from Laura McDermott, Eastern New York Commercial Horticulture Team

Spotted Wing Drosophila (SWD) remains a threat for fall raspberries. To determine the best weekly insecticide program, visit these SWD Pesticide Quick Guides.

Recommendations for Fall Raspberries infested with SWD

• If SWD populations follow a pattern similar to previous years, populations may rise very dramatically during the next few weeks – right as fall raspberries come into peak production. Regular spraying (5-7 day spray schedule) has reduced infestation to manageable levels, although it has not eliminated the threat.
• If you decided to forgo spraying for SWD and are considering mowing primocane raspberries early, STOP!!! There is no evidence that mowing canes early will have an impact on next years populations. What we DO know is that mowing those canes now, before the plants move carbohydrates to the crown of the, will have a serious negative impact on the ability of the raspberry plant to overwinter.
• The best time to remove canes on fall bearing raspberries is from December to February when most of the carbohydrates are in the crown of the plant. Prune the old canes as close to the ground as possible so that the buds for new canes will break below the soil surface. If you don’t do this, the fruiting laterals may form on the remaining cane and could be very low, unproductive and at risk of insect and disease.
• Carbohydrates move from the leaves into the crown during the fall, then back up from the crown into the buds in the spring. Removing canes early essentially removes the stored food available to the canes and can result in winter injury or weak canes the next year. Conversely if you wait until the spring – say March – and it turns warm quickly (like this past spring) the carbohydrates will move into the buds and then you remove those canes with the stored food leaving the new canes with no reserve.
• In the past some growers topped the raspberries – removing the ripening fruit clusters. Again, there is little evidence that this action will have any impact on the population of this pest next year. As for spraying the abandoned canes, there is no information to indicate that this is a good strategy and may likely be a waste of money and time. This also applies for spraying fruiting plants in hedgerows. Both of these strategies are considered illegal pesticide applications and should not be done.