Two of Our Least Favorite Fall Pests May Be Consorting Together: Botrytis Fruit Rot and Spotted Wing Drosophila in Fall Berries

Cassandra Swett, Assistant Professor and Extension Specialist – Berry Pathology, University of Maryland and Penn State University; and Kelly Hamby, Assistant Professor and Extension Specialist – Sustainable Agroecosystems and Integrated Pest Management, University of Maryland;

Warm rains in the spring and now late summer, combined with heavy dews have resulted in medium to high insect and fruit rot activity this fall in berry crops. Based on the Berry Pathology Lab monitoring program, we continue to have infection periods for Botrytis throughout the MidAtlantic (we monitor in western MD and southern PA). So if you have heavy dews or rains, you may want to consider protecting with a short PHI product if you can.


Botrytis-infected raspberries.

Although the most important time for Botrytis protection is during bloom, the fungus can also infect ripe fruit and more easily infects wounded fruit. Wounds can be caused by mechanical injury (rubbing, sun damage) or by insects. Spotted wing drosophila (SWD) has been very active this year. In raspberries, we are trapping SWD at moderate to high levels and have confirmed larval infestation. In grapes, recovery is lower, but SWD is present; we have not confirmed larval infestation in grapes. SWD is likely only able to attack very thin-skinned grape varieties (penetration force of less than 40cN). SWD makes wounds as it lays its eggs, and this may facilitate fruit rot development if not kept in check. For a review of SWD management, please see the recent special alert article (special alert #2—July 10, 2015) in the UMD Vegetable and Fruit Headline News.

We are conducting studies at the University of Maryland to evaluate whether SWD activity can facilitate outbreaks of Botrytis fruit rot in fall raspberries and grapes in the MidAtlantic. Botrytis impacts are not typically severe unless you get a lot of infested fruit, which can provide secondary inoculum to infect new fruit. This secondary inoculum is what causes outbreaks, leading to major losses. In support of this possible relationship in raspberries, we are finding SWD larvae in some Botrytis-infected fruit.


SWD larva in raspberry fruit (circled).

In addition to using fungicide sprays, canopy management is critical for Botrytis control. The open canopy increases air flow and improves fungicide penetration. This is true for raspberries as well as grapes. We typically see very low Botrytis in fall red raspberries where the canes are pulled back and kept thin, and higher levels of Botrytis in fields with a loose canopy. In the future, we hope to use research findings to create dual management strategies that reduce losses from interacting pests. More to come soon! For more information and updates, please refer to the UMD Berry Pathology Twitter site:

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