14 days before planting can reduce the likelihood that high populations will sur-vive to damage the crop; however, this may not be effective if wireworm and white grub population are present. Methods to monitor for these pests can be found on the Penn State Entomology website (ento.psu.edu/OnLineGuides.html) under the Field Crop Training Manual. This manual also provides information on the association of key pest with specific types of environmental conditions.

host-Plant resistanceAlthough listed as a cultural mechanism, host plant resistance is a major method in field crops to manage key pests. Within the last 5 years, new potato leafhopper–resistant alfalfa cultivars have reached the market place. These cultivars are the result of traditional selection methods. The newest varieties now have about 70 to 80 percent resistance to potato leafhop-per and have agronomic characteristic similar to nonresistant cultivars. Selection of these cultivars can greatly reduce the effects of this major pest of alfalfa. By eliminating major issues with this pest, the only other pest of concern is alfalfa weevil; and with efforts to conserve its natural enemies, the frequency of losses can be greatly minimized.

Selecting a good corn variety can also minimize the impact of both European corn borer and corn rootworm. Over the years, plant breeders have increased both tolerance and resistance of corn hybrids to these pests. In their corn variety guides, however, they do not directly indicate the type or level of resistance to either pest. Insight into a hybrid’s ability to deal with both pests is its standability index and ear holding capabilities. Hybrids that con-sistently rate well in these characteristics tend to have less yield loss from these pests (particularly harvest losses). Al-though not listed in most variety guides, root system size can be important in toler-ance of corn rootworm infestations. In general, a plant with a larger root system will tolerate more feeding by the pest. This, coupled with early planting, will reduce yield impacts by corn rootworm. The downside to these cultivars, however, is that if the plant is putting more energy into the root system than aboveground parts, its yield capability may be less than cultivars with smaller root systems.

Soybeans and small grain crops also have been bred to tolerate certain pests. However, this information is often not provided in crop seed guides. Wheat varieties are available that have resistance to Hessian fly and greenbugs. Conducting your own evaluations can provide signifi-cant information on which cultivars to grow in an organic system.

Physical and Mechanical ControlMethods in this category use some physi-cal component of the environment, for example, temperature, humidity, or light, to suppress pest populations or damage. Some examples are tillage, flaming, and flooding. Floating row covers over veg-etable crops exclude pests. Heat or steam sterilization of soil is commonly used in greenhouses for control of soil-borne pests. For field crops, flaming can be used for alfalfa weevil control when timed properly, but you must be careful not to catch materials on fire that might threat-en humans or wildlife. Tillage of corn can help minimize slug damage by helping the plant grow more rapidly (this is not a guaranteed outcome). The principle behind this approach is that the sun will warm up the soil around the plants faster and allow them to outgrow the pest’s feeding. In years when we have significant overcast and cool conditions, slugs can cause damage despite this practice.

organic PesticidesSome types of pesticides are allowed in organic production. Lists of allowed sub-stances are available from accredited cer-tifiers; products are reviewed by the Or-ganic Materials Review Institute (OMRI) (omri.org, phone: 541-343-7600). Because there are differences among certifying agencies, you should check on the status of specific compounds to determine if they are allowed, restricted, or prohibited in your organic system. Some products with allowable active ingredients may contain unacceptable adjuvants, so it is important to check the label and the certifying agency before using a material. Some examples of allowable active ingre-dients are Bacillus thuringiensis (Bt), pyre-thrum, insecticidal soaps, diatomaceous earth, azadirachtin, horticultural oils, and insect-parasitic (entomopathogenic) nematodes and fungi.


WeeDs

Managing weeds in organic systems uses many of the same techniques as conven-tional systems, but relies much more on nonchemical control strategies. To plan an effective weed management program in organic systems, historical pest prob-lems, soil management, crop rotation, machinery, markets, weather, time and labor should be considered. Adjusting weed control strategies based on these factors and observing and avoiding poten-tial problems is a big part of staying ahead of weed problems. The primary methods for managing weeds in organic systems are the use of cultural and mechanical weed control strategies, which primarily focus on prevention, crop rotation, crop competition, and cultivation.

