Year: 1989
Type: book
Abstract: IntroductionWinter wheat yields in the Netherlands increased from approximately 4000 kg dry matter ha" 1 in 1945 to 8000 kg ha" 1 in 1980 (Rabbinge, 1986).This yield increase was the result of improved cultural methods which reduced the significance of yield-limiting factors such as shortages of water and nitrogen, the introduction of short-straw varieties with a higher harvest index and a longer grain-filling period and, finally, the improved control of growth-and yield-reducing factors.The latter are relatively more significant at high yield levels, due to the positive effect of 'good crops' on the increase rate of pests and diseases -mainly as a result of higher nitrogen levels in attacked tissue (e.g.White, 1984).Moreover, in 'good crops' most yield-limiting factors have already been eliminated.This resulted in a tendency to use insurance spraying, i.e. spraying without first establishing the presence of pests or diseases.Overuse of crop protection agents, however, reduces the net profit for a grower, increases environmental side effects and can stimulate secondary pests and diseases by killing their natural enemies.In the Netherlands, three aphid species occur in winter wheat: the grain aphid, Sitobion avenae, the rose grass aphid, Metopolophium dirhodum, and the bird cherry oat aphid, Rhopalosiphum padi.Usually, Sitobion avenae occurs in the highest numbers.Cereal aphids have been economically significant pests in winter wheat since the late sixties.Around that time, top dressings of nitrogen were introduced which prolonged the maturation period of the crop when cereal aphids cause the most damage.It was shown that a high nitrogen content of the crop accelerates aphid population growth by increasing fecundity and inhibiting wing formation (Vereijken, 1979).Because of their uneconomical turnover of food, aphids take up large amounts of phloem sap.Vereijken (1979) showed that yield losses are not only caused by the feeding on assimilates, but that other factors exist which adversely affect the crop physiology.These are: (1) honeydew, excreted by the aphid, covers the stomata. of the leaves and affects photosynthesis, and ( 2) toxins or growth regulators are injected with the saliva, and may influence the rate of leaf senescence.The latter is considered to be of little significance in the Dutch cereal aphid-winter wheat system.Relations between aphid density and damage have been developed, based on regression analysis of field observations (Entwistle & Dixon, 1987).Rabbinge et al. (1983) hypothesized that the yield level of the control treatment should be considered when calculating the damage relation.However, conducting new field experiments at various yield levels, under various intensities of pest attack,
Language: English
Subfield: Insect Science
Domain: Life Sciences
SDG: Zero hunger
Open Access status: green
OpenAlex ID: W1490723415