\m 16 5 6 2 1 'Introduction' \m 47 16 32 3 1 'Crop Rotation' \m 105 35 127 4 1 'Soil Tillage and Sanitation' \m 127 45 46 4 1 'Organic Matter, Green Manures, and Soil Amendments' \m 159 61 14 5 1 'Resistant Varieties' \m 235 95 81 7 1 'Soil Solarization' \m 340 142 66 9 1 'Chemical Control' \t'January 1988' 'II F-' \a Dr. Robert A. Dunn, Extension Nematologist \a \a MANAGING NEMATODES IN THE HOME GARDEN Dr. Robert A. Dunn, Extension Nematologist \h 1 'Introduction' MANAGING NEMATODES IN THE HOME GARDEN Root-knot nematodes are the most important nematode pests of home vegetable and ornamental gardens, but all kinds of nematodes (e.g., sting, stubby-root, lance, reniform, stunt, etc.) which can cause losses in commercial plantings can also be problems in home plantings. Home gardeners have only one kind of chemical nematicide, and it must be used before planting. It is therefore especially important that they take as many steps as possible to minimize nematode reproduction, enhance natural control factors, and help their crops withstand modest levels of nematode damage. These practices are just as useful and applicable to ornamental plantings as to vegetables. Many popular annual ornamentals are susceptible to damage by one or more nematodes. IFAS Extension Circular 399-A, Diagnosis and Control of Plant Diseases and Nematodes in a Home Vegetable Garden, contains a more detailed discussion of an integrated system of nematode and soil-borne disease recognition and management than can be presented here. A few of the most important points in that program are discussed briefly in this section: Crop Rotation Soil Tillage and Sanitation Organic Matter, Green Manure, and Soil Amendments Resistant Varieties Soil Solarization Chemical Control \b\v \h 1 'Crop Rotation' Crop Rotation The single most useful practice to reduce the build-up of injurious nematode populations is rotation or alternation of crops so that those susceptible to the same pests do not follow each other in the cropping sequence. Each kind of nematode has certain plants on which it reproduces readily, others which will not support it, and many intermediate in how well they will support its reproduction. If crops that favor one or more specific pests are planted in the same spot every season, populations of those pests will continue to increase regularly, each season's growth building on the last. If unrelated crops that do not support the same pests are grown in sequence in a specific spot, that progressive accumulation cannot take place. For crop rotation to be effective, it is necessary to know which crops are closely related, since closely related crops are those most likely to support the same pests. These are some common vegetables that belong to the same plant families: 1. Grass family: sweet corn, popcorn 2. Lily family: asparagus 3. Amaryllis family: onion, leek, garlic, shallot, chives 4. Buckwheat family: rhubarb 5. Goosefoot family: beet, chard 6. Carpetweed family: New Zealand spinach 7. Pea family: pea, edible-podded pea, southern pea, beans (lima, pole and snap), soybean 8. Mustard family: kale, brussels sprouts, cabbage, radish, cauliflower, broccoli, turnip, kohlrabi, rutabaga, mustard, Chinese cabbage 9. Mallow family: okra 10. Parsley family: carrot, parsley, celery, parsnip 11. Morning-glory family: sweet potato 12. Nightshade family: potato, eggplant, tomato, peppers 13. Gourd family: pumpkin, squash, watermelon, cucumber, cantaloupe 14. Composite family: endive, lettuce, artichoke, salsify, Jerusalem artichoke In addition, root crops (even from different families) should not be planted after each other because of their susceptibility to many of the same pests. \v \v \v \b\v \h 1 'Soil Tillage and Sanitation' Soil Tillage and Sanitation Nematodes will continue to reproduce and increase their population levels as long as they have living host roots upon which to feed. As soon as a crop is no longer of value in the garden, pull it up or thoroughly till it into the soil so that its roots do not continue to support nematode reproduction. Every month that old roots remain alive in the soil represents approximately one additional generation of increase rather than one more month in which the population should be declining. The effect of this on the numbers of nematodes ready to attack the next crop can be tremendous. In addition, intact plant debris left in the soil when it is time to plant or to treat the soil with a nematicide can easily harbor nematodes that will be protected from any control measures and serve to infect the next crop. Tilling the soil a month before treating it or planting encourages old root tissues to break down, exposing nematodes and other pathogens to soil treatment and/or natural enemies, and improves the ability of soil treatment chemicals to move uniformly through the soil. \h 1 'Organic Matter, Green Manures, and Soil Amendments' Organic Matter, Green Manures, and Soil Amendments Maintaining high levels of soil organic matter usually improves the ability of plants to withstand modest damage from nematodes, and may contribute directly to nematode control. As organic matter decomposes in soil, it forms humus, complex organic chemicals that help bind soil particles together and improve their ability to hold nutrients and water. This essentially increases the "bank" or stored supply of nutrients and water available to plants grown in that soil. When more nutrients and water are available, plants can still support themselves with slightly less efficient root systems. Any organic soil amendment, such as animal manure, compost, peat, and even surface mulches of materials such as leaves will contribute to the formation of