Growers Need to be Aware of Cannabis Loving Field Mice in Pennsylvania

By Louis Bengyella and Francesco Di Gioai

While farmers are still maneuvering and digesting the USDA Final Rule governing industrial hemp (Cannabis species expressing less than 0.3% Δ⁹-tetrahydrocannabinol (THC)) production in the United States, reports of emerging pests, such as fall armyworm, and new diseases are being reported.

In Pennsylvania, a most unexpected pest, yet prevailing and thriving, is the rise of cannabis-loving predatory deer mice (sometimes known as field mice, Peromyscus species) which can be devastating to the crop at tender stages of growth and development, suggesting growers could be in for a rocky start to the farming season. One challenge associated with this new problem for a newly domesticated crop is the difficulty of identifying the footprint of deer mice for both indoor and outdoor growers of Cannabis species within the Cannabaceae family.

Figure 1. Damage caused by deer mice (Peromyscus species) on stored cannabis seeds. The animal easily dehulls cannabis seeds. Photo credit: Louis Bengyella

For instance, a large handful (100 g) of unprotected hempseed can be destroyed by one predatory mouse in a single day during winter when food alternatives are rare (Figure 1). This is worrisome for industrial dual-purpose hemp growers, hempseed storage facilities, and hempseed oil extractors that receive and process grain from farmers. One may be tempted to inquire why field mice might be interested in cannabis seed?

As cannabis seeds mature in the field and are harvested, cleaned, and stored (that is curing), the concentration of the polyunsaturated fatty acids (76.26% - 82.75%, mostly linoleic acid, and α-linolenic acid in a 3:1 ratio [3]) builds up. Seed-predatory deer mice love oily and tasty food and that can be the cause of their untimely death when trapped (Figure 2). Moreover, the health benefits conferred by γ-tocopherol present in hempseeds at an average rate of 28.23 mg per 100 g of hempseed oil could attract the predatory rodents to destroy growers' hard-earned harvests within days. Growers must watch out.

Figure 2. With a trap amended with oily peanut butter, beneficial fatty acids and flavors lead to the mice's demise. The close-up image is an undamaged seedling. Photo credit: Louis Bengyella

Besides seeds, the plant-loving deermice can wreak havoc under indoor production setting compelling a grower to replant and even miss the entire production schedule if the pest is not timely managed. We have identified the footprint of deermice during seed emergence and seedling stages (Figure 2) suggesting that the Peromyscus species might be interested in cannabinoids in the young plants when not satisfied with the cannabinoids content after eating ungerminated seeds.

The deer mouse selectively cut the seed endosperm in emerging seedlings as well as eat the shoot apical bud (Figure 2), forcing growers to replant. The economic impact could be catastrophic for growers. For instance, for elite certified feminized seed costing at least $0.50 per seed for smokable hemp, one night's mouse foraging activity can lead to the destruction of 120 seedlings causing a direct economic loss of $60.0. At this rate of economic quagmire, growers might play safe by storing their precious elite seeds in refrigerators, or sealed bags closed in solid plastic containers. Should the activities of deermice be observed within areas of actively growing cannabis seedlings, growers could consider deterrence strategies such as ultrasonic frightening devices and repellents, trapping and glue boards, and deploying predators such as cats.