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<br />APPENDIX A <br /> <br />PLANTING DENSITY AND WATER STATUS OF WINTER WHEAT <br />(TRITICUM AESTIVUM) AFFECT GREENBUG <br />(SCRIZAPRIS GRAMlNUM) DENSITY. <br /> <br />by <br /> <br />Brent M. Haglund, <br /> <br />Theodore Weaver, and <br /> <br />Asa Aradottier <br /> <br />Abstract <br /> <br />A greenhouse experiment in which winter wheat (Triticum aestivum) seed and <br />culm densities were the independent variables demonstrated a negative <br />relationship of plant and aphid densities. Culm densities were 4, 12, 24, and <br />48 per pot with each pot being watered daily to keep soil at field capa.city. <br />Greenbugs (Schizaphis graminum), a species of a.phid, inhabited, fed, and <br />reproduced on the wheat. These sap-feeding insects were as much as six times <br />more abundant on the 4 culms/pot treatment than the 48 culms/pot treatment. <br />Maximal insect densities were recorded at the two-three leaf stage of ~'heat and <br />declined to near zero on all treatments a month later. Plant osmotic pressure <br />was negatively affected by culm density yet was positively related, and was <br />perhaps controlling aphid density. These results do not exclude the <br />possibility that the most dense wheat plantings resulted in plant nutrient <br />deficiencies which were sensed [and avoided] by the insects. Support is <br />provided for the hypothesis that sap-feeding insects respond to plant <br />conditions and that water delivery and planting can be directly manipulated to <br />alter insect density. <br /> <br />Introduction <br /> <br />The greenbug aphid (Schizaphis graminum Rond.) is one of several <br />sap-feeding insects that are chronic pests of small grain crops (Starks et al., <br />1975). Greenbug feeding has several effects on the plants that may result in <br />lowered productivity, chlorosis, and death (Osborne, 1972). Farmers may have <br />several management choices, besides the use of expensive pesticides, to limit <br />greenbug damage (Starks et al., 1975). <br /> <br />Methods <br /> <br />Twenty plastic pots (150 rom dia) were filled with a soil mixture of 1: 1 <br />sand and Bozeman silt loam, and randomly assigned to four treatments of wheat <br />culm density; each was replicated five times. Wheat culm densities were 4, 12, <br />24, and 48 culms which were achieved by planting twice the number of seeds as <br />culms desired and cutting off the less vigorous seedlings. The potted plants <br />were placed randomly on the greenhouse bench on 19 January 1982 and surrounded <br />by other potted wheat plants to minimize edge effect problems. <br /> <br />55 <br /> <br />