How To Protect Your Trees From Bugs and Disease

Saturday, October 20, 2012


View Larger +

An all-too-familiar site on RI trees in the fall: the cottony egg masses of Hemlock Wooly adelgid.

Fall has several advantages for planting. For one thing, the daytime temperature is slowly but surely dropping. This means plants will be subjected to less heat stress, increasing their chances of surviving. New transplants prefer daily temperatures in the 60-70-degree F. range, but their roots will continue to grow as long as soil temperatures remain above the 40-45 degree F. mark. Adding mulch after planting helps satisfy the latter condition.

New transplants need water, so irrigate during dry periods lasting more than 5 days up until the middle of November. Transplants are also susceptible to insects and diseases in the fall. While many pests and diseases are done for the year, a few active remain active in the fall. Some are more problematic than others. They attack plants as long as there’s warm weather. Below is a brief update on pests and diseases active in the fall and how to treat them:


Scale: Look for crawlers (immature stage) of various species on twigs and the underside of leaves. These sucking insects cause foliage to stipple and yellow. Plant hosts include tulip tree, magnolias and lindens. Apply insecticidal soap, horticulture oils, and registered pesticides to manage them.

Honeylocust Spider Mite: Shake small branches and foliage over white surfaces to discover these reddish-brown mites. Symptoms are similar to those caused by scales. Adults winter in bark crevices, so treatments should be directed at branches and trunks. Treatments are the same as above.

Eastern Tent Caterpillar: Examine branch tips of crabapple, cherries, and apple trees for shiny black egg masses and remove them. The egg-masses are barrel-shaped and long. They usually encircle the branches. Each mass can contain up to 400 eggs. Submerge egg masses in a 1 percent solution of Clorox for about two minutes to kill them.

Hemlock Woolly Adelgid: Inspect base of needles on Eastern hemlock for white, cottony masses. Feeding adelgids hide under this webbing. Initial damage symptoms include grayish discoloration and yellowing of needles. Continued feeding by adelgids kills twigs, large branches, and eventually the entire tree.


Impatiens Downy Mildew: This soil-borne fungus attacks the vascular system of Impatiens walleriana. Leaves yellow then wilt before they die-off and shed prematurely. Fungal spores overwinter in dead plants. Break infection cycle through good cultural measures and get rid of infected plant material. Install New Guinea impatiens next year, which resists this disease.

Powdery mildew: Fungi attacking trees, shrubs, and perennial plants cause this disease. Major affected plants are dogwood, lilacs, and phlox. Symptoms include the white to almost downy casting of infected leaves. Curling, cupping, and early leaf drop are also symptoms of late stage leaf infection. Rake up and dispose of infected plant parts. A preventive fungicide application next spring may be necessary depending on disease severity.

Anthracnose: Cool, wet weather after Labor Day has triggered this fungal disease to crop up again on many shade trees over the past two weeks. This disease causes small, irregular, brown spots on leaves. As the disease progresses the spots get larger and eventually merge together to create big necrotic blotching of the leaf. Anthracnose attacks oaks, maples, horse chestnuts, and dogwoods. Nothing can be done at this time, but suspicious twig die back next spring may be a reason to contact a certified arborist for consultation.

Many pest control treatments require commercially available registered pesticides. We recommend that homeowners seek out certified arborist to help them devise a safe and effective management strategy for problem pests. For more information on fall planting, or insects and diseases, contact RITree at (401) 764-5885) or go to RITree’s Web site.

John Campanini is technical director of the Rhode Island Tree Council. Previously, he was Providence’s city forester.


Enjoy this post? Share it with others.


Sign Up for the Daily Eblast

I want to follow on Twitter

I want to Like on Facebook


Stay Connected — Free
Daily Email