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
National Invasive Species Awareness week: February 27 – March 3, 2017
—Stephanie Parreira, UC Statewide IPM Program
Invasive species are plants, animals, fungi or microbes that are not native to an area, but can quickly establish, multiply, and become pests. These species can hurt the environment, agricultural production, and even human health in some instances (e.g. the mosquito Aedes aegypti). According to the USDA, invasive species are responsible for $137 billion per year in economic losses in the United States.
In agricultural systems, invasive species may reduce yields, render crops unmarketable, or make rangeland unfavorable to livestock. In natural areas, they may squeeze out native species, change soil quality, and increase the frequency or intensity of wildfires.
Some of these species have been introduced intentionally (e.g., yellow sweetclover, which was originally imported from Europe as a forage species for livestock), while others arrived by accident (e.g., the glassy-winged sharpshooter which came to California inadvertently through nursery stock shipments).
Just one species can be detrimental to crop production and revenues. The invasion of spotted-wing drosophila, for example, caused conventional raspberry growers in California to lose $36.4 million in revenue between 2009 and 2014, and would have reduced California raspberry yields by as much as 50% without control efforts.
The spread of invasive pests has become more prevalent in recent decades, and is linked to several factors, including global travel, produce trade, and climate change. Many invasive pests spread by human movement—medusahead, for example, has long awns on its seeds that easily attach to clothing and animal fur, to be carried to other locations. A recent study by UC scientists also determined that due to climate change, invasive weeds are shifting their ranges at a faster rate than native plants, and will likely cause more problems in agriculture and natural resources in the future. The yellow starthistle, an invasive plant that dries out soil and degrades rangelands, is one of the pests that will expand its range further north in California (and beyond) due to climate change.
While invasive pests can be a major challenge to growers and land managers, there are successful stories of stopping exotic pest invasions with well-coordinated eradication efforts. Recently, the California Department of Food and Agriculture (CDFA) declared the European Grapevine Moth eradicated from California after no moths were found in the state from 2015 to 2016. This was due to a rapid response, largely by the UC Cooperative Extension scientists after the moth was discovered in Napa vineyards in 2008.
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.