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in conventional cotton are usually the result of secondary pest flair ups caused by excessive spraying for a primary pest like lygus or boll weevil, because the broad-spectrum insecticides also kill the beneficial insects. Aphids are usually kept below economically damaging levels by predators like the ladybug, syrphid fly larva, lacewing larva, minute pirate bug, and the parasitic wasp Lysiphlebus testaceipes. The damage caused by aphids and other homopterans, like whiteflies, comes from their honeydew excretion that contaminates the lint and causes sticky cotton. A study conducted in Georgia's coastal plain indicates that aphids are initially suppressed by the insect-eating fungus Neozygites fresenii, and were kept at low levels thereafter by parasitoids and predators, most notably the small lady beetles of the Scymnus spp., preventing further outbreak. (Wells et al., 1999)   The choice of cotton varieties influences the abundance of cotton aphids and their associated biological-control agents. A study comparing cotton varieties found lower aphid densities on cotton varieties exhibiting the smooth-leaf characteristics. Parasitism and predation may have reduced cotton aphid population growth early in the season. Disease-causing fungal infection was the primary cause of an aphid population reduction that occurred during the week after peak aphid abundance, and continued disease activity combined with predation maintained aphids at a low density for the remainder of the season. (Weathersbee and Hardee, 1994)   Nitrogen management is an important tool in controlling aphid infestations, though less easily done without commercial fertilizers. Studies have shown that excessive or poorly timed fertilizer-N application will promote tender and succulent plant growth that attracts aphids. In California, experiments showed that cotton aphids reached higher densities in high nitrogen fertilized plants (200 pounds N/acre) than in low nitrogen fertilized plants (50 pounds N/acre). (Cisneros and Godfrey, 2001) This increase in aphid pressure has also increased insecticide application, from an average of 2-3 to 4-6 or more per season in recent years in many areas. (Godfrey et al., 1999)   The concept of induced resistance in plants has generated much interest in alternative pest control circles recently. Plants can be treated with substances that induce resistance to plant pests. One of these substances, jasmonic acid, has been used on cotton to determine the effect it has on cotton aphid, two spotted spider mites, and western flower thrips. Preference was reduced by more than 60% for aphids and spider mites, and by more than 90% for thrips on jasmonic-acid-induced leaves compared with control leaves. (Omer et al., 2001) The effective ingredient from jasmonic acid is an essential oil isolated from the extracts of the jasmine plant, Jasminum grandiflorum. The release of plant volatiles associated with the application of jasmonic acid also attracts natural enemies. Other plant resistance inducers include salicylic acid (aspirin) and salts like potassium phosphate and potassium silicate. Amino acids such as beta-aminobutryic acid and botanicals such as the extract of giant knotweed, Reynoutria sachalinensis, can produce systemic resistance. (Quarles, 2002) Milfana® is a commercial product made from giant knotweed extract. Check with your certifier before applying any of these products. Whiteflies   Whiteflies are similar to aphids in that they pierce stems and suck plant sap then excrete honeydew that contaminates the lint. The adult whiteflies resemble tiny white moths, the nymphs are more like scale insects. They are found on the undersides of cotton leaves, and when their numbers are high enough, the honeydew falls to leaf surfaces below where sooty mold forms, turning the leaf black. Whiteflies are usually kept in check by natural enemies, unless broad-spectrum pesticides are applied for a key pest. If most predators and parasites are killed, then the potential for devastating outbreaks exists. Beneficial insects that prey on whiteflies are lacewing larvae, lady beetles, minute pirate bugs, and bigeyed bugs. Parasites include Ecarsia formosa, Ecarsia meritoria, Encarsia luteola, Encarsia pergandiella, Eretmocerus haldemani, and Eretmocerus californicus. Some of these are specific to the greenhouse whitefly, Trialeurodes vaporariorum, or the sweetpotato whitefly, Bemisia tabaci, or the bandedwing whitefly, Trialeurodes abutilonea, or the silverleaf whitefly, Bemisia argentifolii. Some of these parasite beneficials parasitize more than one whitefly species. These nymphs are what most predators and parasites attack.   