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White Grubs

July 18, 2006
With the high number of Japanese beetles flying this summer, it is important to be aware of the likelihood of turf damage from the resulting white grubs. The numbers of masked chafers that produce annual white grubs was low. Both Japanese beetle and masked chafer adults are attracted to moist soils in which to lay their eggs. Damp soil is easier for the beetles to burrow into; egg and larval survival is low in dry soils.

In late June, nonirrigated turf was dry, browning, and dormant in much of the state. These conditions result in Japanese beetles and masked chafer adults concentrating their egg-laying in irrigated turf. Widespread rainfall in the first half of July has brought the turf out of dormancy and made even unwatered turf attractive to egg-laying. In these conditions, eggs are laid over widespread areas, resulting in few areas of high grub activity. However, egg-laying will still be concentrated in irrigated turf in west central Illinois, where drought continues.

What this means for grub numbers is that we should see high grub numbers in August in irrigated turf in west central Illinois. In the rest of the state, we are likely to still have damaging grub numbers in irrigated turf, with low numbers in unwatered turf. Irrigated turf anywhere in the state should be treated during July with imidacloprid (Merit) or halofenozide (Mach 2) and watered in with one-half inch of water. Mach 2 does not need to be watered in if significant rainfall occurs within 3 days after application. Turf areas that have received intermittent irrigation should be scouted during the first half of August and treated with trichlorfon (Dylox) if there are 10 to 12 or more grubs per foot square.

Author: Phil Nixon


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