Fruit disease control in Ohio orchards and berry patches

Two kinds of trouble show up on Ohio apples in the same season, and they have almost nothing in common except the year they ruin. One is a set of surface blemishes caused by weather that carried fungal spores onto the fruit. The other is a disorder that starts inside the tree's own supply of calcium and shows up as brown pockets under the skin. Learn which is which and the calendar for spraying both falls into place.

The fungi and the physiological problems often reach the packing line at the same moment, and growers sometimes confuse them. Ohio State University Extension puts the distinction plainly in its pages on cork spot and bitter pit: what looks like insect damage or a rot on a harvested apple may be neither.

Why do two problems with the same look get managed apart?

Cork spot, bitter pit and Jonathan spot all damage tissue at or just below the surface of the apple. Fruit affected by all three is edible. The loss is cosmetic, and cosmetic loss is the whole problem when you sell fresh. An unattractive apple raises a customer's eyebrow, and the fruit is downgraded or unsold. One of these three responds to calcium and limestone, another to spray timing against a fungus, and the third has no satisfactory control at all. A spray aimed at the wrong one costs money and changes nothing. That is why the first job in the orchard is not spraying. It is diagnosis.

The apple that pits from the inside out

Cork spot and bitter pit both appear to be linked to reduced calcium availability in the developing fruit. Cork spot generally shows as small green dimples in the outer flesh, starting in June and continuing through the early growth stages. The green spots enlarge into corky, discolored areas that reach a quarter to half an inch into the flesh, and they can turn up anywhere in it. It shows most often on York Imperial, and occasionally on Delicious and Golden Delicious.

Bitter pit looks different: small brown pits of collapsed tissue, one sixteenth to a quarter inch across, sitting just under the skin and concentrated on the blossom half of the fruit. You seldom see them much before harvest. The few that appear on the tree are called tree pits; the ones that appear later are storage pits, and storage pits are the majority. Fruit put straight into low-temperature storage can hold symptoms back for days or weeks. Most bitter pit shows up within a month or two of harvest, and fruit that is still clean at that point usually stays clean. The pits darken, deepen and multiply, but they stay dry and superficial and often corky. Bitter pit is most common on Granny Smith, Delicious, Grimes Golden and Northern Spy in Ohio. Low soil pH, light crops and excessively vigorous shoot growth all raise the odds of both disorders.

Where limestone and calcium chloride fit in

The long-term answer to cork spot and bitter pit is the same: agricultural ground limestone worked into the soil at planting, at the rate your soil test calls for, and again every three to five years after planting. In an established block, calcium sprays may reduce cork spot. Calcium chloride at two pounds per 100 gallons of water, or about one and a half tablespoons per gallon, applied in four sprays beginning two weeks after full bloom and repeated at 10 to 14 day intervals, may help. That same mix can go into the pesticide sprays you already run against post-bloom insects and diseases. For bitter pit, the established-planting approach is foliar calcium chloride at the same rate, four to five applications at 10 to 14 day intervals, the last about two weeks before harvest. Two rules travel with the tank. Do not spray calcium chloride when the temperature is above 85 degrees Fahrenheit. Rinse the sprayer thoroughly afterward, because calcium chloride is highly corrosive. Cutting excessive shoot growth helps too: hold nitrogen off the soil for a year or two, and take out water sprouts with summer pruning in late July or early August.

What are the black dots and smoky smudges on the fruit?

The other half of the problem is fungal, and it is managed as a single complex: sooty blotch and fly speck. They are two separate diseases, but they arrive together and are handled together. More than 100 fungal species are wrapped up in the complex worldwide, and in the eastern and midwestern United States the fungi vary by orchard and by region. They do not rot the flesh. They grow on the waxy cuticle, the outer layer of the fruit, and their cost is fresh-market value, though heavy infection also increases water loss and shortens storage life.

Sooty blotch forms dark olive-green, gray or black mats that read as smudges or blotches with soft, diffuse edges. Colonies stay small or merge until they cover large stretches of the fruit. Fly speck is the opposite: no mat at all, just tight clusters of shiny black dots with sharp borders, commonly 10 to 50 of them, sometimes far more. Both are superficial and can be partly rubbed or washed off, especially when the infection is young and has not dug into the wax. The blemishes are easiest to see on light-colored fruit. Any apple or pear variety can be infected; what drives it is time spent wet, not genetics, which is why late-maturing, light-skinned types such as Golden Delicious and Bartlett and D'Anjou pears show it worst.

The weather that decides an SBFS year

The fungi overwinter on twigs and canes of woody and semi-woody plants around the orchard, including plums, pears, wild brambles, wild grapes, willow, sycamore and smooth sumac. Spores move in on rain and wind from about petal drop, and secondary spread runs through summer and fall while leaves stay wet and the air stays humid. Temperatures near 60 to 70 degrees Fahrenheit with relative humidity above 96 percent favor infection. Hot, dry spells shut it down. Fruit can be infected as early as two to three weeks after petal drop in a wet year, but visible signs lag three weeks or more behind the infection itself. That lag is the reason a spray calendar is not built on what you can see.

Frequent rain, long leaf wetness, high humidity, dense canopies, heavy shade, poor air movement and sites near woods or bramble thickets all raise the risk. The cultural work targets exactly those conditions. Mow groundcover to lower humidity in the lower canopy, and thin clusters to keep fruit apart where you can, so water does not sit around the stem and calyx.

Reading the days since petal drop

Commercial control rests on fungicide, applied on schedule rather than on sight. After the first cover spray, about 10 days after petal drop, the common rule is that a protectant cover is spent after roughly 14 days or about 2 inches of rain, whichever comes first, so sprays go on at least every 14 days. A weather model can set the timing instead. The northeastern United States apple model accumulates leaf wetness hours from first cover, and a conservative approach starts protection just before the block reaches about 190 accumulated leaf-wetness hours. Older guidance used about 270 wetting hours to predict the first visible sooty blotch symptoms, but symptoms trail infection, so preventive timing must come earlier. Leaf wetness accumulation needs a station with a leaf wetness sensor, read daily or fed into the Network for Environment and Weather Applications, known as NEWA, which Ohio State University is a partner in and which is free to Ohio stakeholders. NEWA sorts risk into no, low, moderate or high using days since petal fall, accumulated leaf wetness, rainfall since petal fall or the last fungicide, and forecast precipitation, and shows an eight-day window with a stoplight color scheme. The Midwest Fruit Pest Management Guide 2026 to 2027, published through Purdue, carries current fungicide recommendations and spray schedules. Backyard growers have fewer effective products, so pruning, sanitation, sun exposure and early varieties such as Gala, Ginger Gold, Zestar, Pristine and Sweet Tango carry more of the load there, and any product used must be labeled for apples and mixed exactly to the label.