By Erin Lizotte
Unseasonably warm weather and continued grass growth may be hiding a significant amount of rodent activity. Growers are advised to scout carefully and consider mowing tall undergrowth one more time before snow falls.
Rodents can be a major problem for perennial crop growers. Rodents girdle trees and can directly damage or consume fruits and nuts. Burrows and tunnels may also present tripping and falling hazards for agricultural workers. The most common rodent pest species in Michigan include voles, ground squirrels, deer mice and house mice. Rodent populations expand and contract based on a number of environmental factors and tend to be cyclical. Constantly fluctuating populations can make consistent integrated control programs difficult to maintain, but a regular combination of strategies including monitoring, habitat management and rodenticide application are generally required to achieve reasonable control.
One of the most important steps in successful rodent management is identifying the species that are causing damage. Snap traps, live traps or visual observation may be sufficient to determine the species. Quantifying the population is much more difficult and crop thresholds have not been developed. Michigan State University Extension encourages growers to estimate the per acre crop damage caused by rodents and then consider if the treatment is justified. Growers should also take into account the rodent pressure at each location, specifically the historical pressure and the surrounding landscape when weighing treatment options. For more information on how to identify rodents, refer to the University of Nebraska Cooperative Extension publication, “Prevention and Control of Wildlife Damage.”
Modifying environmental factors to moderate rodent populations can be useful. Burning, mowing, using herbicides or planting low growing ground cover to reduce vegetative cover can help make a site less attractive to rodents. Controlling ground cover also exposes rodents to greater risk of raptors, coyotes and other predators. Removing plant cover surrounding an agricultural area may also help in slowing movement of new rodents into a site. Growers may also consider encouraging raptor predators through perches or nest boxes. Ideally, adjacent landowners can work together to manage large areas of land to prevent high rodent populations from becoming established.
Using rodenticides is an important component of an integrated rodent control program, but it is not a standalone control. Rodents have a relatively short lifespan and a high rate of reproduction, making lethal control strategies effective for a limited amount of time, further enforcing the need for an integrated approach to control. There are a limited number of rodenticides labeled for use in perennial cropping systems in Michigan. Growers should carefully review labels to ensure the site is listed before application. All rodenticides should be used according to the label. In general, rodenticide application to bearing crops is only permitted during the dormant season. Application to non-food crops is genreally less restricted. Many products recommend using bait stations to help protect non-target organisms.
The following table lists the rodenticides currently labeled for use in Michigan. The table is provided as a convenience for growers, and does not supersede the label. Growers must read and follow all label directions to reduce the risk of pesticide exposure to themselves, others, non-target organisms and the environment.
Rodenticides registered for use in Michigan fruit, nut and Christmas tree orchards |
|---|
| Active ingredient | Trade names | Site | Target | Additional info |
|---|
| Anticoagulant |
|---|
| Chlorophacinone | Rozol Vole Bait*, Borderline* | Fruit tree orchards | Voles | Apply after fall harvest (including drops), before new spring growth, and during which three consecutive days of rain-free and snow-free weather are expected. Do not apply within 50 feet of any body of surface water or where raptors are actively feeding on voles. Do not apply over bare ground or crops not specified above. Do not allow animals to graze in treated areas. Do not use hay cut after application for feed or bedding. Apply only by hand spot baiting and ground broadcasting. |
| Nurseries, tree plantations, christmas tree farms | Voles | For control of only voles in commercial nurseries, tree and forestry plantations, Christmas tree farms, and border areas and buffer strips adjacent to crops. This product must not be applied directly to food or feed crops except as specified above. Do not apply within 50 feet of any body of surface water or where raptors are actively feeding on voles. Do not allow animals to graze in treated areas. Do not use hay cut after application for feed or bedding. To avoid exposing nontarget organisms, follow the instructions in the “Pesticide disposal” section to insure proper clean up of any bait for reuse or disposal. Apply only by hand spot baiting and ground broadcasting. |
| Ground Force Paraffinized Pellets Rodenticide* | Orchards, nurseries and ornamentals | Voles, ground squirels, norway rats, and house mice | Directions vary based on site and target-refer to the label. When applying to bearing orcahrds, do not apply until all fruit is harvested and all harvestable fruit is recovered. Bait before snowfall. Do not bait later than March 31. Where possible, recover and bury vole carcasses. |
| Diphacinone | Ramik Brown* | Fruit tree orchards, Christmas tree farms, tree plantations and
commercial nurseries | Mice and voles | Apply after fall harvest (including drops), before new spring growth, and during which three days of rain-free and snow-free weather are expected. |
| Systemic toxicant |
|---|
| Zinc phosphide | ZP Rodent Bait Ag* | Dormant fruit and nut tree orchards | Voles | Apply only after fall harvest (including drops), before new spring growth and when no rain or snow is expected for three consecutive days. Do not graze animals in treated areas. |
| Nursery stock, conifers/Christmas trees, and oranmentals | Voles | Do not apply by air. |
| Prozap Zinc Phosphide Rodent Pellets* | Fruit tree orchards and nut tree orchards | Moles, house mice, and norway rats | Directions vary based on site and target-refer to the label. |
Restricted use pesticide. Requires a pesticide applicators license through the Michigan Department of Agriculture and Rural Development.
Lastly, it is important to remember that even rodents are a critical part of the ecosystem that exists within our agricultural fields. They are significant contributors as seed predators, nutrient cyclers and insectivores. The complete elimination of rodents from perennial agricultural systems is neither necessary nor advisable. Growers should view their programs as rodent damage management and not rodent population control.
This material is based upon work supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, under Agreement No. 2015-09785. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.