PreventionThe primary focus of prevention in organ-ic systems is keeping new weeds out and preventing further spread of weed seed or perennial plant parts. In particular, minimizing the addition or introduction of weed seed to the soil can be critical for successful weed management. Under-standing weed biology is an important component in developing a preventive approach. Weed species have strengths and weaknesses and are vulnerable or resilient at different stages in their life cycle. Disking or field cultivating a creep-ing perennial such as quackgrass or hedge bindweed in the spring may make the problem worse by spreading underground rhizomes or other vegetative structures. Therefore, proper identification and knowledge of weed lifecycle, reproduc-tion, and spread are important factors for developing management strategies.

Some preventive tactics might be clas-sified as sanitation—removing or destroy-ing weeds in fields or near fields prior to flowering and the release of weed seed. Weed seeds can live for a number of years, depending on the species and whether it is exposed or buried beneath the soil surface. This may mean removing by hand if necessary those weeds from the field before they produce seed. Weeds can also be introduced into fields via manure, compost, hay, straw, animal feed, con-taminated crop seed, or other materials. Whenever you plant, apply, or drive some-thing in a field, make an effort to learn whether weed seeds are present and evalu-ate the benefits versus potential risks.

Cultural Weed ControlSome cultural practices—in particular, crop rotation and altering the planting date—can be key components for man-aging weeds in organic systems. Date of planting will influence the type and number of weeds present. Organic grow-ers should plan rotations so that weed species favored in one year or season will not be favored in another year or crop-ping sequence. This generally means mixing summer annual crops with fall seeded species or even perennials that allow different weed management strate-gies. Delaying planting of some spring-seeded crops is common among organic producers. Although some yield potential may be sacrificed with this planting delay, higher soil temperatures will help the crop emerge more quickly, and weeds that emerge earlier in the season can be killed prior to planting to reduce the potential weed seedbank. A stale seedbed is a technique sometimes used in veg-etable production systems that can also be used in agronomic crops. A seedbed is tilled several weeks prior to planting. The weeds are allowed to emerge and then they are killed while still small by shallow cultivation, flame weeding, or other nonselective methods. Depending on the length of time before planting, one or more flushes of weeds may emerge and be killed between seedbed prepara-tion and planting. The success of a stale seedbed depends on the weed spectrum and the time of planting. Delayed or later-planted crops are generally more success-ful. Late-emerging weeds will still be a potential problem. Any tactic that makes the crop more competitive against weeds is considered cultural management and is critical for successful organic production systems.

Crop competition is an important component of cultural weed control and an effective way to control weed growth. Soil open to sunlight is available for weed growth and competition. A vigorous growing crop is less likely to be adversely affected by weeds. Tactics that allow the crop to establish quickly and dominate will help reduce the impact from weeds. Use high-quality vigorous seed, adapted varieties, uniform proper placement of the crop seed, optimal soil fertility, and plant populations that lead to vigorous crop growth and canopy closure.

Mulches and Cover CropsMulches are used in some organic produc-tion systems to help manage weeds. The mulch provides a physical barrier on the soil surface and must block nearly all light reaching the surface so that the weeds that emerge beneath the mulch do not have sufficient light to survive. Plastic mulches are acceptable in some organic programs, but are generally not practical for lower valued large-scale field crops. Mulches of organic material such as straw or newspa-per or killed cover crop residue left on the surface can also effectively block sunlight and are more commonly used in organic row crop production systems.

Cover cropping can help in the man-agement of weeds in several ways. Cover crops can provide an opportunity for crop rotation and rapid turnover of weed seedbanks. In addition, cover crops can provide some weed control by competing with weeds for light, moisture, nutrients, and space. This can be particularly help-ful for suppressing winter annual weed growth or certain cool-season perennials. In addition, cover crops and their residues can act as mulches or physical barriers by smothering weeds, suppressing weed seed germination and growth, and lowering soil temperatures. In general, the larger the cover crop and greater the biomass or dry matter production, the greater the impact on weeds. Cover crops may contain allelopathic compounds, which are released from living or decaying plant tissue that chemically interfere with weed growth. However, these qualities can vary depending on the type and quantity of cover crop and environmental conditions during the growing season. Despite these potential benefits, physical and chemical effects from cover crops may not be to be a major factor for weed control. Mechani-cal control tactics as well as cultural con-trols should still be used to compliment cover crops for weed management.

