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Growing More Robust Tomatoes – Please Hold the Nematodes

January 4, 2009

Nathan Cobb's sketch of a marine nematode

Nathan Cobb's sketch of a marine nematode

The Problem

There is a pest lurking in most garden soil that many are unaware of. It is microscopic and can infest a wide variety of plant roots. One way to diagnose the problem is to pull up your tomato plant at the end of the season and look for bumpy roots. Tomato plants that are smaller, yellower and less productive with lower quality tomatoes are most likely infested. You have a problem with your soil that will not go away without treatment. And it will get worse.

The degree of infestation is proportional to the number of bumps, or galls, root-tomatoon the roots. As this picture shows, roots can be completely overtaken by these. Each of these galls is a female nematode. There can be thousands of microscopic nematodes in one handful of soil. They are roundworms that live in marine, fresh water or land.

Plant Parasitic Root Knot Nematodetomato-roots

The root knot nematode Meloidogyne incognita is a plant parasitic nematode that lives in the roots of the tomato plant (and other plants). It sucks the water and nutrients out of the roots before your tomatoes can use them. They live in the soil, enter the root tip and set up camp. The females become very small round meloidogyneballs with a tiny head. They can not escape once they are in this form in the root. They lay eggs in the soil, the eggs hatch and tiny nematodes find roots to make their home.

The Cure

Currently, there are no chemical controls for nematodes in garden soils. Fumigants and non-fumigants are usually bad for the environment anyway. Therefore, other methods are used such as fallowing. If the bed of soil is left unplanted, the nematodes will starve and eventually die away. The area must be kept moist and weed free or else they will live in the alternate roots. If populations increase again, this technique must be repeated.

Another way to decrease the number of nematodes in the top of the bed is called solarization. Moisten the soil and cover it with a clear tarp for 4-6 weeks for the hottest part of the summer. The nematodes will die at about 130 degrees Fahrenheit. This will not help plants with roots that grow over 12 inches deep.

An ounce of prevention is worth a pound of cure. When you buy plants in the future, make sure you purchase plants and soil that are not infested with nematodes. This would initiate a whole new population infecting your soil. Ask the person who you are buying from if they know if the soil is nematode free. Many people do not realize that sod is a huge source of nematodes.

Many tomatoes varieties these days are resistant to nematodes. So even if there are nematodes present in the soil, they would not be able to live and thrive in the roots and steal essential nutrients from the plant and fruit. Purchasing this type of tomato plant or seed would be the easiest way to produce a crop that is not affected. Varieties with names ending in VFN are resistent.

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Beneficial Nematodes

Not all nematodes are plant parasitic. Some are beneficial. They do not form small balls that live in the roots of plants, but live on insects that are hurting your plants. They kill hundreds of soil dwelling and wood boring insects, including cutworms, armyworms, rootworms, weevils, grubs, fungus gnat larvae, and many more. They are safe with people, pets, other beneficial insects and the environment. They come in a box and are applied with a sprayer directly to the soil.