Apple blister mites

For a few years, our Liberty apple has developed tiny pouches on its leaves. Soon, the leaves turn yellow and drop prematurely. It also seems to affect the developing fruit with dimpled dark spots.

It sounds like your tree has apple blister mites, a type of eriophyid mite. They are tiny, and you would need a magnifying lens to see them. There is information about this mite in the Pacific Northwest Insect Management Handbook, including life cycle, and methods of control with dormant sprays (some of which are accepted for use in organic orchards). The mites overwinter under the outer bud scales on the tree. In case you are wondering where to look for bud scales, when the tree loses its leaves in fall or winter, bud scales form at the ends of branches or stems. The bud scales protect new growth that will emerge here. When buds swell in spring, the mites will burrow into them to feed. Once the blossoms have fallen, they will progress to leaves and developing fruit.

Mites are attracted to drought-stressed trees, and to nearby weeds like clover, mallow, bindweed, and knotweed. They can be carried from tree to tree by wind or birds and other insects. Usually, ample rain and cold winter weather keep mite numbers down, but as the climate changes, we may be creating conditions that are more favorable to them.

You might be able to find a source for predatory mites to help control the blister mites. Washington State University’s Tree Fruit research site describes several species of phytoseiid predatory mites.

Apples–Diseases and pests

Use of horticultural oils

I have a dwarf Braeburn apple tree that gets spotted apples
every year. The leaves drop off and the apples are stunted and not
edible. I am spraying with dormant oil spray per the instructions and it
looks beautiful right now. I need to know how often to spray it and how
long into the season. The instructions aren’t clear on this. Also, does
the dormant oil spray make the apples unsafe to eat at all?

Here is what Michael Phillips says in his book, The Apple Grower: A Guide
for the Organic Orchardist (Chelsea Green, 1998):
“Oil sprays smother the overwintering eggs and emerging nymphs of a
number of foliar feeders. Use of a highly refined oil is tolerable in an
organic orchard, but generally not necessary.” He recommends encouraging
beneficial insects to control aphids. Aphids may be a sign of a deeper
imbalance that needs addressing.

Whether the dormant oil spray makes the fruit unsafe to eat depends
greatly on what the oil is made of: many such sprays are petroleum-based
and would therefore not be safe. See the following information formerly available online from BeyondPesticides.org:

Excerpt:

“Most horticulture oils used today are petroleum based (Grossman 1990),
yet a growing number of horticulture oils are being made with vegetable
oils, which are considered a least toxic pesticide. Carefully read the
label or ask your pest control service provider to determine if the
horticulture oil is vegetable or petroleum based.”

From Washington State University Extension agent Mary Robson:

“How Do I Use Dormant Sprays?”

“Neither the spray nor the applicator is dormant in a ‘dormant spray’: the
plants to which it’s applied are. The term refers to winter-applied
sprays for insect pests and diseases, put on before foliage begins to
leaf out.

“To use dormant sprays, first identify the reason for the spraying. They
are often used on fruit trees to control over-wintering insect pests such
as scale and aphids. (The aphids over-winter as eggs, and the spray
smothers the eggs, preventing spring hatching.) A dormant spray isn’t an
all-purpose winter splashing of pesticide around the garden: it’s a
specific spray chosen for a specific pest. The dormant spray used on
fruit trees is often horticultural oil (sold as superior-type oil), and
it may be mixed with lime-sulfur depending on the pest to be controlled.
It’s sprayed thoroughly to give good coverage on the trunk, branches,
small limbs and shoots.

“Because dormant sprays are generally applied early in the season, they
tend to be less disruptive to beneficial insect predators and parasites
which aren’t in active life stages in mid-winter. While generally used in
fruit tree maintenance, dormant oil sprays are helpful for landscape
plants with similar aphid or scale problems. Ornamental plums
(purple-leaf plums) often suffer from infestations of aphids or scale; if
that’s been the case, a dormant oil spray may help reduce the
populations.”

