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Walnut

Delayed dormant bud start to swellWhy Is the Dormant/Delayed-Dormant Season Important in an IPM Program?

Dormancy is generally defined as the period from leaf fall until growth resumes in spring. Delayed dormancy is the period from the resumption of growth, indicated by bud swell, until flower buds just begin to open. These periods vary according to region, variety, and weather.

The dormant period is less critical for pest management activities in walnuts than other fruit and nut crops. Several key insect and mite pests such as navel orangeworm, scales, and European red mites, overwinter in walnut orchards. It is an excellent time for monitoring and assessing scales and mites because branches, twigs, and buds are not hidden by leaves. 

Dormant versus delayed-dormant oil treatments

Oil applied during the dormant period damages walnut trees. However, oils can be safely used in some varieties during the delayed-dormant season, but timing must be precise because injury can also occur between budbreak and shoot elongation. The main targets of delayed-dormant oil applications are scale (European fruit lecanium, frosted scale, walnut scale) and mites (European red mites). However, if you observe high rates of parasitization, you may delay treatments until after crawlers emerge in late spring when oil treatments are safer.

Water quality issues

Winter sanitation for navel orangeworm control provides effective control and will reduce the need for pyrethroid pesticide sprays at hull split that can run off with winter rains.


Statewide IPM Program, Agriculture and Natural Resources, University of California
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