A simple forecasting model for Septoria spp. in winter wheat was developed based on historical data (1980–89) including precipitation, growth stage, disease severity and yield response to fungicide treatments. The number of days with precipitation ≥ 1 mm, calculated during a 30‐day period starting at the beginning of stem elongation (GS 32), correlated well with attacks of Septoria spp. later in the season and with the yield response in trials with fungicide treatments. Seven or 8 days with rainfall ≥ 1 mm was suggested as a threshold for Septoria treatment. Model development and possible further improvements are discussed.
Pesticides not reaching the intended target may have negative effects on the environment and the ®eld ecosystem. To estimate the potential ground water pollution and risk for soil-dwelling organisms it is necessary to estimate the amount of pesticide reaching the soil in different spraying situations. Literature shows that ground deposition may vary even within equal growth stages due to variations in canopy density. This paper discusses the feasibility of estimating the ground deposition of pesticides from canopy density in cereal ®elds. Spray experiments were carried out in wheat and barley with¯at-fan nozzles of two sizes. Differences of ground deposition between the two nozzle sizes were insigni®cant. Adding surfactant to the spray solution signi®cantly reduced the soil deposition in barley and in wheat cv Sleipner but not in cv Haven. A signi®cant effect of Leaf Area Index (LAI) on ground deposition was obtained. A simple exponential model based on the LAI with an extinction coef®cient of 0.48±0.50 may for many occasions satisfactorily describe the soil deposition of pesticides in cereals. Using non-destructive LAI-measurements combined with the deposition model may be useful in pesticide risk assessment on ®eld, farm and larger regional scale and is optimising the application rate in site-speci®c farming.
The decision in 1986, on an action plan to reduce pesticide use in Denmark by 50% led to increased research on the potential of reducing dosages. A decision support system (PC‐Plant Protection), developed by The Danish Institute for Plant and Soil Science, implements this research. It combines a detailed use of threshold values to support decisions on treatment need, choice of pesticides and the appropriate dosage for actual problems in cereals. The pest and disease module within the system has been available commercially since 1993 and up to the end of April 1995, 2000 licences have been issued for its use at agricultural schools and by advisers and farmers. The recommendation model for pest and disease control has been validated in field trials since 1990. The validation has shown that the model is able to provide recommendations for the control of pests and diseases to a satisfactory level, without affecting farmers' gross margins. The model was able to adjust pesticide use to large yearly variations and the average amount of pesticides in the plots treated according to the model was well below that in the reference plots and in the commonly used strategies in Denmark.
Fungicide inputs in cereals have to be reduced, in order to sustain gross margins and reduce environmental side effects. This can be achieved by using fungicide programmes in which doses and timing of fungicides are influenced by detailed knowledge on inherent properties of the fungicides, cultivar resistance and epidemic development of diseases in relation to crop stage and weather conditions. In 1994 and 1995, field trials were carried out in winter wheat in which strategies using full and reduced rates at fixed growth stages were compared with the computerized weather‐based decision support systems PC Plant Protection and PRO_PLANT. A further strategy was included in which timing and dosage of fungicides was based on expert judgement of the interactions of growth stage, disease pressure, weather conditions and cultivar resistance. Effective control of septoria diseases, brown rust and powdery mildew was achieved by all programmes. There was no programme that always resulted in the highest yield and gross margin.
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