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| DIPLODIA TIP BLIGHT |
Description
The most noticeable symptoms of Diploida Tip Blight are browning, stunting, and twisting of the new shoots and needle growth called candles. Usually the lower branches are the first and most seriously affected, and sometimes infection is concentrated over a small area or one side of the tree. During wet springs, branches throughout the entire crown may show the characteristic brown tips.
Initial infection is caused by one called spores which float in the wind, or are transported by birds and insects, and deposited on the tree. After initial infection, a brown discoloration appears near the base of the needles then progress toward the tips. Infected needles usually die when they reach ½ to ¾ their normally length. Generally, all the needles on an infected shoot die.
Infected twigs commonly exude a resin from developing cankers. Infected cones fail to mature. Black, pinpoint sized specks (fruiting bodies of the fungus which are called pycnidia) from near the base of the infected needles, in the bark of infected twigs, and on infected cones. The spores then overwinter in the infected needles, twigs, cones, and bark.
Although Diplodia tends to disfigure rather than kill trees rapidly, constant and repeated infections will kill trees through the combination of no new candle growth and the natural process of ageing of the older needles. Since evergreens only form new needles at the tips of branches and twigs, killing of these growing points by the Diplodia Fungus causes no new needles to be formed. Needles which were formed 2-5 years ago shed in the fall through natural process called Fall Needle Drop. The amount of needles shed is determined by trees species. Serious problems occur if the new growth sites are killed by Dplodia Tip Blight, and the older needles are shed through natural needle drop. Recurring attacks also result in reduced growth and lack of vigor which makes your trees susceptible to other diseases and insect pest problems.
Diplodia may be occasionally confused with symptoms of low temperature injury, drought, and drying from winter desiccation. Trees damaged by these environmental factors can mimic the symptoms of Diplodia. However, the black fruiting bodies mentioned earlier will differentiate this from Diplodia Tip Blight.
Tip death caused by Pine Shoot Moth and Pine Shoot Moth and Pine Shoot Borer is frequently confused with Diplodia as well. Differentiating Diplodia from Pine Shoot Moth and Pine Shoot Borer is easily done by breaking the infected candles. Brown candles which are woody and resist breaking are infected by the Diplodia fungus. If the candles are weak and brittle, breaking easily when bent, they were probably killed by the aforementioned insects. The presence of frass in the hollowed out candles is a further indication of insect damaged. |
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How
to Treat
THE BEST MEASURE FOR PREVENTING DIPLODIA TIP BLIGHT is to avoid planting susceptible species into the landscape. But, because these species are attractive additions to urban settings, many homeowners are willing to plant these species despite the risk of diseases. The number and severity of infected trees had been steadily increasing in south east Michigan due to the overplanting of Austrian Pines in the landscape. If these trees are present in your landscape, certain steps must be taken to insure the continued health and beauty of these conifers.
CONTROAL OF DIPLODIA consist of preventative fungicide applications performed in the spring: General from late April through June. The exact timing of these applications is dependent upon rain, humidity, and temperature. The cooler and wetter the spring is, the earlier the spraying must be performed.
In most instances, two or three properly timed fungicide will protect the plants from infection. Suring periods of prolonged damp weather, additional spraying may be needed. In case of severe infection of specimen trees, direct trunk injection with Maujet Fungisol may be necessary.
Pruning and burning diseased tips and limbs had proven not to be an effective means of control since research has shown that the incidence and severity cannot be reduced this way. If pruning is desired to improve the appearance of an infected tree, a trained professional arborist should perform this work since proper sterilization techniques are required so as not to spread the fungus.
THE HOMEOWNER CAN CONTRIBUTE to the health of their trees by watering when drought conditions occur (less than 1 rainfall per week). Also avoid walking over the root system since that compacts the soil and reduces the availability of much needed aid and water to the fibrous roots.
As is the case with virtually all pests and disease problems, a healthy, vigouous tree is your best protection against serious damage. Combining this with the proper preventative fungicide applications, as well as reasonable care from the homeowner, will insure the continued health of the pines that add so much beauty and value to your landscape. |
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