The location where an insect or disease takes up residence in a tree can be just as important as the virulence with which it attacks. Root pests such as Armillaria root rot can compromise the structural integrity of a tree, increasing the potential for softening of the tissues and detachment from soil particles, resulting in catastrophic tree failure. Foliage feeders such as bagworms, sawflies and redhumped oakworms can greatly reduce the vitality of a specimen by decreasing the photosynthetic activity of the leaves. As well, insects that feed on, in, or under the bark are great causes for concern.

Scouting and monitoring

As with any pest, an Integrated Pest Management (IPM) approach is best to deal with troublesome bark pests. The first step to an integrated approach is to proactively scout for these pests in your customers’ trees.

In order to spot troublesome pests that attack the conductive vessels, foliage, bark and roots, there are two approaches:

1. Sit by the phone and wait for customers to call and say “My tree just doesn’t look too good… Can you take a look?”

2. Set up a proactive scouting program that involves regular visits to a site, thoroughly inspecting the trees for any sort of malady that might be compromising their vigor.

As arborists and tree care workers, the years of experience and training that you have to offer your clients are valuable, and should be paid for accordingly. Monthly proactive inspection visits – whether or not pests are found – should be a routine service provided and invoiced each month.

In addition to improving the bottom line for the company, scouting services provided on a consistent basis will help you better care for your clients’ trees and be more successful in your control strategies. This approach makes it possible to spot an insect problem early on and puts you, not the insect, in the driver’s seat. The “waiting by the phone” option is strictly reactive, relying on treatments directed toward full-blown infestations for efficacy. All in all, the scouting and monitoring methodology is better for both tree care businesses and facilitation of effective pest control.

Ips beetles

Ips beetles — or engraver beetles, as they are more commonly known — are bark beetles that generally confine their damage to pine and spruce trees. The larvae develop under the bark and produce girdling tunnels that can cause dieback and kill trees. Adult Ips beetles are small (0.125 to 0.375 inches long), reddish-brown to black beetles, with characteristic depression at their rear end, which contains three to six pair of tooth-like spines, depending on the species. Typically, these insects are attracted to and infest trees that are weakened or in decline. However, large populations can build up when large numbers of trees are stressed by drought or other weather conditions. Ips beetles can become a serious factor in tree death at that point.

Bark aphids of broadleaf and evergreen trees can kill branches if left unchecked, underscoring the need to scout on a regular basis.

PHOTO: ANNE GLYNN, CHRISTY RENDER, KYLE TONJES

Adult Ips beetles will bore into the tree, and this creates symptomatic traces of yellow or red sawdust, which accumulates in the bark or on the ground. There also will be small holes visible in the bark from where new adults have emerged and left the plant. As Ips beetle larvae tunnel in the tree the infested areas will “fade.” This fading will start in a few branches but, left unchecked, can affect the entire tree.

The best offense against Ips beetles is a good defense. Make sure that trees are well planted and well maintained. Root compaction, mower injury or drought stress can invite engraver beetles to infest a tree. You also should be sure to not stack cut wood next to living trees. Cut wood is like a beacon to Ips beetles and, if it is next to living trees, they may infest them, too. If you have high-value trees you want to protect with insecticides, two applications (early spring or summer) of products containing permethrin, bifenthrin or carbaryl can prevent infestation. You must follow label directions and apply a thorough application of the spray to achieve success. There are no products that can cure Ips beetles from an already infested tree.

Twig girdlers

Many species of twig girdlers can cause insult to broadleaf trees. As adults, these longhorned beetles are 0.5 to 0.625 inches long with cylindrical bodies and generally grayish-brown wing covers, sometimes with a broad, ashy-gray band across the middle. The eggs are smallish, elongate to oval, and about 0.09 inches in length. The larvae are whitish, cylindrical, legless grubs that reach 0.625 to 1 inch long.

Oak kermes and San Jose scales utilize piercing-sucking mouthparts to extract vital cell sap.

