Grape problem

Asked May 15, 2020, 6:34 PM EDT

Leaves have lots of bumps and underneath are white and powdery.

Marion County Oregon

1 Response

Thank you for the images. The "bubbling"of the leaves is not a disease. It's caused by very tiny grape erineum mites,

The mite feeding causes the upper leaf surface to be blistered, whereas the lower leaf surface of the blister appears hairy and white, resembling fungal growth. The white "fuzz" is actually enlarged leaf hairs caused by the mites' feeding. Later in the season, the white will change to pale brown then, finally, a dark brown.

These mites are far smaller than the spider mites you may be familiar with; they are microscopic.

Fortunately, erineum mites don't affect the vine's health nor fruit set and development.

Management for home use is as follows:
- Dormant-season oils and insecticides which are used for other pests in the fall; also
- Sulfur applications which have been used for powdery mildew.

It's challenging to eradicate grape erineum mites, so it's a good thing they don't negatively affect the vine nor fruit production.