COLUMN: Foliar diseases enjoying the cool, wet summer

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By Jeneen Wiche

The cool, wet weather for summer 2013 is certainly being enjoyed by all including those that are part of the fungi family. Gardeners wondered about the toadstools popping up in their lawns; others were confounded by the stinky, phallic-looking things poking through their mulch, a mushroom commonly called the stinkhorn; and the slimy orange globs on cedar trees got many thinking aliens had landed in their landscape.
Weather can bring on all kinds of naturally occurring oddities. Too wet, too dry, too hot or too cold, there is a pest problem that is favored by every weather pattern imaginable and this year the cool, wet spring favored fungal diseases like rust and anthracnose.
It is already clear that rust diseases like cedar-apple rust, cedar-hawthorn rust and cedar-quince rust are widespread this season. The disease is evidenced in the early spring by bright orange spores (the slimy orange globs) on eastern red cedars or other Juniperus species.  Once development is complete on the cedar the teliospores are released and carried through the air to the next host plant. These other hosts include apple, hawthorn, crabapple or serviceberry. We have some young apple trees that look like they have been splattered in orange paint.
These rust diseases must have two specific hosts in order to complete their life cycles. For example, cedar-hawthorn rust needs a Juniperus species, like the eastern red cedar to develop during the parasitic stage of life; then needs as a second host plant, the hawthorn, to complete the fruiting stage; then it travels back to re-infect the cedars once again. Yellow spots appear on the foliage in the spring, turning orange as the season progresses and fruit is infected.  
Anthracnose will likely be more prevalent this year, too. Trees that are susceptible include dogwood, sycamore, maple and ash. The fungus that causes anthracnose is slightly different for each species of tree, so the fungus that infects sycamores will not infect maples, and so on.  Symptoms vary from species to species so for a definite diagnosis samples should be sent to your county extension service.
Anthracnose on sycamores results in leaf and twig dieback early in the season; the leaves that fall are often replaced by new ones. The infection is still there, however, and may continue to develop into cankers on larger branches and limbs. The fungus will remain viable in these cankers and on the fallen debris and re-infect the tree the following year, so this is why it is important to prune away diseased twigs and limbs and rake up fallen debris. It seems that sycamores suffer no matter the weather or our efforts to thwart the disease.
Ash trees react a little differently to the fungus that causes anthracnose. As the new leaves grow, brown splotches will appear, at first around the edges, and the entire leaflet will fall from the tree. Leaves that are mature will have brown circular scars but you will not see any twig or branch cankers … they are there; we just don’t see them.
Similarly, maples will show leaf spots but they will be irregular in shape and you will see more tip dieback where the new shoots were infected. Some maples show most of the lesions near the leaf veins. Dogwood anthracnose causes leaf spots, blighted foliage and twigs and can cause lower branches to die back completely
It is difficult to distinguish which disease pathogen is causing leaf spots; and, at this point it is essentially too late to effectively use a fungicide. Dr. John Hartman, plant pathologist at the University of Kentucky, recommends that we utilize good housekeeping by raking up leaves and infected twigs that have fallen from infected trees. Removing the pathogen this year will reduce the incidence next year.
So, clean up what falls to the ground and prune out what dies back on the tree in order to prevent re-infection. Keep your trees healthy by irrigating them during times of drought and if you fertilize do so only in the late fall in order to promote healthy root development. Usually anthracnose won’t kill a healthy shade tree, although it does take away from the tree appearance.