Diseases of Weeping Willow Trees
weeping willow image by Edsweb from Fotolia.com
Weeping willows are flowing graceful trees that do best near a water source. If you are planting new willows, make sure that you don’t plant them near underground pipes or septic systems. Their roots can damage property in their efforts to get to water. Be on the lookout for certain diseases that can plague these trees. Most won’t cause any long-term damage, but there are a few that will require some action on your part.
Black canker creates infected areas on the bark of branches, leaving a gray mark with a black outline. Leaves will show brown spots. Trim out all diseased areas by cutting out the branches. Willow trees are fairly hardy when it comes to this disease and should bounce back fine.
Crown gall is a serious disease that causes knots, called galls, to develop on the trunk of the tree. The knots form near the base of the trunk as well as further up into the tree. It is the formation of the galls around the base of the tree, or crown, located near the soil that give it the name crown gall. The trees will have to be removed and disposed of. You won’t be able to garden or plant in the vicinity of where the trees were for two or more years.
Fungus causes many different issues with weeping willows. Willow scab is a disease caused by the fungus Venturia saliciperda, which goes after young leaves. It enters through the new growth stems and kills the new leaves as they develop. Olive green spore congregates underneath leaves, causing spots and killing leaves. Physalospora miyabeana, or black canker, in combination with a second fungus disease called willow scab, can bring on willow blight, which sometimes results in the death of the tree.
The best way to rid a tree of these diseases is to cut out the infected branches. There are also less evasive fungi that do little more than create spots on leaves. Removing leaves in the fall will help prevent the spread of fungus.
Powdery mildew causes white residue on foliage. Tar spot creates black bumps on foliage. These are not typically something to worry about it. Just remove the leaves that fall in order to prevent spread or re-contamination the next year.
Bacterial Twig Blight (bacterium – Pseudomonas saliciperda): Leaves turn brown and wilt and blighted branches die back for several inches. Brown streaks can be seen in sections of the wood. Bacterium overwinters in the cankers, so young leaves are infected as soon as they unfold. The damage can be confused with frost injury. Prune out infected twigs and spray in early spring with an approved fixed copper fungicide.
Crown Gall (bacterium – Agrobacterium tumefaciens): Mainly a nursery disease. Large, rough, woody swellings or galls on the lower part of the stem and crown of the plant. Infected plants may be deformed, stunted or even killed. Weeping willow is susceptible. No practical control is known for this disease.
Cytospora Canker (fungus – Cytospora sp.): Affects willows the same as poplars. Discolored, sunken, often sharply defined areas develop on twigs, branches or trunk. Cankers enlarge and gradually girdle infected parts causing death to portions beyond. Weeping willow is susceptible, but rarely occurs on black willow. Prune out and destroy dead and cankered parts. Spray with an approved fixed copper fungicide.
Leaf Spots (fungi – Cercospora sp., Gloeosporium sp.): Small to large, round to irregular spots of various colors on leaves. Leaves may wither and drop early. Begin spraying when buds begin to swell in the spring.
Rust (fungus – Melampsora sp.): Lemon-yellow spots on lower leaf surface. Later in the season the pustules are dark colored. The disease may be severe enough to cause leaf drop. Although rust infections are not considered serious, they may result in heavy defoliation of young trees.
Powdery Mildew (fungi – Phyllactinia guttata and Uncinula salicis): White powdery growth on leaf surfaces may become heavy late in the season, especially on tender leaves of sprouts.
Tarspot (fungus – Rhytisma salicinum): Spots are very thick, jet black, discrete and about one-fourth inch in diameter. It looks like a drop of tar on the leaf. Rake up an burn dead leaves, as the fungus overwinters on them. Spray early in April with a fungicide.
