Organic Disease Management Sue Colucci Area Specialized Agriculture Extension Agent, Western NC North Carolina Extension Service What the NOP says: When cultural, mechanical, and biological strategies are insufficient to prevent or control crop pests, a biological or botanical substance or a substance included on the National List of synthetic substances allowed for use in organic crop production (www.ams.usda.gov/nop/nationallist/finalrule.html) may be applied to prevent, suppress, or control pests, weeds, or diseases The conditions for using the substance must be documented in the organic system plan Organic Pest Management Approach pests are indicators of how far a production system has strayed from the natural ecosystems it should imitate pests are attracted to a plant that is weak or inferior in a well-balanced system, massive pest outbreaks are rare due to the presence of natural predators, parasites, and disease agents prophylactic, holistic approach vs. remedial approach not just treating symptoms pest problem usually indicates sub-optimal growing conditions and imbalance emphasis on biodiversity and optimal cultural practices The Disease Triangle PATHOGEN HOST DISEASE ENVIRONMENT Good news! You don t have to have diseases on your farm. Really!
The disease triangle is a schematic that explains that in order to have disease you must have: 1. The pathogen present on your farm. You can eliminate some pathogens through crop rotation, only using disease-free seed or plant stock, deep tillage to move soil pathogens deeper into the soil, etc. 2. An appropriate host for the pathogen to live and reproduce. As you see, crop rotation would really help here. One of the most important crop protection methods is using disease resistant varieties. Make sure you are matching the correct disease resistance to the problem on your farm. I hope I am convincing you to get your disease problems properly diagnosed. 3. Suitable environmental conditions are needed for disease to develop. Pathogens require environmental cues, such as humidity, moisture and desirable temperatures to germinate, survive and infect. If these conditions are not met, pathogens cannot survive. Ex. downy mildews require a certain amount of free moisture present on the leaf surface to germinate and infect. If you can increase air flow and the drying of the leaf surface you can make life miserable for the pathogen. What Organisms Cause Disease? 1. Fungi 2. Bacteria 3. Viruses 4. Nematodes What types of symptoms can you expect from these organisms? 1. Fungi cause spots, lesions, blights, yellowing of leaves, wilts, cankers, rots, fruiting bodies, mildews, molds, leaf spots, root rots, cankers, and blotches. Fungi are typically spread by wind, rain, soil, mechanical means and infected plant material. 2. Bacteria cause water-soaking, spots, wilts, rots, blights, cankers, exudates, galls, yellowing, leaf spots, watery blotches, wilting. Bacteria are typically spread by rain, mechanical means, planting material, vectors (ex. bacterial wilt of cucurbits spread by cucumber beetle) 3. Viruses cause mottling, leaf and stem distortions, mosaic patterns, rings and stunting. Viruses cause interesting symptoms, some are beautiful. Viruses are spread by mechanical means, vectors and in plant material. 4. Nematodes cause wilting, stunting, yellowing of entire plants. This is because the roots of the plant are infected and the plant is starving or thirsty. Nematodes are spread by soil on equipment or workers boots or on infected plant material. So how do we control these things? The NOP has a hierarchical approach to pest management starting with System-based cultural practices then Mechanical and Physical Practices and finally Material-based (chemical, botanical, elemental) practices. Cultural Control Cultural control is your first line of defense. Promote healthy soils and healthy plants. Healthy soil is the hallmark of organic agriculture. An unhealthy plant is very attractive to diseases! Soils rich in organic matter are shown to increase soil biodiversity and help to create and abundance of beneficial soil microorganisms. Using compost has been shown to
increase the suppressiveness of the soil by encouraging beneficial microorganisms, as well as inducing disease resistance in plants by simply having healthier plants. Exclusion o Disease-free seeds, transplants or plant stock o Prevent introduction of diseased plants or soil o Disease free water source o Control insects that can carry disease o Soil solarization Disease resistant varieties Good sanitation from the prior season. Remove diseased plants or weeds from the field. Don t put disease plants or weeds in the compost pile! Many diseases are resistant to high heats or can become resistant. Some pathogens form resistant structures that can tolerate unfavorable conditions. Always work infested fields last and clean off equipment. Disinfest tools! Plant on raised beds. Not only helps with avoidance of pathogen, but also good moisture drainage is key. Crop rotation o > 3 yrs between crops in the same family o Some pathogens cause disease among multiple plant families Plants adapted to area Plant at proper depth (below crown or graft) Use only thoroughly composted material Improve air circulation by staking, trellis or pruning Water in the morning Avoid overhead irrigation if possible Make Life Difficult for the Pathogen (not yourself!) Create an unfavorable environment for pathogens Increase air movement Trellising, high tunnels Increase soil drainage Avoid low-lying areas Row orientation Maximize air movement Minimize leaf wetness periods Irrigation management Drip Irrigation Mulches Plastic or plant-based Reduce splash dispersal of pathogens Protect fruit from soilborne pathogens Avoidance Plant your crop when disease isn t as big a problem Early blight and Cucurbit Downy Mildew
