1. Dept. of Entomol. and 2. Dept. of Ag. Econ. & Rural Soc., The Pennsylvania State University, University Park, PA. 16802

3. Agron. Dept., University of Wisconsin, Madison, WI 53706

The primary management tactic for insect pests on alfalfa is the proper and timely application of insecticides. An assessment was conducted to determine the extent of their use on the nation’s alfalfa crop (both hay and seed production), the biologic and economic significance of this use, and the effect of their withdrawal on alfalfa production. Data presented in the surveys covered the period from 1988 to 1992 and represented 99.9% of the 25.6 million hay acres. Data for the alfalfa seed crop represented seven western states growing 168,000 acres of seed alfalfa.

Twenty one insects or insect complexes were identified as requiring pesticide application on alfalfa hay. On average, 25.4% of the U.S. alfalfa, or 6.5 million acres, received annual insecticide applications. When considering multiple applications in a season, the treated acreage rose to 10.6 million acres. Insecticides were applied to 50.9% of the acreage using ground application equipment with the remaining 47.0% and 2.1% being applied by aircraft and chemigation, respectively. Organophosphates were the most common insecticide applied (59.4% of acreage). Carbamates ranked second (32.1%) and pyrethroids (5.3%) third. All treatments accounted for approximately 6.1 million lb. of insecticide per year. Carbofuran was the single most used insecticide followed by chlorpyrifos and dimethoate. Early harvest, host plant resistance, and natural biological control were the most common nonchemical management alternatives. Average efficacy of the 10 most widely used insecticides ranged from 3.4 to 4.6 based on a 5 point scale with 5 rated excellent.

Fourteen insects were identified as pest problems on alfalfa seed acres. The most important insects were Lygus spp. Propargite (a sulfonate) ranked first in both acres treated and volume of insecticide applied to the alfalfa seed crop. Host plant resistance was the most common noninsecticide management practice.

The loss of alfalfa insecticides could have substantial negative impacts on farm-level profitability. Overall, the negative economic impacts would be most keenly felt in the western U.S. because of its large hay acreage and seed production. The North Central U.S. would also experience large negative economic impacts, mainly because this region has the greatest alfalfa hay acreage. Losses of at least $1 million would result from the banning of 12 insecticides. The greatest negative economic impact would result from the loss of carbofuran ($68.5 million), followed by dimethoate ($41.4 million) and methomyl ($33.7 million). As a class, the banning of organophosphates would result in a loss of $103.4 million. If all chemical insecticides were banned in alfalfa production, an annual loss of $331.9 million would result (if cultural practices cost $30/A). In this case, loss of insecticides would have a negative impact of $44/acre for hay production and $368/acre for seed production. A ban on an insecticide would reduce the options available to farmers, forcing the substitution of insecticides which are usually either more expensive, less effective, more difficult to use, or less adaptable to changing production conditions. The profitability of alfalfa production would be seriously affected by the banning of individual pesticides and possibly be eliminated as a crop alternative if all chemical pesticide options were to be banned.