The following link is from the Colorado State University Cooperative Extension: Insect Control: Horticultural Oils. Excerpt from a version of this page no longer available online:

“Most horticultural oils contain naphthene and paraffin compounds.
Paraffins are valuable to gardeners because they’re more toxic to insects
and less toxic to plants than other oil compounds. In contrast, oils
containing naphthene are less pesticidal and more likely to injure plants
than paraffinic types. Oils high in naphthene also contain more
impurities such as phytotoxic aromatic and unsaturated hydrocarbons.
However, the newest horticultural oils contain only tiny amounts of those
compounds.”

Have you determined what the cause of the spotting on your apples is?
Might it be apple scab? In case that is what you have been seeing, here
is what Washington State University Extension says:

“Apple scab is caused by a fungus which also causes scab on crabapple and
hawthorn. The first infections occur during wet weather in the spring.
Initially, the disease causes tiny, pale, chlorotic, water-soaked spots
on the leaves. The spots enlarge and darken to a dark, velvety,
olive-green then to black. Leaves may become distorted, puckered, and
mottled. Leaves may drop, sometimes resulting in severe defoliation of
susceptible trees. Scab can also affect fruit. Fruits infected early in
development show olive-green to brown, roughened or corky spots which may
develop deep cracks. These apples are often misshapen. Fruits infected at
later stages develop small black “pinpoint” scab spots while in storage.
The disease is favored by cool, wet conditions and overwinters in
infected plant debris.

“Management Options:

“Select Non-chemical Management Options as Your First Choice!!

Avoid overhead irrigation.
Plant in full sun.
Plant scab-resistant varieties such as ‘Akane’, ‘Chehalis’, ‘Liberty’, ‘Paulared’, ‘Prima’, or ‘Tydeman Red’.
Rake and destroy (do not compost) fallen leaves, or cover them with
soil.
Space plantings and prune to provide good air circulation and light penetration.
The application of nitrogen to the leaves in the fall will enhance
the decomposition of the fallen leaves.”

The following website is for large-scale growers, but may have
information of interest to you:

Apples: Organic Production Guide by Tammi Hinman and Guy Ames, 2011

Apples–Diseases and pests, Horticultural oil

controlling apple anthracnose

Can dormant oil or lime sulfur sprays help to control or prevent apple anthracnose? Is there any other way to prevent it besides cleaning up old leaves and disinfecting pruning tools between trees?

There are varying opinions on the best approach to controlling apple anthracnose (Cryptosporiopsis curvispora). British Columbia’s Agriculture Department suggests that cultural controls (i.e., good garden hygiene) are key, and fungicides have proven ineffective. Here is an excerpt:
“Spores from new cankers are spread by rain or overhead irrigation during the late summer and fall months, and initiate new infections that appear as cankers during April through July of the following year. Cankers that are allowed to overwinter produce airborne spores during the following spring and summer that can initiate new infections at a distance from the source. The airborne spores function mainly to initiate new infections, while the water-borne spores serve to intensify the disease in trees that are already infected.

Cultural Control:
Prune out and remove all cankers during winter pruning. Prune out any new cankers that develop on limbs and trunks as soon as they are discovered, and remove them from the orchard. Developing cankers often girdle 1-year-old wood; remove any shoots that wilt or die suddenly during April through July as soon as they appear.

Nursery trees should be examined carefully for symptoms of the disease at planting and again the following spring. Trees with cankers should be returned to the nursery for replacement or discarded.

The cultivars Elstar, Empire, Gala and Sinta are very susceptible to anthracnose canker.

Chemical Control:
There are no fungicides registered for control of anthracnose and perennial canker in Canada, and fungicides have not proven to be effective.”

Although Oregon State University’s Online Guide to Plant Disease Control lists several chemical controls, they too indicate that chemical control alone is ineffective.

