Brown Rot

Pull every mummy off the peach tonight, and pick up the brown fruit on the ground, because those wrinkled fruits are next spring's spores. A labeled spray will not rewind a peach that already has tan powder on the skin. Thin so the fruit do not touch, and open the canopy so a wet morning dries before the fungus spreads from peach to peach.

People still say brown rot, then Monilinia fructicola. On peach, nectarine, plum, cherry, and apricot, a firm brown spot spreads fast in warm wet weather and throws a tan or gray powder. The fruit dries into a mummy that hangs or drops. Blossoms that collapse and stay stuck with a gum drop are the same fungus, not frost. The tree usually lives, but the crop does not.

Pull every mummy. A spray will not rewind that fruit

The fungus spends the winter in wrinkled fruit left hanging in the peach, and in fruit that dropped and sat under the canopy, so the first job is to take that fruit away. Pick every mummy off the tree. Pick up every brown peach, plum, or cherry on the ground. Bag it, bury it at least a foot deep, or put it in the trash. A cold backyard pile will not finish live fruit, because the fungus can still throw spores in spring. Municipal hot compost is a different leftover.

Then prune the cankered twigs, because a sunken, gummy patch keeps the fungus in the wood. Cut four to six inches below the dead bark on a dry day, and wipe the blades with rubbing alcohol between cuts so you do not walk the spores down the row. Do not wait until winter to hunt those twigs if you can still see which ones blighted after bloom, because by dormancy they are harder to tell from ordinary dead wood.

Thin so neighboring fruit will not touch when they swell, and prune to open the center, because wet fruit that sits against wet fruit is how a whole cluster goes in two or three days. Keep birds and chewing insects off the skin if you can, because a wound is an open door even on green fruit that would otherwise shrug this. Harvest as soon as the peach colors, handle it gently, and cool it, because a bruise in a warm bowl finishes the job the tree started.

A labeled spray protects blossoms and still-sound fruit. It will not rewind a peach that is already brown. If last year was bad, cover the flowers from pink bud through bloom with a product labeled for brown rot on that tree, then again in the two to three weeks before harvest if the forecast stays wet. Captan, myclobutanil, and propiconazole are the usual home actives. Read the days-to-harvest number in your hand. Do not run the sterol sprays as every pass. Do not put copper on after bloom. Skip the brand aisle if the missing step is still the mummies in the tree. Sulfur is only a light help, and it is a poor bloom spray.

1. Confirm. Tan or gray powder on a firm brown spot, or a wrinkled fruit still hanging. Stuck brown blossoms with gum are the same leftover, not frost.
2. Pull every mummy and every brown drop. Trash or bury deep. Do not leave them in a cold home pile.
3. Prune cankered twigs four to six inches below the gum, on a dry day, and open the canopy so fruit can dry.
4. Thin so ripe fruit will not touch. A labeled bloom and preharvest spray is last, and only if you will cover the tree. It will not rewind fruit that is already brown.

The tree lives. Next year's peaches do not wait on a mummy

Brown rot is a crop disease, not a take-down of the trunk. Wisconsin and home-garden clinics say the same thing: the peach usually lives, even after a year when almost every fruit went brown. Girdled twigs die, and the leaves beyond that canker stay attached and dull, but the scaffold is still there. You do not replace the tree because one wet July emptied the basket.

The fruit already showing tan powder is finished. There is no cure for that peach. Pull it so it stops dusting the ones that are still sound. Next year's bloom gets its spores from this year's mummies and from those cankered twigs, so the winter cleanup is the next crop, not a ritual. A young peach that is shaded, unthinned, and overhead-watered will do this again the first wet week near harvest. Open the canopy and keep the ground clean, because that is what changes the next basket.

Tan powder on a firm brown spot, then a wrinkled mummy

On ripening fruit the first mark is a small, firm, circular brown spot. In warm wet weather it can swallow the peach in two or three days, and the skin throws a tan or gray powder that looks dusty, not like a loose gray beard. Slice it. The flesh is brown, fairly dry, and firm, not a watery collapse. Then the fruit shrivels, turns brown to black, and either drops or hangs as a mummy into winter. That hanging fruit confirms it. It is not a late snack you forgot.

The same fungus starts at bloom. Flowers brown and collapse, and they stay stuck to the spur with a sticky gum drop at the base, because the fungus has already walked into the twig. Frost-killed blossoms fall. During wet spells you may see the same tan or gray tufts on those dead flowers and on the sunken canker. Green fruit usually needs a wound from hail, a bird, or an insect. Once the peach starts to color, it needs only a wet hour or two. At about 70°F, three hours of wet blossom is enough. At 45°F it takes longer, about six hours.

Gray fluff is gray mold. A leathery citrus is not this fungus

Gray mold, also called Botrytis, can rot a ripening peach too, so the fork is the powder and what happens to the fruit. Gray mold is lighter and fluffier. That fruit usually drops and does not hang as a mummy into the next bloom. If that is the leftover you have, see gray mold. Do not run a gray-mold greenhouse calendar here. After harvest, a watery peach with white whiskers and tiny black pinheads is Rhizopus. Cool the bowl below 40°F. That is storage leftover, not a hanging mummy.

English uses brown rot for more than one organism. Citrus brown rot is Phytophthora splashed from wet soil onto low fruit. The rind goes leathery and brown and smells sharp, and you will not see the tan powder this peach throws. Skirt pruning a lemon is not this job. Potato brown rot is a bacterium, Ralstonia, that wilts the plant and browns the tuber rings. See bacterial wilt for that leftover. A sunken tomato blossom end is blossom-end rot, a calcium leftover, not a stone-fruit fungus. Hard black raisins still hanging on a grape cluster are grape black rot. Pull those on the trellis if that is the vine — do not copy that method onto a peach. Bacterial blast kills blossoms and gums the twig too, but it throws no powder, and the dead shoots go black, not brown-tan.

Related reading

• Gray mold or Botrytis — fluffy gray rot that usually drops, not a next-year mummy.
• Black rot — hard black mummies on a grape cluster, not a peach.
• Blossom-end rot — sunken tomato blossom end, not this fungus.
• Bacterial wilt — potato brown rot leftover, a wilt bacterium, not Monilinia.