Apple Tree Diseases & Pests

Spraying Apple Trees

Guide to common apple tree diseases and pests. Pictures to help with identification of plum curculio, apple maggot, codling moth, apple scab, rust, and bitter rot.  Natural fungicide for spraying apple trees.

Men on Truck and on Foot Spray Sulphur on Apple Trees to Prevent Scab
Men on Truck and on Foot Spray Sulphur on Apple Trees to Prevent Scab
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The four insects your trees are likely to be plagued by are:

  1. the codling moth
  2. the plum curculio
  3. the apple maggot
  4. San Jose scale

These are not the only pests to ever prey on Malus trees, just the most likely suspects, and you may not be visited by all of the above every year.  Some insects are prevalent in certain states and nonexistent in others.

Also, some apple varieties are more pest and disease resistant than others.

In most areas, apple trees will need to be sprayed with dormant oil, insecticides, and fungicides to keep them healthy and insure a blemish-free crop.

Bonide Citrus, Fruit, and Nut Orchard Spray

A natural fungicide and insect spray which can be used right up until harvest.

Active ingredients: pyrethrin and sulphur.

Kill two problems with one spray!

The Most Common Apple Tree Diseases

Cedar-Apple Rust Fungus
Cedar-Apple Rust Fungus
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Brown Spots:

In some locations, brown spots in apples can be caused by a boron deficiency in the soil.

This is easily corrected by sprinkling 20 Mule Team Borax beneath the trees.

Star-shaped brown spots are caused by apple blotch

Spray with the Fruit & Nut Orchard Spray for sale above during petal fall.

  1. Fire blight is largely a result of over watering and over feeding.  It causes entire branches to take on a scorched appearance.

    This fungal disease is easily spread by pruning tools and chewing insects.  Treat an infected tree by cutting off affected growth at least 12 inches into healthy tissue. 

    Dip your tools in a bleach and water solution between cuts and clean them with this solution before putting them away to avoid spreading the disease.

    Spray to control sucking insects.
  2. Apple and pear scab is the most serious of all apple tree diseases in the northern U.S.  It can defoliate the trees, reducing their vigor and productivity, and leaving them vulnerable to winter injury.

    Gather and burn the fallen leaves of infected trees.  Spray trees  infected the year before with micronized sulfur when the buds begin to swell in the spring, again at petal fall, and again 12 days after petal fall.  Spray weekly during warm, wet weather to maintain control throughout the growing season.
  3. Bitter rot causes large, sunken brown spots.

    Remove infected fruit and all loose bark.  Remove dead and damaged branches.
  4. Bitter pit causes small brown spots to form in the skin and flesh of the fruit.  It is associated with excessive late season tree growth.  Baldwin and Northern Spy apple trees are particularly vulnerable.
  5. Cedar apple rust leaves light yellow turning to orange spots on apple leaves and fruit.  Control with a ferbam spray.

    Prevent this apple tree disease by siting apples at least half a mile away from juniper or red cedar trees.
  6. Powdery mildew leaves mold on twigs and foliage.  Proper pruning and siting will go a long way toward preventing it as the tree will be in full sun and its center will be open to light and air.

    Once symptoms appear, remove affected stems and spray with a sulfur fungicide every other week.  Treat trees infected the previous season by spraying before bloom and every two weeks thereafter until early summer.
  7. Brown rot is best prevented by spraying with a dormant oil, followed by a fungicide after the flowers open.  Additionally, avoid leaving fruit on the tree after harvest, and practice good orchard hygiene.

Bitter Rot & Anthracnose

Apple Scab

Cedar Apple Rust

Thanks to the University of Georgia Plant Pathology Archive, University of Georgia, for the 3 images above.

Twisted Apple Leaves

Curled leaves may be caused by green, apple, or wooly aphids.  Spraying the tree with a dormant oil just after bud break will smother any eggs on the bark.

If a problem develops during the growing season, use beneficial insects to reduce the aphid population.  Lady bugs and lacewing larvae are the aphid's natural predators.

Lady Bug Lures

Green Lacewings: Chrysopa rufilabris, 1,000 Eggs in Cups

Apple Tree Pest Identification

Codling Moth Damage

Photo above: Eugene E. Nelson,

Photo at right:
Whitney Cranshaw, Colorado State University,

The Codling Moth is the single most serious pest of apples. Its management requires a multi-pronged strategy.  Consult your local Agricultural Extension Service, online or by phone, to discover the most effective control methods for your area.

Plum Curculio

Art Cushman, USDA; Property of the Smithsonian Institution, Department of Entomology,

Apple Maggot

Plum Curculio leaves crescent-shaped scars on the fruit and causes it to fall prematurely.  Spray the tree at pink and again at petal fall with an insecticide known to control curculio.

The adults mature inside the fallen fruit, so bag and burn it before they get the chance to emerge and reproduce.

Protecting Apple Trees from Borers:

Round-headed apple tree borers usually attack young trees. 

Prevent this by painting the trunk of a newly planted tree with a repellant or wrapping it, loosely, with fine mesh wire or paper.

Apple Maggots lay their eggs just beneath the skin and cause the fruit to soften and rot.  Rhagoletis pomenella mainly affects apple trees in the northeastern U.S. and eastern Canada.  Apples are their favorite fruit, but they can also infest crabapples, hawthorn berries, wild rose hips,  apricots, and other fruits.

Your County Extension Service is the best source of information about which chemical to use to control apple maggot in your area.  Spray every 10 days from mid July until you reach the preharvest interval designated by the product's label.

San Jose Scale

Art Cushman, USDA; Property of the Smithsonian Institution, Department of Entomology,

San Jose Scale is a sucking insect which forms a hard circular shell to protect its soft body as it matures.

Check the trees regularly for scale as the sooner you begin treatment the better.  A heavy infestation may be difficult to eradicate.

Spray with dormant oil (during the appropriate season) or lime-sulfur.Poor culture makes trees more vulnerable to scale infestation.

Poor culture makes trees more vulnerable to scale infestation.

Apple Tree Care Guide

The Apple Adventure Continues on These Pages:

Dwarf and Semidwarf Apple Trees for Sale: Includes Heirloom Varieties

Tips for Espaliering, Cordoning, and Trellising Apple Trees

For an Ornamental Apple, You Can't Beat a Flowering Crab

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