Pests in the Organic Pasture

eOrganic author:

Mike Gamroth, Oregon State University


Three tiers of pest management strategies are described in §205.238 of the National Organic Program (NOP) final rule (United States Department of Agriculture [USDA], 2000).

  1. First, the producer must use cultural and management practices—such as selection of suitable species and types of livestock and establishment of appropriate housing, pasture conditions, and santitation practices—that prevent pest and disease problems. These include multiple components of a holistic systems approach to organic farm management and crop production.
  2. In the second tier of pest management, biological and physical methods provide additional protection and need no justification. These practices build on and complement good cultural practices, but cannot compensate for poor cultural and management practices.
  3. The third and final tier, the last resort, may be using an allowed material if the first two tiers of response are ineffective and if the conditions for their use are described in the grower's Organic System Plan (OSP). Use of an input to control pests or parasites may be necessary under some circumstances, but it must be part of an integrated pest management plan, as described in the farm's OSP.

Identification and preventative management of pests are essential to organic production systems. Identification charts are available from many university Extension Web sites and publications. Many provide a useful list of important pests, their hosts, status (potential impact on crop production and quality), identification (adult, immature/larva, pupa, and eggs), life cycle, monitoring/thresholds, and management. 


Parasites, especially internal ones, are the major health concern for grazing animals. Not only are these animals susceptible to internal parasites, but the parasites are rapidly becoming resistant to all of the available anthelmintics (de-wormers), and few new de-wormers are being developed. Therefore, management must be the primary method for sustainable control of internal parasites.

If ample pasture is available and animals are not overstocked, a herd may have little difficulty with internal parasites. However, forcing animals to graze close to the ground and overcrowding stock will cause an increase in parasite load. Animals on highly stocked pastures will usually carry a heavier parasite load, due to the increased amount of fecal matter on the pasture. Reduce parasite problems by having a lower stock density and by rotating animals to different pastures. An understanding of how parasite infestations happen will help to avoid major problems.

All oral parasite infestations occur when the animal ingests the infective larval stage from contaminated pasture, hay, or living quarters. The larvae develop from eggs that were passed from an animal through its feces. If there are no adult worms in any animals in your herd, this infestation cannot occur. Even if larvae are present in the pasture, large animals are less likely than other ruminants to consume them, because they prefer to eat at eye-level, and the larvae do not climb up grass blades to eye level. This is one of several good reasons for managing pastures to prevent grazing them too short. Try to maintain a forage height above four inches, at minimum.

Symptoms of a parasite problem include weight loss, rough coat, depression, and anemia (evidenced by pale mucous membranes, especially in the lower eyelid or gums). Animals that are carrying a heavy parasite load will produce less and lag behind their herd mates. It is important to realize that heavily infected animals are "seeding" the pastures with parasite larvae, thus amplifying the problem over time by contaminating the environment. Also, there is a great deal of variation in individual animal resistance to parasites. Culling animals with severe parasite problems will decrease the herd's problems by reducing pasture contamination and by retaining and encouraging parasite-resistant genetics in the herd. For a complete parasite control program, see the ATTRA publication, Integrated Parasite Management for Livestock.

Flies and Other Insects

In confinement situations and pasture shade areas, implement fly control programs early in the season, before the fly population gets out of control. A sustainable approach is Integrated Pest Management (IPM). Parasitic wasps are a biological control for barn flies. These wasps lay their eggs in fly pupal cases, then wasp larvae kill the developing flies by feeding on them. Light traps, baited traps, and sticky tapes are physical controls for barn flies. Because moist manure, spilled feed, and damp bedding encourage fly populations, practicing good sanitation on a regular schedule is important, especially in confinement areas. Eliminate drainage problems that allow water to accumulate. For more information about controlling flies in the organic herd, see the University of Arkansas Cooperative Extension Service factsheet, Fly Control for Organic Dairies.

While there are many other components to insect and mite pest management, in recent years there has been a good deal of research on vegetation management to enhance natural biological control. Approaches to cover crop and vegetation management include:

  • resident vegetation that harbors beneficial arthropods (insects, mites, spiders);
  • strip management of cover crops to ensure the continuous presence of habitat for both beneficials and pests;
  • insectary mixes of plants attractive to beneficial arthropods; and
  • use of mulch from mowing to harbor generalist predators.

There is also increasing evidence that managing vegetation adjacent to economic crops (fence lines, roadsides, etc.) as habitat for beneficial insects has a positive impact on pest management. These areas often include native plants and shrubs that flower at different times of the year, providing sources of pollen and nectar for beneficial arthropods. See the ATTRA publication, Farmscaping to Enhance Biological Control.

Vertebrate Pest Management

Organic certification calls for an integrated approach to vertebrate pest management, including exclusion, trapping, repellents, scare devices, and protection or development of predator habitat.

Gophers and ground squirrels can be managed on organic farms through integrated strategies. Growers should not expect to eliminate these pests, but will do well to keep populations in check. Persistent year-round trapping is the primary strategy for most farmers, complemented by enhancing the habitat of key predators such as owls and hawks with nest boxes, perches, and appropriate vegetation.

Although explosive propane devices are effective against gophers and ground squirrels, at the present time, the NOP has taken the position that such explosive devices are not allowed, since propane is not on the National List for application to the soil. As always, check with your certifier for the status of this and other inputs.

Only two materials (sulfur dioxide for underground smoke bombs and Vitamin D3, or Cholecalciferol) are on the National List as rodenticides. These may be used only if they are documented in the Organic System Plan, used with care to avoid harming non-target animals, and only when other management practices are ineffective.

For further reading on vertebrate pest management, please see the ATTRA publications, Organic Integrated Vertebrate Management and Predator Control for Sustainable and Organic Livestock Production.

References and Citations


Published January 25, 2009

This is an eOrganic article and was reviewed for compliance with National Organic Program regulations by members of the eOrganic community. Always check with your organic certification agency before adopting new practices or using new materials. For more information, refer to eOrganic's articles on organic certification.