Vertebrate Pests - Organic Alfalfa Production
Agronomic Production Guide
Martin Guerena and Preston Sullivan
NCAT Agriculture Specialists
(Page 6 of 9)
Alfalfa provides a very desirable habitat for several mammal pests. Besides feeding on the nutrient-rich succulent leaves, stems, and roots, mammals may burrow into levees and ditches and damage irrigation systems and harvesting equipment. Mammal pests of alfalfa include mice, gophers, ground squirrels, rabbits, and deer. Proper identification of the species involved is critical, because control measures differ with each one. Assistance in correctly identifying the animals causing the damage is available through the local Extension service.
Field Mice (Mictotus spp), also called meadow voles, dig short, shallow burrows and make underground nests, creating trails about two inches wide that lead from their burrows to surrounding areas of the field where they feed. Control measures consist of cutting the surrounding vegetation in ditches and adjacent fields, trapping (which can be impractical when populations are high), the use of ammonium-based repellents (check with certifier), and habitat creation for raptors and mammal predators such as coyotes, foxes, wildcats, weasels, and shrews.
Gophers (Thomomys spp.) are burrowing rodents that feed mostly on underground plant parts, with alfalfa being one of their preferred foods. Besides weakening or killing the plants, they also damage irrigation ditches and borders. The mounds of soil they push up from their burrows also bury other plants and cause obstacles for the harvesting equipment. Non-toxic controls consist of trapping, flooding the burrows, surrounding a field with plants that repel gophers, such as gopher spurge (Euphorbia lathyrus) and castor bean (Ricinus communis). Depositing predator urine, pine oil, or any other foul smelling substances in the burrows has been reported to provide temporary control. The use of barn owl perches to attract these predators has been successful in controlling gophers in California. On average, a barn owl can eat 155 gophers per year (Power, 2003). Propane devices that ignite injected gas, causing the burrows to explode, are reported effective in reducing populations temporarily. Check with your certifier before using this method. Additional treatments are necessary, depending on the length of the season.
Ground Squirrels (Spermophilus spp.) damage alfalfa by feeding on leaves, stems, and crowns. Their burrows damage plant roots and irrigation levees and create obstacles for field equipment. Controls include trapping, removing rocks and stumps at the edges of fields that provide a desirable habitat, deep tillage to disrupt the burrow system, and shooting. Repellents such as pepper spray, mothballs, and predator urine have been used around plants and burrows with varying success. Again, check with your certifier before using any of these.
Rabbits (Sylvilagus spp.) and Jackrabbits or Hares (Lepus spp.) can be kept out of alfalfa fields with fencing that is at least four feet high and buried at least six inches. Habitat establishment or conservation to encourage natural enemies such as hawks, owls, eagles, coyotes, foxes, and wildcats is recommended if rabbits are a persistent problem. Modification of the rabbits' environment by removing debris and vegetation where they hide is another cultural control. Repellents, frightening devices, traps, hunting, and domestic dogs and cats, can also contribute to reducing rabbit numbers.
Deer and other large grazers such as elk and antelope can cause significant damage to alfalfa plantings. Several methods to control these large mammals have been used with varying levels of success. Odor repellants and devices that produce periodic explosions can be effective for limited periods, but are not long-term solutions because the animals grow accustomed to them. Fencing is probably the most effective method to protect large fields. The use of guard dogs, an odor repellent, and no treatment were compared at a pine seedling plantation in Missouri for protection against grazing deer. The dogs were a better deterrent than Hinder (odor repellent) or no treatment. Browse rates averaged 13, 37, and 56%, respectively, for dogs, Hinder, and no treatment during the three-year study. Browsed seedlings were generally heavier in weight on plots protected by dogs, suggesting that browsing severity was also reduced (Beringer et al., 1994). For more information on controlling deer, see the ATTRA publication Deer Control Options.
This page was last updated on: December 13, 2014