PHOTO: JAMES A. KALISCH, UNL

Twig girdlers are pests of many tree species including oak, pecan and hickory, and, to a lesser extent, several other hardwood trees. Unlike many other tree pests that injure trees as larvae, the adult beetles girdle twigs and small branches causing the injured portions to break away or hang loosely on the tree. It’s common to see the ground under infested trees almost covered with twigs that have been cut off, leaving one to wonder if the damage was caused by a squirrel, an insect, storm damage or a pathogenic disease. Barbecue wood value aside, their action often affects the beauty and aesthetic quality of trees in a landscape planting. In most situations, major structural damage does not occur to important scaffold limbs.

Chemical control isn’t needed, as these insects cause only cosmetic damage. Even in a year where they seem prolific, no tree will die from twig girdler damage. If there is a recurring issue, simply collect the cast off twigs with the eggs in them, or clip them from trees, and burn them in the fall.

Galls

Another pest that commonly affects trees but may not be as consequential as boring insects, galls are odd growths that can occur on leaves, twigs or branches. They may be simple bumps or complicated structures, ordinary bark-brown or beautifully, brightly colored.

There are over 1,600 species of gall producers, the majority of which are insects and mites. Galls are essentially plant tumors; the plant’s cells grow oddly and multiply quickly in response to insects or mites feeding or laying eggs on the plant. They also may develop as a response to infections by several kinds of fungi, bacteria and viruses. Fortunately, galls affecting leaves are seldom, if ever, a serious problem; however, those that affect twig and branches, such as the gouty oak gall and horned oak gall, can be more serious.

Control efforts involving galls on a tree should depend on several factors. Since they rarely cause serious damage, injections or cover sprays should be limited to highly valuable specimens such as historic or memorial trees. For example, if an oak tree infested with galls overhangs the first tee of a famous golf course that has a monument as a tribute to high profile golfers (Jack Nicklaus, Ben Hogan, Arnold Palmer) who have played in previous tournaments, it may justify treatment. Some arborists are reporting that consecutive years of injections with bidrin helps to suppress populations of hazardous gall makers like the horned oak gall.

Scales

Scales are sucking insects that insert their small, needle-like mouthparts into bark, fruit or leaves of trees and shrubs. Depending on the size of the infestations, scales can seriously damage their host or merely be slight annoyances. Scales can be exceptionally cryptic as well due to their immobile nature as well as their coloration, size and shape.

Oak twig galls are examples of bark insects that should be noted in an inspection.

PHOTO: JAMES A. KALISCH, UNL

There are two kinds of scales, armored scales and soft scales, and each type has different control strategies. Soft scales, like cottony cushion scale or European elm scale, secrete sticky honeydew and lack a thick, waxy coat above their body. Armored scales, including oak pit scale and sycamore scale, do not excrete honeydew and have a waxy shell that protects their squishy body. In general, they both exhibit a similar life cycle in which eggs are hidden under the mother’s body, where they will hatch and “crawlers” will move throughout the plant, mate and then settle down to feed for the rest of their life.

Symptoms of a scale infestation can mimic water stress or can include leaves turning yellow and dropping prematurely, dead, brownish leaves that may give the plant a scorched appearance. If the scale produces honeydew, this sticky excrement can become infested with black, sooty mold or attract ants and wasps to the infested area.

Oystershell scales utilize piercing-sucking mouthparts to extract vital cell sap.

PHOTO: JAMES A. KALISCH, UNL

Scale control can be difficult due to their obscure nature and, for the armored scales, their waxy protective barrier. Monitoring for scale insect “crawlers” is essential to maximizing your control success. You can do this through visual inspection or by using tape, with the sticky side out, to find when this susceptible stage is on the move. You can treat with a pyrethroid or carbamate insecticide, being sure that you get thorough coverage on the top and bottoms of leaves. You can also treat using a summer oil, insecticidal soap or neem oil to eliminate these immature scales. One other option would be to treat with a dormant oil when the tree is dormant in the winter.