Hungry roof rats have discovered tasty California almonds and chomped their way through 100,000 acres, much of it in San Joaquin County, an industry group warns.
The Almond Board of California said in article aimed at growers that most of the “unprecedented” damage in San Joaquin County has been in the southern and western portions. It has also struck growers in Merced, Fresno, Kings and Kern counties.
The roof rats use irrigation canals as a rodent highway to get from one orchard to another. The California Department of Food and Agriculture reported in February that the damages at that time had already amounted to $109 million to $310 million.
In some orchards, the numbers of rats is extensive. The CDFA said traps caught up to 32 rats some nights.
Rats are blamed for damaging 10% of the trees per acre, cutting their nut yields by 20% of normal, the CDFA said. The damage went beyond the tree nuts: rats gnawed through wires on tractors, harvesters and bored through irrigation lines. Some trees needed to be replaced.
Growers are trying to deal with the rat infestation with poison bait and aluminum phosphide treatment in rat burrows in the winter. Some have resorted to the methods preferred by homeowners, such as snap traps, the Almond Board reported.
“However, many growers report these tactics are labor-intensive, costly and insufficient for the scale of this infestation,” the Almond Board wrote. “Additionally, growers noted that rotating bait flavors has become necessary as rodents quickly grow wary and ‘bait shy.'”
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