My thriving cucumber season came to an abrupt halt a couple of weeks ago. It started when a strong windstorm knocked over a cage of ‘Amiga’ cucumbers and uprooted the plants completely. All my other cages were staked so I can’t explain why this one was not but anytime you grow anything on a tomato cage, don’t forget to stake it!
I was disappointed but not surprised to find evidence of root-knot nematodes on the roots (see photo). Though my plants had been producing well throughout June and early July I had begun to notice pale green leaves, misshapen fruit, reduced yields and general wilting, all signs of nematodes infestation.
Nematodes are soil-dwelling, microscopic, worm-like parasites that feed on plant roots, causing swelling or galls within the roots, impeding the flow of water and nutrients. They are most active in summer when soil temperature ranges between 85 and 95°F. Cucumbers, okra, squash, beans and non-resistant tomatoes are especially susceptible. Because nematodes are most active at higher temperatures they are not a serious threat to most cool season plants, the exception being carrots and beets which can have severe damage. Alliums and sweet corn are not affected by nematodes.
Because nematodes can devastate a crop it’s important to take action if you discover them in your garden. Below are a few earth-friendly methods for battling nematodes; you may never completely eliminate nematodes but the following methods will help keep their numbers in check so that damage will be kept to a minimum. Note that nematodes can be spread by tools and soil so be sure to clean and disinfect tools after working in soil that contains nematodes, also be careful not to fling soil from infected roots to adjacent parts of the garden.
Summer Fallow: Nematodes are most active in warm soils and they need water to thrive so take advantage of summer’s heat to wither them away. Withhold water from nematode infested areas of the garden and turn or till the soil every 7-10 days during the summer to expose nematodes to the drying effects of the sun.
Crop Rotation: Plant nematode susceptible crops where non-host crops such as onions, garlic and sweet corn were previously grown.
Plant Nematode Resistant Crops: If your garden is too small for crop rotation look for plants that are bred to have nematode resistance. A tomato labeled with “VFN” indicates disease resistance: V= resistance to Verticillium wilt; F = resistance to Fusarium wilt; N = resistance to root-knot nematode resistance. Resistance doesn’t mean they won’t get nematodes but they are able to resist them enough to produce a harvest. Resistant tomato varieties include ‘Better Boy’, ‘Tycoon’, ‘Celebrity’, ‘Big Beef’, ‘Lemon Boy’, ‘Sweet Chelsea’ and ‘Supersweet 100’.
Plant Nematode Suppressive Crops: Certain types of marigolds (Tagetes patula) work by excreting a substance that is damaging to nematodes as well as trapping them in their roots and preventing reproduction. The key is to plant the entire area as a cover crop and leave it in place for several weeks to reduce nematode populations. A late summer planting of French marigolds can be left in place right up to the first frost; effective varieties include ‘Tangerine’, ‘Petite Harmony’, ‘Petite Gold’ and ‘Janie’. At the end of the season remove the tops and turn under the roots. Elbon rye is an effective nematode control that can be planted as a cool-season cover crop that is turned under in early spring. Cut down or weed-whack the tops a couple of times during the growing season and either leave the tops in place as mulch or add them to the compost pile. ‘Pacific Gold’ mustard, also sold as Mighty Mustard®, contains high levels of compounds called glucosinolates that help suppress nematode populations. Cut down mustard before it sets seeds, add the tops to the compost pile and leave the roots to decompose in the soil. Both Elbon rye and ‘Pacific Gold’ mustard are available from Johnny’s Seeds (www.johnnyseeds.com).
Biological Control: In 2010, Dr. Kevin Steddom, a plant pathologist with Texas AgriLife Extension, conducted a trial at the AgriLife Research Station in Overton comparing several products for nematode control. He found that of all the products he tested, which included two soil fumigants, a biological fungicide called Actinovate was the most effective in lowering nematode populations. A 2-ounce packet sells for $18-20 but you only need ½ teaspoon per gallon and it can also be use for powdery mildew, black spot, early blight and other fungal diseases.
Soil Solarization: Rake the soil so it is level and smooth, water well and cover with clear, UV resistant plastic (2-4 ml thick). Pull the plastic taut across the soil and secure or bury the edges with soil. Leave in place for 4-6 weeks, patching any holes with duct tape so heat cannot escape. This is often considered a last resort because the heat generated under the plastic kills everything, good and bad. It’s important to add organic matter at the end of the process; after removing the plastic do not work the soil for couple of weeks then top with a 2-3 inch layer of compost and water well before planting.
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