Specific pest concerns

• Needle damage
• Shoot and branch damage
• Root and root dollar damage
• Main stem damage
• Seed and cone damage

Pest problems & stand development

Sources of technical information

	Diplodia shoot blight damage (USFS).
	Diplodia canker on the main stem  (USFS).

Shoot blight and canker diseases
In the Lake States region, red pine trees are often invaded by two fungi that can kill shoots and develop into cankers on larger branches and main stems of trees. Diplodia shoot blight and canker and Sirococcus shoot blight are two of the most important diseases of red pine. They can be prevalent on trees of all ages but the most significant damage is generally restricted to seedlings and saplings. Both pathogens have unpredictable outbreak patterns that are often dictated by weather events. Diplodia outbreaks tend to occur during droughts or following hail storms, while Sirococcus outbreaks often occur following cool, wet spring weather. During outbreaks many seedlings and small trees can be killed or deformed. Multi-cohort red pine management, or growing small red pine under larger red pine, will increase the risk of disease development. This is because spores produced on infected large trees are rain-splashed onto seedlings and smaller trees growing below them.

Diplodia shoot blight and canker (also referred to as Sphaeropsis) is caused by the fungus Diplodia pinea. The fungus causes shoot blight on large trees, shoot blight and cankers on sapling and pole-sized trees, and shoot blight and collar rot on seedlings. Trees are infected through succulent shoot tissues, branch stubs and wounds. The fungus can grow from infected shoots into branch and stem wood where cankers develop, often girdling and killing trees.

Diplodia is often an episodic disease, existing at low levels for years in some areas without causing significant injury to trees. Some evidence even indicates that many trees carry latent infections that do not express themselves until a stress event occurs. Weather can play a major role in the epidemiology of this disease. Epidemics are often preceded by several years of drought, which stresses trees making them susceptible to Diplodia infection. Epidemics are often initiated locally after hailstorms, which create wounds in branches and stems that can be quickly exploited by the pathogen.  This type of scenario, hail damage and a Diplodia outbreak, can destroy entire plantations in 1 - 2 years.

Infected reserve trees and red pine windbreaks are often the sources of fungal inoculum. Spores are released from fruiting bodies on infected bark, needles and cones during wet weather and are disseminated to adjacent trees. Therefore, growing small red pine trees near larger infected trees is risky.

Planting seedlings that were infected in a nursery but not displaying disease symptoms at the time of shipment has likely contributed to the widespread occurrence of this disease. The risk of Diplodia can be reduced by planting healthy stock obtained from nurseries known to protect seedlings from infection and by not planting or growing red pine near infected trees. Since this pathogen is especially damaging on stressed trees, avoid planting red pine on very dry, nutrient poor sites. These would be areas where jack pine would probably be more appropriate. Control of competing vegetation to maintain high tree vigor can also reduce disease impact.

	Sirococcus shoot blight damage.

Sirococcus shoot blight is caused by the fungus Sirococcus conigenus. Epidemics occur periodically, closely following extended periods of wet spring weather. Damage can be significant. Young red pine seedlings and saplings can be killed outright. Many trees are deformed by the loss of shoots and smaller branches. Trees growing under or adjacent to infected red pine can be severely damaged when conditions are optimum for fungus dissemination and development. Sirococcus shoot blight is most likely to be a problem in northern parts of Wisconsin and Minnesota and in Michigan’s Upper Peninsula.

Spores are released in spring and early summer from fruiting bodies that developed on the previous year’s infected shoots. The fungus infects needles and grows into current year’s shoots. It is not uncommon to have trees and individual shoots infected by both Sirococcus and Diplodia, collectively increasing damage and losses from these diseases.

Similar to Diplodia, outbreaks of Sirococcus are episodic and the incidence and severity of the disease can rapidly increase. Removing infected overstory trees and pruning infected shoots on understory trees before spore dispersal in early spring will reduce the major sources of inoculum and minimize future disease incidence.

	Characteristic lower branch mortality due to scleroderris canker.

Scleroderris canker, caused by the fungus Gremmeniella abietina, is a disease most serious on young trees, seldom causing damage to trees taller than 6 feet. The disease develops on lower branches under snow cover and the incidence and severity of the disease is generally greatest in frost pockets and in areas where deep snow accumulates.

Windblown spores are disseminated during wet weather from April to October. The spores infect buds and needles. Infected branch tips are usually dead by the following summer. The fungus can grow from the branch into the main stem where a canker develops that can girdle and kill young trees. The fungus produces a second spore stage that is disseminated by rain splash from killed branches to adjacent trees, increasing the disease incidence.

Preventing damage by Scleroderris canker begins with planting disease-free nursery stock and avoiding establishment of plantings on sites where Scleroderris canker is present or in frost pockets and cold air drainages where the disease can become most severe. Pruning the lower branches on infected and healthy trees will reduce disease incidence.

Shoot- and tip-mining insects
Shoot and tip-mining insects cause damage by affecting tree form and growth rates. Over most of the range of red pine, this group of insects would not be considered a major concern. However, there are two moth species that do cause considerable damage in some areas. The European pine shoot moth occurs in warmer parts of Lower Michigan and the southeastern portions of Wisconsin. The red pine shoot moth is prevalent in areas dominated by outwash sands, such as the Central Sands region of Wisconsin.

	European pine shoot moth damage (USFS).
	Red pine shoot moth damage.
	Young tree dead in sweetfern.

European pine shoot moth, Rhyacionia buoliana, has been a pest in Lower Michigan since the 1950s. Larvae feed on buds and shoots. Damage occurs when a heavy infestation destroys the buds in the top whorl of young trees, creating twisted, multi-stemmed trees. Distribution of this insect is limited by its inability to survive cold winter weather. It can be found in Lower Michigan, southeastern Wisconsin, and a few other locations where consistently heavy snow cover provides insulation for winter survival. Many trees attacked and deformed when young do, over time, recover and grow into reasonably straight trees.

Red pine shoot moth, Dioryctria resinosella, was initially identified as a significant pest in the 1980s in the Central Sands region of Wisconsin. Larval shoot feeding resulted in height growth losses of 38-65% and radial growth losses of 16-42% over a 9-year epidemic period. Following outbreaks, tree crowns changed from straight-stemmed and conical to a bushy and flat-topped appearance. In some plantations, tree form was altered enough to make it difficult to develop products such as utility poles and cabin logs.

Management of shoot and tip moths can be difficult, very little can be done to limit damage in the areas susceptible to these two insects. On small trees, corrective pruning may be useful, especially on trees that have their terminal shoot damaged.

Sapsucking insects
Sapsucking insects can reduce tree health or vigor by removing large quantities of sap. But, what is more important, their feeding often creates wounds that eventually plug and permanently reduce sap flow through twigs and branches. Wound sites can also serve as entry points for pathogens. Sapsucking insects include aphids, adelgids and spittlebugs.

Saratoga spittlebug, Aphrophora saratogensis, has historically been the most significant insect pest of young red pine across northern portions of Michigan, Minnesota and Wisconsin. Outbreaks were prevalent in the 1950s through the early 1980s. Adult Saratoga spittlebugs insert their straw-like mouthparts into red pine shoots. Large spittlebug populations cause extensive wounding that can kill branches. Tree mortality can occur and plantation failures have been reported. High populations are associated with abundant sweetfern, the plant that serves as a host for the immature stage of the spittlebug. Planting red pine into areas where sweetfern is abundant creates a high risk of spittlebug attack. Several other plants can also serve as an alternate host including willows and raspberries/blackberries.