Are you planning your home vegetable garden now? If so, Stephen Reiners from Cornell University has some suggestions on how to use fewer pesticides while getting a more abundant crop.
First, he urges you to copy the commercial growers and rotate your plantings. If, instead of rotating, you plant your tomatoes or other vegetables in the same place they were growing last year they'll be much more vulnerable to disease.The harmful bacteria, nematodes, fungi and viruses that got a start on your crop last year will usually overwinter in the soil. By spring they'll be right there in greater numbers, waiting for a new shot at the plants they started on last year.
Your goal is to break the cycle. A tomato disease, for example, will not live on corn or peas. So, by planting a different kind of vegetable, you can interrupt the disease's food supply.
"If there is nothing there for the disease organisms to feed on," explains Reiners, "they will eventually die out. For most diseases, waiting two to three years before planting the same crop should do it."
While it's true that a tomato disease won't live on a corn plant, it will live on other members of the same family as the tomato. The solanaceous family, which includes tomatoes, also includes eggplants, potatoes and peppers. Diseases that attack tomatoes may also attack other members of the family.
Surprisingly, tobacco is a member of the solanaceous family. If you smoke, there's a virus that can spread from your hands to a tomato plant. This particular disease, tobacco mosaic virus, is a major problem for the green house growers. It leads to stunted growth, a peculiar spotted look, and, of course, reduced yield. "If you're a smoker," points out Reiners, "the greenhouse growers won't let you in their greenhouses. Or if they do, they'll make you go through an incredible amount of washing."
Rotation will help in reducing plant diseases, but it won't prevent insect damage. That's because insects can easily fly from one field to the next. The tomato hornworm moth, for example, has a wing span of four to five inches and can travel considerable distances. (You've probably never noticed a tomato hornworm moth, even if you have them. The moth is only active at night, and even if you see it you could mistake it for a bat.)
With insect damage, remember your plant can endure a lot and still provide you with a reasonable crop. In Reiners' view, doing nothing is often a perfectly good way of dealing with insect problems.
However, in the case of tomato hornworms, if you aren't squeamish, you can control them by picking them off by hand and killing them. Reiners suggests you wait until it's dark and then go to the garden with a flashlight. You can tell where they are because the leaves where they're feeding will be visibly shaking. On the other hand, if the thought of touching one of these seriously ugly critters is too much for you, you can wait for the hornworm's own natural enemies to attack it.
There's a stingless wasp that feeds on tomato hornworms. The wasps won't necessarily kill the hornworms attacking your plant. But they are likely to reduce the damage the hornworms do.