According to The Apple Grower by Michael Phillips (revised and expanded edition, Chelsea Green, 2005), anthracnose typically follows environmental stresses like cold, drought, or pruning injury. The best control is removing and burning infected parts of the tree. “Bordeaux mixture applied immediately after harvest and again two weeks later can help prevent spore germination in orchards with a severe problem. Any developing cankers the next growing season can be roasted alive using a propane (plumber’s) torch.”

I’m not sure if you feel comfortable getting out the blowtorch. Bordeaux mixture is one type of lime/sulfur combination, and it has its risks (to plants, the environment, and health), and possibly only limited benefits. Below is more information about this from
University of California, Davis Integrated Pest Management.

controlling codling moth on apple trees

What can I do to control codling moth on my apple trees? I’ve tried the nylon footies, but found that the damage was actually greater. It seems as if the rough texture of the stockings actually makes it easier for the pests to get a purchase on the surface of the fruit. Also, the stockings give the fruit a slightly off (petroleum-like) flavor. I don’t want to use toxic chemicals.

The web site for City Fruit has useful information about codling moth, including life cycle, traps, and preventive cultural practices (good garden hygiene includes not leaving fallen fruit on the ground, and thinning your apples when they are small–marble or walnut-sized–to one per fruit cluster).

There are several control options described by University of California’s Integrated Pest Management page on codling moth.
Excerpt:
“Organically acceptable tools for the control of codling moth include cultural control in conjunction with mating disruption and sprays of approved oils, codling moth granulovirus (Cyd-X), the Entrust formulations of spinosad, and kaolin clay (Surround).”

A local home gardener told me that she has had good luck using Surround kaolin clay. You do have to apply it several times (from late June on, every week or two), and it will make your trees look a bit ghostly, but it is worth a try. This Washington State University HortSense page focuses on apple maggot control, but lists kaolin clay as a preventive method.
A thorough description of Surround kaolin clay spray may be found on the site of the National Sustainable Agricultural Information Service.

controlling woolly aphids on apple trees

Is there something I can do to prevent my apple trees from getting woolly aphids? I’d rather not have to spray anything.

Encouraging beneficial insects is one step you can take. A 2013 study at Washington State University found that planting Alyssum flowers attracted syrphids which did a good job of reducing woolly aphid populations. Here are highlights of the paper that was published based on the study’s findings:

Sweet alyssum flowers had the highest attractiveness to syrphids.
Faster suppression of woolly apple aphid occurred on trees closer to alyssum flowers.
Higher densities of natural enemies were observed near sweet alyssum plantings.
Natural enemies were found to move between sweet alyssum and adjacent apple trees.

As Washington State University’s HortSense website (search under “tree fruit,” “apple,” then “aphids”) indicates, encouraging beneficial insects is a good practice for the control of all 3 main types of aphids affecting apples, be they woolly, rosy, or green:

Control honeydew-feeding ants, which may protect aphid colonies from predators.
Encourage natural predators including ladybird beetles, lacewings, syrphid (hover) fly larvae, and parasitic wasps. Avoid use of broad-spectrum insecticides which kill these beneficial insects.
Hand-wipe or prune to control small, localized infestations (when practical).
Provide proper nutrition. High levels of nitrogen encourage aphid reproduction. Switch to a slow-release or low-nitrogen fertilizer.
Wash aphids from tree with a strong stream of water before leaves curl.

managing caterpillars on apple trees

I have a question regarding apple trees and the caterpillars.

We have a great apple tree, that I have just noticed has the early nest of these crazy caterpillars that we get around here. Can you help me with the most effective way to get rid of these things before they hatch and start eating our tree???? Is spraying ok for the fruit??

It is possible that your apple tree has an infestation of tent caterpillars, but without seeing the pests, I could not say definitively. If this is what you have, the information below from Washington State University Extension should be of use.

Also, check out Toxic-Free Future’s page on managing tent caterpillars.
You should be able to prune out the affected part of the tree and dispose of the nest.