As microbreweries sprout up across the continent, there is a revival of interest in growing hops. The crop appeals to more than just the lovers of IPA (Indian Pale Ale); several pests attack and often defoliate hop plants. Main pests include the two-spotted spider mite, hop aphid and potato leafhopper.
Spraying insecticides has been found to increase pest problems. A recent study found that “Natural enemies were present to varying degrees in northeast hop yards and once established they appeared to maintain pest populations . . . Insecticides have the opposite effect, as they kill natural enemies and increase the risk of a twospotted spider mite outbreak.”
Although the insecticide might kill pests initially, it has a greater effect on the beneficial organisms (e.g. parasitoid wasps) that control the pests. So once the insecticide spraying stops, the pests rebound, but their predators do not.
To best control pests (organically or with insecticides), researchers recommend thorough pest monitoring including using sticky traps above eye level and checking leaves. This IPM (Integrated Pest Management) practice allows for the best timing of control methods (sprays or release of parasitoid wasps).
Source: Survey of Northeastern Hop Arthropod Pests and Their Natural Enemies. L. B. Calderwood, S. A. Lewins, H. M. Darby. Journal of Integrated Pest Management. 2015. Vol 6. No. 1. pp. 1-14. http://jipm.oxfordjournals.org/content/6/1/18
- Janet Wallace