CRABAPPLES LOSING LEAVES?

A common ornamental tree disease arborist’s encounter in Michigan is apple scab. This foliar disease infects crabapple leaves in the spring, but does not make itself apparent until later in the summer. After the apple scab fungus has infected enough of the crabapple leaf the leaf will fall from the tree.

Crabapple trees infected with apple scab usually start to show the effects of the disease between mid-June and early July. By August some crabapple trees may have even lost most of their leaves.

If your crabapple tree has lost a lot of its leaves from apple scab it is really not worth spraying the tree with a fungicide at this time. The disease is already in the leaf tissue and further apple scab infection is not going to be significant in the warmer and drier months of the year. Make sure the tree is receiving ample water and you may want to consider fertilizing in the fall to assure adequate nutrients are available to the tree.

The best way to prevent apple scab in the future is to apply a foliar fungicide spray in the early spring. Crabapple spraying for apple scab should start soon after the leaves begin to emerge. A couple follow up treatments will give you the best level of control.

To learn more about controlling apple scab click here:
http://www.owentree.com/Apple_Scab.php

Apple scab infection

 

GROUND COVER DISEASES

Three common ground covers used in Michigan are pachysandra, vinca/myrtle, and English ivy. Although mostly problem-free, on occasion they can be subject to disease problems. In most instances of diseases on ground covers a fungicide program in combination with good cultural practices can eliminate the problem.

 Pachysandra ground cover. 

Photo: Jil Swearingen, USDI National Park Service, Bugwood.org 

 Pachysandra. Volutella leaf and stem blight is the most common disease on pachysandra. The disease is usually promoted by excessive moisture for long periods of time. The fungus causes black blotches on the leaves and black cankers on the stem. To control Volutella leaf blight, avoid excess moisture from overhead irrigation. A fungicide spray program started in the spring can usually prevent the disease from spreading.

 Volutella blight on pachysandra ground cover plants. 

Photo: Mary Ann Hansen, Virginia Polytechnic Institute and State University, Bugwood.org 

 Vinca (periwinkle) ground cover. 

Photo: Jil Swearingen, USDI National Park Service, Bugwood.org 

 Vinca/Myrtle. Phoma stem blight is the most common disease of Vinca in Michigan. The fungus generally rots and girdles lower stems. Often the first symptom noticed by homeowners are wilted leaves as a result of girdled stems. Like Pachysandra, Vinca diseases will be minimized to some extent by avoiding excessive moisture, particularly in shaded areas of the landscape. Excess fertilization will also cause lush dense growth and greater susceptibility to the disease. Fungicide sprays will usually eliminate this ground cover disease over time.

 Phoma stem blight. 

Photo: Howard F. Schwartz, Colorado State University, Bugwood.org 

 English ivy. 

Photo: Jan Samanek, Phytosanitary Administration, Bugwood.org 

 English Ivy. Several fungal leaf spots and a severe Xanthomonas bacterial leaf spot are possible causes for brown or black spots on English ivy. Although bacterial leaf spot often has a yellow halo surrounding the dark lesion on leaves, the fungal and bacterial disease can appear similar. Moisture control is particularly important for the bacterial leaf spot. Fungicides may actually spread the bacterial disease but may inhibit the fungal leaf spots. A lab test may be warranted to confirm which disorder is affecting the plants. Where practical, infected leaves may be picked and destroyed.

 English ivy with bacterial leaf spot. 

Photo: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org