Maximizing Disease Suppression with Compost Compost Cure 4 or more months Incorporate into soil several months before planting Inoculate with beneficial microorganisms, e.g. Trichoderma Application 5-10 tons (dry weight)/a - rule of thumb Apply every year until significant organic matter improvement observed; watch for increases in P Produce Healthy Transplants Practice good sanitation in the greenhouse Use new or sanitized plug trays or flats and pathogen-free mixes Sanitize equipment Install solid flooring; raise seedling trays Limit movement of personnel and equipment between greenhouses Clean benches, greenhouse structure thoroughly after the crop; close up greenhouse Variety Selection Disease tolerance is the ability of a plant to endure an infectious or noninfectious disease, adverse conditions or chemical injury without serious damage or yield loss Disease resistance is when a plant possessed properties that prevent or impede disease development. Pick varieties that are appropriate for your area. Keep records of a cultivar s performance and the disease pressure each season. Local heirlooms are generally better suited for a particular region. Use tissue culture plants (small fruits, some cut flowers, perennials) if available. These plants are often disease indexed. This is especially important for viruses. This is a specialized area and there are not always tissue culture plants available. Physical/ Mechanical Controls Physical and Mechanical controls are very important in insect management on organic farms. They are also very important for disease control, especially in perennial cropping systems like fruit trees, small fruits and tree nurseries. Some options for physical/ mechanical management of plant disease include: Hand-picking Pruning Mulches Soil solarization Pruning Prune out diseased plant parts Increase light into canopy
Increase airflow Helps spray penetrate all surfaces Proper pruning for proper plant health! Soil solarization Used in greenhouses, seed beds, cold frames. In greenhouses or in raised beds you can sterilize the soil or bench using heat produced by steam. You want to heat the coldest part of the soil to 82 C for 30 minutes. Soil solarization, a nonchemical technique, will control many soilborne pathogens and pests. This simple technique captures radiant heat energy from the sun, thereby causing physical, chemical, and biological changes in the soil. Transparent polyethylene plastic placed on moist soil during the hot summer months increases soil temperatures to levels lethal to many soilborne plant pathogens, weed seeds, and seedlings (including parasitic seed plants), nematodes, and some soil residing mites. Soil solarization also improves plant nutrition by increasing the availability of nitrogen and other essential nutrients. Hot Water Seed Treatment Research has shown that hot water seed treatment can help to decrease disease in seeds. Times and temps of seed treatment: Brussels sprouts, eggplant, spinach, cabbage, tomato = 122 F for 25 min Broccoli, cauliflower, cucumber, carrot, collard, kale, kohlrabi, rutabaga, turnip = 122 F for 20 min Mustard, cress, radish = 122 F for 15 min Pepper = 125 F for 30 min Lettuce, celery, celeriac 118 F for 30 minutes It is important to note that cucurbit seeds can be damaged by hot water. Other cautions include: Use new, high quality seed Treat a small sample first and test for germination Treat close to time of planting (within weeks) Treat only once Fact sheet: http://ohioline.osu.edu/hyg-fact/3000/pdf/3086.pdf Material Control Materials include: Elemental fungicides Copper and sulfur Biofungicides/Microorganisms Ex. PlantShield, MycoStop, Companion Particle Film Barriers Ex. kaolin clay Peroxides and Bicarbonates Compost Teas
Sulfur Used effectively for powdery mildew on most crops Labeled for rusts (grape and bean), botrytis (onions), black spot (rose) ph adjustment Component of Bordeaux mixture Lime sulfur - protectant dust or spray to control some fungal or bacterial diseases Helps control rust, powdery mildew (PM), brown rot Copper Controls some fungi and bacteria Free Cu - Copper sulfate: Bordeaux mixture Fixed Cu - copper hydroxide, copper oxide, copper oxychloride, copper octanoate Kocides restricted use, requires license, OMRI approved? Safer Garden fungicide Cu 12% or 0.4% : rust, scab, brown spot, black spot, others Nasty stuff, some certifiers won t let you use it Botanical/Horticultural Oils Used successfully to control insects that spread disease. Especially viral diseases. Some are effective for fungi like powdery mildews and rust. Biocarbonates and Peroxides Bicarbonates - Potassium Bicarbonate (baking soda) disrupts cell membrane K balance PM Black spot, leaf spots, rusts for seed, transplants or established plants Ex. Kaligreen Peroxides disinfest plant surface Pre-plant, plant dip, foliar spray Use on tools, trays, pots, surfaces Ex. Oxi-Date Antibiotics Antibiotics -Streptomycin sulfate many brands for agricultural use to control bacteria, fireblight Fertilome Fireblight spray : also for bacterial wilt, stem rot, leaf spots and crown gall Tetracycline fireblight Biofungicides/Microorganisms Antagonists/Competitors Trichoderma harzianum is the most researched Antifungal properties Bacillus spp. Plant growth aids Healthy roots, soil exploration Trichoderma Activate plant immune system