humus. Green manures are crops grown with the express purpose to be tilled into the soil as fresh green organic matter. Crops that grow rapidly to produce a large mass of green matter are normally chosen for green manuring. When otherwise suitable, legumes (members of the pea family, including clovers, hairy indigo, etc.) are especially desirable for this purpose, since they also increase the nitrogen (fertilizer nutrient) content of the soil when they are incorporated into it and decompose. Adding green manures to soil provides soil microorganisms with a sudden increase in available food, causing a "bloom" of fungi and bacteria. Other small organisms increase to take advantage of the greatly increased food supply, and many natural predators of nematodes are among those that increase. These predators (fungi, predatory nematodes, mites, many others) help reduce the populations of plant parasitic nematodes. The rapid decomposition of green manures has also been claimed by many to contribute directly to nematode control by producing chemicals that are toxic to the nematodes. \v \v \b\v \h 1 'Resistant Varieties' Resistant Varieties No vegetable varieties are resistant to all nematodes, but some have resistance to the most common kind of root-knot nematode, sometimes combined with resistance to one or more important diseases. If they are otherwise suitable, nematode-resistant varieties should be considered a must when no nematicide is used, and desirable even when a chemical treatment is used. It may be necessary to plan the garden far ahead of time so that desired varieties can be selected from seed catalogs and started at home, since garden centers and nurseries rarely have many varieties from which to choose. Temperature can affect plant resistance to nematodes. For instance, tomato varieties designated "N" in seed catalogs are resistant to "southern" root-knot nematode, the species most commonly found in Florida gardens, when soil temperatures are below 80 F, but lose resistance as soil temperatures rise above 82 F. This resistance may therefore be useful for a spring crop which is planted into relatively cool soils, but of little use in fall when the soil is much warmer. There is not enough space here to list all tomato varieties for which root-knot nematode resistance is claimed, but most seed catalogs identify nematode and disease resistance in tomatoes. On the other hand, there are relatively few nematode-resistant varieties of some other crops such as southern peas and sweet potatoes, so it is reasonable to list some of those that have been reported in the following tables. \bSweet Potato varieties with resistance to one or more root-knot nematode (Meloidogyne) species: S = susceptible; M = moderately resistant; R = resistant, --- = not available ------------------------------------------------------------------------------- Meloidogyne (root-knot nematode) species -------------------------------------------- Variety ("southern") ("peanut") ("javanese") ------------------------------------------------------------------------------- Carver M --- M Centennial S M S Georgia Red M R --- Heartogold R R R Jasper R --- --- Jewel R --- S Red Jewel S M R Shore Gold S --- --- Southern Delite M --- --- ------------------------------------------------------------------------------- ------------------------------------------------------------------------------- Examples of Southern Pea varieties with resistance to one or more root-knot nematode (Meloidogyne) species: S = susceptible; R = resistant; --- = not available ------------------------------------------------------------------------------- Meloidogyne species --------------------------------------- M. incognita M. javanica Variety ("southern") ("javanese") ------------------------------------------------------------------------------- California Blackeye No. 5 R --- Colossus R R Floricream R --- Mississippi Purple R R Mississippi Shipper R R Mississippi Silver R --- Pinkeye Purplehull R/S?* --- Zipper Cream R --- ------------------------------------------------------------------------------- ------------------------------------------------------------------------------- * Conflicting reports \v \v \v \b\v \h 1 'Soil Solarization' Soil Solarization This is a method of soil treatment which is relatively new in Florida. We take advantage of the energy derived from the sun to heat the soil sufficiently to reduce populations of nematodes and some other soil-borne problems. Many gardeners and other growers would welcome a soil treatment that would substantially reduce losses to nematodes without using pesticides. "Soil solarization" may provide that alternative. Soil solarization consists of covering the area to be treated with a clear polyethylene tarp for 4-6 weeks during a hot period of the year when the soil will receive maximum direct sunlight. Various forms of the method have reduced damage caused by a wide range of soil-borne fungi, weed seeds, and nematodes in field tests in Israel, Jordan, California, and Florida. The method has not been tested adequately in Florida to be recommended without reservation. It has worked well in some trials but has failed in others in Florida. However, the practice is described here to provide some guidelines for those who wish to experiment with it. Procedures and Precautions: 1. Soil should be covered AT LEAST 4 weeks, preferably longer, during the hottest and sunniest time of the year. June and July appear to be most suitable in Florida, since air and soil temperatures are naturally highest then, and day length and the angle at which the sun hits the earth provide for maximum solar energy hitting the soil at that time. 2. Soil must be well tilled before tarping, to destroy clods and plant debris which might interfere with uniform conduction of heat through the soil and thus protect some organisms from the full effects of the treatment. When soil is well tilled and its surface very smooth before the tarp is applied, there can be maximum contact between the tarp and the soil surface, with few air pockets to interfere with direct heating of the soil by incident sunlight. All other soil preparations such as placement of fertilizer and drip irrigation tubes should be completed before placing the tarp over the bed. This will minimize the need to disturb the treated soil before planting. 