If whitefly populations near threshold levels, use insecticidal soap or "narrow range" oil (check with your certifier to determine which oils are allowed) to reduce primarily the nymph and pupa stage of the whitefly. Botanical insecticides like neem can reduce adult populations and also act as an insect growth regulator affecting the pupal stage. Other botanical insecticides such as pyrethrum can help reduce the adult population. Insect-eating fungi such as Beauveria bassiana are slow acting and require adequate humidity. An effective sprayer that has enough power to cover both sides of the leaf surface is needed, and at least 100 gallons of water per acre is necessary to have sufficient coverage.   In conventional cotton, nitrogen fertilizer management is also a factor in whitefly population levels and the amount of honeydew produced. A California study demonstrated that increasing levels of nitrogen fertilizer increased densities of both adult and immature whiteflies during their peak population growth on cotton. Higher nitrogen treatments also resulted in higher densities of honeydew drops produced by the whiteflies. (Bi et al., 2000) Spider mite   Spider mites, Tetranychus spp., are tiny arachnids (related to spiders, ticks, and scorpions) that live in colonies, spinning webs and feeding under cotton leaves. Spider mites have modified mouth parts that pierce the cells of the leaf to consume its contents. On the leaf's upper surface yellow spots appear when the feeding is moderate. Once the plants are infested, the yellow spots turn reddish brown. If the infestation is severe, mites can cause defoliation and affect yields. Spider mite populations are usually suppressed by natural enemies, unless a broad spectrum insecticide application occurs to disturb this balance. Insect predators of spider mites include minute pirate bugs, damsel bugs, bigeyed bugs, some midges, lacewing larvae, dustywings, spider mite destroyers, lady beetles, sixspotted thrips, and western flower thrips. Other mites that prey on spider mites are Amblyseius spp., Galendromus spp., Metaseiulus spp., and Phytoseiulus spp. When scouting for mites, a hand lens is necessary to distinguish the pest mites from the predatory mites. Spider mites tend to be sedentary, while their predators are very active.   Insecticidal soaps, "narrow range" oils, neem-based products such as Trilogy®, and sulfur are acceptable miticides in organic production (check with certifier regarding specific products). Application instruments must thoroughly cover the leaves' undersides, and products that are diluted must be applied in high volumes (more than 100 gallons of water per acre) to achieve complete coverage.   Cultural controls include keeping dust down along roads that border cotton fields. This is usually done by reducing traffic along those roads or watering down the roads. Reducing water stress on the cotton plants helps prevent mite build up. Pima cotton varieties are less susceptible to mites than highland varieties. (Anon., 2001)   Back to top Diseases of Cotton   Diseases in plants occur when the pathogen is present, the host is susceptible, and the environment is favorable for the disease to develop. Eliminating any one of these three factors will prevent the disease from occurring. Organisms responsible for cotton diseases include fungi, bacteria, nematodes, and viruses. If these organisms are present, then manipulation of the environment and the host, to make it less susceptible, helps to better manage diseases on cotton in a sustainable manner.   Soil health and management is the key for successful control of plant diseases. A soil with adequate organic matter can house uncountable numbers of organisms such as bacteria, fungi, amoebae, nematodes, protozoa, arthropods, and earthworms that in conjunction deter harmful fungi, bacteria, nematodes and arthropods from attacking plants. These beneficial organisms also help in creating a healthy plant that is able to resist pest attack. For more information, see the ATTRA publication Sustainable Management of Soil-Borne Plant Diseases.   