Extra Rainfall Can Cause Fungal Diseases in Your Landscape
December 19, 2018
What a year it has been in the rain department! As we type this post in Dallas, there's the threat of rain, AGAIN! This October and fall season both claim the spot as the wettest on record. All this rain has been good for our local lakes and reservoirs, but it can have some adverse effects on your trees and landscape.
You may already know how constant rainfall causes compacted soil & can damage roots, but that same rain sets the ideal conditions for fungal diseases. Fungal diseases spring up and thrive during periods of increased rainfall. Here are the top fungal diseases we spot around the DFW area:
Anthracnose is one of the most common fungal diseases and it attacks a wide variety of deciduous trees. You will notice brown spots on leaves – especially on the leaf veins, along with twig cankers and dieback. Depending on the severity, some trees will drop leaves completely. Rarely is anthracnose fatal to trees, but defoliation can severely weaken trees.
Anthracnose overwinters on fallen leaves and on the bark of trees. Since leaves have already fallen for the year, you may have trouble spotting the disease. If you suspect your trees have the disease, its best to remove fallen leaves from your landscape.
Powdery mildew attacks many landscape plants – not just trees. Besides annual and perennial landscape plants, you will often see this disease attack crape myrtles. Powdery mildew is aptly named – the fungus covers leaves in a white-grey powder, blocking out sun and limiting photosynthesis. The disease thrives in cool, wet conditions, so, you will often see it in late fall and early spring.
Powdery mildew isn’t difficult to control with fungicides, but repeated applications will be necessary. Of course, proper spacing and placement of plants - to improve air circulation - can prevent the disease.
There are many different diseases that exhibit as leaf spot disease. Tabukia leaf spot attacks oak trees, while a separate fungus takes their aim at Indian Hawthorns and Photinia. The sizes and colors of leaf spot can vary by fungus and my cause leaves to yellow and drop.
Not all fungus attack the leaves of plants – others attack the roots. Phytophthora root rot is probably the most common disease brought on by excess rainfall. It is common in areas where rainwater collects, or on old or previously inured trees. Our heavy clay soils, which hold excess water, make conditions more favorable for root rot. As it’s more difficult to diagnosis root rot, look for symptoms like canopy dieback, chlorotic foliage, or leaf drop. Azaleas and oaks are especially susceptible to phytophthora, but it attacks many different trees and landscape plants.
Root rot can be difficult to treat, so preventing it is always the best option. Make sure you have good drainage, and plant specimens above grade – not below. That means don’t plant them too deep. Remove any soil or mulch that has piled up around the base of trees and don’t run your irrigation if conditions are wet.
Periods of intense rain can bring about multiple fungal problems. If you are unsure about the health of your trees and landscape, have a trusted arborist out to your property for proper diagnosis and treatment.