Bacillus pumilus Compost Teas Compost tea, in modern terminology, is a compost extract brewed with a microbial food source molasses, kelp, rock dust, humic-fulvic acids. The compost-tea brewing technique, an aerobic process, extracts and grows populations of beneficial microorganisms. Results often variable, but some people have amazing successes. Try them out, but take notes! For more information, read the ATTRA publication Notes on Compost Teas at http://attra.ncat.org/attra-pub/compost-tea-notes.html This publication also has sources of commercially available compost tea. Pre-Plant Options Biofumigation Mustards, broccoli residue Muscodor Broad-spectrum activity Biocontrols Contans, Advan LLC Coniothyrium minitans a fungi used pre-plant Narrow-spectrum (Sclerotinia only) Ex. lettuce drop, sclerotinia blight on peanut Scouting for Disease Why scout? Identify disease problems during the season To change practices this year For next year Scout your crops on a regular basis (calendar). Scouting supplies include: hand lens (10X or higher) paper for notes self sealing bags for samples a marker or pen field guide digital camera Using the Plant Disease and Insect Clinic: General Guidelines Collect fresh, don t send over weekend. Send several examples Crush proof container Provide lots of information Don t pull plants-do bag roots Don t get soil on foliage Press leaves Contact lab Use your extension agent for help Collect as much information as possible
Examples Early blight (potato, tomato) Early blight is caused by two fungi (Alternaria solani and Alternaria tomatophila) that are a serious problem in tomatoes and potatoes but rarely effects peppers and eggplants. All of the above-ground portions of the plant can be affected throughout the growing season. The disease starts on the lower leaves with small circular spots that have a target appearance of concentric rings. Leaves develop yellow blighted areas and later the tomato fruit may rot on the stem end. Potato tubers can also become infected, but this is quite rare. The pathogen can overwinter in the soil on diseased plant residues. Cultural Control: 1. Use crop rotations of at least 3 years to non-hosts (away from tomato, potato and eggplant). 2. Provide optimum growing conditions and fertility. Stressed plants (including drought) are more susceptible to early blight. 3. Stake or cage plants to keep fruit and foliage away from soil. 4. Drip irrigation is preferred, or overhead irrigation starting before dawn, so that the plants are dry early in the day. The key is to keep the period of leaf wetness to a minimum. 5. Mulching helps to prevent splashing of spores from soil up to lower leaves. 6. Indeterminate tomato and late-maturing potato varieties are usually more resistant/tolerant to early blight. 7. Early blight can be seed-borne, so buy from a reliable supplier. Hot water seed treatment at 122 F for 25 minutes is recommended to control early blight on tomato seed. See chlorine treatment procedures under bacterial diseases. 8. Disinfect stakes or cages with an approved product each season before using. Sodium hypochlorite at 0.5% (12x dilution of household bleach) is effective, and must be followed by rinsing, and proper disposal of solution. Hydrogen peroxide is also permitted. Materials Approved for Organic Production: 1. Copper products showed one good and one poor result in recent studies. 2. A Trichoderma harzanium product, PlantShield HC, used as a drench at planting, showed fair to good results in NY state on tomatoes over three seasons. 3. Serenade, Bacillus subtilis. A protectant. Labeled, but considered only partially effective in UNH trails. Downy Mildews Not true fungi Watermolds Swimming spores Like cool wet weather
Overwinter as resistant spores in soil or infected plant material or blow in seasonally from diseased plantings Effects vegetables and perennials, especially important in cucurbits, grapes and hops Important to note that downy mildews are very host specific. Ex. the downy mildew that infects cucurbits is not the same as the one that infects grapes. Cultural Control Resistant varieties Planting date We will get it in fall Avoid overhead irrigation! Forecasting site If transplanting- make sure transplants are disease-free! Rotation important for overall plant health High tunnels? Materials for control of downy mildews OMRI-listed products copper, neem oil, biofungicides (ex. Serenade or Sonata), peroxides (ex. OxiDate), and bicarbonates (ex. Kaligreen) Compost teas? Best option as an organic grower is to use a copper product Spray early in the morning to avoid phytotoxicity Spraying copper prior to disease development or at very early onset (very few, mild symptoms), may help suppress the disease, but will not offer 100% control under favorable conditions (cool, wet and humid weather) Powdery Mildew Effects many plants, but like downy mildew powdery mildews are host specific. Powdery mildews like it hot and relatively dry (humid but not wet). Powdery mildew is perhaps one of the easiest diseases to diagnose. Cultural Control Resistant varieties Plant in sunny areas with good air circulation Avoid overhead irrigation Avoid excess fertilization Slow release better Remove infected plant material Materials for powdery mildews Sulfur is very effective
Kaligreen and Armicarb (potassium bicarbonate-baking soda); dilute solutions of hydrogen peroxide (Oxidate) These materials burn out the fungus growing on the surface, but do not provide protection against new infections; thus, repeated applications are important Oils Saf-T-Side Spray Oil, Sunspray Ultra-Fine Spray Oil, or one of the plant-based oils such as neem oil or jojoba oil (e.g., E-rase) Be careful some plants are sensitive, esp. when used in conjunction with sulfur Dilutions of milk and whey (the dairy by-product) have been effective for controlling powdery mildew (Australia)