3. Soil moisture must be high when the tarp is applied. Wet soil conducts heat better than dry soil, so moistening the soil before tarping will provide for a deeper treatment. In addition, most pest organisms are more susceptible to lethal effects of heat when they are in moist soil; they may be dormant if dry. 4. It may be desirable to raise the beds to be treated slightly to reduce the chances of recontamination after planting, but do not build them higher than necessary. High, narrow beds expose more surface area from which heat can be lost at night. This may reduce the maximum temperatures attained, thus reducing the level of control achieved in a given period of treatment. Covering broad areas, including row middles, will reduce the overall load of weed seeds, fungus spores, and nematodes near the bed, and thus reduce opportunities for recontamination of planted areas. \v \b 5. Raise the center of the bed to form a small "crown" or peak to enable it to shed water. Solarization seems to have been less effective in periods of high rainfall, probably because water standing on the plastic absorbed heat from the soil. 6. Use clear polyethylene, NOT black mulch. Clear plastic produces higher soil temperatures, faster, than black plastic. Sunlight passes through clear plastic to heat the soil directly. Black plastic intercepts the light, and soil is heated primarily by conduction only where the plastic actually touches the soil. Some of the heat generated when sunlight hits black plastic is lost directly to the outside air. 7. Thin plastic mulch (1 to 2 mil) may permit more sunlight to penetrate to the soil and has been reported to favor more rapid and deeper control of soil-borne fungi than thicker plastic (6 mil). However, equal control was eventually obtained with both thicknesses, and the thicker plastic is less likely to tear. 8. Leave tarp in place until you are actually ready to plant. Leaving the tarp there has no detrimental effect on the soil, so it will only maximize the period of treatment and reduce the chance of recontamination before planting. When ready to plant, it may be possible to remove the plastic carefully enough to save it for re-use, especially if 4-6 mil thick plastic was used. Clear plastic mulch enables soil temperatures to get higher than black plastic, so it should probably be removed before planting any crops that require relatively cool soil for best growth. However, it MAY be safe to leave clear plastic over the beds as a mulch in autumn for warm season plants that could benefit from higher soil temperatures. 9. When planting, be very careful to avoid bringing contaminated plants or untreated soil into the treated bed, and do not till or otherwise disturb the treated soil if possible. Deep tillage can bring soil up from depths that were not adequately heated, thus contaminating the crop root zone. How does soil solarization work? It seems likely that much, perhaps all, of the effect is obtained from the prolonged increase of soil temperatures at normal root depths. Temperatures of tarped soil 6 inches deep were 111 F to 122 F, 14 to 23 F higher than those of uncovered soil, in several California tests. Many nematodes and other soil pests will be controlled by prolonged exposure to these temperatures. In Florida (GCREC Bradenton), 30 days of solarization of soil infested with root-knot nematodes and wilt fungi increased yields of tomatoes 48% over those grown in soil that had been kept fallow for the same 30 days. Wilt affected 80% of plants in the fallow plots but only 8% of plants in the solarized plots. \v \v \v \b\v \h 1 'Chemical Control' Chemical Control Gardeners presently have one chemical available to use as a nematicide, metam-sodium, sold as Vapam, Fume-V, and perhaps other trade names. It is a water-soluble liquid that, when applied to soil at correct temperature and moisture content, releases fumes toxic to nematodes and many other soil-borne pests and pathogens. It can reduce nematode numbers enough that they will have little or no effect on initial growth and production of annual crops, but it leaves no "residual" or long-lasting effect in the soil. Reinfestation of treated soil by nematodes migrating from adjacent or deeper soil not reached by the treatment, by the few individuals that usually survive treatment, or from contaminated plants or soil brought into the plot is nearly inevitable. Therefore, no one should expect this or any other chemical treatment to provide "control" for more than one crop season. By the end of the growing season, there are often as many nematodes in a treated area as in an untreated area, because the few nematodes that reached roots in treated soil had an abundant food supply and no competition. Detailed instructions for using metam-sodium are presented in Nematology Plant Protection Pointer No. 12, "Home Garden Nematode Control with Vapam," available from County Extension offices or from Dr. R. A. Dunn, Extension Nematologist, Bldg. 78, IFAS, University of Florida, Gainesville, Florida, 32611.