The leaf surface can also host beneficial organisms that compete with pathogens for space. A disease spore landing on a leaf surface has to find a suitable niche for it to germinate, penetrate, and infect. The more beneficial organisms on the leaf, the greater the competition for the spore to find a niche. Applying compost teas adds beneficial microorganisms to the leaf, making it more difficult for diseases to become established. For more information on foliar disease controls, see the ATTRA publications Notes on Compost Teas, Use of Baking Soda as a Fungicide, and Organic Alternatives for Late Blight Control in Potatoes. Seedling diseases   These diseases are soil-borne fungi and are associated primarily with Rhizoctonia solani, Pythium spp., and Thielaviopsis basicola. Cool wet soils, deep seed placement, soil compaction, and cool temperatures contribute to seedling disease development. Spreading compost and using green manure crops, especially grasses, can reduce the pathogen levels in the soil. Various organisms have been researched as potential biological controls, these include Burkholderia cepacia, Gliocladium virens, Trichoderma hamatum, Enterobacter cloacae, Erwinia herbicola, rhizobacteria, and fluorescent pseudomonads as seed treatments. (Zaki et al., 1998; Lewis and Papavizas, 1991; Howell, 1991; Nelson, 1988; Demir et al., 1999; Laha and Verma, 1998)   Of these organisms, Burkholderia cepacia is available commercially in a product called Deny®. Another microorganism, Bacillus subtilis, sold under the trade name Kodiak®, is recommended as a seed inoculant for controlling damping off fungi. The following organisms have been used as soil treatments with varying levels of success: Stilbella aciculosa, Laetisaria arvalis, Gliocladium virens, and Trichoderma longibrachiatum. (Lewis and Papviazas, 1993; Lewis and Papviazas, 1992; Sreenivasaprasad and Manibhushanrao, 1990) Soil diseases   The three most important fungal soil diseases that cause economic damage are Fusarium oxysporum, Phymatotrichum omnivorum, and Verticillium dahliae. Nematodes are soil-dwelling, microscopic, worm-like animals. Only a few species are damaging to cotton. They will be classified in this publication as a soil disease.   Fusarium alone rarely causes economic problems, but when associated with nematodes, it forms a complex in which the nematode damage weakens the plant, making it susceptible to the fungus. Organic matter and its associated microorganisms can serve as an antagonist to this disease. The use of Bacillus subtilis products (Kodiak®) as a seed inoculum is recommended. The strategies for nematode control will be discussed further on in this publication.   Texas root rot, caused by Phymatotrichum omnivorum, is found in the alkaline soils of Texas and the Southwest. It is difficult to control and occurs on more than 2,300 broadleaf plants. (Goldberg, 1999) This fungus is active in high temperatures and in low organic-matter soils, so adding compost or incorporating green manure crops will increase organic matter and microorganism competition. Avoid growing cotton on ground that is known to harbor this disease.   Verticillium wilt caused by Verticillium dahliae is widespread, attacking many other agronomic, horticultural, and ornamental crops, as well as some weeds. It is persistent in the soil because of survival structures called microsclerotia. These microsclerotia are produced throughout the infected plant and when the crop is disked, these seed-like structures are also incorporated into the soil. Cultural controls include resistant varieties (Pima cotton is tolerant), rotation with grass crops, management for short season production, and avoiding excessive nitrogen and irrigation. Soil solarization done 6-11 weeks before planting was effective in one study where the pathogen was reduced to negligible levels. (Basallote et al., 1994)   There are many types of nematodes in soils, most are beneficial, and a few are cotton pests. Where nematode infestations are heavy, sampling and laboratory analysis can be used to determine the length of rotations and the non-host crops to use. If the problem is root-knot nematodes, rotation to resistant soybean varieties or sorghum is a possibility. Rotation to wheat, corn, grain sorghum, or resistant soybeans is possible if the nematodes are the reniform species. (Lorenz, 1994; O'Brien-Wray, 1994) Nematodes that attack cotton are the root knot nematode, Meloidogyne incognita, reniform nematode, Rotylenchulus reniformis, and the Columbia lance nematode, Hoplolaimus columbus. In sustainable production systems, nematodes can be managed by crop rotation, resistant varieties, and cultural practices. Eventually a "living soil" will keep harmful nematodes and soilborne fungi under control. (Yancy, 1994) Crop rotation is a good strategy, but make sure to identify the type of nematode you have and rotate with a crop that is not an alternate host for that nematode. For example, the reniform nematode also feeds on vetch, tobacco, soybeans, tomatoes, and okra, so these crops are not suitable for rotation with cotton for reniform nematode reduction. Check with your seed supplier to identify varieties