Diplodia Tip Blight

Diplodia causes tip blight and dieback of Austrian pine, Scotch pine and white pines. These are three of the most common evergreen trees used in many landscapes in Grand Blanc. Only the expanding candle, the current year’s growth tip is killed in tip blight. The candle turns brown and the needles will only partially be expanded. The symptoms of Diplodia tip blight occur after infection; the only effective time to use tree disease control sprays is during the infection period. Diplodia tip blight is best controlled with three disease control applications. Fungicide applications must be timed to coincide with the opening of the buds. Then every 10 to 14 days for the next two applications. Thorough coverage of developing buds and elongating candles is essential for effective control.

Rhizosphaera Needlecast

Colorado blue spruce can be found on many residential and commercial landscapes throughout Grand Blanc. Rhizosphaera needlecast can cause serious damage to Colorado blue spruce trees and has also been identified on white spruce, Black Hills spruce and Engelmann spruce in Grand Blanc. This disease causes premature needle loss on the interior foliage of the host tree.

Although spores of the fungus may be found on infected needles at different times during the growing season, infection by the fungus occurs mostly during the spring and symptoms appear the following year. Infected needles turn yellow in mid-summer and purplish-brown by late August. Needles on lower branches are affected first and the disease gradually progresses up the tree. Spores are found in greatest numbers on the purplish-brown needles, but they may also be found to a lesser extent on yellow and green needles.

Early identification of Rhizosphaera is helpful because light infections can be controlled before significant damage to the tree canopy is done. Heavy infections can cause severe thinning of the tree canopy. This can minimize the purpose for which the tree was planted, such as a visual screen or sound barrier.

Disease control sprays should begin after the buds open and continue until early to mid summer.

Swiss Needlecast and Rhabdocline of Douglas Fir

Douglas fir trees are less common in Grand Blanc landscapes, but if you are experiencing needle loss on your Douglas fir it is probably due to one of these two tree diseases.

To limit damage from either of these tree diseases fungicide treatments should be started as soon as buds break on Douglas fir. A good rule to follow is to apply fungicide sprays when 10 percent of buds have broken and continue to apply treatments until all buds have opened. In areas where Swiss needlecast is the culprit, initial fungicide sprays should be applied when new shoots are ¼ of an inch long.