Sampling:
To identify cornfields at risk from Asiatic garden beetle, sampling should be done two to three weeks before corn planting. Recommended methods for pre-plant sampling include baited wire traps (Fig. 4) and direct soil sampling methods.
It should be noted that the corn/wheat bait station method (another preplant soil sampling technique) was designed for sampling wireworms only (Fig. 5).
Recent Virginia field trials have indicated that the corn/wheat bait station often attracts various species of annual white grubs; however, no economic thresholds currently exist for this method.
The baited wire trap method consists of placing 20 untreated corn seeds spaced evenly along a 2-foot long by 3-inch wide wire-mesh strip (1/4-inch wire mesh opening) that is bent lengthwise at a 90° angle to keep the seeds in place.
Traps should be installed in 2-inch deep furrows and covered with soil at least two weeks before planting.
A good rule of thumb for fields up to 10 acres in size is to install one to two baited wire traps per acre that are spaced uniformly throughout the field. For larger fields, one baited wire trap per acre is suggested.
Keep in mind that the more traps used the better the sampling estimate will be. After two weeks the traps should be removed from the soil to inspect the seeds and developing roots for signs of feeding injury. An average of 5 percent feeding injury to corn seeds per trap is a nominal economic threshold for annual white grubs.
The direct soil sampling method consists of counting all white grubs in a 4- to 5-inch deep 1-foot square of soil. One soil sample per acre should be taken in fields up to 10 acres in size. For fields larger than 10 acres, one soil sample per two acres should be sufficient.
An average of two or more annual white grubs per soil sample is considered a nominal economic threshold for this method. An advantage of soil sampling over the baited wire trap method is that only one visit per field is necessary.
The baited wire trap method requires two visits, one to install the traps and one to inspect them. Scouting methods and research-based economic thresholds for the adult stage of the Asiatic garden beetle have not been developed.
Chemical Treatment:
Many soil insecticides labeled for corn rootworm control often provide acceptable control of annual white grubs and other secondary soil pests, such as wireworms and seedcorn maggots. However, it is important to carefully check the label for specific rate information because some products require higher application rates for annual white grubs than for corn rootworms.
In addition, current Bt corn hybrids for corn rootworms are ineffective against annual white grubs and other secondary soil insects. Because rescue treatments are largely ineffective for annual white grubs after the crop has been planted, insecticide application at the time of planting is often necessary to protect the crop and to avoid replanting.
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