University of Maryland Extension

White Grub Management

White Grubs and Their Management

Text and Photo By: Paula Shrewsbury, UMD
July 2, 2015


Based on the abundance of scarab beetle adults, especially Japanese and Oriental beetles, that are active this year there is a pretty good chance it is going to be another bad white grub year. There is still time to monitor for white grubs and if warranted apply a control measure. But you should be thinking about your management plan now.
                                                                                    
White grubs are the immature stages of scarab beetles (family Scarabaeidae). In this area, the most damaging white grubs are larvae of Japanese and Oriental beetles. We sometimes have large populations of masked chafer grubs, but they tend to be less damaging. White grubs can be a problem in lawn, golf, and nursery turf, and container and B&B nursery stock. So far this summer we have seen high levels of adult scarab beetle activity, and a pretty steady occurrence of rain, both of which suggest this will be another great year if you are a white grub. Of course there will be the corresponding grub damage - similar to the last few years. This story could change if there was a drought for the next month or so. Scarab beetle eggs, which are laid in the soil, need moisture to survive. So a drought would result in high white grub egg mortality. For some reason it doesn’t seem right to wish for a drought!  I recommend you monitor your turf and nursery stock closely for white grub damage and activity.    

Monitor:  If you have observed areas with significant adult scarab beetle activity you should monitor now in those areas to determine if grubs are present. White grubs should be 1st and 2nd instars now. Dig soil cores or cut 1 sq. ft. sections of turf (about 2” thick) in areas where adult scarab beetle activity has been high and/or turf appears drought stressed or discolored. White grubs will be active in the upper few inches of soil in turf or root zone. Identify which species of grubs you have in your turf. They vary in the amount of damage they cause. White grub species can be identified by the rastor (hair) pattern on the underside of the abdomen. A hand lens or some type of magnification will be needed. For help in grub identification go to:
http://ohioline.osu.edu/hyg-fact/2000/pdf/2510.pdf

Management:  If you have high scarab activity and / or have had historical problems with white grubs, sometime within the next few weeks would be optimal to treat. If you have white grubs in your turf you should treat sooner than later to stop feeding damage. Once you get past late August the effectiveness of these products on the later instar grubs goes down. If white grub control is warranted in turfgrass many of the neonicotinoids such as imidacloprid, clothianidin, and thiamethoxam are labeled (read pollinator warnings carefully) and give good control. Mach2 is an insect growth regulator that provides good control of grubs. Acelepryn is a newer class of chemicals that has shown excellent control of grubs. Acelepryn has very low toxicity to mammals (no signal word required by EPA in MD) and pollinators (see below). Most of these products have long residual activity so an application within the next few weeks should provide control through the end of the season. The class of control products that you use from year to year should be rotated to reduce the likelihood of insect resistance.  

What about the pollinators that might be active in turf?  Do not forget to pay attention to pollinators and flowering plants and weeds. Everyone should already be aware of issues associated with pollinator health and the implications of the effects of pesticides on pollinators. In particular, pesticides in the neonicotinoid class have received a lot of attention as a cause of bee decline although most studies suggest that honey bee declines are caused by a complex of factors and neonicotinoids fall relatively low on the list. However, neonicotinoids like many chemicals can be harmful to bees if misused. Therefore, read and follow the directions on the label of products carefully. Be especially aware of warnings related to pollinators. One issue to be aware of is that many turf areas support flowering weeds that will attract pollinators such as honey bees, bumble bees, and other bee and insect groups. Entomologist Dan Potter and his group at the University of Kentucky demonstrated that bumble bees that fed on white clover following an application of a neonicotinoid were detrimentally affected, whereas applications of Acelepryn did not appear to have a detrimental effect on bumble bees. They also found that if you mowed the flowers off of white clover in the turf following application of a neonicotinoid, the new flowers no longer detrimentally affected bumble bees. So the take-home messages are to mow flowering weeds prior to or immediately following applications of neonicotinoid insecticides; or choose another product like Acelyprin for white grub management.  Also read / follow the pesticide labels.

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