Landscape IPM Advisory

USU Landscape IPM Pest Advisories provide periodic updates on current insect and disease occurences, biology, and treatment recommendations for Utah. 

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Bronze Birch Borer, Verticillium Wilt

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June 7, 2007

In this Issue:

What's In Bloom


Catalpa: bloom
Clematis: bloom
Climbing roses: bloom

Cranberry viburnum: end bloom
Elderberry: end bloom
Hypericum sp.: bloom
Japanese tree lilac: end bloom
Mock orange: bloom
Privet: end bloom
Shrub roses: full bloom
Smokebush: full bloom
Smooth hydrangea: full bloom

Insect and Disease Activity


Elm Leaf Beetle

elm leaf beetle adult
Elm Leaf Beetle Adult

Continue to monitor for elm leaf beetle adults and larvae.

Treatment: imidacloprid (Merit and Bayer Advanced Tree & Shrub Insect Control), neem oil, Bt (Bacillus thuringiensis--Dipel, larvae only)

Two-Spotted Spider Mite

Two-spotted spider mites will be active all summer. Monitor for their activity, and keep plants healthy with optimal watering. Avoid excessive use of pyrethroids which can cause mite outbreaks by killing the beneficial predatory mites that often keep spider mite pests in check.

Treatment: acephate (Ortho Systemic Insect Killer Concentrate, Bonide Systemic Insecticide Liquid), sulfur (Bonide Sulfur Dust, Ferti-Lome Dusting Sulphur), horticultural oil (Ferti-Lome Scalecide), copper sulfate (Bonide Garden Dust, Green Light Rose and Flower Dust), malathion, or Sevin.

Bronze Birch Borer

death of birch canopy
Flagging (death) of the tree canopy caused by bronze birch borer

Bronze birch borer can be a devastating pest of white-barked birches. Larvae of this beetle feed on the cambium of the tree, eventually girdling it and causing death. (Death may take several years.) When the top of a birch or large limb near the top dies, it is a sure symptom of bronze birch borer.

Adults lay eggs on birch bark crevices in early summer, and when the larvae hatch, they bore directly into the tree. There the larvae stay until they pupate and emerge as adults either the following first or second spring. The pupal chambers and sometimes the feeding appear as raised swellings under the bark.

Adults are emerging from birch trees now, leaving behind distinctive D-shaped holes on the bark. Look for these holes on your trees to determine if you need to treat your birch trees.

IPM practices to keep your birches healthy include applying adequate water and mulch over the root system, and avoiding pruning during adult flight (late May - late June).

Treatment: Protectant materials are sprayed on the bark and larger limbs to prevent larval entry, so they must be applied before egg laying: acephate (Acecap), permethrin (Hi-Yield products), Systemic insecticides can also be used (Bayer Advanced Tree and Shrub Insect Control) to kill hatching larvae and larvae within the tree.

Lecanium Scale

Crawlers are active in Salt Lake and Tooele counties and will be active in Box Elder, Carbon, Davis, Utah, and Weber counties next week.

Treatment: neem oil, horticultural oil, imidacloprid (Merit), carbaryl, or malathion.

Honeylocust Plant Bug

If you see that leaves on your honeylocusts are heavily fed upon, but cannot find any bugs, that is because the honeylocust plant bug adults finished feeding. To avoid future injury, plan on treating your tree next year 7-10 days after bud break with insecticidal soap, horticultural oil, or imidacloprid.

Rose Stem Girdler

The rose stem girdler feeds on shrub roses, rugosa roses, and caneberries. Adults lay eggs on stems and canes in late spring, and the hatching larvae chew directly into the cambium through the bottom of the egg. The larval feeding causes the stem just above to die. Swelling is evident just below the feeding. The larvae spend the year within the cane, pupate, and emerge in May.

Treatment: Controlling with chemicals can be difficult. The best option is to prune out canes and stems with obvious swellings or when they die. Destroy the debris to kill the larvae within.


Verticillium Wilt

 Discolored streaking on wood caused by verticillium wilt  Slow decline caused by verticillium wilt

Verticillium wilt is caused by a soil-borne pathogen that enters through the root system and clogs the xylem (water-conducting tissue), thereby causing a wilt. Some trees can have an acute infection that kills the tree in one season, and some can have a chronic infection that causes a slow decline. Chronic symptoms include small, yellow leaves, slow growth, and dieback. As the mycelium of the fungus grows in the wood, it causes a green to black streaking that is sometimes visible on a freshly-cut stem.

If you suspect verticillium wilt, there unfortunately is no “cure.” Chronic infections can be managed with careful watering, mulching, fertilization, and pruning (i.e., TLC). If a tree dies from verticillium wilt, remove it and replant with a species that is resistant to the pathogen. These include beech, birch, fir, ginkgo, hawthorn, honeylocust, larch, oak, pine, spruce, sycamore, willow, and others.

Coryneum Blight (Shot Hole)

shot hole blight

Coryneum blight is a disease of ornamental peaches and plums (as well as orchard trees) that affects the leaves and stems. It is caused by a bacteria that is spread by rain or irrigation splash. It can cause cankers (sunken dead tissue) on stems or large branches. These cankers produce bacteria in spring, which then spreads to leaf tissue later in the season. The infected tissue on the leaves turns brown and then drops, leaving an almost perfect hole in the leaf.

Treatment: Make sure water from irrigation does not land on the upper tree canopy; prune out any cankers you find (these are easiest to see in the dormant season); apply a copper fungicide after leaf fall in autumn.

Precautionary Statement: All pesticides have benefits and risks, however following the label will maximize the benefits and reduce risks. Pay attention to the directions for use and follow precautionary statements. Pesticide labels are considered legal documents containing instructions and limitations. Inconsistent use of the product or disregarding the label is a violation of both federal and state laws. The pesticide applicator is legally responsible for proper use.