"On Wednesday, May 8, 2019, the State of California announced it would ban the use of chlorpyrifos by canceling registration of the pesticide by the Department of Pesticide Registration. Chlorpyrifos use in agriculture has been under federal and state regulatory review for the last several years. Chlorpyrifos for use in structural pest control and for sale in consumer products ended in 2000 due to a voluntary agreement between the manufacturers and EPA.
"University of California Agriculture and Natural Resources (UC ANR) carries out the Land-Grant mission of University of California to seek scientific solutions to address society's needs and problems. As a part of UC ANR, the Statewide Integrated Pest Management Program (UC IPM) provides research-based information to manage pests while protecting human-health and the environment. UC scientists have spent many years researching alternatives to chlorpyrifos and educating state-licensed pest control advisers on effective use of the alternatives. For example, improved integrated pest management of insects in almonds eliminated the need for winter application of chlorpyrifos on the 1,390,000 acres of almonds in California. Overall, this work contributed to the greater than 50% decrease in chlorpyrifos use in all of California agriculture from 2006 to 2016.
"In 2014, UC IPM started a two-year project, funded by California Department of Pesticide Regulation, to identify the pest-crop situations where there were no or few alternatives to chlorpyrifos. That project identified specific needs for additional research on alternatives to manage weevils and aphids in alfalfa, leaf-footed bug and stink bugs in almond, ants in citrus, and aphids and whiteflies in cotton. UC research and extension continues to seek solutions to these difficult pest management problems. Previous research in many other pest-crop situations had already identified and supported implementation of alternatives to chlorpyrifos.
"UC ANR will continue to work closely with the State of California and agriculture to protect the health of Californians and our environment while providing effective pest management solutions to farmers."
For more information, contact:
- Author: Pamela Kan-Rice
Monitor for rodent activity and use bait stations before the growing season to prevent problems, UC ANR scientists recommend.
Roof rats are running rampant in California orchards this year, according to UC Agriculture and Natural Resources scientists.
“In pistachio and other nut orchards, roof rats are burrowing and nesting in the ground where they're chewing on irrigation lines, causing extensive damage,” said Rachael Long, UC Cooperative Extension advisor. “They are also nesting in citrus trees, feeding on the fruit and terrifying field workers when they jump out as people are picking fruit. The chewing pests are also girdling citrus limbs, causing branch dieback.”
Holes in the ground around the base of pistachio trees throughout a Yolo County orchard puzzled the grower.
“We looked for ground squirrels, but never saw any,” Long said. “We set up game cameras, but only got birds and rabbits. We put rodent bait in the holes, but the digging didn't stop.”
Long, the pest detective, cracked the case by consulting Niamh Quinn, UC Cooperative Extension human-wildlife interactions advisor based in Irvine. “She informed us that the damage we were seeing was from roof rats.”
Burrowing roof rats sounds like an oxymoron. While roof rats generally don't burrow in urban environments, their country cousins have been known to burrow.
“It's not true that they don't burrow,” Quinn said. “When I worked as staff research associate for Roger Baldwin, UC Cooperative Extension wildlife specialist, that is mostly what we studied, burrowing roof rats in orchards.”
Baldwin said, “It seems to be a good year for rats in a number of different areas and crops throughout the state. I've received more questions and comments about rats this year than perhaps the last 10 years combined. As for bait application, putting bait down burrow systems for rats doesn't usually work too well, so I'm not surprised that approach didn't work. Growers will likely have better luck with bait stations in the trees.”
Because the rats climb, Baldwin suggests attaching bait stations to tree branches.
“In addition, elevating the bait stations will eliminate access to bait for many protected mammal species, such as kangaroo rats,” Long said. “The bait diphacinone grain can be purchased from some ag commissioners' offices. This is what Roger Baldwin said they tested and it worked.”
As for the bait stations, they should be designed so that there isn't any spillage for nontarget animals to eat, Long said.
When roof rat outbreaks occur, rodenticides are often needed to prevent crop damage. However, timing is critical as diphacinone use is highly restrictive and not allowed during the growing season, which is beginning as the weather warms.
“Check the product label for application instructions,” Long reminds growers. “It's the law.”
Identifying the pest
“Roof rats can forage away from their nest, so you won't likely find signs of their activity, such as rat droppings outside their burrow, to help identify them,” Long said.
Ground squirrels are active during the day, so they are more likely to be seen, dig holes about 4 inches in diameter and forage above ground near their burrows. Vole and mouse holes are 1- to 2-inches in diameter. Roof rat holes are typically 3 to 4 inches in diameter and might have nut shells in front of them, for example pistachio or almond shells. Rabbits will feed on seedling crops, but do not dig burrows.
“Rats are sneaky and hard to spot,” Long said. “If you see damage, including digging in the soil but no wildlife, suspect rats.”
For more information on controlling roof rats, download Quinn and Baldwin's free UC ANR publication 8513, Managing Roof Rats and Deer Mice in Nut and Fruit Orchards at http://anrcatalog.ucanr.edu/Details.aspx?itemNo=8513.