Control of silverleaf nightshade (Solanum elaeagnifolium) increases the grain yields of wheat

Abstract

The effect of controlling silverleaf nightshade with 2,4-D or glyphosate for 4 consecutive years on the yield of wheat was determined in a field experiment in southern New South Wales. Silverleaf nightshade was either controlled throughout summer with 2,4-D or glyphosate, or treated once with 2,4-D each February from 1979 to 1982. After 4 years, the initial density of silverleaf nightshade increased from 8 to 17 shootsJm2 in both the untreated controls and the plots treated with 2,4-D in February. Treatment throughout each summer with 2,4-D retarded this increase to 11.4 shootslm2, and treatment with glyphosate reduced the population to 1.6 shoots/m2. The grain yield of wheat was not affected by prior control of silverleaf nightshade in 1979 or 1980, but in 1981-82 there was a significant (P<0.05) yield increase from some herbicide treatments, compared with the unsprayed controls. In 1981, repeated application of glyphosate or 2,4-D increased yield by 14 and 9%, while the application of 2,4-D in February increased yield by 5%. In 1982, a drought year, the responses were much greater, with corresponding yield increases of 69, 49 and 17% from these treatments.