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Larry Sagers Horticultural Specialist Utah State University Extension Service Thanksgiving Point Office © All Rights Reserved
The umbrella site for IPM, Insect Diagnosis, and Plant Disease information: http://extension.usu.edu/cooperative/ipd/
The Home Orchard Pest Management Guide: http://extension.usu.edu/cooperative/ipm/files/PDFDocs/2004HomeOrchardPestManagementGuide.pdf
Home Use Pesticides: http://extension.usu.edu/cooperative/ipm/index.cfm/cid.660/
Delayed-dormant applications, in particular, are an effective way to suppress certain pest species before they become more troublesome in-season. “Delayed-dormant” refers broadly to a tree’s developmental stage, and it has come to be associated with the breaking of dormancy (not really dormant at all).
For all the tree fruit varieties grown in Utah, the delayed-dormant spray timing begins around bud-swell. For apples, the delayed-dormant timing is anytime between bud-swell and 1/4-inch green. For pears, the period extends through cluster bud.
For peaches and nectarines, the period extends through pink bud (or early popcorn). The application typically is dormant oil (2% by volume), and sometimes an insecticide or fungicide is tank-mixed. Uniform coverage is critical with this spray (spray to drip).
SAN JOSE SCALE, APHIDS, PEAR PSYLLA, EUROPEAN RED MITES: A horticultural oil (Volck Oil, SunSpray Ultra-Fine, Orchex) provides good control when applied at a 2% dilution (1 gallon of oil in 50 gallons of water). Overwintering eggs laid by aphids, pear psylla, and
European red mites, as well as San Jose scale, can be controlled by thoroughly coating all tree scaffold surfaces. Green peach aphid has been a problem at times, and an insecticide application (Asana, Pounce, or insecticidal soap) at first pink might be warranted. Black cherry aphid has also been a recent problem for some sweet cherry orchards.
Apples, peaches, nectarines, tart/sweet cherries are either starting to break bud or very swollen and ready to shed some bud scales. Apricots, however, are another story with bloom in Utah County. Delayed-dormant applications should not be made once bloom has initiated.
Apples and Pears: Some sites are a bit ahead of others, but most apples are at or near green tip, which means that the bud is starting to open, revealing the silvery green tips of young leaves. Pears are at early cluster-bud at sites in Davis and Utah Counties.
Peaches: Most peach flower buds are at first-pink (swollen bud with pinkish color at top), and very few (1% of buds) are at pink-bud (bud has opened slightly revealing pink petals within).
In some orchards in Utah Co. (which seems to be ahead of Davis and Box Elder Counties), 1/8-inch long leaf tips are visible emerging from leaf buds.
Cherries: Buds are swollen and greenish at the tips, but none of the sweets or tarts that I observed had yet reached true green-tip (leaves poking from tips of buds).
Delayed-dormant applications can probably still be made, depending on weather.
Be aware that pruning cuts on stone fruits right before significant rain events can sometimes lead to bacterial or fungal infections (e.g., cytospora) at the site of the wound.
CORYNEUM BLIGHT (shothole): If you had a problem with this fungal pathogen in your stone fruit trees last year (see pictures at http://extension.usu.edu/plantpath/fruit\_diseases/fd\_coryneum\_blight.htm), then a delayed-dormant application of fixed copper, copper sulfate, captan, or chlorothalonil (Bravo for commercial acreage; Daconil for homeowners) would be advisable.
Petal fall or shuck-fall sprays can be made as well, though copper should not be applied after leaf-out since it can be phytotoxic.
POWDERY MILDEW: This disease is caused by a couple different fungal species, each targeting apple/pears, peach/nectarine, or cherries. In apples and pears, it overwinters underneath the bud scales, so as buds open and young leaves emerge, they can be exposed to infection.
Treatments should begin around first pink (Bayleton, Funginex. Rally, Rubigan, Sulfur, Flint, Procure). In peaches and nectarines, the fungus overwinters as mycelia under the bud scales, and treatments should be made around petal fall (Rally, Rubigan, Funginex, Sulfur, Elite, Topsin).
FIRE BLIGHT: Last, but certainly not least, is fire blight. If your apple or pear trees (or a neighbor’s trees) had symptoms of fire blight last year, then it is critical that you remove all blighted tissue as soon as possible.
Look for dark gray flower and/or leaf clusters remaining on the tree and make cuts 18 inches below the infection site. Remove and/or burn the cuttings. Bloomtime treatments of streptomycin (Agrimycin) or oxytetracycline (Mycoshield) will suppress the bacterium from initiating new infections during bloom.
