Photo Credit: Alabama Cooperative Extension System
Rodents, particularly rats, have wreaked havoc in California orchards and vineyards this year. Some growers have reported yield losses, damage to trees and destruction of irrigation lines, electrical wiring and other infrastructure.
Farmers face soaring costs to replace what has been destroyed or damaged, but also to control populations of the pests.
The rodent problem was initially reported in San Joaquin Valley nut orchards. But Roger Baldwin, a wildlife specialist and expert in rodent management at the University of California, Davis, said the problem is more widespread. He has heard about rodent damage on the west side of the Sacramento Valley and along the Central Coast, particularly in citrus orchards.
One reason for increased rodent activities this year could be abandoned orchards, which provide plenty of food and shelter for rodents to proliferate, Baldwin said.
“Rodent damage, if ignored, can lead to substantial losses,” Baldwin said.
Rats and other rodents can damage trees by removing the bark, which can cause disease and, if severe enough, kill the tree. The animals also chew through drip hoses.
Baldwin has studied different rodenticides for controlling roof rats in almond orchards. He found that using 0.005% diphacinone-treated oats inside elevated bait stations resulted in more than 90% reduction in rat activity.
Baldwin recommended constructing a bait station from PVC pipe and placing it roughly 4 feet above ground by attaching the stations to branches. He placed stations either 98 feet or 165 feet from each other throughout the orchard. Using 165-feet spacing reduces the cost, but efficacy drops to about 75%, he said. “The closer the stations are, the more likely it is that it’s going to work,” he said.
After knocking down much of the rat population using bait, Baldwin placed trapping tunnels, or snap traps, 250 feet apart throughout the orchard. During a five-month period, the tunnels further reduced rat activity by 90% to 95%, he said.
After trapping, growers should still do periodic monitoring, Baldwin said, as some rats will evade the traps over time, and populations may start to rebound.
Using a diphacinone application remains a good strategy for initial knockdown of rodents, Baldwin said. He added there are other tools for keeping populations down for a longer period. One is burrow fumigation, with aluminum phosphide being the most effective, he said.
Other control measures include pressurized exhaust machines that inject carbon monoxide into burrows. But there’s not much data on their effectiveness on rats, Baldwin said. He thinks they probably don’t work as well as aluminum phosphide but could provide some relief.
Source: California Farm Bureau
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