In 1953, the serious spreading decline of Florida citrus was traced
to the burrowing nematode as the carrier. Since that time, nearly
$3,000,000 has been spent in an effort to eradicate this pest from
citrus groves, but the end is not yet in sight.
IN THE GARDEN
We now know that every commonly-grown fruit and nut crop is attacked by one or more nematode species. Vegetable crops are parsitized regularly, even in the North, and damage done to these food crops is estimated at over $100,000,000. It is on these crops that the home gardener is most likely to encounter nematodes. They form knots or lumps on the roots of many plants, most conspicuously on carrots. Other crops are attacked internally without visible symptoms other than a decline in vigor and productivity. Tomatoes, beans, okra and many vine crops can drop as much as 50 per cent in productivity without any sure sign of infestation. Foliar symptoms on many plants, such as premature dropping of leaves, stunting
and yellowing are not clear-cut enough to mark them as different from the symptoms caused by certain nutritional or insect disorders.
Ornamentals are also attacked. Over 600 different species of trees, shrubs, flowers and lawn grasses are known to attract nematodes. The root-knot nematode alone attacks more than 500 different species, causing severe loss of plant vigor. One of the worst in its effect is the foliar nematode that attacks chrysanthemums in the greenhouse bench. It is able to move up stems and across leaves on the film of water that forms on the leaf by condensation. When it reaches a stomatal opening, it penetrates into the heart of the leaf where it is all but immune to any form of control.
During the past two years many members of the American Rose Society have become increasingly aware of the damage done by nematodes, and numerous articles on these pests have appeared in the Society's journal.
WHAT CAN BE DONE?
The nematologist in one southern state told me recently that he had never checked a garden soil without finding one or more nematode species parasitic on plants. He was reasonably sure that no such thing as a nematode-clean soil existed in his state. Most scientists feel that once a soil has become infested, complete eradication is almost an impossibility, even if only non-cyst-forming types are involved.
Since eradication is impractical the one course open to us is to reduce the population to a point where plants can survive and grow reasonably well in spite of some infestation. The first step in such a program should be exclusion.