Cherry Leaf Spot

A bottle in July will not put those gold, spotted leaves back on the tart cherry, because the infection on that leaf is already finished, so rake them tonight. Cherry leaf spot is the fungus Blumeriella jaapii. It waits out winter in last year’s fallen leaves, then shoots spores onto new foliage when spring stays wet long enough for the underside of the leaf to stay damp.

On tart cherry, especially Montmorency, the first useful sign is a small circular purple spot on the upper side of an older leaf in late May or June. Flip the leaf in damp weather and you should see a whitish-pink sticky fuzz in the center of that spot. The leaf then yellows, often gold, and drops, and a badly spotted Montmorency can be nearly bare by August. The fruit itself rarely carries the spots, but early leaf drop leaves cherries small, pale, and low in sugar. Holes in a cherry-laurel hedge without that gold drop are a different disease, and tan powder on a rotting cherry is brown rot, not this fungus.

Rake the yellow leaves. A July spray will not put them back

Once the leaf is gold and spotted, that tissue is already infected, so a bottle now cannot rewind it. The useful job this season is to cut next spring’s spore load, because the fungus spends winter in the fallen leaves under the tree. Rake those leaves before snow covers them, then destroy them, bury them, or run a hot compost. A cold pile of intact spotted leaves still shoots spores when it wets up at petal fall. If raking a big yard is too much, chop the litter with a mulching mower, because chopped tissue rots faster than whole leaves, and a leaf that is fully decayed before bud break is no longer where the fungus waits until spring.

Winter prune so air can move through the canopy and dry the foliage after rain, then keep lawn sprinklers off the leaves, because this fungus needs hours of wet underside to start a new spot. Take out crowding uprights. Do not pack a second tart cherry tight against the one you mean to keep, because splash carries the pink fuzz from leaf to leaf in the same wet week.

If last year the tree dropped most of its leaves before September, and you still want fruit that ripens, a labeled protectant has to start at petal fall, when the first true leaves are open, and keep going through wet weather. Most home products coat the surface rather than move inside the leaf, so rain washes them and you spray again on the label interval, shorter when the week stays wet. Skip the spray this year if the canopy is already yellow and dropping. One cover after harvest, if the label allows it on cherry, helps the tree hold leaves into September. Do not reach for an ornamental-only mix on fruit you will eat, because that label is not a food crop. Captan and myclobutanil are the usual home actives; alternate them if you spray more than once, because this fungus can stop responding to one chemistry. Read the days to harvest in your hand. Skip the brand aisle if the missing step is still last year’s leaves on the ground.

1. Confirm. Small circular purple spots on the upper leaf, then a whitish-pink sticky center on the underside in damp weather. The leaf yellows gold and may drop. Holes without that gold drop, or tan powder on fruit, are different diseases.
2. This year’s gold leaves are already infected, so skip a rescue spray. Pick the fruit that is sound, then rake.
3. Rake or mulch-mow the fallen leaves before snow. Destroy them, bury them, or hot-compost them. A cold intact pile still carries next spring.
4. Open the canopy in winter and keep overhead water off the leaves so they dry after rain.
5. Next spring, on a tree that defoliated last year, a labeled protectant from petal fall, when the first true leaves are open, through wet weather, and once after harvest if the label allows it. Read the cherry line and the days to harvest. Skip the bottle on a sweet cherry that only spots a little, and skip it on an ornamental if gold July leaves do not bother you.

Purple spots, then gold leaves, confirm cherry leaf spot

Look at an older leaf first, because that is where spring spores land once the blade has unfolded. The spot is small, circular, and purple on the upper surface. It grows to about a quarter inch and turns reddish-brown, and several spots can run together into a dead patch. Flip the leaf after a wet night: a whitish-pink sticky fuzz sits in the center of the spot on the underside. That fuzz is this season’s splash, so a second wave of spots follows every rainy week. After some weeks the dead center can dry and fall out, which gardeners call shot hole. Then the leaf goes gold and drops, often about a month after it first spotted. Petioles and fruit stems can pick up the same purple marks, and that is why a cherry can stay pale even when the skin looks clean.

The cycle is simple enough to use. Last year’s infected leaves on the ground make ascospores around petal fall. Those spores need a wet underside to infect. About ten to fifteen days later the new spot sheds the pink fuzz that splashes through the rest of a wet season. Cool, wet late springs in tart-cherry country are the usual years. Dry heat slows it. Sweet cherry can spot and still hold most of its leaves. A Montmorency in a wet June often does not.

Holes without the yellow drop are a different disease

Holes in a cherry, plum, peach, or cherry-laurel leaf, with the blade still green and hanging on, are often shot hole from another fungus, Wilsonomyces carpophilus, or from a bacterium such as Xanthomonas. Those holes share a nickname with this disease, which is why a July bottle aimed at “shot hole” so often misses. This fungus yellows the tart-cherry leaf and drops it. A cherry laurel that keeps its holed leaves through winter does not need a tart-cherry spray program. A fungus spray will not rewind bacterial holes. Do not spend the afternoon coating a hedge for a job that lives in last year’s tart-cherry litter.

Tan or gray powder on a firm brown cherry, then a wrinkled fruit that hangs or sits under the tree, is brown rot. That fungus ruins the crop. This one spots the leaf. Pulling mummies will not replace raking spotted leaves, and a leaf-spot spray will not rewind a peach that is already brown. See that disease if the fruit is the problem.

A hard black spindle on plum or cherry wood is black knot. Cut that in late winter. It is not a leaf spot. White powder on new shoots in hot, dry spells is powdery mildew, a different fungus. A young shoot that wilts, blackens, and bends over like a shepherd’s crook, with leaves that cling as if scorched, is fire blight. That is a bacterium. It can kill a limb. This fungus spots a leaf. Do not run a bloom streptomycin program here. A leaf that yellows with no purple spots and no pink underside is often hunger or wet feet, not this spray.

One bare August rarely kills the tree

Cherry leaf spot is not a one-year death sentence even when a Montmorency is bare by August. Live with an ornamental if the ugly month does not bother you, water it through dry spells so the wood does not go into winter weak, and keep raking so the next year is not worse. Several years of early leaf drop do cut next year’s bloom, leave the fruit small and pale, and open the door to winter injury, so a tart cherry that yellows every wet June is a candidate for petal-fall covers if you want fruit you will actually pit.

Sweet cherry is usually milder. It can spot and still hold most of its canopy, so many backyard sweets never need the bottle if you rake. Montmorency is the name garden centers stock that takes this fungus hardest. Northstar and Meteor are the tart names more often listed as holding leaves better. Resistant is not a promise against every wet June, and a spotted neighbor still sheds spores onto your new tree, so sanitation still matters. If you keep a susceptible favorite for pie cherries, plan on petal-fall covers in wet springs rather than hoping July will be kind.

Related reading

• Brown rot — tan powder on fruit and a wrinkled mummy, not this leaf spot.
• Black knot — a hard black swelling on plum or cherry wood, not a leaf spot.
• Powdery mildew — white film on new shoots in dry heat, not wet-weather purple spots.
• Fire blight — a blackened shepherd’s-crook shoot, not a gold leaf.