MONOCULTURE ISSUES A CASE STUDY OF ELM YELLOWS ON THE PENN STATE UNIVERSITY MAIN CAMPUS

Elm Yellows Previously known as Elm Phloem Necrosis The disease is caused by a phytoplasm Vectored by White-banded elm leafhopper

Phytoplasm in a Plant Cell Similar to a bacterium without a cell wall

Elm Yellows Phytoplasm Causes a systemic infection of the phloem sieve cells Inoculation occurs in the small twigs and is translocated throughout the elm tree into the root system Kills fine rootlets

Susceptible to Elm Yellows (5 North American Elms) American / White Elm (Ulmus americana) American / White Elm (Ulmus americana) Slippery / Red Elm (U. rubra) Slippery / Red Elm (U. rubra) Winged Elm (U. alata) Winged Elm (U. alata) September Elm (U. serotina) September Elm (U. serotina) Cedar Elm (U. crassifolia) Cedar Elm (U. crassifolia) Chinese Elm (U. parvifolia) Chinese Elm (U. parvifolia)

European and Asian elms growing in affected areas may escape disease (but are susceptible when inoculated artificially….possibly a feeding preference for the vector) Dutch elm disease resistant American elms are not resistant to elm yellows

Elm Yellows Characteristics Spectacular regional flare-ups Trees that show symptoms in late August may survive the winter, but will die the following summer Infected trees will never recover – there is no known cure

Symptoms Rapid yellowing of foliage in mid-July to mid- Sept (with bright yellow leaves) Downward bending of the leaf petioles – “Petiole Wilt” Highly susceptible elms decline and die quickly, often within a few weeks; death usually occurs in the same year as the infection ( mo. incubation period)

Remedies Be aware of the disease/pest potential of your area. Be aware of the disease/pest potential of your area. Communicate with your peers. Communicate with your peers. Hope for the best, prepare for the worst. Hope for the best, prepare for the worst. Act decisively. Act decisively.

Diversify species selection within your urban forest. Begin this NOW, don’t wait until it becomes the issue. Diversify species selection within your urban forest. Begin this NOW, don’t wait until it becomes the issue. Prepare government officials before situation becomes epidemic. Prepare government officials before situation becomes epidemic. Seek out funding alternatives. Seek out funding alternatives. Be ready to act. Be ready to act.

Other examples

Do you know this guy? EAB is on the move and threatens all native Ash trees

How about this one? Gypsy moth caterpillars can completely defoliate a forest within days. Affected areas have full time program coordinators to combat this pest.

So we can always have…