Mechanical Weed ControlMechanical weed control is generally considered critical for managing weeds in organic systems. In organic row crops such as corn or soybean, mechanical culti-vation is generally necessary for adequate weed control. Mechanical weed control includes the use of preplant tillage such as plowing, disking, and field cultivating. These primary and secondary tillages can help reduce the rate and spread of certain perennial weeds and can also kill emerged weed seedlings and bury weed


seeds below the germination zone. Most organic corn and soybean producers pre-pare a conventionally tilled seedbed prior to planting their spring crop. Cultivation should generally begin a few days after planting. To control weed seedlings that are just beneath the soil surface or barely emerged, implements such as a rotary hoe, chain-link harrow, or tine weeder are dragged over the field for control of these very small weed seedlings. These implements will displace small seedling weeds and expose them to the drying ef-fects of the wind and sun. Rotary hoes or similar implements are the best method for controlling weeds in the crop row. Operate a rotary hoe at 10 to 12 miles per hour with enough drag to stir the soil and displace the small seedlings .Continue to use a rotary hoe or similar implement about every 5 to 7 days, as long as the weeds are germinating or until the crop is too big. Do not rotary hoe soybeans when the soybeans are in the “hook” stage (the stem is exposed and the cotyledons have not yet opened above the ground). Also, use rotary hoes or similar implements in the afternoon when turgor pressure is less and soybeans and corn are more flexible. In general, up to three rotary hoeings may be performed within 2 to 3 weeks after planting.

Crop rows planted 30 inches or more apart allow for row cultivation. Once soy-beans have three trifoliate leaves and corn is beyond the two leaf stage (V2) and 8 to 10 inches tall, use a row cultivator to control small weed seedlings. Shallow cultivation at 1 to 2 inches deep will avoid harming crop roots. Continue to cultivate at 7- to 10-day intervals until the corn is too tall and the soybean canopy closes the rows. Organic corn and soybeans generally require between one and three cultivations, depending on weed species, severity, and rainfall. Cultivation works best when performed during the heat of the day in bright sunlight; weeds quickly desiccate and die under these conditions. Rainfall shortly after cultivation or wet cloddy soils at or following cultivation may allow weeds to recover and survive. Hand-pulling escaped weeds will help assure maximum crop yield and prevent weed seed production, which can affect future weed problems.

Mowing may also play a critical role in managing weeds in forage crops or noncrop areas. Repeated mowing re-duces weed competitive ability, depletes carbohydrate reserves in the roots, and

prevents seed production. Some weeds, mowed when they are young, are readily consumed by livestock. Mowing can kill or suppress annual and biennial weeds. Mowing can also suppress perennials and help restrict their spread. A single mowing will not satisfactorily control most weeds. However, mowing three or four times per year over several years can greatly reduce and occasionally eliminate certain weeds including Canada thistle. Also, mow along fences and borders to help prevent the introduction of new weed seeds. Regular mowing helps prevent weeds from estab-lishing, spreading, and competing with desirable forage crops, and also can keep them from spreading into tilled fields.

herbicidesChemical weed control is generally not allowed in organic crop production systems. The USDA National Organic Program rule (NOP) does allow certain nonsynthetic soap-based herbicides for use in farmstead maintenance (roadways, ditches, right of ways, building perim-eters) and in ornamental crops. In addi-tion, several products that contain natural or nonsynthetic ingredients are classified as approved by the Organic Materials Re-view Institute (OMRI). The OMRI listing does not imply product approval by any federal or state government agency. It is the user’s responsibility to determine the compliance of a particular product.

Corn gluten meal is sold as an organic fertilizer that has some preemergence herbicide activity on certain small-seeded annual weeds. Because of the volume of product necessary and the associated cost, corn gluten meal is generally not practical for agronomic crop production systems but may be suitable for smaller areas such as home gardens and lawns. In addition, the need for and use of corn gluten for weed control must be explained in the Organic System Plan and the product must not be derived from genetically engineered sources. To learn more about corn gluten, visit the corn gluten meal research page at Iowa State University (www.gluten.iastate.edu).

