"Sand Chafer" What the #@&%! is it by Keith Jarvi, IPM Extension Assistant, UNL Northeast Research and Extension Center, Norfolk Introduction Photo Reports have come in regarding potential late season damage to corn and potatoes caused by white grubs. These grubs are much more common in sandier fields west of Highway 81. Large populations have been found in corn fields that had been in soybeans the previous year, or, in the case of potatoes, corn the previous year. There have been reported problems in other potato growing regions as far as northeast Colorado, as well. Specimens have been collected and sent to the USDA for identification to species. As of this writing they have not been identified. However, in past years, we have had specimens sent in. They have been identified as Strigoderma arboricola. They have no officially recognized common name, but since they appear to prefer sandy soils, they have been called "sand chafers". They are normally very abundant but they may have been even more so in 1998 possibly due to the mild winter of 1997-98. We also can not discount the possibility that there is more than one species involved. Biology White grubs are members of the "June beetle" family. There are dozens of different species in Nebraska. Typical white grub problems are caused by 3 year white grubs, Phyllophaga spp., which remain in the soil in the larval stage for more than one year and can be very harmful to crop and grass seedlings. Nearly mature larvae feed early in the spring on the roots of seedlings and can decimate crop stands. The sand chafer has a different life cycle. There is little biological or ecological information about this insect, but this is what we believe. It is an annual that goes through one generation a year. The adult is a medium sized beetle similar in appearance to the June beetle, although about 1/2 the size. Some have described them as "Japanese beetles" because they have a similar size and shape. But there are no Japanese beetles in Nebraska except some that have been found in the Lincoln area. The adults emerge from the soil and are active during the latter half of June into early July. Field scouts are familiar with the beetles’ annoying habit of landing on light colored clothing and getting into a person’s hair and underneath clothing. Mating occurs and eggs are laid. Apparently, the eggs hatch into small larvae and the grubs develop to be large enough by September to begin to cause some major damage in potatoes, and root feeding on corn. The grubs overwinter deep in the soil, becoming active in the spring as the soil temperature warms. Apparently the overwintering grubs feed little or not at all in the spring before pupating and turning into adults, since they have not been identified as an early season pest. The beetles have been observed feeding on many plants, including clover, rose, wild rose, blackberry, water willow, cactus, red clover, timothy, elderberry, dewberry, dog fennel wild parsnip, water lily fireweed, and peony. Wild plant hosts of the larvae have not been documented, although in the lab they have been reared on blue grass sod. They have been reported as pests of peanuts in Virginia. Other annual white grubs have been suspected of damaging corn and beans in eastern parts of the corn belt, mainly in heavy textured soils, but little has been mentioned in the last 5 years. Larval feeding damage appears to be concentrated to fine root hairs in corn, with little damage to main roots. Yield reports are sketchy, with some reporting fields unaffected, and others suspecting possible losses. However, potential lodging may cause harvest concerns. In potatoes, the application of herbicides to kill vines prior to harvest apparently kills root hairs on potatoes and the grubs transfer feeding activity to the tubers, causing quality reduction. Attempts to control them in potatoes have had little obvious impact. Colorado entomologist report the best control they got with any treatment was 10%. Late vine-kill to keep the roots alive until just before harvest (possibly 5 days) so the grubs might not feed as much on tubers. Feeding ceases as the soil cools and the grubs move deeper in the soil. Management There are more questions than answers regarding this insect. The first thing to examine, particularly in corn, is to determine whether or not the feeding has caused economic damage through feeding or lodging problems. Are there other factors potentially involved with lodging or yield loss? Are fields with high populations still yielding well? Remember this is a common insect and until this year has not been suspected as a pest of corn. No economic thresholds have been developed for the sand chafer. Since it is not a pest of seedling plants, and current soil insecticides will not persist much longer than 6-8 weeks in the soil, a soil insecticide will not affect these insects. Since they have been found in fields previously in soybeans or corn, rotation is probably not an effective tool for reduction. Insecticide treatments in corn or potatoes may need to be targeted at adult beetles, killing them before eggs are laid in late June- early July. However, no studies have been done about timing of application or what insecticides may provide the best control. Insecticide treatments targeted at the grubs in the soil late in the season have not been researched. Post emergence treatments of white grubs in the spring have not been successful. Caution should be taken regarding insecticide treatments until economic damage is documented. It is advised that fields with large populations of chafers be monitored carefully in 1999. Adult populations can be monitored with sticky traps or possibly pheromone traps. Roots should be dug and washed, and possible grub counts on a per foot or per yard basis be done on a weekly schedule after August 1st to observe any potential feeding damage. |