resistant to the nematodes present in your field. Cultural practices include cover cropping with plants that are antagonistic to nematodes, such as rapeseed or marigolds, planting cotton on soils that are less sandy, controlling weeds, incorporation of chicken litter and other manures, and solarization. For more information, see the ATTRA publication Nematodes: Alternative Controls. Boll rots   Boll rots are a problem in areas with high humidity and rainfall and where bolls are starting to open or have been damaged by insects. Most pathogens are secondary invaders relying on insect damage for access. Diplodia spp., Fusarium spp., and other fungi have been associated with a basal type of rot where bracts are infected first, followed by invasion through nectaries and the base of the boll. (Anon., 1981) Other organisms that infect cotton bolls are Alternaria macrospora, Puccinia cacabata, and Xanthomonas, which are also responsible for foliar diseases. The boll-rot organism of most concern is Aspergillus flavus, which produces aflatoxins in the cottonseed. Aflatoxins are carcinogens to some animals and to humans. It contaminates cottonseed oil and cottonseed meal, which then cannot be used for feed. If Aspergillus is a problem in your area, consider cultural practices that reduce humidity, such as lower density seeding to allow more air circulation. Avoid tall, vegetative cotton growth - often a result of late planting, excessive nitrogen fertilizer, fertile soils, and/or excessive moisture. Rank growth often renders cotton plants more attractive and susceptible to late season insects, more susceptible to boll rot, and more difficult to defoliate. (Bacheler, 1994) Foliar diseases   Bacterial blight caused by Xanthomonas campestris pv malvacearum is common in areas with warm, wet weather during the growing season. It causes defoliation and reduces lint quality. Leaf spots are angular, restricted by leaf veins, water-soaked when fresh, and eventually turning brown before defoliation. Boll symptoms are small, round, water-soaked spots that become black. Affected bolls may shed or fail to open and have poor-quality lint. Quick plow down of crop residues after harvest to give ample time for decomposition will assist in the control of the disease. Crop rotation and using resistant varieties are also effective strategies.   Alternaria leaf spot caused by Alternaria macrospora starts off as a tiny circular spot that enlarges to half an inch. Concentric rings form as the spot enlarges, with the center sometimes falling out to form a shothole. Spots can also be found on bolls. High humidity increases the incidences of the disease, causing defoliation in severe cases. Controls include using resistant varieties and avoiding prolonged leaf wetness.   Southwestern cotton rust, Puccinia cacabata, first appears as small, yellowish spots on leaves, stems, and bolls, usually after a rain. These spots enlarge, developing orange-reddish to brown centers. Later, large orange spots appear on the lower leaves and discharge orange spores. Rust diseases require more than one host in order to complete their life cycle. For Puccinia cacabata the alternate host is grama grass, Bouteloua spp., and its proximity to the cotton field may determine the severity of infestation. If there is grama grass near your field, removal by burning, plowing, or grazing is recommended. A season of heavy rains and high humidity with grama grass close by has the potential for problems with cotton rust.   Cotton leaf crumple virus is transmitted by the silverleaf whitefly, Bemisia argentifolii. Control of the vector and stub cotton, which serves as an overwintering site for the virus, and the use of resistant varieties are strategies for disease reduction. Symptoms include wrinkled leaves that are cupped downward and plants that are small or stunted. This disease causes economic losses if the plants are infected when young.   Back to top Defoliation   Defoliation is a significant obstacle to organic production. The organic options available to defoliate cotton include flame defoliation and waiting for frost. Vinegar has not been cleared for use as a defoliant under the NOP rules. Ceasing irrigation can assist in leaf drop and boll maturation in low rainfall areas. Citric acid has been used by at least one Missouri cotton farmer. (Steve McKaskle) Citric acid is organically approved if it comes from natural sources. Otherwise, the only alternatives are to wait for a frost or hand harvest.   Research reports from the 1960s show that considerable work was devoted to developing butane-gas flame defoliators. Several models were developed by engineers in various parts of the cotton belt. To our knowledge no such equipment is available on the market today, having been replaced by chemical defoliation methods.   