Pear psylla

About

A tiny insect, about a tenth of an inch long, that looks like a miniature cicada with clear, roof-like wings. USU calls it the most serious insect pest of pear in the United States.

Spotting it

Damage

Nymphs drip so much honeydew that trees turn sticky and black with sooty mold, and fruit gets dark russet marks. Heavy feeding ('psylla shock') makes leaves blacken and drop and shoots stunt, and pear psylla spreads pear decline, a disease that can kill trees.

How to find it early

Look for sticky leaves, sooty mold and tiny, soft, creamy-yellow nymphs on new growth. Penn State uses half a nymph per leaf early in the season as the action level.

When

Late winter through fall.

Life cycle

Adults spend winter in bark cracks or ground litter and start laying eggs on fruit spurs in late winter once temperatures pass about 40°F. There are about four generations a year in Pennsylvania and five in California.

What to do, gentlest first

Start at the top. Sprays are a last step; always read and follow the product label.

1. Go easy on nitrogen and summer pruning Prevent

   Lush growth feeds psylla. Minimize nitrogen fertilizer, avoid summer pruning, and remove water sprouts in late June and July (USU, Penn State). Keep trees watered.

2. Protect natural enemies Natural enemies

   Minute pirate bugs, lacewings and parasitic wasps attack psylla (USU); broad-spectrum sprays kill them.

3. Dormant horticultural oil Organic spray

   Spray oil at least once in the dormant season, and again before bloom if damage was heavy (UC IPM). Penn State says early oil sprays cut egg-laying by over 95% for about five weeks.

   Oil can stun or kill bees it hits (PNW 591); do not spray during bloom. Follow the label.

4. Use sparingly Conventional spray

   Pear psylla quickly becomes resistant to insecticides (USU), so rely on oil and natural enemies first.

   UC IPM mentions an imidacloprid soil drench only after flowering is completely over; imidacloprid is highly toxic to bees and shows up in pollen and nectar (PNW 591), so avoid it on fruit trees unless the label names pears. Follow the label and pre-harvest interval.

Garden friends that go after it

Crab spiders (flower spiders), Jumping spiders, Snakeflies

Protect these helpers: skip broad sprays when they're around.

Plants it goes after

Pear

Pressure by region

UC IPM says European pears are hit harder than Asian pears. Sourced for Pennsylvania, Utah and California; the Pacific Northwest rating, and the low ratings elsewhere, are estimates.

Ratings come from extension sources where available; some are estimates, as noted above.