Grape leaf rust mite (Calepitrimerus vitis) is a pest specific to grapevines and severe infestations can cause economic losses – generally more problematic in later bud bursting varieties. The most widely recognised and distinct symptom of grape leaf rust mite is ‘bronzing’ (a reddish-brown tinge) on the upper surface of vine leaves in late summer and early autumn.
Rust mite can also inflict damage in early spring through feeding within bursting buds and at the base of young shoots. The damage causes stunted growth, crinkling of young leaves and small (<1mm) pale spots on the leaves. Pre-budburst chemical control is required for the following season when over 50 per cent of vine leaves are ‘bronzed’ on more than 50 per cent of the vineyard.
Applying sulphur at budburst or woolly bud will help control mites early in the season. If targeting mites, apply a high rate of sulphur at high water rates to ensure good coverage into bark crevices.
However, if trying to control powdery then the first spray is best applied at the time the first leaf is separated from the shoot tip or an average growth stage of EL 7.
If sprays are applied too early there will be not enough leaf area for the chemical to adhere to, and therefore powdery mildew control will be limited.