Milky disease, milky spore disease

Bacillus popilliae, Bacillus lentimorbus

Milky disease, caused by a bacterium known as Bacillus popilliae and some of its immediate relatives, destroys larvae of Japanese beetles and some related species. Most commercial forms are effective only against Japanese beetles; some may also work against June beetles and some other grubs; read the product specifications. It is highly selective, and safe for humans, other mammals, birds, fish, and other insects. Spores remain present and viable in soil for at least several years.

Milky disease spores are ingested by beetle larvae; milky disease bacteria multiply over several weeks, turning the grubs a classic milky white. When the grubs finally die, billions of spores (per larva) are released back into the soil.

Because it affects only beetle larvae, milky disease does not affect adult beetles. It works only when grubs are feeding, typically, on the roots of lawn grass in August. It takes several years' worth of feeding and reproduction cycles to achieve good control, but once established, control can last twenty years.

Milky disease is most effective if applied to larger areas. If only your lawn is treated, it will prevent lawn injury, but gardens, trees and shrubs remain unprotected: adult beetles can fly over easily from neighbors' untreated lots.

Apply milky disease powder at rates recommended by the manufacturer: roughly, 1 kg per 800 m² (2.5 lbs per 10000 sq.ft.), and per manufacturer's instructions. Three applications per year for two years are typical, as are concentrated treatments spaced 1 m or 3-4 feet apart. Diluted and sprayed, or spread thinly over the target area will not infect larvae well enough to propagate the disease - but concentrated spot treatments will, and over several years, grubs themselves will inoculate the areas between.

Water lightly after application to soak the spores into the soil; do not overwater. Reapply if heavy rain follows within a day or two of application. And do not use other insecticides in this time: larvae must be able to reproduce in adequate numbers in order for milky spore disease to become established.

Spores are resistant to heat, cold, and drought; milky disease has virtually unlimited shelf life if stored cool and dry.

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