Austrian pine trees are stunning conifers that can add beauty and elegance to any landscape. However, these trees are susceptible to attack by destructive microscopic pests known as nematodes. Once a pine tree is infected with pine wilt nematodes, the tree will die. There is no way to treat an infected tree that is already dying. The only option is injections with abamectin nematicide to try to prevent infection in the first place. If you want to save your Austrian pines from the devastation of nematodes, early intervention and prevention are key. Let’s take a detailed look at how to identify and get rid of nematodes on Austrian pine trees.
What are Nematodes?
Nematodes are tiny parasitic roundworms that live in soil and attack plant roots. There are many different species, some of which specifically target pine trees. Two types in particular wreak havoc on Austrian pines – the pine wood nematode and the pine wilt nematode. These microscopic worms burrow into the roots and vascular tissues of the tree, obstructing water and nutrient flow. Left unchecked, they can kill an Austrian pine within just a few months of infestation.
How To Identify Nematode Damage
Catching nematode infestations early is crucial to save your trees. Here are some key signs that may indicate the presence of parasitic nematodes:
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Stunted growth and yellowing foliage – Damaged pine roots cannot take up adequate water and nutrients.
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Wilting and drooping – Infested trees often wilt even when soil moisture is sufficient.
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Small holes or lesions on pine roots – Caused by nematodes burrowing into the roots,
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Sudden and rapid decline of tree health.
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Presence of sawyer beetles – These insects transmit nematodes
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Swollen, knotted appearance on roots.
If you suspect nematodes, confirm with soil tests or root examinations under a microscope. Once an infestation is verified, take action immediately.
Effective Methods to Eliminate Nematodes
Preventative Systemic Nematicide Injections
The most effective treatment is abamectin nematicide injections done preventatively before infection occurs. Abamectin kills nematodes before they can infest the tree. Injections should be administered by a professional arborist every 1-2 years.
Solarizing the Soil
Solarization uses sunlight to heat and disinfect the soil, killing nematodes. Cover soil with clear plastic for 4-6 weeks in summer to solarize.
Remove and Destroy Infected Trees
Pine trees already infected with pine wilt cannot be saved. Remove diseased trees right away to prevent spread. Burn or chip infected wood onsite.
Plant Nematode-Resistant Plants
Certain plants like marigolds repel and disrupt nematodes. Intercrop with resistant species.
Maintain Tree Health and Vigor
Healthy pines better withstand pests. Ensure trees get proper sunlight, watering, nutrients to bolster defenses.
Avoid Moving Contaminated Soil and Tools
Carefully clean tools and equipment between uses to prevent spread. Do not transplant trees in nematode-infested soil.
Biological Control
Introduce predatory nematodes or fungi to naturally suppress plant-parasitic nematode populations.
Protect Your Austrian Pines with Prevention
Vigilant monitoring and early intervention provide the best chance of protecting your Austrian pines from lethal nematode damage. Schedule regular tree care and immediately treat any signs of infection. With preventative abamectin injections, solarization, and prompt removal of diseased trees, you can defend your landscape against these tiny but deadly pine killers. Keep your beautiful Austrian pines thriving for years to come through proactive nematode control and care.
Pine Sawyer Beetles and Spread of Pine Wilt
Pinewood nematodes have a unique relationship with longhorned beetles known as pine sawyer beetles (Figure 6). At least two species of pine sawyers, Monochamus carolinensis (Oliver) and M. titillator (Fab.), occur in Oklahoma. Both species occur widely in the southern and eastern U.S. and west into eastern Oklahoma and Texas. Adult pine sawyer beetles measure ¾ inch to 1 ¼ inches in length and have a gray and green body (Figure 6). Pine sawyers have long antennae; the antennae of males may be two to three times the length of the body. Larvae are legless white grubs, have a brown head, and are about 2 inches long when fully grown (Figure 7). While feeding, the larvae make an audible noise that sounds like sawing; hence, the insect’s common name.
The life cycle of pine sawyer beetles is usually completed in roughly 50 days to 60 days. There is an average of 2 ½ generations per year in Missouri (details for Oklahoma are lacking). The female beetle chews a small hole in the bark of recently dead, dying or declining pine trees and lays her eggs. Young larvae feed on the inner bark, cambium and outer sapwood, forming shallow excavations (surface galleries). Older larvae bore into the heartwood and then tunnel back toward the surface, forming characteristic U-shaped tunnels (Figure 8). At the last stage of larval development, they form a pupal cell at the outer end of the tunnel near the surface of the wood. After pupation, the adult emerges by chewing a hole through the remaining wood and bark.
