Sphaeropsis tip blight of pine.
|Severity:||4 out of 5|
|Frequency:||4 out of 5|
The fungus attacks young, healthy, unwounded needles of new candles. However, on stressed evergreens, twigs may be attacked. Since the fungus increases inoculum on old dead cones, trees thirty years and older are more likely to be attacked. Young trees severely stressed or growing near old infected trees may also be attacked. Browning, stunting, and twisting of new shoots and needles are the first symptoms. One side of a tree or the lower part may be the first area affected. During wet springs, every branch may have brown tips. A brown discoloration starts at the base of needles and grows toward the tip. Needles die by the time they are one half to three fourths normal length. Sometimes needles curl and twist.
Small black fruiting bodies of the fungus can be seen with the unaided eye at the base of needles, just under the fascicle, or sheath tissue. Fruiting bodies also form on scales of two-year-old seed cones and on bark of infected shoots. Infected stems often result in droopy candles (new growth). Resinous cankers may appear on stems at the youngest branch whorl or base of blighted needles. Resin from infected areas may cause dead needles to stick to the tree. Large resinous cankers may occur on older branches where wounds occur. Winter injury is a common site of branch infection. Injury to pine may be very severe in landscape plantings. Rarely is the disease a problem in forested areas or sites with trees that are within their natural range. Repeated infection of branch tips results in deformed tree growth and loss of vitality. The fungus can also cause cankers with excessive and obvious sap exudate. Branches that become girdled will die. Sapwood may be discolored with a gray to black stain.
|Cycle:||The fungus overwinters in infected cones, shoots, and needles. Spores are released in the spring during rainy periods, but high relative humidity is required for infection to occur. Therefore, the disease is usually more severe in wet springs. New shoots are susceptible to infection from two weeks after budbreak until about mid-June. The fungus penetrates the needles and quickly causes necrosis. Second-year seed cones are infected in late May or early June and serve as a reservoir of future inoculum. In addition, research on Austrian and Scotch pine in Illinois and Kentucky indicates that the pathogen resides on and within symptomless shoots from both diseased and apparently healthy pines. These symptomless infections may become active during periods of tree stress and result in branch dieback.|
Control of the disease requires that all affected twigs and cones be removed. Fertilize trees stunted by the disease to stimulate growth. Fungicide sprays are recommended in conjunction with cultural controls. Spray three times: 1) when buds begin to elongate/swell, 2) just before new needles begin to emerge from the fascicle sheath, and 3) 10-14 days later. Effectiveness of the treatments and severity of the disease are affected greatly by the weather conditions at the time of shoot emergence.
The causal fungus infects needles directly but can also infect wounded tissue. Therefore, take care to avoid wounding trees, and do not prune or shear in wet weather when spores are being released. Do not plant susceptible trees near mature, infected pines. Mulch and water as needed to reduce stress. Consider avoiding the use of the most susceptible pines in landscape plantings.