Simulation of damage in winter wheat caused by the grain aphid Sitobion avenae. 3. Calculation of damage at various attainable yield levels

Abstract

A dynamic, process-based simulation model is used to evaluate the effect of injury by Sitobion avenae F. on yield of winter wheat at a range of attainable yield levels. The attainable yield is defined as the yield in the absence of pests and diseases, at the prevailing temperature and radiation and the available amount of soil nitrogen. Water limitation is not taken into account. Only the period from flowering to ripeness is considered. Aphid infestation intensity is expressed in aphid-days, the integral of aphid density (tiller-1 ) over time (day). The calculations show that damage per aphid-day decreases from flowering to ripeness because damage caused by honeydew decreases with advancing crop development stage while damage caused by aphid feeding is about constant. Damage per aphid-day during a particular period of crop development increases in a nearly linear fashion with the attainable yield level. At attainable yield levels over approximately 9000 kg ha -I and until crop development stage early milky ripe (DC 73), however, damage per aphid-day increases at a higher rate with the attainable yield level as compared to lower yield levels. The crop-physiological causes are discussed.Regression models are constructed that relate simulated aphid damage both during various periods of crop development and averaged over the entire post-anthesis phase, to the simulated attainable yield level. The accuracy of these simulation-based regression models and five published models of damage in winter wheat caused by S. avenae is evaluated using 21 data sets, obtained in experiments carried out between 1973 and 1984 in the Netherlands. Attention is focussed on two aspects of model accuracy: the agreement between predicted and measured damage and the size of the error in model predictions. In both aspects the simulation-based regression models are as good as the best published empirical models.

Simulation of damage in winter wheat caused by the grain aphid Sitobion avenae. 2. Construction and evaluation of a simulation model

“…In practice only low aphid densities are tolerable due to the low costs of chemical control so that errors in the estimation of weather-dependent honeydew damage will remain below the level of detectability. An analysis of the accuracy of the damage model when used for the purpose of decision support is presented elsewhere (Rossing, 1991). If priority is given to the aphids as in hypotheses II and IV, the model becomes: fa = min (da, ftot) fg = max lftot -da, 0)…”

Patterns and Management of Crop Multiple Pathosystems

“…The damage function may involve the yield pertaining to a given production situation as an explanatory variable (the attainable yield; Rabbinge and De Wit, 1989). As is the case with the damage caused by single harmful agents (see, e.g., Rossing, 1991, for the grain aphid on wheat, and Rabbinge et al, 1985, for powdery mildew in wheat), the amount of damage caused by a multiple pathosystem may depend on the level of attainable yield. This has been exemplified in the case of the multiple pathosystem of groundnut in Coˆte d'Ivoire (Savary and Zadoks, 1992b), and in the more complex and diverse multiple pathosystem of lowland rice in Asia (Savary et al, 2000b).…”

Systems approaches in epidemiology and plant disease management

“…Studies of damage relations from a systems point of view, therefore, inclulk experimental work to quantify effects of different pest intensities on whole-plant processes. In EPIPRE, damage relations derived from a wheat growth model into which uptake of assimilates by aphids and decreased leaf photosynthesis by honeydew was introduced, were as accurate as empirical damage relations derived from 15 years of field data on more than 20 locations (Rossing, 1991 ). Due to the mechanistic nature of the model and the inclusion of the effect of nitrogen shortage on growth and development, assessments of damage at lower attainable levels of crop production could be made.…”