Potato Grower

WWW.POTATOGROWER.COM 21 Some growers may find them only a nuisance or fun target practice, but ground squirrels, voles (sometimes called mead- ow mice) and other rodents can cause real financial headaches for farmers and ranchers. Ground squirrels and voles cause yield losses in pulse, seed, grain and forage crops. They can clip and reduce perennial native grasses and stand life in forage, facilitating the spread of inva- sive weeds, and create burrows that can cause soil collapse and irrigation water loss, as well as pose safety hazards for workers and livestock. Are they broaden- ing their diet and taking a bite out your potato profits? Ground squirrels damage irrigation lines, and their burrows can slow harvest and damage equipment. They can also contaminate crops, causing food safety issues. Both voles and ground squirrels can contaminate and compro- mise the quality of stored pota- toes. When it comes to disease transmission, the primary con- cerns with voles are E. coli, sal- monella and hantavirus. Ground squirrels, voles and mice can be hosts of fleas and ticks, which can carry Lyme disease, plague and tularemia. With the advent of soy-based wiring in newer ve- hicles and farm equipment, these warm nesting sites now offer another costly snack for rodents. VERTEBRATE PEST PRESSURE Vertebrate pest pressure may depend on the growing region, time of the year and/or local environmental conditions. Ground squirrels hibernate from early fall through early March and wake up hungry. Under protective winter snow cover or canopied crops like alfalfa or potatoes, voles can breed unchecked by predation from raptors. Fields near wild areas are often the most vulnera- ble to these pests. Landowners finding evidence of ver- tebrate pest feeding such as mounds or burrowing need to properly identify the pest first so that it can be most ef- fectively managed, since management options for each are different. GROUND SQUIRRELS Richardson's and Townsend ground squirrels are typically found in range- land prairie and foothills, while Colum- bian and Wyoming ground squirrels are more common in higher-altitude intermountain steppes. Following mild winters with minimal spring flood- ing, ground squirrels can invade and quickly colonize newly planted crop fields. Ground squirrels live in burrow systems varying from 5 to 30 feet in length. Understanding their life cycle will help make pest management more effective. Ground squirrels become inactive for two periods during the year. Aestiva- tion is the period of dormancy that takes place during hotter, drier periods between late July and early September. Squirrels typically come out of aesti- vation as temperatures cool and crops mature. As harvest approaches, squir- rels feed aggressively to store energy for their hibernation. They typically hi- bernate by October and do not emerge before early March, so it is critical to be ready to apply bait as soon as they emerge. Depending on weather and eleva- tion, squirrel reproduction can begin as early as late March. Males typically emerge 10 to 14 days before females and immediately begin to forage. Peak mating season is March to May, with gestation of 23 to 28 days. Females produce one litter per year. CONTROL MEASURES Measures that have been found to only have moderate success include trapping, shooting, and habitat modifi- cation. Typically, these methods are not done consistently enough to reduce or frustrate newly migrating rodent pop- ulations. However, baiting has consis- tently proven effective. Squirrels feed on grasses or other plants in the spring and transition to seeds and crops in early fall, when they store calories for upcoming hibernation. There are two types of rodenticides: anticoagulants and acute toxicants. First-generation anticoagulants such as chlorophacinone (Rozol) or dipha- cinone (PCQ) are multi-feed materials, meaning the target pest generally needs to ingest it over a few days. While it may take slightly longer to see results with an anticoagulant, Tunneling voles and ground squirrels can cause soil collapse and water loss, leading to extensive damage to crop and rangeland. Damage caused to mid- season potatoes by voles

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