COOL, WET SPRING MEANS FUNGAL DISEASES IN TREES

ALSO, WORMS AND SCALE ARE COMING BACK

 

Much of this page is the same as last spring, which was a very cool and wet spring.

This spring of 2020 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

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.

Although some companies may offer a spray for anthracnose, avoid the temptation to contract for that service.  Sprays can help prevent anthracnose, but only if applied before the leaves open and when they are small, before you even know if they might get anthracnose.  Sprays after the spots and leaf damage has occurred will not accomplish anything.  The damage has been done, and as noted, is not often a serious problem for the tree.    

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

 

                  

SOME PICTURES OF MAPLE ANTHRACNOSE

 

 

CANKERWORMS AND GYPSY MOTHS

We have seen a fair number of cankerworms this year for the first time in many years.  And......... GYPSY MOTHS are showing up in many locations.  Cankerworms eat holes in leaves and are often seen coming down on a thread of silk, hanging and wiggling in the wind.  Gypsy moth caterpillars are fuzzy, colorful caterpillars that eat the leaves of oaks and aspens and some other trees and even some evergreens.  

Both types of leaf-eating worms can be treated with soil injected or trunk injected insecticides.  They can also be killed with sprays, but they often are on trees that are too large to effectively spray.  Also, sprays of insecticides into the air exposes good bugs (beneficial insects) and animals to the insecticide chemicals.  

 

SOFT SCALES

We are seeing a resurgence of some soft scales this year-  cottony maple scale, lecanium scale, magnolia scale.  These are the scales that feed on twigs and leaves and drip copious sticky sap on surfaces below.  All of these scales can be controlled with soil or trunk injected insecticides.  Sprays are not a good alternative because they kill the beneficial insects that help to control the scale populations. 

 

VERTICILLIUM WILT

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.