Plant Pro
Common Yard Diseases

Each year as summer comes upon us, we spend more time in our yards. We start to enjoy the fruits of our labor, but if we take a closer look, we might notice some unwanted garden guests. In this episode, URI Plant Protection Specialist, Dave Wallace, joins us to go over some common yard problems. Dave, along with other URI horticultural experts, emphasizes accurate diagnosis of landscape problems before taking action. "If you are not sure what is causing your plant problem, you can waste time and money and still not save your plant." explains Wallace. "If you don't know what the problems is, ask experts at reputable garden center or visit the URI Plant Clinic."

"Cedar Apple Rust"

Cedar Apple Rust is a common fungal disease that requires two hosts: eastern red cedars or junipers, and apple or crabapple trees. On crabapple or apple trees, the disease manifests as small, yellowish-orange spots which appear on leaves in the spring. These spots continue to enlarge and turn more orange, often with a red border. The fungus grows through the leaf, and fringe-like structures arranged in a ring appear on the underside of the leaf in midsummer. These structures produce spores, which are infectious to junipers. Junipers and cedars become infected in late summer or autumn. Galls form on the branches, growing from a combination of plant and fungus tissue. During spring rains, the galls swell and form bright orange horn-like projections. Despite the dramatic appearance, damage to junipers is generally mild though some twig dieback may occur.

Cedar Apple Rust on crabapples and apples is unsightly and may result in defoliation. However, it will not kill the tree. The most effective means of controlling rust is to plant cultivars with proven resistance to the disease.For a list of disease resistant crabapples and other control tips, go to URI's Greenshare Fact Sheet on Cedar Rust Disease of Ornamental Plants.

"Lawn Mower Damage"

Lawn mowers bouncing off the base of young, smooth-barked trees can cause severe damage. The injury may cause a canker which will slowly move throughout the trunk and eventually kill the tree.

Prevent lawnmower damage problem by placing shredded hardwood mulch in an area with about a five-foot or greater diameter around the base of the tree. Be careful not to mound mulch up around the tree trunk. For more tips on lawn mower damage prevention and information and other common tree injuries go to URI's Greenshare Factsheet on Tree Injuries.

"Tip Blight"

Begin by looking at your junipers for the black fruiting bodies of a fungal disease known as juniper tip blight. Look for branches that appear off-color or brown. Be sure to check new shoots as well - they can appear healthy now but turn brown and dry by midsummer. Infected branches should be pruned out and disposed of. If a plant becomes heavily infected, it should be removed. Try replanting with more resistant juniper varieties see URI's Greenshare fact sheet for Juniper Tip Blight.

"Over-Mulching"

Correct mulching is an effective method of preventing weeds, conserving moisture and adding organic matter to the soil. Unfortunately, in many New England landscapes, over-mulching has become a serious problem. URI Professor of Ornamental Horticulture, Dr. Brian Maynard has described over-mulching of trees and shrubs as "a plague that is slowly and methodically annihilating ornamental trees and shrubs in established landscapes". It is a serious problem responsible for the decline and death of many shallow rooted shrubs as well as large coniferous and deciduous trees.

As noted in the URI GreenShare fact sheet on over-mulching, the best way to determine if you have a mulch problem is to dig through the mulch layer to see how thick it is. If you already have a 3-4 inch layer, don't add more. Sometimes you need only to lightly rake the existing mulch to give it that "finished" look. As a rule-of-thumb, for optimum health of plants, keep the mulch a minimum of 3 - 5 inches away from the trunks of young trees and shrubs and 8-12 inches away from mature tree trunks. See the URI GreenShare Factsheet "Are You Guilty of Over-Mulching?" for more information.

If you have any question about problems in your garden, contact the URI Plant Protection Clinic. The URI Plant Protection Clinic identifies insects on plants and in the home, and will diagnose plant diseases. You may drop off or mail in a sample of the item to be identified. The cost is $10, and if mailed in, please allow 7 days for a response. For more information go to URI's Plant Protection Clinic.

URI Greenshare Factsheets-
Cedar Apple Rust
Lawn Mower Damage
Tip Blight
Over-Mulching

Written by James Proctor

Picture Credits: "Apple Cedar Rust" University of Minnesota Plant Disease Clinic, "Mulching tips" Whittney Farms