Diplodia Tip Blight on Pines

By The Old House Web

Diplodia Tip Blight on Pines

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Diplodia pinea causes tip blight and dieback of Austrian, Scotch, mugo, red, white and jack pine. Exotic pines are the most susceptible to Diplodia, particularly Austrian pine. In decreasing order of susceptibility are Scotch, red, Swiss, mountain, ponderosa and white pines. In rare instances, Douglas fir, Norway spruce and some cedars can be mildly infected. In the landscape, the disease is most severe on Austrian pine.

Symptoms: Diplodia tip blight of pines is a relatively easy disease to diagnose -- a homeowner can become acquainted with its symptoms by examining older pines in landscape plantings. Tip blight kills the expanding candle, the current year's growth tip. The candle turns brown, giving the tree brown tips, particularly in the lower branches on older trees. The needles in the killed candle will be only partially expanded.

The symptoms of Diplodia tip blight are similar to the browning and death of expanding candles caused by the northern pine shoot borer and the Nantucket pine shoot moth. To differentiate the two causes of tip blight, break the brown candles. Those infected by Diplodia are woody and do not break easily. If the candles are weak and brittle and break easily when bent, the candles were more likely killed by a shoot-borer insect. The insect leaves a brittle, hollow tip with frass (droppings) inside the hollow.

Cause: Diplodia tip blight becomes progressively worse as infected pines mature because the fungus infects 2-year- old cones. The cones are not noticeably diseased, but the fungus forms many spore-bearing fruiting bodies on the scales. The cones cling to the tree for several years. During that time, spores shower onto the branches below during every significant rain.

Diplodia-killed candles often have small black spots, the spore-bearing fruiting bodies, usually under the needle sheath. The primary source of spores, however, is the fruiting bodies on old cones. NOTE: The symptoms of the disease occur after infection; the only time to use fungicidal sprays is during the infection period.

Control: Use native pines in plantings, such as eastern white pine and red or Norway pine. Keep infected trees vigorous by fertilizing and especially by watering during the short droughts of midsummer. Diplodia tip blight can be controlled with one to three applications of an effective fungicide. The fungicide application must be precisely timed to coincide with swelling and opening of the buds, usually late April and early May. When candles begin expanding (usually in mid May), it is too late.

Visuals associated with this text.

Visual title - Visual size Visual title - Visual size
Diplodia, fruiting bodies on cones - 38K Diplodia, fruiting bodies on infected needles - 30K
Diplodia tip blight on pine, close up - 41K
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