Survey of Rodent and Rabbit Damage to Alfalfa Hay in Nevada

A survey of alfalfa hay producers was conducted to characterize vertebrate pest problems in Nevada alfalfa hay and help attract research funding. Damage to alfalfa hay by pocket gophers (Thomomvs spp), ground squirrels (Spermophilus spp), black-tailed jackrabbits (Lepus californicus) and meadow voles (Microtus montanus) was assessed. Presence of vertebrate pests along with a ranking of cost-related problems they pose to alfalfa hay operations was determined. Pocket gophers were the most costly pest followed by ground squirrels, jackrabbits, and meadow voles. The number one problem caused by vertebrate pests was identified to be a decrease in hay production. Control techniques were rated as somewhat effective for all rodent and rabbit pests. The costs associated with farm management practices were ranked from highest to lowest in this order: irrigation, rodents and rabbits, weeds, insects, and fertilization. Proc. 14th Vertebr. Pest Conf. (L.R. Davis and R.E. Marsh, Eds.) Published at Univ. of Calif., Davis. 1990. INTRODUCTION Rodents and jackrabbits can be extremely damaging and costly to alfalfa operations if their populations are allowed to exist above economically significant levels (Piper 1909, Sauer 1978, Dunn et al. 1981, Luce et al. 1981). The damage costs associated with these pests are difficult to estimate and can differ on each farm. Crop losses and potential future losses caused by vertebrate pests must be assessed to determine if control is warranted (Rennison and Buckle 1988). A survey designed to reveal alfalfa producers’ perceptions of rodents and rabbit pest problems in Nevada was conducted in October of 1988. The use of surveys is a cost-effective means of gathering data on vertebrate pests (Crabb et al. 1986). The purposes of this survey were twofold: first, to identify the grower's perception of the economic significance of vertebrate pest problems; and second, to help attract research funding. METHODS A list of Nevada alfalfa hay producers (approximately 1,000) was compiled. Five hundred producers were randomly selected to participate in the survey. Each of the 500 participants was mailed a cover letter, a survey with identification number for follow-up purposes, a business reply envelope and a complimentary pencil. After 3 weeks, a second survey packet was sent to all nonrespondents. Two hundred seventy five surveys (55 percent) were returned. All producers who responded were thanked and sent a summary of the results. A copy of the survey form is in Appendix 1. RESULTS Pest Presence Producers were asked to identify which vertebrate pest(s) are present on their farm (1/farm indicates presence). Pocket gophers are present on 87 percent of the Nevada alfalfa hay farms. Ground squirrels and black-tailed jackrabbits are found on 51 percent of the farms. Meadow voles, also known as meadow mice, are present on 26 percent of the Nevada farms. Pest Cost On a scale of 0 to 5, producers were asked to rate the damage and control costs attributed to each of the four vertebrate pests (0 = no cost, 1 = low cost through 5 = high cost). Pocket gophers are considered by producers as the most costly pest with a mean rating of 3.0. Ground squirrels are thought to be half as costly as pocket gophers with a rating of 1.4. Jackrabbits follow closely behind ground squirrels with 1.3, and meadow voles are considered to be very near no cost with a rating of 0.4 (Table 1). Table 1. Number of Nevada alfalfa grower responses in each rating category of the costs attributed to four vertebrate pests on their farms and the cost-rating category means. Problems Caused Rodents and rabbits are costly because they impair or burden various aspects of alfalfa production. Nevada producers were asked to identify the No. 1 problem caused by vertebrate pests. Decrease in hay yield is considered to be the biggest problem for 42 percent of the producers with damage to equipment and reduced equipment longevity for 32 percent. Increased labor and fuel costs are the biggest problem for 17 percent of the producers. Nine percent of producers feel the decrease in hay quality is the No. 1 problem caused by vertebrate pests.