Crop Protection Component: Cultural Practices PDF

LEARNING CONTENT / TOPIC. 5 CROP PROTECTION COMPONENT CULTURAL PRACTICES INTENDED LEARNING OUTCOMES (ILOS): AT THE END OF THE TOPIC, STUDENTS SHOULD BE ABLE TO: DISCUSS THE PHYSICAL METHODS AND CULTURAL PRACTICES FOR DISEASE MANAGEMENT.  Cultural P...

LEARNING CONTENT / TOPIC. 5 CROP PROTECTION COMPONENT CULTURAL PRACTICES INTENDED LEARNING OUTCOMES (ILOS): AT THE END OF THE TOPIC, STUDENTS SHOULD BE ABLE TO: DISCUSS THE PHYSICAL METHODS AND CULTURAL PRACTICES FOR DISEASE MANAGEMENT.  Cultural Practices Cultural practices are invaluable tool that a grower should consider in designing an integrated disease control system. Cultural control aims to prevent contact with the pathogen, to create environmental conditions unfavorable to the pathogen, or to reduce the amount of pathogen inoculum available to the infected crop plants. Some cultural control practices include host eradication, crop rotation, sanitation, tillage, improving crop growth conditions, and selection of resistant cultivars to name a few. Strategies to Reduce Pathogen Inoculant Historical evidence indicates that where pathogens have been introduced into previously clean sites, disease epidemics usually follow. The spread of disease to new areas, new plants or new plant products can be prevented or reduced by practicing quarantine and sanitation (crop hygiene or ways of maintaining plant health) together with methods for disinfesting soil, potting media and irrigation water so they do not carry inoculum  Site Selection. A grower can incur significant losses if susceptible crops planted in fields known for having a history of soil pathogens. Plant-pathogenic fungi such as Armillaria, Fusarium (the wilt-causing species), Plasmodiophora, Sclerotium, and Verticillium are true soil inhabitants and will persist in soil for many years, even in the absence of a plant host. Soilborne fungi such as Phytophthora, Pythium, and Rhizoctonia often are much more widespread, so site selection might be less of an option in avoiding these pathogens. If possible, avoid planting crops in low-lying, wet areas given the higher incidence of soilborne diseases.  Selection of Resistance Cultivars. The use of resistant cultivars is one of the most important and economical components of an integrated disease management program. Resistant cultivars offer one of the most successful approaches to the control of pathogens of many crops, especially those diseases that cannot be controlled by other means. Eradication of Hosts to Reduce Level of Inoculum. Crop plants remaining from previous seasons, weeds or wild plants may act as hosts providing a source of inoculum in the new growing season. For example, grasses such as Hordeum leportnum are hosts of the wheat take-all fungus Gaeumannomyces graminis. Many dicotyledonous weeds are infested with root-knot nematodes (Meloidogyne spp.) and other nematodes.  Physical Removal and Destruction of Crop Residues. Crop residues provide suitable substrates for many pathogens. Physically removing and destroying (e.g., burning, burying, etc.) crop residues are important cultural control practice performed during intercrop periods. The effect of destroying crop residues on particular pathogens depends on the type of crop (annual, perennial, or harvested product), the extent of the cropping area and the survival mechanisms and host ranges of the target pathogens Planting Pathogen-free and High-quality Seed. Planting pathogen-free and high- quality seed is a critical first step in managing diseases. This is particularly important for vegetatively propagated material such as tubers, bulbs, and slips. True seed can also contain pathogens, however, and all can serve as the source of entry of pathogens into new areas.  Crop Rotation. Some pathogens that causes diseases survive in the soil from year to year in one form or the other, usually as sclerotia, spores, or hyphae. Continuously cropping the same crop builds up the population levels of any soilborne pathogen of that crop that may be present. The populations can potentially build up so large that it becomes difficult to grow that crop without yield losses. However, by rotating crops soilborne pathogens will eventually decline without a suitable host. Sanitation in Preventing the Build-up of Pathogens. Wash soil off of farm equipment, including brushing off soil particles from shoes. These practices are especially important to prevent movement of soilborne pathogens such Sclerotinia sclerotiorum (causal agent of White mold), Phytophthora capsici, Verticillium dalhiae, and different species of Fusarium. A power washer is an important piece of equipment in the battle against these diseases. Strategies to Reduce Rate of Disease Spread Tillage Practices. Deeply burying infested crop debris and pathogen survival structures by moldboard plowing reduces disease incidence. For this to work, the residue must be buried deeply enough that it is not pulled back up during seedbed preparation and cultivation. Adjust Crop Planting to Disrupt Pest Habitat. Crop planting can be adjusted both in space and time to reduce the development of large pest populations. o Timing of Planting Dates. Alternating the time of planting to avoid high levels of pathogen inoculum or conditions conducive for development of a particular disease can lead to reduced severity of some crop diseases. For example early-planted fields of soybeans may have a greater incidence of seedling blights caused by Fusarium solani and Pythium if planted early in cool and wet soils. The incidence of these two diseases can be reduced by delaying planting