Ips is a common group of bark beetles that infest pine and spruce trees. Ips are small (1/8 to 3/8 inch long), reddish-brown to black beetles. Using a hand lens one can differentiate from other bark beetles by the pronounced cavity on its rear end along with 3 to 6 pairs of tooth-like spines. They rarely attack healthy trees. Most problems with Ips occur to newly transplanted or stressed trees. They develop under the bark and produce girdling tunnels that can cause dieback and kill trees. Chemicals are not effective on already infested trees but insecticidal drenches can be used as a preventative on the trunk and branches of susceptible trees. newly transplanted trees, trees suffering root injuries, and trees that are close to other infested trees are at risk and can benefit from preventive insecticide applications.* Infested trees should be removed and chipped. Never stack infested would against other coniferous trees.
Oyster shell Scale is the most common type of scale. They attach themselves to the bark of twigs and branches and feed by sucking out plant sap. They can weaken and even kill a tree when the infestations are heavy enough. Scales overwinter in the egg stage under a shell-like covering. The eggs hatch in the spring and the newly emerged insects quickly attach themselves to the plant. Scale can easily be managed by just scrubbing them off or pruning off heavily infested branches. Dormant oils can be used during the overwintering stage to kill scale. Most insecticides are only effective for a brief time once they have emerged from their shell so timing is tricky. Systemic insecticides are not recommended for Oyster shell scale control.*
Aphids feed by sucking sap from leaves. They can cause leaf curling especially on emerging leaves. When the number of aphids on a plant are very high and for an extended period, their feeding can cause wilting and sometimes even dieback of shoots and buds. A clear indication of aphid presence is the sticky honeydew that cover leaves, branches, sidewalks and anything that lies beneath an infested tree. Gray sooty mold may grow on the honeydew as well, further detracting from plant appearance. Ants, wasps, and flies, are usually attracted to the honeydew in trees. There are numerous predators that feed on aphids including lady beetle larvae, green lacewing larvae and syrphid flies and parasitic wasps. If possible, just wash them off with a garden hose. If natural enemies are not sufficient and or a garden hose is ineffective, an insecticidal soap can be sprayed, or for those pesky aphids that are hiding under the leaves a systemic insecticide can be used.*
Bronze Birch Borer
This borer mostly attacks European White Birches but will attack others as well. Adults emerge from late May into June, and leave D-shaped exit holes in the bark. They deposit eggs a few weeks later in the bark. Emerging larvae bore through the bark and start excavating galleries. There is one generation a year. Trees that survive attack have swollen black areas around trunk. Chlorotic leaves and sparse foliage are early indications of borer presence. This borer only attacks trees that are stressed so proper cultural practices are key. Birches grow best in shady, cool, moist locations so a birch planted in an open, sunny, hot, urban lawn is going to be susceptible to attack. Make sure your Birch tree gets plenty of water. Preventive chemical sprays can be effective but timing is critical.*
You will mostly see Spider Mites on Spruce and other hardwood trees that are dry and dusty especially on hot summer days. They feed on the underside of leaves and are smaller than the head of a pin so seeing one is very difficult. These mites suck plant fluids, giving broad-leaved plants a speckled appearance and a fading color to conifers. To identify look for webbing or use a white sheet of paper underneath plant and shake- you will see tiny red or brown dots moving around on the paper. Some management options are to keep your tree watered to avoid drought. Spray tree with water to avoid dust and to help disrupt mite activities. Insecticidal soaps and dormant oils can help reduce mite populations but when infestations are heavy try using an insecticide registered for use on Spider Mites.*
White Pine Weevil
Similar looking to a bark beetle but with a long snout-like appendage, this ¼ inch long pest will kill the top 2 to 3 feet of a pine or spruce leaving the leader crooked and slowly turning brown until it’s dead. This will not kill the tree but will disfigure the top, adding stress to the tree. The first sign of attack are small puncture wounds at the base of a new leader with resin oozing out and solidifying. If this has happened to your tree, prune out dead infested branches and destroy them. Train a new leader from a lateral branch. Clean up duff around tree each fall, this eliminates spring adult migration from the duff the terminal leader. You can also apply a registered pesticide to terminals in the spring when adult feeding begins.*
Pinewood Nematode is the cause of Pine Wilt in some non-native Pines such as Scotch Pine and Austrian Pine. This pest is transmitted by Pine Sawyer Beetles (long-horned beetles) and reproduce rapidly in the sapwood, killing the tree. Symptoms of Pinewood Nematode are a rapid change of color from green to grey-green to brown beginning in summer. Once a tree is infected there is no cure so prevention is the only management strategy. If you have these trees in your landscape make sure they are watered well and store recently cut trees close to other trees.
Longhorned Beetles/Roundheaded Woodborers
Longhorned Beetles are known for their very long antennae and large size. Roundheaded Woodborers are the larvae of these beetles. They can penetrate deep into the wood while feeding. Most borers only attack stressed trees due to drought, injury or disease. The primary course of management should be making sure your tree is watered correctly and mulched well so it’s roots are not competing for water with your lawn. Mulch can also prevent trunk injury.
Emerald Ash Borer
Emerald Ash Borer or EAB for short is a 1/2 “ metallic-green beetle that attacks mostly Green Ash but can attack other Ash species as well and is a concern here in Billings since Green Ash makes up 32% of our urban forest and could wipe it out if not detected early. EAB has not been detected as of this publication but Montana has begun widespread monitoring for the pest. EAB was discovered in Boulder County Colorado in 2013 and is suspected to have come from firewood being carried in to the state. Early detection of EAB is difficult since the larvae remain under the bark and symptoms are similar to other causes of tree decline. Look for D shaped exit holes on trunk, thinning canopy and branch dieback, serpentine galleries under bark, increased woodpecker activity just to name a few. If any of these symptoms are noticed, please contact Billings forestry.
*It is advised to hire a certified arborist who holds a pesticide applicators license whenever chemicals are to be used.