Plant Diagnostic Clinic
573-882-3019

Elm

Anthracnose (fungus)

Irregular brown to reddish spots develop between veins and along margins. Infected leaves turn yellow and drop prematurely. Use chlorothalonil, copper products, mancozeb, maneb, myclobutanil, propiconazole, sulfur, thiophanate-methyl or triadimefon.

Elm black leaf spot lesions.

Black leaf spot (fungus)

Small, irregular spots that become shiny, tan to black and raised. Some varieties have resistance. Mancozeb may be used.

Somewhat resistant to black leaf spot
Chinese
Japanese
Siberian elms
Resistant to black leaf spot
Dynasty
Groeneveld
Homestead
Jacan
Pioneer
Regal
Sapporo Autumn Gold
Thompson
Urban.

Brown streaks are apparent in sapwood, left, and initially, trees infected with Dutch elm disease have scattered dead branches.

Dutch elm disease (fungus)

Leaves wilt, turn yellow and brown. Terminal parts of tree affected first and later the entire tree. Brown discoloration occurs in sapwood just under bark in wilting branches. Positive identification requires laboratory culturing. Send specimens to the Plant Diagnostic Clinic.

Elm branches Flagging of leaves on affected branch.

Fungicide injection.

There is no control for Dutch elm disease once the infection reaches the trunk and roots. At present, control consists of the following preventive steps:

Sanitation
Remove dead and dying elms that serve as breeding sites for the insect vector.
Sever root grafts
Use metam sodium (sold as Vapam) or by mechanical means. Dutch elm disease can be transmitted from a diseased elm to an adjacent healthy tree through root grafts.
Therapy for infected trees is questionable
Therapeutic fungicide injection is only effective if less than 5 percent of the crown is symptomatic and not at all effective if the trees are infected through a root graft. Use of a fungicide-injection program is most beneficial to protect valuable specimen trees. Use copper sulfate pentahydrate (Phyton 27), debacarb (Fungisol) or propiconizole (Alamo), thiabendazole (Arbotech). Some hybrids and cultivars are resistant.

Elm leaf beetle larvae feeding

Lower surface of the leaf between the main veins is chewed off. Smaller veins remain intact. Damaged areas become brown.

Elm yellows (Elm phloem necrosis) (phytoplasma)

Formerly called elm phloem necrosis. During June and July, leaves roll upward, turn yellow or brown, wither and drop pre maturely. Death of tree is fairly rapid. Inner bark near trunk base is yellow to butterscotch colored. Infected trees cannot be cured. Use vector control for leafhoppers. In localities where elm yellows is active, plant resistant or tolerant hybrids.

Wetwood or slime flux (bacterium)

Sap flows from branch stubs, split crotches, trunk cracks or other bark wounds. When slime flux occurs, sap ferments, foams and bubbles. No control recommended.

Updated 3/2/07