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KAC Citrus Entomology
University of California
KAC Citrus Entomology

Degree Day Units are Finally Leveling Off

As the graph shows, degree day unit accumulations for California red scale were not quite as bad this year as the previous two years, but were still well above the 30 year average. Which explains why California red scale is so difficult to control lately - an extra generation! If we get prolonged cold this winter and average daily temperatures (max + min divided by two) stay below the scale's developmental threshold of 53oF, then two things will happen: 1) the scales will stop developing until the weather warms in March, and 2) younger instars will experience overwintering mortality, leaving mostly adult females and males.  A synchronized scale population is easier to control with insecticides, because crawler emergence occurs over a short period of time in the spring and summer and crawlers are the easiest stage to kill with insecticides.  

Posted on Tuesday, December 20, 2016 at 11:26 AM

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