Watch for late season apple pests

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

There are several insects that can cause injury to apples late in the season, particularly in blocks that have poor weed control. This year growers are trying to keep their expenses down given the rough looking hail-pecked apples that are all too common. While a third generation of codling moth doesn’t seem likely for 2008, other insects such as European corn borer and dock sawfly could show up, particularly in apple blocks under mating disruption for codling moth, because general cover sprays are not used as routinely in these blocks.

European corn borer can be a sporadic pest in apples. Typically, it is of more concern where apples are growing next to a corn field. When the corn is harvested, there could be some migration to nearby apples as a secondary food source. However, European corn borer damage does occur in apples even where corn is not grown adjacent to orchards.

Corn borer excavates rather large tunnels in apple fruit, feeding in the flesh. The larvae tunnel into fruit, usually entering at the calyx end, and feed inside until early fall. This differs from codling moth damage, which makes a smaller tunnel extending to the seed cavity. Typically, this pest is a problem when weeds such as pigweed and lambsquarters grow up into the canopy. Weeds should be mowed to reduce the risk of problems from this pest. Problems develop in late August and September, as corn fields dry down and orchard spray programs wind down. The damage is usually confined to the border rows in orchards. Since it is difficult to predict which orchards will be damaged, it is wise to check the fruit for damage as harvest nears. Corn borers have also been found to tunnel into the shoots of young, non-bearing trees, causing dieback. Where corn borers have been a routine problem in apples, maintain insecticide spray programs later in the season, especially in the border rows of the orchard.

Dock sawfly can also cause late season damage in apples by burrowing into the fruits. This insect is usually only a problem in orchards with poor weed control, and where hollow-stemmed weed species, such as dock, are found growing up into the canopy. Dock sawflies seek an overwintering location and generally choose hollow-stemmed weeds, but if apples are nearby the weeds, they have been known to burrow into the fruits as well. They usually don’t become evident until the bins are removed from CA storage; when the bright green larvae become active again and begin to emerge from fruits. Adequate weed suppression via herbicides or mowing is the best prevention for damage from dock sawfly. The insect is far too unpredictable to try to manage with insecticides.

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