COOL, WET SPRING MEANS FUNGAL DISEASES IN TREES
This spring of 2019 definitely qualifies as a cool, wet spring. That usually sets the table for fungal diseases in the home landscape. We have had numerous calls about these problems. Below is some information regarding the most common of these problems:
Anthracnose is a fungal leaf disease that affects many different plants, including landscape trees. Especially common is ash, sycamore and maple anthracnose. Leaves develop necrotic spots and then get distorted, curled or twisted and fall to the ground. Sycamore trees sometimes become 80 to 90 % defoliated. Ash and maple trees seldom defoliate more than 10 to 20 %.
In most cases, this problem is more stressful to the homeowner than to the tree. Granted, there are leaves to pick up in the spring or early summer, but the tree suffers little stress and if some new leaves are needed, the tree will refoliate, as commonly happens with sycamore trees that are significantly defoliated.
We do have an injectable product, Phosphojet, that can assist the tree in refoliation. It has both nutritional and fungicidal benefits for the tree and we have seen good results. And the best news is that it is not a very expensive product, so if warranted, the cost is low.
For sycamores that have suffered recurrent defoliation and may develop branch cankers and witches brooming, a preventive fungicide may be warranted. That would be injected in the fall for prevention of anthracnose the following spring. Alamo gives two seasons of control and Arbotect can give 3 to 4 seasons of control.
Verticillium wilt, sometimes known as Maple Wilt because it is most common in maples, is a vascular fungal disease that can affect many species of trees and plant material. The fungus plugs the vascular system of the plant and causes wilting because water cannot move up the transport vessels (xylem) of the tree.
When a maple tree develops infection with verticillium, it may progress slowly, with wilting, small foliage, discolored foliage and then branch death with loss of leaves. The tree battles the disease and may live for several years. Or the tree may succumb rapidly. Our experience has been that severely cold winters seem to exacerbate the problem and cause more rapid progression, just as we see more expression of branch cankers after a severe winter.
We have no specific "silver bullet" treatment for this disease. Supportive care to help the tree in its battle may include injection of a phosphite fungicidal chemical (Phosphojet) and watering the tree deeply during hot, dry, breezy weather.
Some suggest replacing a dead or dying tree with verticillium resistant trees. Trees that are NOT known to be susceptible include: arborvitae, baldcypress, beech, birch, boxwood, crabapple, ginkgo, hackberry, hawthorn, hazelnut, hickory, holly, honey locust, hornbeam, ironwood, Katsura tree, mulberry, oak, pine, serviceberry, spruce, sweetgum, walnut, willow, and yew.
LEAF SPOT AND SCAB ON FLOWERING TREES
Crabapple trees can develop leaf spot early in the season and experience some defoliation and then later develop scab and have major defoliation. The same products mentioned above can be helpful for treatment or prevention. Also, sprays, beginning very early in the season as leaves are opening, can greatly reduce the development of leaf fungal diseases.
LEAF SPOTS ON MAPLES
MAPLE TAR SPOT is a late season leaf spot that is dramatic in appearance, but, like the anthracnose mentioned above, is of more stress to the homeowner than to the tree. Large black spots develop and a very noticeable in late summer on silver maples and especially Norway maples. It is a minimal defoliation stress to the tree, so is mainly a cosmetic issue. Although sprays in early spring or fungicide injections might prevent future development of the problem, those treatments are entirely unnecessary for the health of the tree.
EVERGREEN NEEDLE BROWNING
FUNGAL DISEASE in evergreen trees will also be exacerbated by this wet spring. This includes tip blight in pines and junipers and needlecast in pines and spruces. Please refer to the webpage with info on these problems.
NORWAY MAPLE BRANCH DIEBACK
We have received many calls about branch dieback in Norway maples. In many cases it is similar to what we experienced a few years ago, the last time we had a seriously cold winter with Polar Vortex subzero condtions.
The branch cankers, especially cytospora or valsa cankers, that are common in these maples, seem to be more numerous and severe after that type of winter. Pruning out the affected branches is all we have to offer these trees. Phosphojet could theoretically be helpful, but that would be a purely empiric treatment with no certain scientifically proven basis.
The other problem that commonly causes dieback in Norway maples is girdling roots or "choke" roots. These are roots that wrap around the trunk or other roots and impair sap flow. Sometimes they can be removed with resulting benefit to the tree. Often, however, they are too large or imbedded to be safely and effectively removed.