Pest Control Methods for the Organic Garden

Learn the best pest control methods for the organic garden, including methods of controlling insects, timing of crop planting, creating barriers to pests, non-toxic sprays, pest traps and integrated pest management.


| February/March 1997



Tomatoes and hornworm pests

There are only two sprays that I will use: Bacillus thuringiensis (Bt) and Bacillus thuringiensis var. san diego—the former for cabbage loopers, cabbage worms, and tomato hornworms; and the latter for the Colorado potato beetle. I use them because they are non-toxic and because they only kill the target insects, and even then only if they eat a leaf that has BT on it.


PHOTO: FOTOLIA/FOTOSENMEER.NL

The best pest control methods for the organic garden is to keep your garden healthy, pests don't become a problem until there is a weakness in the health of the garden. 

The best method of controlling insects that damage crops is to keep your garden a secret. Don't invite them to the party. Think of insects like germs. There are always plenty of them around, but they don't become a problem until there is a weakness. What pest control methods for the organic garden work? Who cares if the sphinx moths fly around your garden, as long as they don't lay eggs on your tomato plants that will hatch into tomato hornworms? If we assume they are only going to lay eggs on weak plants, we can be assured they will leave alone our happy and healthy plants growing in humus rich soil. It is clearly better to avoid an insect problem than to have to deal with it. A nutrient balanced soil is the best way to get insects to avoid your garden.

Garden Pest Barriers

Another way to keep insects from getting to your plants is to create a barrier they cannot surmount. You need to know a little bit about the insect to erect the most effective barrier. Someone might have the image of a garden enclosed in mosquito netting. That might work but it is not very cost-effective. I say might, because there are a lot of different insects and if their motivation is strong enough, they are likely to find a way in. Netting can be a cost-effective barrier in some circumstances. Root maggots are the larval form of a fly that lays eggs on the stems of young plants. The flies may lay eggs on more mature plants, but if they do the plants are growing fast enough to survive. Young plants can be protected by a netting barrier laid right over the seedling or even over the seed bed before the seedlings emerge. A square foot of netting will protect a hill of cucumbers. Clearly there is not much work or material involved in this and the hill will produce a lot of cucumbers if helped through the tender stage.

Unhappy radishes will also attract root maggots. Since you would have to cover the whole row with netting to protect them, and considering that radishes reach maturity in a little over three weeks, a barrier hardly seems worth the effort. Radishes also attract flea beetles—usually radishes planted too early in the spring in my garden. While the radishes are shivering in the cold, growing slowly while they wait for the air and ground to warm up a bit more, the flea beetles are feasting, sometimes setting the plants back so severely I lose the crop. No problem: I just throw in some more seeds. Flea beetles will do the same number on broccoli directly seeded in the garden. Since I am going to transplant this crop later, the seedlings can all be grown in a foot-long row which can be covered easily. When the plants are four or five inches tall and ready for transplanting, there is enough when they cut down the leaf surface of transplants. After all, we prune larger plants when we transplant them so the damage to the roots is balanced with a decrease in the above ground portion of the plant.

While on transplants, we must not forget the insect most often combated with barriers: the cutworm. Cutworms also get around on wing but generally the grub is already in the ground when we have to deal with it. A collar of tar paper, cardboard, or some similar material that can be formed into a circle about three inches in diameter and a couple of inches tall and pushed into the soil an inch to make a wall around each transplant.

Diatomaceous earth can also be used as a barrier. This is a powder made up of calcified one-celled plants. To soft-bodied insects it is a sea of razor-sharp edges. What insects crawl on the surface of the ground to reach plants? None, actually, but slugs do. Slugs are mollusks, not insects, but gardeners can find little reason to make this distinction. A band of diatomaceous earth around the cabbage and/or lettuce if these are the crops being plagued, or around the whole garden, will keep slugs at bay if they are coming "from away" as we say in Maine. The diatomaceous earth cuts the bodies of slugs and soft-bodied insects that come in contact with it.





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