SHRUB DISEASES

SHRUB DISEASES 2017-12-20T20:07:49+00:00

Ornamental shrubs add beauty to any home environment and landscape. Appropriate fertilizer and disease prevention are the primary factors for keeping them healthy and thriving. Plant diseases in the Mid-South take a toll on our shrubs every year. We at Herbi-Systems have a dedicated department that specializes in shrub diseases in Memphis. With six treatments per year, we inspect all ornamentals and shrubs for continued good health. If treatments are needed, only a certified professional will administer them for the target disease and apply the correct product at the correct rate. Below are the most common problems for shrubs in Memphis.

Mulch Volcanoes

Technically, mulch volcanoes are not a disease but they can cause damage.  Mulch can be good for your trees and shrubs, but you can carry a good thing too far. A common problem is creating a “Mulch Volcano”, or piling too much mulch near the trunk. Unfortunately, many people think mulch volcanoes look pretty, but too much mulch near the trunk can actually damage the tree. Once your tree develops cankers, the situation usually cannot be reversed, and the tree may die within a few seasons. Resist the temptation to make a “mulch volcano.” Leave that donut around the tree trunk.

Establishing Shrubs

Problems may arise for a number of reasons. Usually, the site is unsuitable for the type of plant, or maintenance after planting is faulty. Soil-borne plant diseases, such as root rots, wilt diseases, or nematode infestations can cause problems even if the site previously supported plants of the same kind. The transplants are more vulnerable to the effects of the disease. Sometimes plants produce toxins that leach into surrounding soil and discourage growth of other plants that might be competing with them. Walnut trees are well known for this. In these cases, one may have to wait a year or more after the removal of the toxin producer to plant replacements.

Tree Decline

Tree decline is a progressive deterioration in the health of a tree that is attributed to a combination of factors, such as competition among plants, environmental stresses, injuries and diseases like defoliating leaf diseases, root rots, wilt diseases, and nematode infestations in the soil. Although each of these may be unimportant individually, in combination they may cause decline and death of the plant. Avoid unnecessary injury. To avoid stress, know and supply the maintenance needs of the plant. Water deeply during dry periods. Don’t induce rapid top growth by applying high nitrogen fertilizers to the root zone.

Fall Needle Shed

Inner branchlets turn yellow, then brown. Outer foliage remains healthy. Normal part of growth cycle. No control is necessary.

Iron Chlorosis

Leaves may become yellow, cream colored, or white, usually caused by reduced availability of iron in high pH soil. Correct the site-related conditions such as high soil pH, water logging, and poor aeration. Iron chelate applied to foliage may provide temporary greening, but for long term control, lower the soil pH.

Leaf Scorch

Leaf Scorch is a symptom that can occur any time the leaves need more water than they receive. It may be caused by diseases of the roots, crown and vascular system; cankers; inadequate available water; high air temperatures; damage to the roots from transplanting, soil compaction or excavation or natural gas leaks; chemical injury such as herbicides, excessive fertilizer and road salt; root girdling; “pot boundness” that occurred in containers before planting or following planting if roots fail to extend beyond the planting hole. Be sure soil is moist in the fall. Provide windbreaks around plants. Plant adapted varieties in sheltered locations or erect wind barriers.

Wet Feet

Plants turn yellow and brown. Whole plant may die rather rapidly. Usually occurs in spots where moisture has been excessive. It can be complicated by root and crown diseases, or in long established plantings if periods of drought alternate with periods of saturated soils. Maintain good drainage. Plant yews in spots that do not get overly wet.

Winter Injury

Foliage will be brown and scorched. Twigs die back. Bark will split. No control is necessary. Protect plant from injury as in frost situations.

FUNGUS

Black Spot

Leaves will have black spots with irregular margins. Collect and remove fallen leaves.  A fungicide application may be necessary in spring as leaves expand.  For the best control, varieties that are susceptible to black spot must be protected with a fungicide before the disease is present.

Blight

Needles, twigs and smaller branches turn brown to reddish-brown as they gradually die back. Tiny black dots will appear later on infected parts. May be confused with normal fall browning, winter injury, spider mites, etc. Prune or remove blighted plants. A fungicide application may be needed.

