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A Technical Guide for Wine Producers
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Degree day estimation as a warning tool for vine mealybug infestation in vineyards
Vaughn Walton, Department of Entomology and Centre for Agricultural Biodiversity
Key words: Degree days, Planococcus ficus, Warning tool, Pheromone trap monitoring, Physical monitoring
Heat accumulation is widely used by economic entomologists to predict the outbreak of pest populations. It is expressed in degree-days (°D), and is determined by the rate of development of the insect at different temperatures. Information resulting from the use of °D models can be used as additional inputs in a pest management system for a key pest such as Planococcus ficus (Signoret).
The number of degree days required for P. ficus to complete one generation was 235 °D. In many cases this number of °D coincided with the visible increase of P. ficus in vineyards. The number of °D for the development of P. ficus accumulated rapidly from early October in all areas. This was also the period during which P. ficus populations increased rapidly in trial sites. There further appeared to be an indirect qualitative relationship between bunch infestation and cumulative °D.
°D can be used as an additional tool for P. ficus management in vineyards. The completion of an estimated one P. ficus generation (235 °D) in a specific grape growing area should serve as a warning tool for pending P. ficus infestation. This benchmark (235 °D), together with monitoring with pheromone traps and physical monitoring should aid producers in the decision processes for timely P. ficus management.
Five grape growing areas were initially selected and cumulative degree days are calculated for each of these on a weekly basis. The nearing toward 235 °D should serve as an early warning sign to producers. It should be noted that this information is supplied on an experimental basis and not be used as a stand-alone method for P. ficus management. It should be stressed that this tool cannot be used as a stand-alone. Male vine mealybug pheromone trapping, and physical monitoring (as highlighted in the vine mealybug control protocol) should be done before control is planned.
The table for the seven weather stations in five viticultural areas will be available on the IPW website, www.ipw.co.za and updated on a weekly basis with cumulative degree days. When the value approaches 235°D a possible outbreak of the disease is indicated. Producers should use it in conjunction with monitoring data (pheromone traps and physical monitoring) to determine whether they should take action.
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