Cotton Root Rot (fungus – Phymatotrichum omnivorum): Most willow species are highly susceptible. Plants suddenly wilt and die, leaves usually hanging on the plant. Roots will be decayed with the bark peeling off very easily. (See section on Cotton Root Rot)
What Is Willow Scab Disease – Learn How To Treat Willow Scab Disease
Willow scab disease attacks different types of willow species in Europe and the United States. It can attack weeping willows but is not one of the more common weeping willow diseases. Willow scab is caused by the fungus Venturia salciperda. Scab on willow trees usually doesn’t cause serious harm unless the black canker fungus (Glomerella miyabeanais) is also present. Read on to learn about how to recognize and how to treat willow scab.
Scab on Willow Trees
Willow scab is a fungal disease that causes leaf symptoms, followed by brown spore masses at the base of leaves. The symptoms of scab on willow start with dark spots on the leaves. These can be brown or black, and cause the leaves to wilt, shrivel up and die.
In time, as the willow scab disease progresses, the
fungus spreads to the stem tissue at the bases of leave petioles. There, it forms olive-brown velvety spore masses. This happens most often in wet spring weather. Look on the underside of the leaves and along the rib and veins for these fruiting bodies.
Although scab on willow trees can attack any almost any Salix tree, it is not considered one of the common weeping willow diseases. In fact, weeping willows (Salix babylonica) are the most resistant willow species to this disease.
How to Treat Willow Scab
Willow scab disease causes only minor damage to your trees if they are healthy. However, repeated infections may slow a willow’s growth and reduce its vigor.
If you are wondering about whether effective willow scab treatment exists, you’ll be happy to hear that it does. You can control willow scab on your backyard willows with a combination of good cultural practices and chemical applications.
How to treat willow scab with cultural practices? First, you’ll need to trim out all of the infected parts of the willow tree, including stems and twigs. Don’t forget to sterilize your pruners with a bleach and water mixture to avoid spreading the fungus.
In addition, keep your trees vigorous with sufficient irrigation and regular fertilizer. The disease does much less damage to healthy trees than vulnerable ones.
Finally, properly timed fungicide applications can be part of your willow scab treatment. This is especially important if your tree is also infected by the black canker fungus.
Can my willow tree be saved?
It looks like your tree has a severe case of Black Canker and Willow Scab – both fungal diseases and can lead to the demise of the specimen if not treated in the early stages.
Willow scab is a disease is caused by fungi that attack the growing leaves, branches and the twigs. It is characterized by olive green spore masses that tend to appear on the veins that are found on the leaves underside. Willow scab can sometimes occur with black canker. Black canker is a serious willow tree disease that is caused by the black canker fungus in combination with the willow scab fungus. It presents itself as dark brown spots on the affected leaves, gray whitish lesions that have black edges and appear on the stem and twigs. It also causes die back, defoliation and death of the affected tree.
Since more than 1/2 of your tree’s crown is not producing adequate foliage to support the entire vascular system … and … the cankers are large and extensive, I would suggest having this tree removed and replaced with a ‘native’ specimen that is not in the Salix spp. family.
From the first photo, it appears almost the entire lower trunk does not support outer bark tissue. This tree is dying from the inside outwards. ~DOT
weeping willow leaves have black spots
Unfortunately, willow trees are susceptible to an unusually large number of foliage blights and stem canker diseases.
Your options are fairly limited. All the foliar diseases are dependent on reinfection by spores released from dropped foliage. Keep the fallen leaves cleaned up completely and dispose of off-site.
The dead branches could be related to the foliar disease or any of a number of canker diseases. For this, using clean sharp by-pass pruners, prune back to a side branch or to the branch collar where this is clean living tissue. If your pruners cut through diseased wood (i.e. dead, brown, etc.), clean the pruners with a 10% bleach solution before making another cut.
Treatments are limited. While there are fungicides that can combat several of these diseases, an accurate identification of the disease needs to be made to decide which would be helpful, and legal to use.
To get an identification done for you, bring some samples of leaves and stems to your county extension office at:
Fayette County Cooperative Extension
650 McConnell Loop
Fayette, AL 35555
Phone: (205) 932-8941