Gadenin日本語Get the appPear rust: bright orange spots and a juniper nearby
In mid to late summer, vivid orange or red-orange spots appear on the upper leaf surface, a quarter to half an inch (5-12 mm) across, with a darker center. Turn the leaf over in late summer and the matching patch underneath has swollen into a warty growth with fine bristly tubes standing out of it. Nothing else on a pear looks like this.
The fungus cannot complete its life cycle on pears alone. It spends the winter on juniper, where it makes swellings on the twigs that in wet spring weather turn into orange jelly-like horns and release spores onto pears up to several hundred yards away. Spores from pear then go back to juniper in autumn. Break the cycle by removing junipers within range, or by cutting out the galled juniper twigs each late winter before they swell.
A light infection costs a mature tree very little; the leaves work well enough to finish the crop. Heavy repeated attacks defoliate a young tree by late summer and weaken it. Rake up and remove fallen pear leaves, and thin the canopy so leaves dry quickly after rain. There is no useful garden treatment once the spots are out.
Pear midge: fruitlets that swell fast and turn black
The classic sign is a fruitlet that is noticeably larger and rounder than its neighbors a few weeks after petal fall, then blackens at the base and falls. Cut one open and you find a hollow, wet cavity with a dozen or more tiny white or cream maggots inside. On a bad year a tree can lose almost the entire crop this way and the grower blames frost.
The adult is a small dark fly that lays into flower buds just before they open. The larvae feed inside the developing fruitlet for a few weeks, then drop with it or leave it, burrow into the soil beneath the tree and stay there until the following spring. The infestation lives in your soil, and it builds year on year if the fallen fruitlets are left where they land.
Control is purely mechanical and it works. Pick off every swollen, deformed fruitlet you can see while it is still on the tree, and collect and destroy every one that has dropped, before the larvae get into the ground. Do not compost them. Cultivating the top inch or two of soil under the canopy in late winter exposes overwintering larvae. Two consecutive years of thorough picking usually breaks a bad population.
| Problem | What you see | When | What to do |
|---|---|---|---|
| Pear rust | Orange spots on leaves, bristly warts beneath | Mid to late summer | Remove nearby junipers or their galled twigs; clear fallen leaves |
| Pear midge | Fat black fruitlets full of maggots | Weeks after petal fall | Pick and destroy every affected fruitlet, on tree and ground |
| Pear psylla | Sticky honeydew, black sooty mold, curled shoots | Spring through summer | Wash off honeydew, encourage predators, avoid heavy nitrogen |
| Pear scab | Olive-brown blotches, then cracked, scabby fruit | Wet spring and summer | Prune for airflow, clear fallen leaves, cut out scabbed shoots |
| Fireblight | Shoots suddenly brown and dead, tips hooked over | Warm, wet weather at and after bloom | Cut out well below the damage, disinfect tools between cuts |
| Codling moth | Single tunnel to the core, crumbly frass at the eye | Midsummer onward | Pheromone traps at bloom, remove and destroy affected fruit |
| Pear leaf blister mite | Pink then black blisters in bands on leaves | Spring into summer | Pick off affected leaves early; a mature tree tolerates it |
Psylla, scab and fireblight
Pear psylla shows first as stickiness. The nymphs sit on shoot tips and leaf undersides producing honeydew, black sooty mold grows on it, and the tree ends the summer looking sooty and grimy with curled, stunted shoot tips. Heavy attacks weaken the tree and mark the fruit. Soft, sappy growth is what psylla wants, so easing off nitrogen and avoiding hard winter cutting reduces it; a wash of water on the worst shoots and a garden full of earwigs, ladybirds and lacewings does the rest.
Pear scab is the same family of trouble as apple scab and shows the same way: olive-brown velvety blotches on leaves, then dark corky patches on fruit that crack as it swells. It overwinters on fallen leaves and on scabby lesions on young shoots. Clear the leaf litter, cut out cracked and scabby twigs in winter, and prune to open the canopy so foliage dries fast.
Fireblight is the one that kills. In warm, wet weather at or just after bloom, a shoot wilts, turns brown or black as if scorched, and the tip curls over into a hook while the dead leaves stay attached. It moves down the branch fast. Cut out affected wood at least twelve inches (30 cm) below the visible edge of the damage, back into clean, healthy wood, and disinfect your blades between every cut. Burn or bin the prunings; never chip or compost them.
Working out which problem you have
Most misdiagnosis on pears is between three things that all end in fruit on the ground. Frost damage leaves a small fruitlet with a russet ring around the base and a dead brown center, but no maggots. Pear midge gives an oversized black fruitlet, hollow and crawling inside. Codling moth affects nearly full-sized fruit with a single tunnel to the core and crumbly brown frass at the eye or the entry hole. Cut the dropped fruit open; that decides it in seconds.
- Walk the tree weekly from bud burst Look at shoot tips, leaf undersides and the fruitlet clusters. Nearly every problem here is cheap to fix in the first week and expensive a month later. Five minutes a week is the whole program.
- Cut open anything that drops Do not sweep up windfalls without opening two or three. The inside tells you whether you are looking at a pest, a disease or simply the tree shedding its natural surplus in early summer.
- Clear underneath the tree in autumn Fallen leaves carry scab and rust into next season, and dropped fruitlets carry midge into the soil. Rake and remove rather than mulching the litter back in place.
- Keep a running note of first sightings Record the date you first see each problem, on which tree and how bad it got. Pests arrive at close to the same point in the season every year, so the previous year's first-sighting date tells you when to start looking and when treatment is still worth doing.
Not every mark is worth acting on. Rust on a handful of leaves, a few blister mite patches, or slight sooty mold on a mature tree cost you nothing. Reserve effort for midge, fireblight and codling moth, which take the crop or the tree.