Q. I was traveling and missed the time frame for a dormant oil
application to my fruit trees. Should I go ahead with it, or just
follow the rest of the spray schedule?
A. Once trees start to leaf out and bloom, it is too late for a
dormant oil application. The oil can severely burn the tender new
foliage and flowers. Once the foliage matures and hardens off, a
summer-weight application of horticultural oil can be useful to
control soft-bodied insects such as aphids and scale crawlers
(immature scale insects). A summer-weight application is 1-2 percent
solution (1.28 to 2.56 ounces of horticultural oil per gallon of
water). Avoid applying horticultural oils when trees are under
drought stress, or when temperatures are over 80 degrees and/or
humidity is over 80 percent.
Scale "shells" along a branch
can look like part of the tree
applications are a useful tool to manage insects that overwinter on
trees, even those that overwinter as eggs. Eggs have to exchange
gases just as humans need to breathe. Dormant oil applications can
suffocate eggs, and have a similar effect on immature and adult
insects as the oil creates a film over their breathing pores
Dormant oil can also affect insects’ cell membranes and
disrupt their functions, and perhaps create some toxins in the
process. There is some evidence that horticultural oil also deters
females from laying eggs on treated plants.
applications are mixed at a lower concentration to avoid burning
foliage and otherwise damaging the plant while maintaining the
benefits of these less-toxic materials. Their main action is on
insects present when the oil is applied. Once the sprays dry,
beneficial insects and pollinators that visit treated plants are
unlikely to be impacted by them.
Girdling tree roots
spots after parking under trees?