Modeling phytophagous mirid nymphs in cool-climate vineyards

In temperate regions, mirids may be occasional pests of vineyards where risk-averse growers use control measures. In that context, an optimal sampling scheme would allow determination of risk at minimal cost. A model driven by the accumulation of degree-days (DD) was developed to predict cumulative total captures of mirid nymphs (mainly the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois)) at 5%, 50%, and 95%. The model was based on 23 data sets collected over 4 years in three vineyards in southern Quebec. Lower and optimum temperatures for development were set at 10 o and 32°C, based on experimental results and previous studies. Cumulative total captures at 5%, 50%, and 95% levels occurred, respectively, at 229, 331, and 479 DD for the first generation and 630, 806, and 1000 DD for the second generation. Paired t- tests and the forecasting efficiencies confirmed the reliability of the predictive model. The model indicated that monitoring for mirid nymphs of cool-climate in vineyards should be initiated at 200 and 500 DD calculated from 1 March for the first and second generations, respectively. Using the same lower and optimum temperatures for the development of mirids, another degree-day model was developed to predict grapevine phenological stages in relation to the modified Eichhorn-Lorenz system. Superimposing the mirid model over the grapevine model allows relating mirid total captures to grapevine phenological stages, and thus optimizing resources to monitor mirid populations in cool-climate vineyards.