WSU CAHNRS

Washington State University Extension

Western Washington Tree Fruit & Alternative Fruits

Frequently Asked Questions

The ornamental tree fruit arboretum at WSU Mount Vernon NWREC includes flowering crabapples, cherries, and plums.

The ornamental tree fruit arboretum at WSU Mount Vernon NWREC includes flowering crabapples, cherries, and plums.

Pests & Diseases

Pruning & Grafting

Varieties & Sources

Harvest & Storage

Cultural Methods

What are the most serious plant diseases in western Washington? Apple scab, apple anthracnose and powdery mildew are diseases affecting apples and and crabapples. Powdery mildew can also affect pears. Pear scab is similar to apple scab in its effects. Peaches and nectarines are affected by peach leaf curl, brown rot, coryneum blight, and bacterial canker. All of these but leaf curl also attack plums, apricots and cherries. Sour (pie) cherries are less susceptible to bacterial canker than sweet cherries. A very good diagnostic site is available through the Kearneysville, West Virginia research station with photographs and information on disease problems.

What insects are the most damaging? In apples, codling moth and apple maggot are very serious problems, and can destroy entire crops if not controlled. Spotted wing drosophila, a newly introduced insect threat, attacks soft fruits and berries of all kinds and has potential for major crop destruction. Methods of control  are being investigated. Aphids are a common pest and may attack young shoot tips, particularly in plums. Information on insect identification and life cycles is available from WSU bulletins (see bulletin catalog).

Can you tell me what disease/insect has damaged my fruit? For a positive diagnosis take a sample of the damaged fruit or plant part to your local County Extension where it can be sent for analysis to identify the problem, along with the C0084 Plant Disease Identification Request Form (also available at county extension offices.) For sources of information, see WSU bulletins online The Kearneysville, West Virginia research station web site includes a photo gallery for identifying pests and diseases.

Where do I find out what treatments to apply? There are some very good guides available from the WSU Bulletins. Be sure to READ LABELS and FOLLOW LABEL DIRECTIONS when using any pesticide.

What about organic methods of pest control? What is IPM? There are several sources of information for those who want to try Integrated Pest Management techniques in managing their orchard. They include WSU’s Organic & Integrated Fruit Production Page and the UCDavis IPM Project.

Is there some way I can get hands-on instruction in pruning and grafting? There are classes in pruning and grafting at Field Days held annually in spring by garden and orchard groups such as the Western Washington Fruit Research Foundation, Western Cascade Fruit Society and the Seattle Tree Fruit Society. These programs include talks on pruning and grafting techniques and may be followed by field demonstration with opportunity for hands-on participation and questions.

What is “summer pruning” and how does it work? Summer pruning is removing shoots or branches from a tree when there are leaves or flowers on it. Summer pruning should be used with caution, because the effect of removing parts of the tree is much stronger when the leaves are active than when they are dormant. There are several things to consider when summer pruning. First of all, the effects on next year’s crop can be unpredictable. The tree relies on photosynthesis in existing foliage to grow at a constant rate. If too much foliage is removed, resources must be diverted from cell differentiation. Shoot growth may also be stunted. Because most fruit trees develop floral buds over a complete growing season, stunted growth may reduce bloom or fruit set in the following year.

When to use:

  • To control growth of young trees
  • To improve light quality in the fruiting zone
  • To thin heavy fruit loads
  • To remove water sprouts – large vigorous upright shoots in the center of the tree

Guidelines for summer pruning:

  • Only summer prune strong, vigorous trees
  • Some trees, such as plums, send up many water shoots in the center of the tree. These can be removed by hand early in the season, before they harden up
  • Take out no more than 10% of total canopy
  • Keep early summer pruning to a minimum. Pruning in mid June to mid August has a stronger effect on tree vigor than later pruning (September), and response is less predictable
  • Pruning to expose fruit to light 3- 4 weeks before harvest is the most beneficial, and has less impact on the tree’s response
  • When pruning, thin out, do not head the shoots to be eliminated.

What’s the name of this unknown fruit tree in my back yard? There are thousands of known varieties of tree fruit, and even more random seedlings, so identifying fruit is always tricky. Best suggestion: Collect 3 or more typical fruit, in good condition, store in the refrigerator, and bring them to a Field Day or to the All About Fruit Show where there is a panel of experienced fruit identifiers. It helps if you can add information about the tree: how old the tree is, when the fruit was picked, etc.

Why doesn’t my tree bear much/any fruit? There are several things to look for.

A. If the tree has plenty of flowers at bloom time, but fruit doesn’t set, the most likely problem is pollination. Sometimes if the weather is bad, bees and other pollinator insects don’t work the blossoms. Or there may not be a suitable tree nearby to provide cross-pollination. Frost (in early blooming trees like apricots) or disease can also destroy the blooms after pollination.

B. If a tree has few blooms, the problem is probably cultural. It can be incorrect pruning (too many areas of the tree are shaded) or lack of training (branches are too upright and vigorous.) All areas of the tree need to be well opened to sunlight in order to stimulate growth of fruit spurs. Spreading upright branches or tying them down to a 45 degree angle with the main trunk will encourage better set of fruit. Sometimes lack of nutrients in the soil is also a factor, and may need soil or leaf tests for diagnosis.

Do I need to fertilize my trees? Do I need irrigation here in western Washington? Fruit trees usually need annual applications of fertilizer to replace the nutrients that are removed with the crop. Some basic information on fertilizer application for the home garden is covered in our publication Home Orchard Fertilizer Applications. A soil test is the best way to find out the amount and kind of soil nutrients that you need. Information on soil and fertility can also be found in EB1804 Growing Jonagold in Western Washington including material that applies to tree fruit in general (see sections “Site Preparation/Soil Fertility” and “Irrigation, Fertigation, Nutrition”). Since the months when the tree fruit crop is ripening (July, August and September) can be quite dry even in western Washington, irrigation at that time helps the trees to mature a full crop of high quality fruit. Drip line systems are the most practical for orchard irrigation, especially if there are more than 2 or 3 trees to be watered.

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