By fall the grubs are half grown. They feed on roots until checked by cold, resuming again in spring. D.D.T. treatment will control grubs in soils for up to six years, while chlordane will do so for at least four years. Even longer effectiveness is provided by a biological control measure-the introduction into the lawn of the so-called milky disease. Prepared spore cultures are on the market.
Termites: Although these pests are usually considered destructive only to foundations of houses, they can become serious pests in soils containing any amount of partially decayed wood or other woody matter. They work beneath the surface and burrow inside stems and are not detected until dying plants lead the gardener to investigate. They are much more troublesome where organic fertilizers are used.
To control, remove any wooden stakes, edgings or other sources of cellulose, then dose soil with chlordane. Where termites are active, be sure to protect fences, stakes and other wood used in gardens with a wood preservative such as copper naphthanate or pentachlorophe-nol. Avoid using organic fertilizers.
Slugs and Snails: Baits containing metaldehyde will lure these pests out of their holes to feed and die. Remove flat stones or shingles under which they hide. Dusting paths and walks with hydrated lime or dry wood ashes often traps them and dehydrates them. Sometimes dabs of either material placed on the soil and covered with a shingle will trap them by the dozens.
Millipedes, Sowbugs and Pillbugs: Chiefly these are signs of poor housekeeping in greenhouses: remove all organic matter and dust under benches with chlordane. (Dusting with chlordane is also the outdoor remedy.)
Sweet Potato Weevil: Grubs burrow through sweet potato roots and stems. Apply one pound of 10 per cent D.D.T. dust to 1,500 square feet of garden or use 20 ounces of SO per cent wettable D.D.T. to a gallon and a half of water, applying this to 1,000 square feet.
Wireworms: Hard, buff or ecru-colored segmented worms are very destructive to root crops. Same treatment used for sweet potato weevil will control wire worms.
Many of the more destructive insects are sheltered and fed by partially-decayed organic matter. This is one reason why composting plant wastes in a compost pile is better practice than applying
them to soil and plowing under. In the compost pile, insect control measures can be more easily taken. The use of calcium cyanamid in the last turning of the pile will check breakdown temporarily, but will get rid of grubs.
Earthworms (see Chapter Ten) will be killed by most of the previously mentioned treatments.