University of Vermont Extension 
Department of Plant and Soil Science

Summer News Article
line
APPLE PESTS AND DISEASES
 
Dr. Leonard Perry, Extension Professor
University of Vermont
           
There are 3 main insect pests you may find on apple trees in our region, and 4 main diseases.  Knowing what to look for, and how to control these at early stages or even to prevent them, will make your growing easier, more productive, and with less use of chemicals.
           
The four main apple diseases, common in many areas of the country, are apple scab, cedar apple rust, powdery mildew, and fire blight.  Hopefully you’ve chosen cultivars (cultivated varieties) resistant to some or all of these, such as ‘Freedom’ or ‘Liberty’.  Other cultivars may tolerate these diseases, so you still won’t have to spray.  If looking to buy some trees from your local nursery to plant, check for their disease resistance. Other diseases you may see on apples are black rot and bitter pit.  More cultivars and their disease resistance can be found online (homefruitgrowing.info).
           
Apple scab is the most common disease.  This fungus causes olive-colored and velvety splotches on leaves, and dark unsightly blotches on fruits.  Fruits infected early in the season may fall off, and those infected later often aren’t fit to eat.  This is more a problem in rainy and wet seasons.  Other than dormant oil sprays in early spring, and fungicide sprays beginning in spring, keeping fallen leaves and fruit picked up in fall will help prevent this disease.
           
There are several rust diseases that attack leaves and fruit of apple trees, with cedar apple being the worst.  As its name indicates, it makes rusty spots on leaves, and attacks cedars too (and, in fact, needs them to complete its life cycle).  Remove cedars and junipers from within a few hundred feet (if possible) and you may eliminate this disease.  

Powdery mildew is descriptive of the symptoms you’ll see on leaves, particularly in warm and humid seasons.  In addition to good pruning to allow air circulation, there are several fungicides for it including some organic ones. 
           
Fire blight too is a descriptive name, its injury resembling burned tips of branches.  Prune such injury out at the first signs, disinfecting your pruning tools periodically with a dilute solution of bleach or household disinfectant (such as Lysol).  This disease is from a bacterium, so won’t respond to fungicides, and is worse in some years than others. 
           
Unfortunately, there is isn’t the same cultivar resistance to insects on apples as there are to diseases.  The main insects to watch for are apple maggots, codling moths, and plum curculios (the latter is a problem in eastern states).  Other pests of apples you may see include aphids, spider mites, sawflies, and San Jose scale. 
           
Apple maggots may be known as “railroad worms” as they resemble small worms that railroad through the fruit leaving tunnels.  Small insects that look like houseflies lay eggs in growing fruit.  These hatch into the larvae, which live in dropped fruit in fall and in the ground overwinter.  So removing such fruit in fall helps in control, as do maggot traps.  The latter are red-shaped spheres with a sticky substance.  Another control is to place plastic sandwich bags over developing fruit after you’ve thinned them in early summer.  There are sprays, including the organic kaolin clay, which you can use in early and mid-summer if the problem is severe.
           
Another “worm” you may find in apples is the larvae of the codling moth.  Look for holes in fruit with white to gray grubs inside.  Since the moth lays its eggs in the flower at bloom time, the best control is to spray right after bloom, after the petals have fallen and the bees are gone.  Special traps can be put in the orchard to lure the moths.  Once the fruit start forming, thinning them will help prevent the larvae moving among fruit to non-infected ones.
           
The plum curculio, as its name indicates, also attacks plums as well as most other tree fruits east of the Rocky Mountains.  The weevils leave a characteristic crescent-shaped scar on fruits as they’re forming, where they lay eggs.  This either causes fruits to drop, to become infected with brown rot, or to be knobby and gnarled.  Control these with sprays after petals fall.  Regularly pick up fallen fruit which may contain larvae, and discard in a trash can.  If not severe, birds and predators may keep insect populations tolerable. 
           
More on all these and their controls can be found online from Cornell University (www.nysipm.cornell.edu/factsheets/), and in the Fruit Gardener’s Bible by Lewis Hill and Leonard Perry.  If using sprays, make sure to read and follow all label directions to protect yourself, the environment, and to ensure proper control of pests and diseases.

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