Dormant Oil Spray Time

This information comes from the USU Extension Service.

It's time to apply dormant oils to your fruit trees. If you have questions IFA, CAL Ranch or any INDEPENDENT Nursery (the best source other than USU themselves) can help you with information on the oil itself, and the other chemicals that you may need to add to address specific diseases. Dormant oil is only applied once a year, and must be done right around when the buds are swelling. If you wait too long, too bad too sad; you only get one shot.

Dormant sprays are targeted to insects that overwinter as eggs (mostly aphids), or as nymphs/adults withing trees (mostly scale). Keep in mind that dormant sprays are not required every year. You should keep track of your aphid and scale populations from year to year (by examining leaves and twigs for insects). When damage is slight to non-existent, you can skip the dormant sprays. The "aphid swarms" of fall 2010, however, may have led to a larger than normal population of eggs laid, and may require a dormant spray this year.

The ideal time to apply a dormant spray is after the buds of fruit trees have started to swell, and up to the point where leaves have begun to emerge.

This is called the delayed-dormant timing. Waiting for this timing rather than when buds are completey dormant is beneficial because eggs and overwintering adults become more "active" and susceptible to treatment. Also, beneficial insects and pollinators are not affected, oils and other materials for this purpose are relatively inexpensive, and the developing ground vegetation will help to prevent runoff. The exception to spraying only at delayed dormant is pear psylla, which would require one spray during dormancy (just before buds swell) and a second spray 2 weeks later.

Usually horticultural oil alone is sufficient for dormant or delayed dormant sprays, particularly for backyard growers. Most oils are simply sold as "dormant oil" and the ingredients will be "98% (or higher) petroleum oil". This type of oil is suitable for sprays in the dormant season (2% rate) as well as sprays during the growing season (1% rate).

Commercial growers may consider mixing oil with an insecticide such as Lorsban. When applying dormant or delayed dormant sprays, make sure you thoroughly cover all bark cracks and crevices. Also, oils should be used when the air temperature is above 40 F and when there is no threat of freezing temperature for the following 36 hours. Applying between 50 and 70 F on clear days is ideal.

The dormant and delayed dormant sprays can be effective against the following insects.


Brown Mites


Brown mites are related to European red mites, and overwinter as eggs in protected sites on trees. Because of the past three cool springs, we are starting to see these mites more often in commercial orchards and more rarely, in backyard trees. If this pest was a problem for you, oil alone at delayed-dormant timing should be sufficient. peach twig borer: delayed dormant spray of horticultural oil plus spinosad targets overwintering larvae as they emerge to find food; this is a very important spray for managing peach twig borer .



Ahpids:

Horticultural oil alone or with Lorsban (restricted use) at delayed-dormant timing; repeat if infestations were high last year blister mites: these mites cause tiny galls on the leaves of apple or pear. Apply oil, or oil with Sevin at dormant or delayed dormant timing.

Pear Psyllia:


pear psylla: use horticultural oil alone; apply two applications starting at dormant timing San Jose scale: horticulture oil alone or with pyriproxyfen (Esteem). Apply at dormant or delayed-dormant timing.

Soft Scales:

horticultural oil is very effective on soft scales, particularly at delayed-dormant timing when temperatures have started to increase shothole (coryneum blight of peaches, cherries): chlorothalonil (Bravo) at delayed-dormancy

Fire blight:



Copper spray at silver tip stage (late dormant timing) and when temperatures are above 45° (Bordeaux mixture, copper hydroxide, copper oxychloride, copper sulfate). Do not apply copper after ¼-inch green leaf stage or when drying conditions are slow, as severe injury can occur. Fixed coppers such as Kocide and C-O-C-S can be tank mixed with early season oil sprays, but do not combine copper sulfate alone with dormant oil.

If you have questions, please feel free to contact us at RockyMtnSurvival@gmail.com