Nonsynthetic (natural) postemergence herbicides contain plant-based ingredi-ents including eugenol (clove oil), cin-namon oil, citrus oil, lemongrass oil, and others, and act as nonselective contact type herbicides. They will injure or kill all vegetation they come in contact with, including desirable vegetation. Weed species, its size or age, and environmen-

tal conditions at application time are important for optimum performance. As a general rule, these products are only effective on small seedling weeds and activity increases with air temperature, hu-midity, and sunlight. Seedling broadleaves are most susceptible, while grasses are harder to control. We suggest a minimum air temperature of 75°F, 50 percent rela-tive humidity, and sunny conditions. Cool temperatures, low humidity, and cloudy conditions will reduce performance. The effectiveness of a clove oil product (Ma-tran II) on several annual weeds is pro-vided in Table 1-11.2.

The need for the use of herbicides derived from plant or animal sources should be explained in the grower’s Or-ganic System Plan and the farmer must obtain permission from their organic certifying agencies to use these materials. Acetic acid or vinegar is an ingredient in a number of products, and distilled white vinegar is on the OMRI approved list but not as an herbicide. The performance of vinegar is similar or less effective than that of clove oil (Table 1-11.2). As a gen-eral rule, a 20 percent concentration (200 grain) is necessary applied at a minimum of 60 gallons per acre. Individual certify-ing agencies can help decide the merits and need for acetic acid as an herbicide. Several products are labeled as organic herbicides, and additional products and ingredients are currently under review.

Remember that an adjuvant (i.e., sur-factants and wetting agents) is often nec-essary to enhance herbicide performance. All synthetic adjuvants are prohibited, which includes most adjuvant products in the market. A number of plant-based adjuvants are available and are often derivatives of pine resin (Nu-Film P) or yucca (Natural Wet) or other plant-based substances. Some products contain acidi-fying agents as well as other ingredients touted to enhance pesticide or nutrient uptake. Check with your organic certi-fier concerning the allowance of these additives. Table 1.11-3 contains some herbicides listed by OMRI or others at the time of printing. Some of these products already include surfactant-type adjuvants in their formulation. Penn State does not ensure the effectiveness or allowance of any of these products.


DIseAses

Disease management for organic field crop production should focus on several aspects of plant disease management, including host resistance, site selection, exclusion, crop rotation, cultivation, and plant disease diagnosis. It is unlikely that all diseases can be avoided by utilizing any one of these management strategies alone. However, the damage of many plant diseases can be greatly reduced by the integration of these practices. The sections below provide more information regarding these management options.

host resistanceMany plant diseases can be effectively managed by selecting varieties that are naturally resistant to specific disease-causing organisms. Host resistance can be either partial or complete. Varieties with complete resistance are completely im-mune to attack by a specific pathogen or a “race” of the pathogen population. In contrast, varieties with partial resistance may still develop symptoms of the disease, but the disease will progress slowly and have less of an impact when compared to susceptible plants. The use of host resis-

table 1.11-2. effect of Matran II (34 percent clove oil) application rate on annual weed control three and ten days after application.

Matran II was applied at 7 to 14 gallons per acre in 30 to 60 gallons of water with 80-degree flat fan nozzle tips. Weeds were 2 to 10 inches tall and air temperatures were in the mid-70s. Skies were clear and relative humidity was about 50 percent.

Giant FoxtailCommon Lambsquarters Smooth Pigweed

Common Ragweed

Days After Application

Gallon per Acre 3 10 3 10 3 10 3 10

Percent Control 1

7 71 a 66 a 87 a 76 a 92 a 83 a 88 a 76 a

10 77 b 69 a 91 b 81 b 94 a 86 a 91 a 79 a

14 76 b 68 a 93 b 82 b 94 a 83 a 90 a 77 a

1. Same letters within a column are not significantly different at the 5 percent level.

tance can be highly effective in reducing disease pressure. Knowing the pathogen or race of pathogen you wish to control is necessary to ensure that host resistance is targeted to the most important disease issues. Contact your seed dealer or Penn State Extension office for more informa-tion about resistant varieties.