until the soil warms up. o Seeding Practices. Deeper seeding may promote germination but it also lengthens the (usually) susceptible pre-emergence seedling phase. Smuts and seedling diseases caused by Fusarium spp. and Rhizoctonia spp. are more serious if seeds are planted too deeply. Similarly, potato seed pieces are more readily attacked by Rhizoctonia if planted too deeply. o Crop Density. Crop density can exert considerable influence over disease incidence due to the ease with which the pathogen inoculum can be transferred closely between closely spaced plants. In closely planted crops, temperatures are more uniform, humidity is higher, and foliage is wetter for longer periods of the day, all of which provides favorable conditions for pathogen infection and subsequent development. Diseases such as downy mildew and Sclerotinia stem rot (white mold) are greatly, affected by high humidity.  Intercropping. The incidence of disease is often less in mixed plantings than in monocultures because the distance between similar plants is greater than in more intensive growing systems so it is less likely that propagules or vectors of pathogens will successfully move from one host to another. Strip farming. This practice separates areas of one crop with intervening strips of another crop or fallow. Part of the rationale for adopting strip farming practices is that crops in adjacent strips rarely share common pathogens. The rates of spread of more specialized parasites are also restricted because of the discontinuous distribution of suitable hosts Mulching and soil amendments Mulching, the application of a covering layer of material to the soil surface, is a commonly used cultural practice, especially in horticulture. Natural materials used for mulching include cereal straw and stalks, crop debris, sawdust, leaves, grass, compost, and manureWhen crop residues are used as mulch they provide many pathogens with a food source as well as an environment in which to live and reproduce and can, therefore, increase the incidence of a disease.  Organic amendments incorporated into the soil may suppress pathogens by increasing the activity level of organisms that reduce their growth or survival. Phgtophthora cinnamomi causes severe root rot of avocados.Adding large amounts of chicken manure to the soil around the base of plants almost completely eliminates the problem. Similarly, the addition of chitin from crustacean, fish or other animal wastes to soil stimulates the parasitism of nematode eggs by fungi and reduces the level of inoculum Cover Crops. Disease suppressive cover crop rotations may provide an additional tool for managing soilborne diseases. The effect, however, is highly variable, differing between locations, and between years. At least three mechanisms are at work.  Irrigation Management. Irrigation management is clearly an important factor when it comes to disease control. Regardless of the irrigation method a grower chooses (furrow, sprinkler, or drip), timing and duration of irrigations should satisfy crop water requirements without allowing for excess water. Flooding. The paddy system of growing rice is perhaps the oldest example of using flooding for plant disease management. The primary purpose of flooding is to control weeds. However, it also reduces the number of fungal propagules, insects and nematodes in the soil probably by subjecting them to attack by soil-borne bacteria. By reducing the number of weeds which may harbor rice pathogens and insects, it also indirectly affects disease development. The destruction of crop debris carrying inoculum can also be hastened by flooding.  Plant or Crop Nutrition and Fertilizer Application. A properly nourished plant can withstand or tolerate the attack of pathogens much better than a plant that has nutrient deficiencies or has been excessively fertilized. For example, fertilizing with phosphates can delay the onset, and lessen the severity of take-all in barley (Gaeumannomyces graminus) and reduce the incidence of potato scab (Streptomyces scabies). Roguing involves the removal (and destruction) of diseased plants (rogues) to prevent further spread of the pathogen(s). To minimize disease spread, affected plants must be removed immediately after symptoms are observed. Roguing may need to be repeated regularly as newly diseased plants appear. To reduce the spread of banana bunchy top virus, both affected plants and adjacent, apparently healthy, plants are removed and destroyed  Trap and decoy crops. Trap (or catch) crops are susceptible plants that are grown land known to contain various pathogens. The pathogens infect the crop which must be destroyed before the life cycles of the pathogens are complete. Suitable methods of destroying the crop include ploughing in, applying various biocides or grazing off with livestock. For example, the parasitic plant Striga spp. can be partially controlled by ploughing in infected cereal crops. Trap crops can be grown simultaneously with more valuable crops. The efficiency of trap crops in reducing the spread of pathogens depends on the plant, growth habit differences including height differentials and position relative to the ‘protected' crop. PLANT DISEASES 1. FUSARIUM OXYSPORUM f.sp. In banana 2. Fusarium oxysporum in tomato Downy Mildew Powdery Mildew Blight Black spot Phytopthora infestans Rhizoctonia solani sclerotia Sclerotium wilt Sclerotinia sclerotium Sclerotinia in stem rot/white mold Root-knot nematode/meloidogoyne spp. Xanthomonas campestris Aspergillus flavus Plasmodiophora brassicae) bacterial wilt (Ralstonia solanacearum) Septoria lycopersici verticillium wilt of tomato