Common Insects & Diseases of Trees & Shrubs
Common Insects of Trees & Shrubs
Leafminer
Leafminer larvae feed inside a leaf, between the upper and lower surface. They may be the larvae of flies, moths, sawflies, or beetles. They produce a blister or tunnel in the leaf which turns yellow or brown as the tissue dies. If more than one larva is mining the tissue, the tunnels often run together, forming large blotches that cover much of the leaf. The leaf takes on a scorched appearance. To control the larvae, a systemic (penetrating into the tissue) insecticide should be used. Clean up well around infested plants.
Mites
Mites are microscopic spider-like pests which suck the sap out of their host plants. A wide range of plants are affected. Damage from mites can range from yellow stippling of the foliage to complete browning and death of infested foliage. Fine webs are often present during mite infestations. Mites may attack during any part of the growing season, but prefer hot, dry conditions. Look for very fine irregular webs on the leaves and stems of plants. The webs afford protection for young mites and the eggs. Mites may be controlled by spraying whenever infestations occur. A preventive spray program begun in spring may reduce the risk of heavy mite infestation. Repeat applications of insecticide, by label directions, will kill existing adults as well as new generations, which have hatched between sprayings. Use a spreader sticker to give better coverage and retention of chemical on the leaf. Wet weather slows reproduction and favors the development of mite's natural enemies. Frequent high -pressure spraying with cold water from the garden hose may help to reduce red spider mite infestation.
Borers Lilac and Privet Borers
The adult is a clear winged moth that resembles a wasp. It is rarely observed. Adult moths emerge from infested canes in May. After mating, eggs are deposited on canes of lilacs, privet or pussy willow, usually on lower portions. Larva bore into stems, causing leaves to yellow, wilt, and eventually die. Frass, a sawdust-like material, is produced by borers and expelled from burrows. Stems may become very loose in the soil and break off easily. In early spring severely infested canes should be removed at soil level and destroyed. Non-infested canes can be sprayed. Spray May 1st and repeat twice at fourteen day intervals.
Aphids
Aphids are a small, sap sucking insect which primarily attack the leaves and soft tissue of many plants. They often feed in dense clusters, which can stunt or disfigure foliage. This disfigurement can result in "witches brooms" on some honeysuckles. Aphids will secrete a sugary substance (honeydew) which can coat leaves and branches. This honeydew can encourage mold growth and also attract ants. Roses, honeysuckle, ash, forsythia, lilac and quince are a few of the shrubs affected by aphids. Aphids are soft-bodied insects and can be controlled by spraying or using predator insects. Spraying following the label directions may be done whenever infestations become severe. This may be difficult if the leaves have curled around the aphids or if the aphids are very small.
Scale
Scale infestation can be devastating to some varieties of plants, and if left unchecked can infest most plants in the landscape. Occasional inspection of plants is recommended so that scale can be detected in its early stages. Scale is relatively easy to detect. It appears as small shell like nodules along the bark, or on the leaves, of affected plants. Inside each nodule is a small insect, which after hatching, hooks its beak into the sap stream of the plant, secretes a shell over itself, and lives on the sap within the plant. Spraying for scale should be done immediately after the eggs hatch. This generally takes place at the end of April or early May depending on the temperature. A second application ten days later is recommended. Winter spraying with parafinic oil also diminishes scale populations by destroying eggs before they hatch.
Borers
Redheaded Ash Borer - Apply the first spray in late April and respray every 3-4 weeks until early August. It is unnecessary to spray branches and leaves.
Ash Borer - Apply the first spray in early August and retreat in early September. It is unnecessary to spray branches and leaves, only spray the trunk.
Cottonwood Borer - Spray lower trunk in late May and late June.
Bronze Birch Borer - Spray entire tree in late May and repeat in 2-3 weeks.
Common Diseases of Trees & Shrubs
Anthracnose
Anthracnose is one of the most common fungal diseases of shade trees in the Midwest. It can affect sycamore, ash, maple, oak, linden, elm and others as well as many shrubs. Fortunately, the damage is mostly cosmetic and inflicts little permanent damage although it may cause girdling of twigs on sycamores. These twigs die and a "witches broom" may develop. The foliar symptoms of anthracnose are the easiest to identify. It generally appears as irregularly shaped brown patches often resembling leaf scorch. Control of anthracnose is complicated because different pathogens affect different plants and each has a distinct life-cycle. In season spray can be effective at controlling anthracnose. Please ask for specific control spray and dates at Mulhall's.
Cankers
Cankers refer to "sores" on the trunk, stems or branches of affected plants. These sores, caused by fungal or bacterial pathogens can appear on dogwoods, barberry, pussy willow and many others. As the infection advances, sunken, discolored patches of bark will appear as the tissue underneath dies. Moist, cool conditions in spring and fall stimulate fast growth and spread of these pathogens. Control is difficult. It is important to prevent damage to the trunk where the disease can enter. Since canker predominates on weakened plants, maintaining high plant vigor will lesson its occurrence. Some infected tissue can be removed by pruning. Always prune 8-12" lower than where the canker is found. All cutting tools, blades should be dipped in a mixture of 70% denatured alcohol for several seconds between cuts. Apply fungicide as applicable.
Powdery Mildew
Leaves and stems of affected plants are covered with a thin layer of grayish-white powdery material. Infected leaves may turn yellowish or reddish and drop. In the late fall, tiny black dots (spores) are scattered over the white patches like ground pepper. Plants growing in shady areas are often severely infected. The spores are spread by the wind to healthy plants. A wide range of plants are affected. Spray to control beginning in mid June and continue every 10-14 days.
|
![[ Yahoo! Maps ]](http://us.i1.yimg.com/us.yimg.com/i/us/mp/gr/mplogo.gif){kind=small}
