Apple trees are a treat in a home garden, but they are susceptible to a variety of diseases. One of the most common problems of apples in Iowa begins to show up about this time of year – sooty blotch and flyspeck fungi. Horticulturists with Iowa State University Extension and Outreach identify several causes of apple blemishes and how to reduce their presence. To have more questions answered, contact Hortline at firstname.lastname@example.org or call 515-294-3108.
What are the black spots and blotches on my apples?
The problem may be sooty blotch and flyspeck. Sooty blotch and flyspeck are regarded as a complex of several different fungi that often occur together on apples. Sooty blotch appears as dull black, blotches or smudges on the surface of the apple. Flyspeck produces clusters of shiny, round, black dots. Individual dots are about the size of a pinhead. Environmental conditions that favor disease development are moderate temperatures and an extended wet period in late summer or early fall.
Sooty blotch and flyspeck live on the surface of the fruit. The damage is mainly cosmetic. The apples are still safe to eat. They are just not very attractive.
Cultural practices and fungicides can reduce the incidence and severity of sooty blotch and flyspeck. Proper pruning of apples trees and thinning of fruit promote drying and create environmental conditions less favorable for disease development. Protective fungicide sprays are also helpful.
If control measures fail, sooty blotch and flyspeck can be removed with vigorous rubbing.
There are brown streaks in my apples. What produced them and how can they be prevented?
The brown streaks in the apples are probably due to the apple maggot. The apple maggot is the most serious insect pest of apples in home gardens. Apple maggot damage appears as knobby, misshapen fruit with small pits or blemishes on the fruit surface. In addition, brownish streaks run through the flesh of the apple. The apple maggot is sometimes referred to as the “railroad worm” because of the slender brown streaks or tracks in the apple’s flesh.
The apple maggot is a type of fruit fly. Female apple maggot flies insert eggs beneath the skin of fruit from about mid-June until shortly before harvest. The punctures produce small holes that later appear as blemishes on the fruit. Upon egg hatch, the larvae tunnel through the flesh of the apple producing the distinctive brown streaks.
Control of apple maggots in home gardens is difficult. Picking up and destroying apple maggot infested apples that have fallen to the ground helps to a limited degree. Placing apple maggot traps (red spheres coated with a sticky substance) in apple trees may provide satisfactory levels of control. Insecticides are the most commonly used method of controlling apple maggots in commercial and home orchards. The effectiveness of insecticide sprays in home orchards is often limited due to poor spraying techniques, rainy weather and other factors. Substantial damage may still occur despite spraying.