site selection Soil and environmental conditions can play a key role in disease development. Prior to planting a crop, it is important to understand what soil or environmental conditions may exist that can exacer-bate disease development. Issues such as compacted soils or poor soil drainage can lead to root diseases in seedlings and mature plants. Low-lying areas or soil located next to a forest or river can have extended periods of dew or fog, which is a key factor in the development of many foliar diseases of crops. Optimum fertility and soil pH will also help ensure plant health and the ability to defend against pathogens.

exclusionExclusion is the practice of keeping mate-rials and objects that may be contaminat-ed with a pathogen out of the production system. Some diseases are spread through seed, so it is important to purchase seed from a reputable source. Although some

table 1.11-3. herbicides listed by organic Materials review Institute (oMrI) or by manufacturer for use in organic production. Check with your certifying agency for specific use information.

Product Active ingredients Application Manufacturer

Blackberry & Brush Block 20% citric acid Foliar contact Greenergy, Inc. www.greenergyinc.com

Corn gluten meal (fertilizer product) Corn gluten meal Preemergent soil-applied For more information, see www.gluten.iastate.edu

GreenMatch EX 50% lemon grass oil Foliar contact Marrone Organic Innovations www.Marroneorganicinnovations.com

Herbicidal soap Various salts of fatty acids Foliar contact Several brands; may be synthetic and used for farm stead maintenance on nonfood crops only

Matran EC 50% clove oil Foliar contact EcoSmart Technologies Inc. www.ecoipm.com

Matratec AG 50% clove oil Foliar contact ClawEl Specialty Products, Brandt Consolidated Inc. www.clawel.com

Racer 40% ammonium nonanoate (3.3 lbs active ingredient/gal)

Foliar contact Falcon Lab www.falconlabllc.com

Weed Zap 45% clove and 45% cinnamon oil Foliar contact JH Biotech Inc. www.jhbiotech.com

Worry Free Weed and Grass Killer Concentrate 70% citrus oil Foliar contact Worry Free products by Lilly Miller www.lillymiller.com


seeds are designated as “pathogen-free seed,” it is impossible to be certain that a seed lot is entirely free of all pathogens. Other considerations include cleaning tools and equipment to avoid spreading diseased tissue and pathogens between fields, especially if you know of problems in one field (e.g., white mold of soybean or Phytophthora root rot).

Crop rotationA large number of the pathogens that cause disease in field crops survive in association with crop residues left on the soil surface. A diverse crop rotation can contribute to the reduction of pathogens through lack of susceptible hosts in the field and allow for crop residue harbor-ing pathogens to decompose. During the decomposition of the crop residues, the disease-causing organisms will be forced to compete with other organisms for limited resources (i.e., food, water, and space). The pathogen population will also decline as it is attacked by naturally occur-ring pathogens of that organism. Rotation to a nonhost crop for 2 to 3 years is desir-able. Proper weed control is also impor-tant since weeds can act as alternative hosts to some crop diseases.

CultivationTillage can also be used to hasten the de-composition of crop residues and encour-age the decline of a pathogen population. In this case, the goal is to bury crop resi-dues or place the residue in contact with the soil so that it is quickly colonized by organisms involved with residue decom-position. These soil microbes will com-pete with the disease-causing organisms, reducing their populations. However, many fields in Pennsylvania are not suit-able for tillage because of soil erosion concerns, and producers should carefully evaluate the potential risk of erosion on their farm.

Plant Disease Diagnostics An important step in disease manage-ment is proper diagnosis of the pathogen and disease. As soon as certain symptoms become a problem in the field, it is im-portant to determine the causal agent in a timely matter to help reduce spread and potential impact. Once identified, information about the disease can then be used to determine the best control measures and reduce the impact on yield and quality. Infected plant samples can be

sent to the Plant Disease Clinic, 220 Buck-hout Lab, University Park, PA 16802 for proper diagnosis.

Applying Control MethodsMany products are available that help pre-vent fungal and bacterial diseases from developing. Products may include sulfur, lime, copper, or combinations of two or more. It is important that the product you use is certified for use on organic opera-tions. For a list of products, go to omri.org/simple-opl-search/results/ fungicide.

organic crop production

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