Leaf discolouration caused by apple rust mites

 Apple leaves can tolerate very high populations of rust mites before leaf damage occurs. Whereas European red mite and twospotted spider mite are visible to the naked eye, rust mites are extremely small. Damage by these mites can be confirmed by examination of the leaves under a microscope or using a high power hand lens (20x or better). Damage is accompanied by extremely high number of the mites.

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