Improved management of grapevine powdery mildew

Abstract

Trials to improve powdery mildew management by reducing primary infection from diseased shoots produced from over-wintered infected buds

Summary

Powdery mildew is a widespread and persistent disease for which the industry has been seeking more effective and lower cost control measures. This research, conducted at the Department of Primary Industries at Irymple (Vic.), was assisted with input from Primary Industries and Resources at Loxton (SA). It was aimed at improving management by reducing primary infection from over-wintered infected buds. Work involved evaluation of inoculums and bud inoculation techniques to assist studies of the fungal disease, studies of susceptibility of buds, evaluation of fungicide treatment programs, and tracking of disease development after inoculation. Colonies of surface and internal infections in plant tissue were studied in controlled glasshouse conditions, using microscopy and histology. Importantly, a greater understanding of the nature of bud infection leading to flag shoot formation and finding ways of preventing it, were the main interests. Results have been new tactics for improving management of powdery mildew by reducing primary infection from diseased flag shoots. It was found that normal foliage spray formulations could be effective in controlling bud infections if timing was right and pruning method was taken into account. Spray programs aligned to prevent bud infection reduced initial spore loads and the cost of control. Findings included a relationship between flag shoot numbers and disease severity on the surface of buds in the previous season, noted that hot dry weather in spring appeared to reduce bud infection and flag short formation and confirmed there could be varietal differences (e.g. Verdelho has a high propensity to produce flag shoots). Field trials and experience have shown that attention to reducing bud infection and carry-over can mean a big reduction in disease load and the need for repeated sprays after three years. The benefit to the industry is having a means of reducing powdery mildew infections and the annual spraying bill.