- Tiphia wasp
and B. lentimorbus
are microbial insecticide products that kill grubs and adult Japanese beetles. Infected grubs are filled with a milky white liquid full of bacterial spores. They inoculate the soil as they move (Ellis; Bradley, 1996: pp. 460-461). The advantages of using commercial preparations of B. popilliae
are; they are host specific meaning, only effective against Japanese beetles and
their persistence is longer lasting (Cornell University, 2003).
white grub population prior to planting. To sample, in 50 x 50 cm soil area, dig soil about 15 cm deep using shovel or hole-digger. Sieve the soil. Repeat this method randomly at least 10 times. Economic threshold levels
are: 1 white grub found in sandy soil and an average of 2 white grubs in silty-loam soil (University of Illinois Extension, 1999).
Management and cultural practices
- Remove old plants and weeds. Plow and harrow the field twice during sunny days to expose grubs to predators and weather. Hot sunny days destroy many of the exposed eggs and kill newly hatched grubs.
- Grow healthy plants by planting good seeds, providing enough water and fertilizer. Healthy plants can tolerate grub feeding without serious damage. Other healthy ones compensate for damage to one root.
- Ensure proper drainage. Grubs love moist soil, especially with decaying organic matter. Female beetles prefer to lay eggs on moist-decaying organic matter.
- If heavy infestation occurs, avoid planting the same crops the whole year. Practice crop rotation always. Soybean is found to be resistant to white grubs.
- Good trap crops are African marigold, sunflower, mirabilis, and castor. Repellents plants are chives, garlic, tansy, and catnip. The crops trap and repel adult beetles from attacking the main crop grown (Golden Harvest Organics, 2003).