How to Manage Pear Blister Mite

If your new pear tree leaves have small yellow to reddish-colored pointed blisters on them and are maybe even showing some curling (from blister damage), you may have a Pear Leaf Blister mite infestation. Understanding their life cycle will help you eliminate the mites from your tree. Pear Leaf Blister mite is not usually considered a problem for established pear trees, but they can have an impact on newly planted trees or drought-stressed trees.

Pear Leaf Blister mite is a very small sausage-shaped mite, a 10x -30x hand magnifying lens is needed to see them. They overwinter under the outer bud scales of the buds that set during the fall. In spring as the first leaves swell within the bud the mites move from their protected overwintering site to the new leaves, feeding and depositing eggs, when blisters form from their feeding they move inside, all before the leaves emerge. The mites will remain inside the football-shaped blister they create, feeding and depositing eggs, until the blister becomes crowded. To move to a new location they exit their blister, move toward the tip of the shoot or branch their leaf is on, and find a new unoccupied spot to burrow in and start a new blister (home).

The amount of time between migration waves is impacted by temperature. During cool spring temperatures, the life cycle from egg to adult takes 20-30 days, during the warmer summer months the life cycle may only need 10 days. The warmer the average air temperature the faster they complete their life cycle within the blister and migrate again. The mites can only be impacted by control sprays when they are outside of their blisters, inside the blisters they are protected from predators and sprays.

There are a couple of control options. Remove any new leaves that you can see are infested with Pear Leaf Blister mites except the terminal leaf, seal them in a plastic bag, and discard, or burn them. Do not put them in your compost pile. If there are only a couple of blisters on a leaf you can leave it long enough for more leaves to emerge and contribute to photosynthesis, or even cut the portion with the blisters off (if it is toward the tip of the leaf). Continue to check for leaves to remove every day or two, or as often as new leaves are emerging. There will be a limited number of mites in a bud, so at some point new leaves will not be infested.

Temperatures are also usually cool enough in the spring that the first migration of the mites from the original leaves to a new one is often several weeks after the first leaves emerge. If the temperature has warmed, and you haven’t been able to remove all of the infested leaves yet, and there is a possibility of migrating occurring, you can apply a spray of summer-weight horticultural oil, or neem oil (do not use dormant season oil, it will damage the leaves). 2-3 applications might be needed, 7-10 days apart. Follow label instructions and do not apply the spray when temperatures may be higher than 90 degrees F, or the air is very humid, at the time of spray or for three days afterward. You may also continue to monitor and remove infested leaves if new blisters appear, so long as there are plenty of healthy leaves left on the tree to keep it growing and establishing.

The most effective time to apply sprays is in the fall (this is the correct time to use a dormant season oil), just after leaf drop, or in late winter, just as the buds are beginning to swell. Target the buds with the spray.