The species Aculus schlechtendali is commonly known as the apple rust mite and can be found in all regions of apple production in Canada.
Apple rust mite inserts its mouthparts into plant cells and sucks their liquid contents. This feeding produces a silvery cast to the leaf in the early stages and may result in the leaf rolling up. This type of damage severely disrupts photosynthesis and water intake, resulting in a decrease in fruit size and/or quality. The adult mite can be distinguished through its light tan color; however, they are extremely small and a hand held magnifying glass (of at least 20X) may be required in identification of this pest.
Optimal conditions for infestation
The development of the apple rust mite is more rapid under conditions of higher temperatures (<22°C) and dryness, to the extent that progression is increased by a factor of three, due to the short life cycle and rapid development of the mite.
Scouting should take place before the petals fall and continue through to early August. A hand held magnifying glass will be required and focus should be placed on the mid-vein-base of leaves. Inspect 10 leaves from 10 different trees in order to get a good diverse reading of the infestation. A quick estimate should be done on numbers due to their small size: when more than 200 mites are found on a leaf then immediate treatment should be considered.