Economic damage and preliminary economic thresholds for mealybugs ( Pseudococcus longispinus T‐T.) in Auckland vineyards

Mealybugs are considered to be pests in Auckland vineyards because they may (i) debilitate the vine, (ii) affect the taste of the resulting wine, (iii) exacerbate the problem of Botrytis cinerea rot, or (iv) lead to the growth of sooty mould on the vine which may in turn (a) affect photosynthesis, (b) affect fermentation, or (c) taint the wine. These possibilities were examined and only sooty mould was found to cause economic damage. The population level (economic injury level) of mealybug required to cause sooty mould formation was found to be about 20 mealybugs of all stages/bunch at harvest. Economic thresholds of less than 0.8 and 34 mealybugs/leaf respectively in the first and second generations resulted in economic injury. Sampling for mealybugs in vineyards to determine economic thresholds is considered too time‐consuming for practical application. However, the development of the mealybug population can be related to vine development, with the first generation beginning at bud‐burst and the second during December before bunch closure. Because of the very low mealybug numbers initially required to lead to economic loss, it is recommended that insecticides be applied at bud‐burst and before Christmas if any mealybugs are found in the vineyard during the previous harvest or pruning.