NGA Articles: Summer's Bad Guys

Summer's Bad Guys (cont)

By: Charlie Nardozzi

Biological Controls

Biological sprays are probably the safest sprays to apply in the garden. Most gardeners are familiar with Bacillus thuringiensis (Bt), but in recent years, the discovery of different strains of bacteria and fungi has expanded the number of pests you can control. These pesticides target specific pests, are relatively nontoxic to beneficial insects as well as animals and humans, and can be very effective. Remember that these are living organisms, so to survive they must be applied under proper conditions.

One well known biological spray, milky spore disease (Bacillus popillae), used for more than 50 years to control Japanese beetle grubs, has come under question by scientists. Recent research at the University of Kentucky indicates that supplementing the natural population of this bacteria in soils with the product doesn't increase the number of beetle grubs killed.

New on the market are biologicals such as Botanigard (Beauveria bassiana), a widely occurring fungus that attacks whiteflies. It is being used effectively on whiteflies in greenhouses. Research is currently being conducted for its use on a broader range of garden insects including caterpillars.

Bacillus thuringiensis (Bt). This is probably the most widely used biological control. The bacteria attack specific insects: B.t. kurstaki. attacks most caterpillars (which may be the young of butterflies you are trying to attract to your garden), B.t. 'San Diego' attacks beetles such as Colorado potato beetle. These kill only at early larval stages, so you must spray at the first sign of infestation. They're most effective mixed with a sticking agent and sprayed in early morning or late afternoon. It may take a few days before you actually see the insects dying.

Beneficial nematodes. These microscopic wormlike creatures will parasitize a variety of soil-dwelling insects such as Japanese beetle grubs, borer larvae, and even beneficial ground beetles. For best results, spray in early morning or evening on large areas when the soil is moist and warm, and reapply annually.

Grasshopper protozoa (Nosema locustae). This parasite affects only grasshoppers and some crickets, is most effective on the young larvae, and takes two to three weeks to kill. It is best applied in spring at the first signs of grasshoppers and is most effective when treating a large area.

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