Pinewood nematodes are microscopic and cannot move from tree to tree without assistance from pine sawyer beetles. These nematodes have developed an intimate relationship with these beetles to facilitate transmission to new trees. As adult pine sawyer beetles emerge from wood colonized by pinewood nematodes, large numbers of nematodes have al-ready moved into the beetles’ respiratory openings (spiracles) and are thus carried in the tracheal system. Beetles become vectors for the nematodes as they visit healthy trees to feed on bark, thereby introducing nematodes into the tree through feeding wounds.
Pine sawyer beetles are most active from May through late September with disease symptoms usually appearing shortly thereafter from July through December. Newly emerged adults may visit healthy pines and feed on the bark and/or visit stressed or dying trees while feeding, mating or laying eggs. It should be noted that pine sawyer beetles rarely attack healthy, vigorously growing trees. Therefore, it is important to maintain the health of pine trees to reduce the spread of pinewood nematodes.
Figure 6. Southern pine sawyer, Monochamus titillator (male). Photo by Lacy L. Hyche, www.bugwood.org.
Figure 7. Larvae of southern pine sawyer. Photo by Lacy L. Hyche, www.bugwood.org.
Figure 8. Gallery of southern pine sawyer larva. Note blue stain fungi in xylem vessels. Photo by Lacy L. Hyche, www.bugwood.org.
Inspection and Control of Pine Wilt
Pine wilt disease differs from other pine tree diseases due to rapid decline of the tree (within a season). The disease is more common on exotic pine species, although native pines under stress are susceptible. Differences between pine wilt and other pine tree problems are noted in Table 2.
A map of the current known distribution of pine wilt disease in Oklahoma is shown in Figure 9. To positively confirm a case of pine wilt in a new area, a sample from the tree should be collected. Please follow the sampling recommendations in EPP-7675, Sampling for Pinewood Nematodes and submit samples through your local county OSU Extension office.
It is possible to treat healthy trees with an insecticide to kill beetles and prevent pine wilt infection. Preventative injections of abamectin can be made every year to two years to reduce the likelihood of pine wilt establishment. Injections can only be made by a tree care specialist, so a certified arborist should be consulted. Pine sawyers do not enter diapause during the winter, so some larvae feed, pupate and emerge during warm periods all year. Therefore, prevention of the disease using this method is not always successful. Once a tree is infected with pinewood nematodes, pesticides are no longer effective.
There is no cure for pine wilt once a tree is infected and dead trees left in the landscape are sources of both nematodes and pine sawyer beetles. Diseased trees should be destroyed by burning, chipping or burying. The stump should be removed or ground down and buried under 6 inches of soil.
Figure 9. Pinewood nematodes have been confirmed by sampling in the Oklahoma counties marked in yellow. At least one sample has been examined from the counties marked in green, but pinewood nematodes were not recovered. Counties marked in white have not submitted samples for testing. Based on data as of 2/19/2021.
Table 2. Comparison of pine wilt to other pine tree problems.
| Observation | Possible Pine Wilt | Other causes suspected |
|---|---|---|
| Pine hosts | Mainly non-native pines | All pine species |
| Age of tree | Usually, older than 10 years | Any age |
| Symptoms | Rapid discoloration and wilt | Stunting, spots, needle drop |
| Time symptoms appear | Late summer to winter | Any season |
| Progression of symptoms | Trees killed quickly, one to three months | May be rapid, but usually months or years |
| Resin flow | Lacking | Present |
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FAQ
How do you treat pine nematodes?
What are the symptoms of pine wood nematodes?
What is killing my Austrian pine trees?
What is the disease in the Austrian pine?
Can a pine tree get a nematode?
Exotic pines including Scots, Austrian, and mugo are susceptible to infection by the nematode. Some degree of resistance has been observed in native pines, however they may still be infected. High summer temperatures are required for the nematode to develop in the beetle and within infested trees.
Is Austrian pine pest resistant?
Austrian pine was thought to be relatively pest resistant, however, there have been losses and disfiguring diseases in most area. The most common disease is Diplodia tip blight (Sphaeropsis sapinea). This fungus commonly infects stressed trees over thirty years old starting at the branch tip and killing the branch back to the main trunk.
Do Austrian pine trees die if left unprotected?
Left above ground and unprotected, a potted tree’s roots may die. The Austrian pine is prey to many fungal diseases, such as lophodermium needle cast, diplodia (sphaeropsis) tip blight, as well as various wood rots and decays. Remove affected branches as you spot them.
Are Austrian pine trees prone to wind damage?
Aside from its susceptibility to pests and fungal diseases, Austrian pine can be susceptible to wind damage, especially in the winter if heavy snows weigh down the branches. Prune away dead branches as you spot them. With young trees, shake off heavy snow from the branches to reduce weight.