Disease threat to poplars

Press, 26 February 1977, Page 9

Disease threat to poplars

Palmerston North scientists have confirmed a potentially dangerous outbreak of poplar leaf-spot disease (Marsonina brunnea). Hie disease, of American origin, was discovered by scientists at the Ministry of Works’ plant-materials centre last February. The original infection was very light and all known infected material was destroyed. The new outbreak, in a wider area, has struck again in Palmerston North. Surveys are being made throughout New Zealand to detect further outbreaks. Initially the disease caused serious damage to black and balsam poplar hybrids, however selection of resistant varieties has gradually reduced the problem

Poplar trees that are already resistant to poplar rust are also resistant to the leaf spot, the department reports. Cold, wet, and‘windy weather in the spring and the early summer of the last two years have provided favourable conditions for the development of the fungus.

Detection of the disease is difficult and tiny black spots forming on the plant leaves can be confused with other plant diseases. As the number of spots increases, the leaves turn yellow and as with poplar rust, fall prematurely.

A spokesman for the Ministry of Works and Development in Christchurch said that so far the disease was restricted to Palmerston North.