Blueberry Insect Scouting Report for May 14-20, 2012

Bloom is ending in blueberries across southwest Michigan and aphid populations are growing.

Crop stages

As of May 18, bloom was complete or nearly so for most varieties in Van Buren County. Bluecrop and Rubel in Paw Paw, Grand Junction, Gobles and Covert, Mich., have green fruit with pea-sized or larger berries, while Jersey and Elliot have small, green fruit. In West Olive, Mich., in Ottawa County, Bluecrop, Rubel and Blueray were at almost through petal fall, and Jersey were mid-way through petal fall, while Elliot were just starting to drop petals.

Weekly insect pest report

Cherry fruitworm moth flight is declining at all the farms we visit in Van Buren County and flight is past its peak in Ottawa County. Egglaying by cherry fruitworm is predicted to continue at the sites we are scouting. Cranberry fruitworm flight is increasing at Van Buren and Ottawa counties. The flight of this moth should increase greatly with the warm nights that are predicted for the next week. We have reached the growing degree day accumulation for the start of cranberry fruitworm egglaying in Van Buren (first capture May 5) and Ottawa counties (first capture May 11).

Cranberry fruitworm egglaying begins approximately at 85 GDD (base 50°F) after cranberry fruitworm moths are caught consistently. Growers and scouts in northern areas of blueberry production should be checking fruitworm traps twice weekly until the first moth is caught to allow accurate setting of the biofix. The cranberry fruitworm model on Enviro-weather can be used to see when growing degree accumulations have reached the point when cranberry fruitworm egglaying is expected in your area of the state. Growers and scouts should continue checking cherry fruitworm and cranberry fruitworm traps until harvest. A detailed article about fruitworm management has been posted at the MSU Extension Fruit News website.

The number and size of blueberry aphid colonies is increasing at all the farms we visit. The colonies we observed were still mostly small (one to five individuals), but colonies with more than 10 individuals are becoming easier to find. The percentage of shoots that are infested with blueberry aphids is increasing (0 to 35 percent) at the farms we visit. To scout for aphids, examine two young shoots near the crown on each of 10 bushes and record the number of shoots where aphids are found. Also, record the number of shoots with parasitized aphids. Be sure to sample weekly from as wide an area in the field as possible to have a better chance of detecting whether aphids are present. Although natural enemies (parasitic wasps, lady beetles, lacewings,hover fly larvae) can keep this pest in check, aphids can transmit blueberry shoestring virus, so growers may want to consider using an insecticide to control aphids if there are blueberry varieties that are susceptible to shoestring on the farm. Insecticides that are toxic to bees should not be used for aphid control where bees are still present. . See the Blueberry Facts website or this previous article from the BlueberryIPM Newsletter for more information on aphids.

We did not see any leafroller larvae at the farms we scouted, and it is likely that insecticide applications targeting cherry and cranberry fruitworm have controlled other moth pests such as leafrollers. To scout for leafrollers, examine five flower clusters and five leaf clusters on 10 bushes on the field border and five flower clusters and five leaf clusters on 10 bushes in the interior of the field. Look for leaf or flower clusters that have feeding holes or webbing in the cluster. These pests are generally not economically important in Michigan, but if 3 to 5 percent of buds have feeding damage, growers may want to consider a specific control targeting these insects. Once growers begin their fruitworm control programs, scouting for leafrollers becomes less critical. View more information and pictures of leafrollers from our scouting pages posted at blueberries.msu.edu.

Gall wasp emergence at infested sites in Ottawa County has slowed over the last week and we should see emergence decrease over the next week. Emergence will likely end in the next two weeks.

Dr. Isaacs’ work is funded in part by MSU’s AgBioResearch .  

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