Cankers

Cankers are diseased areas of the bark. Many different kinds of fungi and a few bacteria may cause them. The outer bark may appear abnormal. Inner bark is brown and discolored. In time, the bark may fall off. Leaves beyond the canker may yellow, scorch or die. Usually canker-causing pathogens can infect only hosts that have been injured or stressed. Trees in decline often lose branches to cankers. Management of canker disease includes avoiding unnecessary injuries and knowing and supplying the maintenance needs of the host to reduce stress. Prune out diseased branches well below the visible infection. After each cut, disinfect pruning tools with rubbing alcohol or 10 percent household chlorine bleach in water. With Rhizoctonia/Phoma canker or “die back,” stems and leaves may become blackened or blighted. Shoots beyond the necrotic area wilt and die. Remove severely affected plants. It may be necessary to increase air circulation by pruning overhanging shrubs and improve drainage by amending soil.

Crown Gall

Use certified and disease-free stock from known suppliers or nurseries. Avoid nursery stock with galls. Avoid wounding stems or roots. Prune out and destroy affected plant parts. Use disinfectants on cut surfaces. Destroy severely affected plants. Carefully remove and destroy infected plants or plant parts. Avoid wounding. Use strict sanitation measures.

Fire Blight

New shoots suddenly appear as if scorched by fire. Leaves cling to twigs. Cankers may be present on twigs and branches. Prune blighted parts in dormant season or in late summer or fall when weather is dry. Dip pruning tools in 70 percent alcohol or 10 percent household bleach between cuts. No chemical control suggested. Cultivars vary in susceptibility.

 Leaf and Flower Gall

Leaves become thickened or fleshy galls that then turn pale green or white. The entire blossom may become a fleshy gall covered with a whitish bloom. Usually, chemical control is not warranted. Pick off and destroy galled parts, if feasible. If there is severe infection, apply the appropriate fungicide.

Leaf Spots

Leaf spots may be caused by a variety of fungal pathogens and a few bacterial ones. Anthracnose causes brown lesions on the leaves, in which tiny fruiting bodies may be seen with a hand lens. Anthracnose is a term used for a group of loosely related fungal diseases that often cause blotches along leaf veins or leaf spots, and can cause twig blights and cankers. Bacterial leaf spot has small, water soaked circular spots that eventually turn brown to purple. Twigs may become girdled, resulting in a blight.  Prune and remove affected parts. Apply a fungicide several times beginning when leaves emerge in the spring. Some leaf spots are characterized by large, brown irregular blotches. Others are small, silver gray circular spots or target shaped. Most are uncommon or secondary, following injury to leaf. Few leaf spots seriously damage the host and control can seldom be achieved after the infection is seen. Reasons for considering chemical control on woody ornamentals in subsequent years vary. In some cases, non-chemical management practices should be used. Remove and destroy fallen leaves and twigs. Prune out dead twigs and branches. Avoid the use of high nitrogen fertilizers that can cause new leaves to be very succulent and more disease prone.

Powdery Mildew

Powdery white moldy patches will appear on leaves. Remove badly affected shoots. Prune to thin out branches. Spray with fungicide when mildew appears.

Phytophthora Root and Crown Rot

Usually, plants slowly decline in vigor and die. Brownish cortical tissues appear in the root and crown areas. Often associated with wet feet. Maintain good drainage.

Root Rot

Root Rot can be caused by a wide number of fungi. Few of these can be controlled in the landscape, especially on large trees. With Phytophthora root rot, the leaves wilt. Growth is stunted. Fine roots decay and cankers may develop at the base of the stem. Fungicides are available, but their use generally is not recommended for established plantings. Remove and destroy affected plants. If practical, improve soil drainage and replant with a more tolerant variety.

Scab

Scab is serious in wet weather. Dull, olive-to-black velvety or scurfy spots will appear on leaves. Leaves may yellow and fall off. May also appear on fruit. Varieties vary in susceptibility.

Shoot Blight

Common and severe in wet springs on shaded or crowded plants. Immature leaves turn black and die. Flower buds may be entirely black. Spots and blotches appear on leaves.  Prune annually for good air circulation. Prune out blighted portions. Disinfect tools between cuts with 70% alcohol and 30% bleach. Avoid over fertilization with nitrogenous materials. Control borers.