What Is Pecan Scab?
Pecan scab (also known as pecan palygonia) is a fungal infection affecting trees. It causes leaves to turn brown and fall off prematurely. The symptoms are similar to those of white pine blister rust, but it affects many different types of trees including oaks, maples, birch and hickories.
Symptoms: Leaves turning brown and falling off prematurely
Causes: Infection with the fungus Pseudotsuga menziesii (Peanut Scab). It is spread from infected plants to healthy ones through wind or waterborne spores. Symptoms usually appear within 2 years after initial infection.
Treatment: Pesticides such as permethrin and carbaryl are effective against the fungus. They may also reduce the severity of symptoms. If not treated early enough, pecan scab can cause death. Treatment is often delayed until late summer when temperatures reach 100 degrees F (38 C). However, some trees do not respond well to pesticides and require treatments later in the season.
How Can I Prevent Pecan Scab From Affecting My Tree?
As with most fungal diseases, pecan scab spreads from tree to tree through the wind or water. These vehicles for spread are enhanced during wet weather and in areas with high humidity. Use mulch to keep the soil around your tree dry. Do not plant other types of trees that are known to be susceptible to the disease. Avoid overhead watering, as this increases the likelihood of fungus infestation. Do not plant pecan trees if they are already infected with any kind of fungus.
How Can I Tell If My Tree Is Infected With Pecan Scab?
In the early stage of infection, leaves will turn yellow and begin falling. The tree does not produce normal growth rings. Instead, concentric rings appear. Trees infested with pecan scab may be stunted in size and produce very small nuts. Leaves tend to curl at the edges.
What Are Some Ways To Prevent Pecan Scab?
Once you have noticed the early symptoms of pecan scab, it is too late to take preventative measures. It is best to plant resistant varieties when possible. American varieties are more likely to be infected than English and French varieties. Trees that are grown from seed are more likely to be infected than those started through other means (cuttings, grafting).
How Can I Tell If My Tree Is Infested With Other Pests?
Hickory shuckworm causes leaves to curl and turn light green in color. In later stages of infestation, webs begin to appear on the surface of the foliage. The caterpillar spends most of its time in these webs and feeds at night.
Leaf notcher caterpillar causes notches in the top side of hickory leaves. It is light green in color and up to 1 inch long.
Striped hickory borer causes S-shaped tunnels in the bark of hickory trees. It is yellow and up to 1.5 inches long.
Hickory cocksfoot causes leaves to appear wilted and generally unthrifty. It is tan and up to 3/4 inches tall.
Hickory leaf tier caterpillar causes leaves to turn light green in color with irregular white spots. It is up to 1.5 inches long and has a black and yellow stripe running lengthwise down its back.
Paper shell gall wasp lays eggs on the undersides of hickory leaves. Eggs hatch into larvae, which causes leaves to form a globular growth known as a galls. These galls are up to 1.5 inches across and less than 1/10 inch in thickness.
What Other Pests Might Affect My Pecan Tree?
In addition to the pests mentioned above, pecan trees may suffer attacks by borers, caterpillars, leafhoppers, mealy bugs, scale insects and mites.
How Can I Prevent Other Pests From Attacking My Tree?
Keep trees pruned regularly in order to provide them with good air circulation. This prevents the buildup of insects and diseases that thrive in shady, damp areas.
Trim away any dead or weak limbs to help prevent pests from making a home in the tree.
Water trees during extended periods of drought to prevent dry conditions that are conducive to insect and fungal infestations.
If possible, do not plant trees in low-lying areas that are prone to flooding or areas that remain wet for extended periods.
What Should I Do If My Tree Is Infested?
Once a tree is infested with pests, it is necessary to take action to prevent the problem from worsening.
If a tree has a fungal infection or infestation of insects and their eggs, thoroughly clean away any debris that may be harbored there. This may mean removing several inches of soil from the base of the tree. Dispose of the debris and replace the soil once the cleaning is done.
If a tree is severely infested with insects or diseases, it may be wise to remove it and replace it with a new tree.
When a tree has a problem with borers, such as those that affect pecan trees, you can try to treat the area with BT (bacillus thuringiensis). This is available from most garden supply stores. It is a bacteria that attacks the intestinal tracts of caterpillars and can be quite effective against many species.
Insects may also be controlled through the liberal use of sprays made with kaolin, which is a substance that is also effective against fungal growths on plants. It can sometimes help to treat the soil where tree roots are with this substance as well.
Sources & references used in this article:
Effects of an abbreviated pecan disease control program on pecan scab disease increase and crop yield. by TR Gottwald, PF Bertrand – Plant disease, 1988 – cabdirect.org
Challenges of managing disease in tall orchard trees-pecan scab, a case study. by CH Bock, TB Brenneman, BW Wood, KL Stevenson – CAB Reviews, 2017 – cabdirect.org
First description of the sexual stage of Venturia effusa, causal agent of pecan scab by ND Charlton, M Yi, CH Bock, M Zhang, CA Young – Mycologia, 2020 – Taylor & Francis
Notes on Hyphomycetes. XC. Fusicladosporium, a new genus for Cladosporium-like anamorphs of Venturia, and the pecan scab-inducing fungus. by EC Partridge, G Morgan-Jones – Mycotaxon, 2003 – cabdirect.org