|Oil burn on needles|
Types of oil. Not all oils are alike. To get the best pest control without foliage burn, use a highly refined horticultural oil. These are often called summer oils. Do not use a dormant oil as these will cause foliage burn. Look for oils with at least 92% unsulfonated residues on the label. But the higher, the better! It will list this value under the active ingredients.
Applying oil. Typically a high pressure sprayer will give better coverage. If a limited number of trees are being treated, you may also use a backpack mistblower. Treat trees from opposite directions to get the best coverage. If you are controlling BWA, you have to wet the tree all the way to the trunk.
The encapsulated oil can be used with any type of sprayer. Other oils should only be used if there is good agitation in the spray tank. A paddle type agitator is better than by-pass pressure recirculating into the tank because the agitation is continuous. The oil and water can separate in the hose if you stop spraying for awhile, so if you do spray what's in the hose back into the tank to remix the solution.
|Twig aphid egg killed by oil|
A 2% solution of oil applied in mid-March will do a good job of controlling the following pests:
- All stages of HRM -- actually oil works as well as expensive miticides when controlling rust mites
- BTA eggs
- SSM eggs
- BWA crawlers, nymphs, and adults though the adults are covered with white wool and are therefore harder to wet.
- Cinara aphids
- BWA eggs – however, there shouldn’t be any BWA eggs present in mid-March
- BTA nymphs or adults. Therefore be sure to treat before the twig aphid eggs start to hatch
- EHS -- this is really too early in the year to get good EHS control. You can treat for this pest in the summer with oil, but problems with burning foliage increase in hot weather.
Be sure to keep scouting through the spring to make sure treatments have worked.