The winter can be a good time to brush up on agronomy-related topics. Over the years, there have been sporadic reports of injury due to highly variable populations of grape colaspis. Grape colaspis is generally considered an occasional and infrequent pest.
Grape colaspis has one generation per year, and adults can mate multiple times in a growing season. Females deposit clusters of about three dozen eggs in the soil, and larvae hatch about one to two weeks later.1 Larvae have small cream-colored bodies (5.0-6.5 mm in length at 10th instar) with an orange head capsule and resemble very small white grubs (Figure 1).2 Adults are about 5 mm long and brownish-bronze-colored beetles with rows of grooves on their wings (Figure 2).2
Grape colaspis can potentially cause damage in the larval stage of multiple crops (including corn and soybean). Larvae feed on fine root hairs and can channel within larger roots. Ultimately, the predation on the roots can cause plants to wilt and potentially die. Plant injury due to grape colaspis can sometimes resemble the purpling from phosphorus deficiency due to the disruption of nutrients and water uptake. If the roots of an injured plant are not examined closely, it could be mistaken for herbicide or fertilizer injury. Feeding injury by the adults, which has not been documented to be economically significant, appears "jigsaw puzzle-like" in shape.1
If larval injury is suspected, dig up the impacted plants and look for the small larvae to positively identify the cause of injury. There are no established economic thresholds. Also, wash and examine the root system for signs of root pruning and/or channeling. For noticeable injury to occur, multiple larvae should be present. In many situations, the larvae may have already pupated, and adults may have emerged before plant injury is discovered.
Options for grape colaspis larvae control are limited because insecticidal rescue treatments are not available; however, seed treatments can provide protection. For corn, Acceleron® Seed Applied Solutions ELITE and Acceleron® Seed Applied Solutions BASIC and for soybean, Acceleron® Seed Applied Solutions STANDARD seed treatments can help protect seedlings against grape colaspis larvae, respectively.
If you have any questions, please contact your local Channel Seedsman.
1Montgomery, M. 2003. Grape colaspis. Some background. The Bulletin. University of Illinois.
2Kaeb, B.C. 2006. Management of grape colaspis, Colaspis brunnea (Coleoptera: Chrysomelidae), in seed corn production. Iowa State University. https://lib.dr.iastate.edu/.
Web source verified 10/15/19
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