Dormant oil for San Jose scale management in 2014

Considerations for effective and safe use of dormant oil on San Jose scale in apples.

Michigan State University Extension educators and growers around the state reported higher than normal San Jose scale numbers on apple fruit in bins in 2013. Dormant oil is an effective method to control San Jose scale and should be considered for use in 2014 if the weather and growth stages are right.

The term “dormant” in dormant oil can be a little misleading as the more commonly used timing is delayed dormant, or as close to green tip as possible and up until the pink stage. Keep in mind that oil and green tissue are not very compatible. Phytotoxic damage to buds, blossoms and fruitlets is possible, thus care must be taken to avoid weather extremes. Do not use oil sprays 48 hours before and after a frost event. Avoid using oils in very hot (over 85 degrees Fahrenheit) and humid conditions.

Good coverage is important for all spray applications and especially when using oil to target San Jose scale where the treatment target is on and under bark scales where the overwintering scales are. A common way to use dormant oil is 2 gallons/100 at 100 gallons of water per acre at green tip with copper. Some growers will break up their oil applications into two sprays: once at green tip with copper and another at 1 gallon/100 at tight cluster with Lorsban.

Rates need to be reduced as the oil is applied closer to pink. Spur and bud damage is a high risk at pink and should be down to no more than 1 gallon oil/100. Late applications will offer the best help to control scale and mites and adding Lorsban or another insecticide will help control rosy aphids.

Different crop protection retailers have different products and they all work similarly. Be sure to work closely with your spray salesperson for the best recommendation and use of their products. Dormant oil needs to be applied with care and attention to the weather conditions before and after the application.

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