By Gardener Jack Perhaps as you are reading this someone who has been gardening for a year or two is discovering that one of his promising tomato plants is wilting. This is puzzling because the plants were watered well. The gardener will give them more water and go to work. This evening the plant will still be wilting, and getting worse by the day. Welcome to the world of plant nematodes. These microscopic worm-like organisms are attracted to certain plants and drill their way into the roots. Congregating in the millions, they block the passage of water and cause the plant to die of dehydration. With tomatoes that usually occurs when the fruit is about half grown. The good news is that nematodes that live in the soil can be controlled. The bad news is that you need expensive fumigating equipment, expensive chemicals, expensive protective wear, and a government license to operate. More about nematode control later. Different nematodes live in soil, under the sea, and in animals - including human beings. They have teeth-like structures at their front end and a digestive tract that lacks a stomach. Nematodes vary in size from microscopic to over 20 feet long in whales. In human beings different varieties of nematodes are called filarias, hookworms and pinworms. Filarias enter the blood vessels and lymph passages and cause filariasis or elephantiasis. In dogs nematodes are called heartworms. The staggering fact is that as individuals, nematodes constitute 80 per cent of the animal kingdom. Just think of the six billion people in the world, the cows and sheep grazing in fields, flocks of birds, shoals of fish, clouds of locusts, armies of ants. Add together all the people, animals, birds, fish and insects in the world and they are outnumbered 4 to 1 by nematodes. Get rid of them? I don't think so. So how do we control them? From mediaeval times it was known that nematodes were crop specific. Nematodes that attacked the roots of one crop would not be attracted to another. A system called crop rotation was set up by dividing an estate into four. Different crops were grown in three of the quarters and the fourth was left fallow, usually with grass to feed cattle and sheep that added manure. Each year the crops were rotated and most of the damage from nematodes was avoided. Crop rotation is much harder to maintain in a garden. Here in The Bahamas we have a long vegetable growing season and nematodes can establish themselves in numbers in a few months. Marigolds are known to exude nematode deterrents so if you intersperse your veggies with marigolds you will obtain a degree of protection. During the summer you can fill your empty vegetable gardens with marigolds and remove them at vegetable planting time, saving the seeds for next year. Not as pretty but far more effective is to solarise a garden using clear plastic. Done during the summer, the heat produced and the antiseptic qualities of the sun's rays will kill off nematodes and all other organisms. When the new season starts you will have a fairly sterile environment. I will remind you about solarisation at the beginning of summer. Some vegetables are generally unaffected by nematodes and these include sweet corn, peppers, strawberries, cabbage and cauliflower. When you dig up a plant that has been infected by nematodes you will see that the roots are ugly and knobby. This gives rise to the name root-knot nematodes, those that attack plants. Dig up the plant rather than pull it because any root ends you leave in the ground will contain thousands of hungry nematodes ready to go on to your next vegetable. gardenerjack@coralwave.com