The impact of DED losses in urban areas has resulted in an increased emphasis on the use of surveys for early detection and on the prompt removal of diseased trees. Control of both DED and elm phloem necrosis requires early diagnosis and appropriate action. This leaflet is designed to assist in the field identification of these two serious diseases of elm.
Dutch Elm Disease. Usually, one or several small branches in the upper crown show earlier symptoms caused by beetle related infections (Fig. 4). Root graft infections usually show first in the lower crown on the side nearest the root graft (cover). Symptoms may appear anytime during growing season.
Elm Phloem Necrosis. Usually, the entire crown shows symptoms at the same time (Fig. 5). Symptoms appear from July to late September.
Dutch Elm Disease. Leaves wilt, turning yellow and then brown. They may remain on infected branches for some time after death.
Elm Phloem Necrosis. Leaves turn yellow and may drop prematurely. On trees that survive over winter, leaves in the spring are small and sparse.
Dutch Elm Disease. The wilting branch tip may form a Shepard's Crook. There are streaks of brown discoloration in water-conducting tissues (Fig. 6).
Elm Phloem Necrosis. There is no twig wilting. Discoloration is lemon-yellow to butterscotch, and is confined to the inner bark surface (Fig. 7).
Bark and Trunk
Dutch Elm Disease. Bark beetle galleries are found between the bark and wood surface in the main trunk or in large branches (Figs. 8-11). Streaks of discoloration are found in all infected parts of trees.
Pesticides used improperly can be injurious to man, animals, and plants. Follow the directions and heed all precautions on the lables.
Store pesticides in original containers under lock and key-out of the reach of children and animals-and away from food and feed.
Apply pesticides so that they do not endanger humans, livestock, crops, beneficial insects, fish, and wildlife. Do not apply pesticides when there is danger of drift, when honey bees or other pollinating insects are visiting plants, or in ways that may contaminate water or leave illegal residues.
Avoid prolonged inhalation of pesticide sprays or dusts; wear protective clothing and equipment if specified on the container.
If your hands become contaminated with a pesticide, do not eat or drink until you have washed. In case a pesticide is swallowed or gets in the eyes, follow the first aid treatment given on the label, and get prompt medical attention. If a pesticide is spilled on your skin or clothing, remove clothing immediately and wash skin thoroughly.
NOTE: Some States have restrictions on the use of certain pesticides. Check your State and local regulations. Also, because registrations of pesticides are under constant review by the Environmental Protection Agency, consult your local forest pathologist, county agricultural agent, or State Extension specialist to be sure the intended use is still registered.
Lester Paul Gibson, Research Entomologist, Northeastern Forest Experiment Station, Delaware, OH 43015
Arthur R. Hastings, Entomologist, Northeastern Area, State and Private Forestry, St. Paul, MN 55108
Leon A. LaMadeleine, Plant Pathologist, Northeastern Area, State and Private Forestry, Broomall, PA 19008