Continuing Education and
Communication Services
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
9/17/01
Contacts:
Jean Carlson Batzer, Extension Plant Pathology, (515) 294-1160
Del Marks, Continuing Education and Communication Services, (515) 294-9807,
delmarks@iastate.edu
Yard and Garden Column for the Week Beginning Sept. 21
Apple Smudges Are Only Skin Deep
By Jean Carlson Batzer
Extension Plant Pathology
Iowa State University
Cooler days signal the start of autumn's apple harvest. What could be more "a peeling" than a fresh crisp shiny apple? As you eagerly head out to the backyard, you find fruit with ugly smudges, spots and blotches. Yuck!
Is your perfect crop ruined? Not really. These blemishes are only skin deep. Fungi grow on the surface of apple and pear skins and cause a set of problems known as sooty blotch and flyspeck.
Many different species of fungi cause sooty blotch and flyspeck. These sooty critters never enter the fruit and do not change the taste. You can simply wash the fungi from the skin with a stiff brush. Commercial apple growers can soak blemished apples in a dilute solution of chlorine bleach for about five minutes, then brush and rinse them using a grading line. Researchers at Iowa State University have shown that more than 90 percent of the blemishes can be removed this way.
Growers have difficulty selling apples blemished with sooty blotch and flyspeck fungi. You might say they are "unsootable." Most c"onsumers demand picture-perfect fruit.
Local growers can lose most of the market value of their harvest because of these homely fungi. For example, a roadside market can sell a bushel of blemish-free apples for about $32, but a bushel of apples with sooty blotch and flyspeck will bring only $2. Blemished but otherwise sound apples usually are made into cider.
Sooty blotch and flyspeck fungi thrive in rain and high humidity. The spores of these fungi spread from surrounding wild plants and land on developing apples and pears throughout the spring and summer. The fungi patiently wait for the right weather conditions to slowly grow upon the surface of the apple.
In Iowa, apple growers spray fungicides every few weeks from late May through August to keep their apples blemish-free. But there are ways to reduce the number of fungicide applications.
When apple trees are well-pruned, rain and dew dry off faster and the amount of blemishes can be greatly reduced. Mowing the grass around trees can also increase airflow through the trees. During drier seasons fewer fungicide sprays may be needed to control the growth of these fungi.
With careful monitoring of the weather, growers can spray fungicides only when they are needed. This new style of disease control saves growers money, safeguards the environment and keeps sooty blotch and flyspeck away.
Iowa growers who used the new weather-watching system, in cooperation with ISU Extension specialists, saved two or three fungicide sprays per season but still kept sooty blotch and flyspeck in check. Not spraying when you don't have to is worth good money, since each spray costs about $20 per acre.
Meanwhile, don't let a few smudges ruin your enjoyment of the new apple crop. If sooty blotch and flyspeck offend you, brush them off. If you don't have a brush, just close your eyes before you bite in. A smudged apple tastes the same as a spotless apple and is just as good for you.
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