Back to top Marketing Organic Cotton   As previously mentioned, marketing cotton as "organic" requires certification of the field production practices. Certification also must continue throughout the manufacturing process, from the ginner, yarn spinner, and cloth maker, to the garment manufacturer. Each step of the process must use only materials (dyes, bleaches, etc.) that meet organic specifications. Manufactured products that are not already on the National Organic Program's approved list must go through a lengthy process to gain approval. If any unapproved product is used in the processing of cotton, the fiber cannot be labeled as organic. (Spencer, 2002)   Organic cotton farmers usually sell either to a mill or a manufacturer. It is usually up to the farmer to negotiate the price with his buyer. Buyers of organic cotton are limited. (Parkdale Mills) is perhaps the largest organic cotton buyer in the U.S. Located in Belmont, North Carolina, Parkdale makes yarn from organic cotton. They buy mostly from the southern states and occasionally from California. They purchase organic cotton when demand from a garment maker warrants. They buy from farmers, co-ops, and merchants.   Sandra Marquardt of the Organic Trade Association's Fiber Council says price premiums range from around $.95 to $1.25 per pound, depending on the quality and staple length. This premium may decline as stiff competition from foreign organic cotton increases. The Organic Fiber Council lists companies that could be approached as potential buyers of organic cotton, especially the mills.   The International Organic Cotton Directory offers an extensive listing of people, companies, and farmers involved in the organic cotton industry. They are dedicated to the sustainable production, processing, and consumption of organic cotton worldwide. They have directories listed by product type, business type, and alphabetically. There are a number of U.S. merchants/brokers and eight U.S. mills listed that could be potential buyers of organic cotton. As well, there are several farmers and farm organizations listed that are involved with organic cotton.   Back to top Economics and Profitability   Results from a six-year study in the San Joaquin Valley of California (Swezey, 2002) showed organic cotton production costs running approximately 50% higher than those of conventional cotton. The researchers found no difference between fiber length, strength, or micronaire between conventional and organic cotton. They concluded that organic cotton production was feasible in the northern San Joaquin Valley and that effective marketing of organic cotton must include a price premium to offset higher production costs.   Costs that typically differ from conventional cotton production include fertilizer materials such as manure, compost, or cover crop seed and their associated application and establishment costs; mechanical weed control costs; organically acceptable insect and disease management materials, such as compost tea and beneficial insects; additional hand weeding labor; and costs associated with being certified organic.   A detailed organic cotton budget is available from The University of California Extension Service.   Back to top Summary   Prospective growers should be aware that growing organic cotton is not quite the lucrative proposition it sounds and that there may be more money made, and less risk involved, in growing other crops instead. Cotton has many pests that must be controlled without conventional pesticides under an organic system. Weed control options are limited to those done without synthetic herbicides. Defoliation can be a major challenge, with limited options to accomplish the task. Transitioning from conventional crop production to organic cotton is fraught with risk, not to mention that the transition process takes three years before the fields can be certified as organic. Additionally, in the absence of institutional support and infrastructure, organic growers are unable to move organic cotton around as easily as do conventional growers. Markets for organic cotton are limited, and demand plus foreign supplies influence prices. Finally, most organic cotton is grown in the northern fringe of the Cotton Belt, out of the main range of the boll weevil. With weevil eradication programs, however, organic cotton may have a better chance than before to produce well throughout the Cotton Belt منبع:     www.ake.blogfa.com     منبع:     www.ake.blogfa.com     منبع:     www.ake.blogfa.com