Rhizosphaera Needle Cast

Once again, many blue spruce samples showing signs of Rhizosphaera needle cast having been arriving in the Plant Disease Clinic. This fungal needle disease causes browning and early loss of needles. Trees of any age may become infected, especially those that are stressed. Symptoms are most obvious on second-year (inner) needles. Diseased needles turn purplish brown and fall from the tree during summer and autumn.. Small black fruiting structures (pycnidia) of the fungus can be seen in the pore-like openings (stomata) of infected needles. These fruiting bodies typically appear in rows along the length of the needle. A hand lens or magnifying glass is helpful in viewing these structures.

Infected trees can be sprayed with a fungicide such as chlorothalonil (e.g. Daconil 2787) or Bordeaux mixture when new shoots are 1/2 - 2" long (late May or early June), and 4-6 weeks later. Also, improve tree vigor through mulching and watering when needed. Promote good air circulation by adequate tree spacing and weed control. Do not shear trees when foliage is wet. Finally, inspect trees carefully for fruiting bodies before planting.

Rhizosphaera needle cast is pictured in Pm-1528 Common Diseases of Conifers in Iowa. This publication is available from your local Extension office .

This article originally appeared in the May 8, 1998 issue, p. 51.


Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Horticulture and Home Pest News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on May 8, 1998. The information contained within may not be the most current and accurate depending on when it is accessed.