Fall Pest Control
And Scott Hininger
University of Wyoming
Cooperative Extension Service
Dry Wyoming weather can contribute to severe infestations of aphids and
scale insects in ornamental trees and shrubs. Foliar treatments with broad-
spectrum insecticides against these pests are often ineffective or provide just
temporary relief. In addition, when these insecticides are applied to the
foliage, many beneficial insects are killed with the pests. The casualties of
these foliar spays include pollinators as well as predators and other natural
enemies of pests. As a result, gardens become more prone to pest attacks and
need even more frequent insecticide interventions.
One answer to this dilemma is a special group of insecticides called
“systemics” which offers a viable alternative. These insecticides are taken into
a plant through leaves or roots. Insects are killed only when they feed on the
treated plants. Such insecticides may be applied to foliage, but there are also
granular or drench formulations, which can be applied to the soil near the base
of an infested tree or shrub. Compared to foliar sprays, soil applications have
obvious ecological advantages because they minimize the negative impact on
beneficial pollinators or predators.
Other benefits of using a systemic include continuously protected plants
throughout most of the growing season without the need for repeat applications,
insecticides that are not susceptible to ultraviolet light degradation or “wash
off” during watering, and minimized risk of overexposure to applicators. Certain
formulations of systemic insecticides claim to provide year-long control against
aphids and soft scale insects; however, to be effective, such insecticides must
be taken in by the roots, move through the plant’s vascular system and reach the
leaves. On average, a systemic insecticide moves up a large tree at a rate of 1
foot per day, so it may take months until it reaches the top branches of a large
Do not wait until next summer to protect trees and shrubs. Apply systemics
in the early fall, and this will protect trees throughout next growing season.
Systemics work best on insects with piercing or sucking mouthparts such as
aphids, soft scales and mealybugs. They can also provide suppression of leaf
miners, thrips, whiteflies and, in some cases, armored scales and some borers.
These insecticides do not affect spider mites. Check the label for the pests
that are controlled. With the threat of grasshoppers, again next year, this
would be a good defense against them for next year.
There are many systemic insecticides available over the counter. Two of the
most common include the active ingredients dinotefuran (marketed as Safari) and
imidacloprid (marketed as Bayer Advanced Garden Tree and Shrub Insect Control,
Merit, Confidor, Marathon® and other brand names). Pesticides are poisonous.
Be sure to read and follow directions and safety precautions on labels. Handle
them carefully and store in original, labeled containers out of reach of
children, pets and livestock. Properly dispose of empty containers immediately,
and do not contaminate forage, streams or ponds.
One reminder this time of year is to make sure your trees and perennial
plants are well watered going into winter. Even with the moisture we have
received the last several weeks now is a good opportunity to provide plenty of
water under the trees before wintertime. The soil needs to be wet at least 18
inches deep going into winter.
Most of the damage (brown needles or leaves) I am seeing particularly on
evergreens is probably from spider mites, use a piece of white paper under the
leaves or needles to check, they are very small. Regular insecticides do not
work use a mitacide or insecticidal soap.
The University of Wyoming and the United States Department of Agriculture,
Sheridan county Office cooperate. The University is an equal
opportunity/affirmative action institution.