Inspector Findings in Kentucky

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For those of you that did not receive last month’s issue, this is a new newsletter that we have put together. The plan is to write six issues per year beginning in April.
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Pests to watch for in May

Look for Anthracnose Diseases of Shade Trees

by John Hartman, Extension Plant Pathologist

Ash

Maple

Oak

Sycamore

Disease spread

Control

Twospotted Spider Mite

Twospotted spider mites spend the winter as adults in the soil or on weeds. Each female can lay more than 100 eggs during her lifetime. The life cycle may take as few as five days during hot, dry weather or as many as 20 under cooler conditions.

Twospotted spider mites are an important pest that are capable of feeding on over 180 host plants. Mites pierce the epidermis of the host plant with their mouthpart to extract the sap. When they do this, mesophyll tissue of the leaf collapses in the area of the puncture which produces a chlorotic spot. After a heavy attack, an entire plant may become yellowed, bronzed or killed completely. The mites may also spin so much webbing that the entire plant becomes covered.

Because of the small size of mites and their ability to rapidly increase in numbers, mite populations often go unnoticed until symptoms become apparent. A simple way to monitor plants for spider mites is to hold a piece of white paper under a branch and tap the branch to dislodge any mites. Although the mites are tiny, you will be able to see them crawl across the paper. To achieve good control, a thorough application of pesticide to the underside of the plant foliage must be made. In hot weather, another application may be needed 7 to 10 days later to kill mites that were in the egg stage during the first application. In hot weather, be sure to check plants for reinfestation or for the offspring of mites that were missed on the first application.

Several products are listed for control of spider mites. Insecticidal soap, summer oil, Cygon (dimethoate) Diazinon, Dursban (chlorpyrifos), Dycarb (bendiocarb), Kelthane (dicofol), Mavrik, Ornamite (propargite), Tame (fenpropathrin). Note: oils should not be used on certain plants. Read label to make sure plant is labeled for use.
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Gypsy Moth Traps Going Up

Pheromone traps are also available for other insect pests and can be used as a very powerful monitoring tool. A case in point would be a pheromone trap for the dogwood borer. A grower could hang a couple of traps around dogwood trees and monitor them for presence of the borer adults. When the first borer adults are caught, the grower would then be able to apply an insecticide at the correct time to coincide with egg hatch. The obvious advantages of this system are decreased insecticide sprays. On the other side, it does take a little more effort on part of the grower to make sure that the traps are set out when they need to be and they are monitored on a regular basis.

Your local county extension office should have copies of ENT 53, Vendors of Beneficial Organisms in North America and ENT-54, Vendors of Microbial and Botanical Insecticides and Insect Monitoring Devices. These are good references and list several vendors.
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Insect Borers in Trees and Shrubs

by R.A. Scheibner, D.A. Potter and L.H. Townsend

Borers that riddle the heartwood (or non-living wood) may weaken the tree’s structural strength so that it is easily knocked down or its limbs broken off by strong winds. Borer injury also allows disease organisms to enter the tree and compound its problems.

It is necessary to know which borers are likely problems for a tree so you will know how and when to apply appropriate control measures. Awareness of the habits and seasonal development of the borer is critical to the timing and placement of insecticidal controls. The general biology of all borers is similar, but each species differs in particular aspects.

General biology

Some borers are attracted to a wide range of hosts, while others are very restrictive in selecting hosts. Generally, borers prefer weak or injured trees of suitable host species. Eggs are usually laid on the surface or in niches of the bark. Hatching occurs within a week or two, and the tiny borer immediately burrows to an internal layer where it feeds and grows. Larvae grow in increments by periodically molting. The number of molts and time between molts vary with the species. The larval period may vary from a few months to two or more years. When the larva is fully grown, it changes to a pupa. The pupa is sometimes referred to as a resting stage because it does not feed or move around much but internally makes the radical transformation to the adult form. The pupal stage for borers lasts a few weeks. The adult then emerges, mates and lays eggs for the next generation.

Clearwing Moth Borers

These borers occur under the bark of host trees. Typically clearwing moth borer infestations cause off-colored or wilted foliage or die-back of terminal growth. The site of attack is often marked by scars, callous formation, unusual growth or patches of loose bark. Sawdust or ooze may exude from borer holes. Empty pupal skins protruding from the injury site may be seen occasionally.

One of the most common clearwing moths is the dogwood borer. Its preferred host is flowering dogwood, but it may attack pecan, hickory, apple and cherry trees. Research in Kentucky shows that dogwoods growing in full sun were attacked three times more often than trees in full shade, and trees with bark injuries were attacked twice as often as those with little or no injury. Young trees were usually infested near ground level around lawnmower wounds; older trees were usually infested at crotches or at cankers, pruning scars and roughened bark on main limbs. One or two borers were sometimes sufficient to girdle and kill small trees.

