Dutch elm disease

Dutch elm disease is a fungal disease that affects elm trees. It is caused by two species of fungi: Ophiostoma ulmi and the more aggressive Ophiostoma novo-ulmi, which are spread by the elm bark beetle. The disease has been responsible for the death of millions of elm trees in Europe, North America, and Asia, and has drastically altered the landscape of many cities and towns.

History

Dutch elm disease was first identified in the Netherlands in 1910, hence its name. It was brought to the United States in the 1930s, likely through imported timber. The disease spread rapidly, decimating elm populations across the country. In the 1960s, a new, more virulent strain of the fungus, Ophiostoma novo-ulmi, emerged in Europe and North America, causing further devastation.

Symptoms and Diagnosis

The first symptoms of Dutch elm disease are wilting, yellowing, and curling of the leaves, followed by leaf drop. As the disease progresses, branches die back and the entire tree may eventually die. Diagnosis is typically confirmed by isolating the fungus from infected tissue in a laboratory.

Transmission

The primary vector of Dutch elm disease is the elm bark beetle. The beetles lay their eggs in infected trees, and the emerging larvae feed on the fungus, carrying it to other trees. The disease can also spread through root grafts between neighboring trees.

Management and Control

Management of Dutch elm disease involves a combination of sanitation, resistance breeding, and chemical control. Sanitation involves the removal and destruction of infected trees to reduce the number of beetles and the amount of fungal inoculum. Resistance breeding involves the development of elm varieties that are less susceptible to the disease. Chemical control involves the use of fungicides to protect healthy trees and to cure infected ones.

Impact

The impact of Dutch elm disease has been profound. It has led to the loss of millions of elm trees, changing the character of many urban landscapes. The disease has also had economic impacts, due to the cost of tree removal and replacement, and ecological impacts, due to the loss of habitat for wildlife.