Once again, we are having hot dry weather conditions in the San Joaquin Valley. This means that the first male California red scale are already flying in Kern and Tulare counties (Biofix) and degree days are accumulating 1-2 weeks ahead of 'normal'. Unless we get cooling weather, this means that the first generation of crawlers will be emerging earlier than usual. See degree day calculations for Kern and Tulare counties.
New UC IPM photo repository shows plant damage from herbicides
—Tunyalee Martin, UC Statewide IPM Program
—Chris Laning, UC Statewide IPM Program
Identifying nontarget crop and ornamental plant damage from herbicides has become much easier with the launch of a new online photo repository by the Statewide IPM Program, University of California Division of Agriculture and Natural Resources.
Herbicides applied to manage weeds may move from the site where it was applied in the air or by attaching to soil particles and traveling as herbicide-contaminated soil. When an herbicide contacts a nontarget plant, a plant it was not intended to contact, it can cause slight to serious injury. Herbicide injury also occurs when the sprayer is not properly cleaned after a previous herbicide application. Herbicide residue can be found in the spray tank, spray lines, pumps, filters and nozzles so a sprayer must be thoroughly cleaned after an application. Dry herbicide particles can be redissolved months later and cause herbicide damage to plants. Economic damage includes reduced yield, poor fruit quality, distorted ornamental or nursery plants, and occasionally plant death.
Accurately diagnosing plants that may have herbicide injuries is difficult. In many cases, herbicide symptoms look very similar to symptoms caused by diseases, nutrient deficiencies, environmental stress and soil compaction. Plant disease symptoms such as mottled foliage, brown spots or stem death and plant pests such as insects or nematodes cause foliage to yellow and reduce plant growth similar to herbicide injury.
Dr. Kassim Al-Khatib, weed science professor at UC Davis and director of the UC Statewide Integrated Pest Management Program (UC IPM), has gathered nearly a thousand photos of herbicide-damaged plants, drawn from his own and others' research. The images are cataloged to show damage that can occur from 81 herbicides in more than 14 specific herbicide modes of action, applied in the field to demonstrate the symptoms or when known herbicide spray has drifted onto the plant.
Each image is characterized with the name of the plant, mode of action of the herbicide, and notes the specific symptoms of damage. Together these photos provide a comprehensive archive of damage to over 120 different crops and ornamental plants by known herbicides, which users can easily compare with what they see in the field.
Also included in the repository is information about the modes of action of various herbicides and an index of example herbicide trade names and active ingredients. Users can learn how unintended injury from herbicide occurs from misapplication and carryover from previous crops in addition to drift and herbicide-contaminated tanks.
The repository can be found at http://herbicidesymptoms.ipm.ucanr.edu. Increased knowledge about what causes herbicide damage and how it occurs can lead to fewer cases of herbicide injury occurring through drift or herbicide-contaminated tanks. Using the repository can increase the skill to correctly identify plant damage. Correctly identifying damage as herbicide injury and not from a plant pest or nutrient deficiency can prevent unnecessary applications of pesticides or fertilizers. Fewer applications can lessen the risk of harm of pesticides and fertilizers to people and the environment.
This year was a 'perfect storm' for California red scale; combine the drought with higher than normal average daily temperatures and pesticides that disrupt scales and you have a crisis.
Drought: Some insect populations increase when trees become water stressed and California red scale is one of those. It could be a direct response to the tree or it could be because increased dust reduces the effectiveness of natural enemies.
Higher than normal temperatures: Typically, San Joaquin Valley conditions produce 4 to 4.5 generations of California red scale per year. Usually, by November 1, the female scales stop producing crawlers and shut down for the winter. This year, the degree days (heat units) were higher than normal the entire red scale season (from March 1 - Dec 1). This produced a full 5th generation of scale and scale crawlers were still emerging in December. Many growers struggled to control California red scale because the problem appeared late in the season and this pest is very difficult to control with insecticides once it reaches the fruit. Degree day units were high not only this year, but have been higher than the 30 year average for the past 3 years, accumulating extra scales each year.
Insecticides: Research has demonstrated that systemic neonicotinoids such as imidacloprid can reduce scale on fruit and leaves but are not effective in controlling California red scale on woody tissues such as bark and twigs. These insecticides are also toxic to natural enemies. Using these products year in and year out builds scale on the wood, that eventually makes its way to fruit.
Below are the flights and five generations of crawler activity at Lindcove Research and Extension Center. Also shown are the degree day units accumulated at Lindcove through the season. See degree day units for California red scale for other locations.
Author: Cheryl Reynolds, UC Statewide IPM Program
An online course highlighting how pesticide resistance develops among pests is now available on the UC IPM Web site. Created primarily for pest control advisors and other licensed pesticide applicators, this course describes the mechanisms of resistance in pathogens, insects, and weeds and discusses ways to manage resistance within the different disciplines.
The online course is divided into three narrated presentations followed by a final test for each section. This course has been approved for 2 continuing education units in the “Other” category from the Department of Pesticide Regulation.
This course is based on a series of workshops held in Davis, Fresno, and at the Kearney Agricultural Research and Extension Center during the spring of 2014 presented by Dr. Doug Gubler (Dept. of Plant Pathology, UC Davis.), Dr. Larry Godfrey (Dept. of Entomology and Nematology, UC Davis), Dr. Beth Grafton-Cardwell (Lindcove Research and Extension Center and UC Riverside), and Dr. Kassim All-Khatib (UC Statewide IPM Program).
Check out the new course at http://www.ipm.ucanr.edu/training/pesticide_resistance.html.
On September 30, an in-depth workshop was held at the UC ANR Lindcove Research and Extension Center to discuss the biology and management of California red scale. Twenty seven participants spent the day viewing scales under microscopes and learning about Aphytis and Comperiella wasps. The hot topic (literally) this year, above and beyond the usual complexities of managing scale, was the much higher than average accumulation of heat units. Normally there are about 4 generations of scale per year in the San Joaquin Valley, but this year a 5th generation is developing. This is the third year in a row that temperatures have been above the 30 year average. We also discussed the fact that systemic neonicotinoid insecticide use is becoming very common place and repeated use of the systemic neonicotinoids results in a build up of scale on the wood that is difficult to control with natural enemies or insecticides. So, the combined problems of scale build up due to changes in insecticide use patterns and high average daily temperatures have resulted in outbreaks of California red scale in the San Joaquin Valley.