San Jose scale is a small, slow moving insect that can cause significant, long term economic damage to prune orchards.  The orchard in the picture below was removed shortly after the picture was taken due to extensive scaffold damage and loss of bearing wood caused by a buildup of San Jose scale.

Scale populations build slowly over time, so an annual scale “checkup”– and treatment when necessary -- can avoid this kind of damage.  Especially if you have been following an “aphid only” dormant spray program of a pyrethroid (Asana^®, Warior^®, etc.) only or pyrethroid plus less than 2 gallon of oil/acre, a program that will not control scale, check your orchard for scale this winter.

Dormant spur sampling – done by the grower or PCA – is the annual scale checkup.  The timing for this key part of an overall prune orchard management program is now through January.

Details on how to take a dormant spur sample and how much scale is enough to recommend a spray treatment are found by calling your local University of California Cooperative Extension office or on the internet at:  http://ipm.ucdavis.edu/PMG/r606900511.html.

If San Jose scale shows up in the dormant spur sample, the best time for a control spray is before bloom.  A high oil rate (4-6 gallons/acre) applied in the dormant (good) or delayed dormant (best) timing is enough to control low to moderate San Jose scale populations.   The oil smothers the pest.  The higher the oil rate, the better the control.  If the San Jose scale population is high in an orchard (more than 20% of spurs checked show live scale) then oil plus a pesticide labeled for San Jose scale (Seize WP, Centaur, diazinon, etc.) will be needed.  Consult with a PCA when deciding what pesticide(s) to use.

A dormant spray with a high rate of oil has the added benefit of advancing prune bloom several days.   How many days?  That depends on the year and is impossible to predict.

 Finally, the higher the spray volume per acre, the better the scale control.  If you have a real problem and want to get the best control, use 400 gallons per acre (gpa) of spray volume and spray in the delayed dormant period.  Spraying in the dormant period with 100 gpa gives good control, but not great control. 

Don’t let scale sneak up on you.  Schedule your scale checkup now.