NITROGEN-FERTILIZER MANAGEMENT AND GRAIN-YIELD LOSS TO RUSSIAN WHEAT APHIDS

Laboratory research has indicated that grain yield loss to Russian whe at aphids (Diuraphis noxia Mordvilko) in wheat (Triticum aestivum L.) can be reduced by increased levels of nitrogen fertilizer. Field appli cation of nitrogen fertilizer, therefore, might be a useful strategy f or limiting grain yield loss caused by Russian wheat aphids. To test t his hypothesis, a field experiment with nitrogen fertilizer as main pl ot treatments and Russian wheat aphid infestation as subplot treatment s was conducted. Soil tests from an established winter wheat field in early spring.indicated that 78 kg ha-1 nitrogen was needed to attain a potential grain yield of 4800 kg ha-1. Nitrogen (liquid urea-ammonium nitrate) was then sprayed onto plants at rates of 0, 39, or 78 kg ha- 1. Plants were infested with Russian wheat aphids for a period of 17 d ays. Plants given N fertilizer had increased plant dry weight, filler number, leaf area, leaf chlorophyll content, and grain yield compared with plants given no N ferfilizer. Russian wheat aphid infestation red uced grain yield approximately 31 percent. A lack of significant inter action between nitrogen fertilizer treatment and Russian wheat aphid i nfestation suggests that aphid infestation affected grain yield simila rly for all fertilizer treatments studied. These results indicate that application of nitrogen fertilizer to winter wheat improves grain yie ld performance independently of the effects of Russian wheat aphid inf estation.