JAPANESE BEETLES ON TREES & SHRUBS IN GRAND BLANC

Japanese beetles are starting to hatch out in the Grand Blanc area. First discovered in the United States in 1916, the adult Japanese beetle lives for 30 to 45 days. These insects feed heavily on several common landscaping plants used in Grand Blanc including, flowering crabapple, Japanese maple trees, linden trees, Norway maple, ornamental cherry trees, rose bushes and sycamore trees.

Using Japanese Beetle Traps

Japanese beetle traps are highly effective at attracting adult beetles, but do not necessarily prevent damage to your ornamental trees or shrubs. If you decide to give Japanese beetle traps a try, place them on the border of your property and away from susceptible landscape plants.

Because Japanese beetles move around extensively, frequent tree spray applications may be needed to keep the beetles from causing significant damage to valuable landscape trees. Even with a tree spray program some feeding damage is likely to occur. Our Japanese beetle control program includes up to three tree sprays starting in late June to early July, and continuing through early to mid-August.

After Japanese Beetles Are Gone

The larva of the Japanese beetle is a white grub that feeds heavily on grass roots. Grub feeding in August puts a lot of stress on a lawn because of warm weather and drought stress. If you’ve experienced a lot of Japanese beetle adults feeding on your trees there is going to be some eggs laid in your lawn. You might need to consider a grub control treatment for your lawn to minimize feeding damage from grubs.

BROWN FOLIAGE ON JUNIPER PLANTS

                        

Phomopsis blight is a fungal disease that affects juniper shrubs, and to a lesser extent, cypress, false cypress and arborvitae plants. This disease infects the foliage and then can move into smaller stems and kill them by creating cankers and girdling the stem. Larger stems can also develop cankers but usually don’t die back.

Plant tissue infected with Phomopsis blight fades to a lighter green before dying and turning a reddish brown color. Drought stressed plants can show similar dieback but the line between live and dead tissue is not as clear as it is with Phomopsis. Other needle blights in junipers usually begin with older needles and work their way up the stem but Phomopsis starts at the tip and works down toward the center of the shrub.

Another disease, Kabatina blight is, to the naked eye, nearly indistinguishable from Phomopsis but is active earlier in the year. Kabatina blight can become active as early as March in Michigan.  Kabatina is infective in the fall of the previous year. Phomopsis is active in late March and April and again in August and September, and the dieback can occur any time during the season. Even short periods of high humidity and temperatures can initiate the development of Phomopsis spores. 

Control of Phomopsis blight involves planting resistant varieties, spacing new plants so they can dry, avoiding shaded areas, watering in the morning so the foliage can dry, and pruning on dry summer days.

Because this shrub disease is hard to diagnose in the field it may be necessary to submit a foliage sample to a laboratory before starting a fungicide program. Phomopsis blight can be reduced with a regimen of proper watering, adequate soil fertility, sanitation pruning, and spraying with fungicides when necessary. 

SCALE INSECTS

Scale insects spend most of their life as an immobile bump on a leaf or stem, siphoning off fluids from the host plant. Some scale insects excrete a fluid called honeydew that attracts a variety of nuisance pests like ants, bees and wasps to feed on the sweet exudates. The honeydew also is a great growth medium for sooty mold, a black staining mold that can cause a sticky mess on a car or driveway or anything beneath it. 

           

There are two broad categories of scale insects, soft and armored scales.  Armored scales are, as one might expect have a rigid and hard body covering, like pine needle scale or oystershell scale. Soft scale insects are squishy and juicy and are best exemplified by the magnolia scale. These body coverings, coupled with their immobile nature, can make scale insects very hard to control.

Most scale control strategies revolve around trying to kill the vulnerable crawlers (newly hatched scale insects) and many insecticides are labeled for this purpose. The problem is that each scale insect species has a different time when the crawlers appear and some have more than one generation of crawlers per year. Dormant oils can help suppress over wintering adults and prevent some egg hatch, but the need for thorough coverage (as in every square inch) makes this hard for larger trees. Another factor is location and the pests can often be found in greater numbers when the plants are sheltered from the elements or surrounded by paving.  Stressed plants are also more often infested with scale insects. Even if you get control of the scale insects the other factors that make the plant vulnerable are beyond your control so they can become re-infested. 

           

In recent years some systemic products that target feeding adults have become available. Armored scale insects are susceptible to a product called Safari and soft scales can be controlled with Merit.  Acephate injections can provide a fairly quick kill but have a short residual in the tree.  An acephate injection followed by an imidicloprid (Merit) treatment will provide an immediate and more lasting control for scales like cottony maple scale. 

           

UNUSUAL GROWTHS ON YOUR OAK TREE?

Are you seeing knotted twigs with round growths on your pin oak trees?

On closer examination, the affected branches have gray-brown, round galls with many small teeth or horns protruding from the galls. These galls are called horned oak galls. Heavily infested oak trees can become so heavily knotted that the tree becomes unsightly, particularly in winter, without benefit of leaf cover.

Horned oak galls are caused by a tiny (1/8 inch long) wasp. The female gall wasps emerge from twig galls in May and fly to oak leaves to deposit eggs. The larvae cause galls to form in the veins of the oak leaves. In midsummer adult wasps emerge from the vein galls, mate and deposit eggs in twigs. The twig galls usually require two years to reach maximum size.

There’s a couple times each season when oak trees can be sprayed to control horned oak galls. Infested pin oak trees can be sprayed in mid-May when wasps emerge from twig galls and again in mid-summer when the next generation of wasps emerge form vein galls.

Horned oak gall. Photo courtesey of John A. Weidhass, Virginia Polytechnic Institute and State University, Bugwood.org

Horned oak gall. Photo:  Lacy L. Hyche, Auburn University, Bugwood.org