Effect of Non-crop Vegetation on Insect Infestations and IPM in Reduced-Tillage Corn and Sorghum Production Systems in Low and High Technology Agriculture

Nan-crop vegetation in conservation tillage systems can influence the abundance and importance of phytophagous insects and plant diseases Honin contrasting ways in low and high technology agriculture. In duras, non-crop vegetation in fields of interplanted corn and sorghum may either increase or reduce damage to the crops by insect pests, depending on larval host food preferences, and the timing and efficacy of weed removal procedures. A complex of four lepidopterous species attacks broad leaf weeds and grasses in subsistence production fields prior to crop planting. The larvae move from this vegetation onto the seedling corn and sorghum and damage or destroy the crops. Weed removal from production fields is recommended to lower insect pest abundance and reduce damage to the crops. Corn production in the high input crop production systems in the southeastern United States can heused to illustrate the divergent roles of weeds in influencing insect vector abundance and incidence of two insect-borne diseases, namely maize dwarf mosaic and corn stunt. Johnsongrass, an early season host for maize dwarf mosaic virus and host for aphid vectors, is responsible, in part, for aphid population buildup during early spring and is a source of innoculum to the aphid vectors, particularly the corn leaf aphid. Removal of Johnsongrass would eliminate this host for aphids and the maize dwarf mosaic virus. Conversely, the incidence of corn stunt disease may he correlated directly with amounts of non-crop vegetation in production fields. Conservation tillage methods may help reduce lossesto corn stunt disease by allowing weeds to develop in the field. The black faced leafhopper vectors prefer to feed on the non-crop grasses and remain on these weeds, feed less on corn and thus the incidence of corn stunt disease is lower in the field. Weedy corn fields have the highest number of leafhopper vectors, hut a lower incidence of corn stunt disease than weed-free fields. 1Publication No. S7203. Mississippi Agricultural and Forestry Experi­ ment Station, Dept. of Entomol. , Drawer EM, Mississippi State, MS 39162. Corresponding author Introduction Eighty-two percent of the world’s population is found in developing countries. These countries occupy 62% of the world’s land area. The needs of agriculture in developing nations can differ greatly when compared with developed nations, and the solutions to many of the agricultural prob­ lems in the former, must of necessity, be different from those of the latter (Mellor, 1988). In developed nations, agricultu­ ral production relies heavily on inputs of fuel, fertilizer, insecticides, fungicides, nematicides, and herbicides. Crop varieties are developed and chosen for optimal yield under these high-input conditions. Agriculture in developing na­ tions has evolved differently, and remains more vulnerable to climatic and pest uncertainties. Here, human and animal power have not been replaced by fossil fuels (Oram, 1988). and agricultural chemicals are not in common use. A major goal of high technology, mechanized agriculture is to optimize return on investment, or stated another way, the goal is to derive the maximum dollar return per dollar spent on production. The farmer’s profit depends upon inputs, yield, and the value of his crop at the time of harvest or some future date after storage. Laws of supply and demand, global grain supplies, and governmental programs influence directly the value of the high technology farmer’s commodi­ ty. The low technology farmer in a developing nation often faces different circumstances. His crop will usually be con­ sumed on farm, and a portion may be sold for capital. Choice