The peachtree borer and the lesser peachtree borer are pests of peach, plum and cherry trees, including both the fruit and the ornamental varieties. The peachtree borer feeds under the bark, preferably of young trees, from the root crown up to 18 inches above the ground. Sawdust and gum exude abundantly from the infested site. Overwintering larvae are of all sizes, and in spring they resume their growth and complete their development in sequence according to their overwintering size. As a result, there is a single prolonged flight period. The first adults appear in early June, but usually only small numbers are caught in traps until July. Flight activity peaks in early August and declines by mid-September.

The lesser peachtree borer, which infests the same hosts as the peachtree borer, prefers older trees and attacks the upper trunk and scaffold limbs at narrow crotches or areas injured by pruning, freezing, cankers or sunscald. It is less likely than the peachtree borer to attack healthy trees. In Kentucky, a single heavy sustained flight period occurs from early May to September.

The lilac borer is a serious pest of lilac, privet and ash. It lays its eggs on rough or wounded bark, mostly in an area from the root crown to about three feet above ground. The borer undergoes most of its growth under bark but enters the sapwood in its later stages. In average years, flight activity begins in late April, peaks in early June and declines by early July.

The banded ash borer, attacks only ash from ground level up to eight feet or higher on the trunk. Moth flight is in August and September, well after the flight of lilac borers, with which it may be confused. Since both the banded ash borer and the lilac borer are common pests of ash, two properly timed insecticidal sprays are needed to control both species.

The oak borer is a pest of oaks throughout the eastern U.S. and Canada. However, it is not as prevalent in Kentucky as the other previously mentioned clearwing moths. In Kentucky and Ohio, it is most damaging to young trees, especially pin oaks, but in the South it attacks mainly mature red oaks. The adult flight period is from mid-May to mid-June in Kentucky. Coarse brown residue oozing from burrows and areas of dark sap-stained bark on trunk and limbs are indicative of oak borer infestation.

Beetle Borers

The 1/2 inch-long adults are slender, olive-bronze, hard-shelled beetles. They begin emerging through D-shaped holes in the bark in late May or early June but may continue to emerge sporadically into August. Emerging beetles feed on birch and aspen leaves for about a week before egg laying begins.

Eggs are laid in groups in cracks or under loose flakes of bark on birches. They hatch in two weeks, and the young borers tunnel to the inner bark, feeding there and in the outer wood layers. Although eggs may be laid in vigorous trees, the larvae do not complete their development, and the site is healed over. This type of injury is often marked by spiral ridges on the surface of limbs or the trunk.

Trees stressed by drought or low vigor cannot withstand borer attack. Successful attack usually begins in the crown of the tree where the effects of stress develop first. As the tree becomes progressively weaker, the borer infestation progresses down the tree.

The twolined chestnut borer, is similar to the bronze birch borer except that the adult has two pale stripes on the back. Also, the chestnut borer attacks chestnut, oak, beech and American hornbeam. Adults emerge in May and June and feed on leaves for several weeks before laying eggs under bark scales. Newly hatched larvae bore to the inner bark and outer sapwood where they grow for one to two years.

The flatheaded apple tree borer, is a common and serious pest of many species of deciduous shade, fruit and nut trees. Newly transplanted trees, especially young maples, or those under stress are particularly susceptible to attack.

In the adult stage this flattened, metallic beetle emerges in the spring and summer, mates and lays eggs around bark crevices on the trunk or larger branches. The larvae feed beneath the bark, damaging cambium, phloem and outer sapwood. They make irregular tunnels tightly packed with sawdust-like residue. Full-grown larvae overwinter in the sapwood or hardwood and pupate the following spring. There is one generation each year.

Control

Use of Flowering Plants as Indicators for Timing Management Actions for Landscape Insect Pests

* begin treatment at time indicated

** treatment for leafminers can be done either at adult flight or can be postponed for approximately 4 weeks and a systemic insecticide can be used to target the larvae

*** make one treatment for these borers. Treatment should be done approximately 10 days to 2 weeks following adult flight. Treatments should be made as a bark spray with an insecticide that has some residual action such as Dursban, Lindane, Thiodan.

**** make two treatments at three week intervals
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Did You Know?

Also, did you know that gas containers placed in the bed of pickups with plastic bedliners are subject to combustion. It seems that as the containers are in the bed they can build up static electricity. When these containers are refilled in the bed of the truck, sometimes a spark is created between the metal gas nozzle and the container. This spark can in turn ignite the gas in the container. One county agent had this happen to him this past fall. If you have a plastic bedliner, you might want to remove the container before filling.
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