Web Author: Dr. Beth Grafton-Cardwell, conducts research in the San Joaquin Valley on insect and mite pests of citrus. These web pages provide up-to-date information about the pests and their natural enemies, including basic biology, hosts, distribution, monitoring methods and management tactics. Please join us in exploring this subject through blogs, information and resources.
Citrus Bugs Blog
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.
During 2014 and 2015, abnormally warm weather generated a rapid accumulation of degree day units, well above the 30-year average, that allowed an additional generation of California red scale to complete their development. In addition, the excessively warm winters we have had during those years allowed California red scale, and other pests, to continue to develop during the winter in the San Joaquin Valley. This is quite unusual. While the 2016 season was well above the 30-year average through August, the accumulated degree day units at the end of the season were less than the last two years. Hopefully we will have a cold (but not freezing) winter that will prevent California red scale populations from continuing their development and cause mortality to the younger instars.
The California Department of Pesticide Regulation (DPR) runs the most extensive Pesticide Residue Monitoring Program in the nation and is hard at work ensuring that the fruit and vegetables we purchase and consume are free from illegal pesticide residues. Just last month, DPR detected residues of a pesticide not registered for use on grapes and fined the grower $10,000 for using a pesticide in violation of the label and for packing and attempting to sell the tainted produce.
Cases like this are rare in California but remind growers how important it is to apply pesticides correctly by following all pesticide label directions. Understanding and following label instructions is the focus of a new online course developed by the University of California Agriculture and Natural Resources Statewide Integrated Pest Management Program (UC IPM).
Proper Pesticide Use to Avoid Illegal Residues is targeted to those who apply pesticides or make pesticide recommendations. It explains what pesticide residues are, how they are monitored, and highlights important residue-related information from several sections of pesticide labels. In addition, the course identifies the following as the most important factors leading to illegal residues:
- Using a pesticide on a crop or against a pest for which it is not registered
- Applying pesticides at an incorrect rate
- Ignoring preharvest intervals, re-treatment intervals, or plantback restrictions
Course participants are presented with several real-life scenarios. They must search through actual pesticide labels to determine if the scenario illustrates proper use of pesticides or if the described situation could potentially lead to illegal residues.
The overall goal of this course is to have participants follow pesticide label instructions when they return to the field. Following the label can eliminate incidences of illegal pesticide use.
Sara Scott and Joshua Reger, Staff Research Associates with the Dept of Entomology, UC Riverside are stationed at the Lindcove Research and Extension Center. Their research program centers on citrus integrated pest management. On October 14, they presented information about citrus fruit and citrus pests for Woodlake High School career day and talked to students about their careers in agricultural research.
On Sept 13, a field day was held at Lindcove Research and Extension Center to discuss citrus thrips biology and management. We utilized the mobile laboratory for a powerpoint presentation and to support microscopes that showed various stages of citrus thrips and flower thrips. We also visited a pesticide spray trial to talk about efficacy of various pesticides.
Take home messages:
- The immature stages of citrus thrips are the most damaging
- In mature trees, protect fruit not foliage
- In young trees, be careful of spraying too much or you will select the thrips for resistance
- Thrips are tough to control in drought years
The entomology lab at Lindcove is going to start monitoring for resistance this fall.
If you have sites that have thrips that you would like tested, contact Joshua Reger email@example.com.