Aphids – Fall & Winter Preventative Management

Adapted from the article “Fall spray for prune aphid management” by Franz Niederholzer, UC Farm Advisor, Colusa/Sutter/Yuba Counties in the Sacramento Valley Prune News, October 2012

Prune aphids – mealy plum and/or leaf curl plum aphid – are key pests of prune. High populations of these pests can reduce tree vigor, fruit sugar content and return bloom the next year. Honeydew from feeding aphids dropped on fruit can increase cracked fruit.

Mealy plum aphid.

Mealy plum aphid.

Recent University of California research shows that a fall pesticide application gives excellent prune aphid control the following season. Effective timing for this spray is late October through early December. After early December, leaves have dropped and a standard dormant spray is very effective. In the fall, soils are usually dry, and spraying is easier and less expensive than in the full dormant season (winter).

Not all pesticides give good aphid control as a fall spray. Research shows that pyrethroids – Asana, Warrior®, Baythroid®, Mustang®, etc. – all give excellent control anytime between mid-October and mid-December. The neonicotinoid (neonic) materials – Provado® (and generics), Actara®, and Assail® – work well in late October but not after leaves drop because neonics must be absorbed into the leaf to be effective on feeding aphids. Organo-phosphate pesticides – diazinon, Imidan®, etc. – don’t work well for aphid control when sprayed before December 1. After December 1, these materials are very effective. Oil is not needed in the tank in a fall spray.

Leaf curl plum aphid.

Leaf curl plum aphid.

Not all orchards need a spray program for aphid control. If you have a regular history of aphid damage anywhere in an orchard, then a fall spray or dormant treatment is required to control aphids. If you haven’t ever seen aphid damage around hard-to-cover areas near buildings or power lines following a dormant spray by air or after every-other row dormant spraying, you may not need to spray for aphids. If other tasks keep you from a fall or dormant aphid spray, there are a range of pesticides for good spring and summer control.

A fall spray for prune aphid control is a solid option for growers without a scale problem who are looking to control a regular aphid problem. A fall spray provides good aphid control with low cost and little hassle (no mud) while avoiding in-season spray issues such as complying with “no spray” lists and flaring spider mites.

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