Rose chafer management considerations in chestnut orchards
Rose chafer adults are emerging in southern Michigan. Chestnut growers with young trees with limited leaf area should be on the lookout.
Rose chafers are considered a generalist pest and affect many crops, particularly those found on or near sandy soils or grassy areas conducive to grub development. The adult beetles feed heavily on foliage and blossom parts of numerous horticultural crops in Michigan and can cause significant damage to chestnut orchards. Rose chafers can be particularly damaging on young trees with limited leaf area.
Like Japanese beetles, rose chafers skeletonize chestnuts, giving them a fine, lace-like appearance. They cause simple mechanical damage, so growers should consider that established chestnut trees can sustain a significant amount leaf feeding from rose chafers with no negative implications to the tree or crop. Young trees with limited leaf area may require more aggressive rose chafer management. Growers should be aware of potential flower damage later in the season as that could have potentially substantial implications on yield.
Rose chafers are a light tan beetle with a darker brown head, long legs and are about 12 millimeters long. There is one generation per year. Adults emerge from the ground during late May or June and live for three to four weeks. Females lay groups of eggs just below the surface in grassy areas of sandy, well-drained soils. The larvae (grubs) spend winter underground, move up in the soil to feed on grass roots and then pupate in the spring. A few weeks later they emerge from the soil and disperse by flight. Male beetles are attracted to females and congregate on plants to mate and feed. Populations may be larger around large areas of turf or grasses.
Rose chafers are are often found in mating pairs and fly during daylight hours. Visual observation while walking a transect is the best method for locating them. Because of their aggregating behavior, they tend to be found in larger groups and are typically relatively easy to spot. There are no established treatment thresholds or data on how much damage a healthy chestnut tree can sustain from rose chafers, but growers should consider that well-established and vigorous orchards will likely not require complete control. Younger orchards with limited leaf area will need to be managed more aggressively.
Managing rose chafers can be a frustrating endeavor as they can reinfest from surrounding areas quickly. This reinfestation is often misinterpreted as an insecticide failure, but efficacy trials have shown a number of insecticides remain effective treatment options. Carbamate, organophosphate, pyrethroid and neonicotinoid insecticides all have good activity against rose chafers and can provide some control. Organic options including azadirachtin products and surround are marginally effective. Growers choosing to use kaolin clay should remember good coverage is key and those considering pyrethroids or neonicotinoids should be aware these products may potentially increase pest mite populations. For a complete list of pesticides in these classes currently registered, refer to “Michigan Chestnut Management Guide, 2016” by Michigan State University Extension. Be sure to note each product’s “beneficial insect toxicity” when choosing a pesticide to limit unintended negative impacts on beneficial insects.