In recent decades there has been an increasing use of Integrated Pest Management (IPM) in weed control. How may we define IPM? IPM is a pest control program that employs a combination of techniques to reduce pest populations to economically acceptable levels. In this definition the term pest has a very broad meaning. It can refer to insect pests, weed pests, disease problems, or even animal pests.

With regard to weed control in forages, one of the main motivations for using IPM has been societal pressure to reduce or even eliminate the use of chemical methods of weed control, i.e. herbicides. A number of major concerns are expressed by environmentalists and the public at large with regard to chemical weed control. These include potential contamination of ground water supplies, potential human health hazards from chemical residues on food, and potential toxicity to wildlife that may graze cultivated forages.

How is the concept of IPM applied in controlling weeds in forages? First, a forage producer should carefully examine a pasture, forage crop, or range area to determine whether or not the degree of weed infestation is serious enough to require human intervention. For example, a pasture does not need to be a monoculture, that is, completely one species. In cash crops such as wheat or corn, a monoculture may be dictated by the market demand. However, a pasture may actually be more productive with several species present. In addition, some weeds may be reasonably nutritious to livestock. As long as a weed is not eliminating the main forage crop and is not poisonous to livestock, it may be acceptable to tolerate a certain level of the weed. Finally, the forage producer must balance the economic loss due to weeds against the cost of controlling the weeds. Thus, IPM practitioners use the term economic threshold.

Economic threshold, in terms of weed control, may be defined as the point at which economic damage to a forage crop is about equal to the cost of controlling the weed. In practice this means that weed control measures would not be used by the producer until this economic threshold is exceeded. For example, suppose having significant weeds present in a hay crop lowers the profit margin by $20 / ton. As long as effective weed control costs the producer less than $20 / ton, it may be profitable to implement weed control measures in this crop.

Applying the concept of economic threshold to a real world situation requires an understanding of weed ecology as well as the true economic value of the forage crop. In the case where a new, highly competitive weed (e.g. a noxious weed such as leafy spurge) invades a forage stand, the economic threshold is reached immediately. In other words, this weed must not be allowed to reproduce because once established it will be extremely expensive to control in future years. When dealing with weeds that are not aggressively spreading, are not poisonous, and are reasonably nutritious to livestock, a higher density of weeds may be tolerated before any control measure is implemented. In summary, the decision of when to treat weeds based on economic threshold requires balancing the potential harm of the weed (e.g. replacing desirable forage, poisonous to livestock) with the potential benefits (e.g. higher profits, better animal performance) of control. An inexperienced forage producer may do well to consult with an IPM expert.



IPM Links

Agro Engineering
Iowa State University IPM
Meister Pro
Round Up
USDA Grain Marketing and Production Research Center
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