Tuesday, July 9, 2013

U of I Tree Disease and Pest Update: July 1, 2013

Monthly Summary

Average Temperature and Precipitation

Modified Growing Degree Days (Base 50⁰ F,  March 1 through June 30)
Station Location
Actual Temperature
Historical Average   (11 year)
One-Week Projection
Two-Week Projection
St. Charles
Rend Lake
Dixon Springs

Invasive Species News from the Illinois Cooperative Agriculture Pest Survey (CAPS) Program
Visit the Illinois CAPS blog for all the latest news on invasive pests in Illinois or contact Kelly Estes (kcook8@illinois.edu) with any questions.

Update from the U of I Plant Clinic
(Courtesy of Stephanie Porter, Diagnostician and Outreach Coordinator and Travis Cleveland, Pesticide Safety Education Specialist)
U of I Plant Clinic Website:  http://web.extension.illinois.edu/plantclinic/
U of I Plant Clinic Facebook Page:  https://www.facebook.com/UofIPlantClinic
Follow Stephanie Porter on Twitter @skporter

There were many tree issues seen at the U of I Plant Clinic during the month of June and they are as follows:

Oak wilt
Red oak found to be infected with oak wilt at the Plant Clinic.
Oak wilt (Ceratocystis fagacearum) has been recently diagnosed at the U of I Plant Clinic.  This deadly disease to oak is nothing new for Illinois and most of Illinois has reported its occurrence.  The problem this year will be to separate oak wilt infected trees from those that have been stressed and declining from previous drought or other problems such as construction damage, soil compaction, changes in the soil grade or water table, lightning damage, nutritional disorders, insect and animal injuries, chemical damage, cankers, and root decay. None of these causes show the distinct vascular discoloration found with oak wilt, although cankers can cause a localized browning that could lead to misdiagnosis.  Recent research has shown us how critical it is to keep oak wilt samples cool, so that Plant Diagnosticians can recover the oak wilt fungus for accurate diagnosis.  Please read the following article for the proper recommendations for sending oak wilt samples to the U of I Plant Clinic:  http://hyg.ipm.illinois.edu/article.php?id=506

Oak scorch -Were the symptoms caused by environmental factors or bacterial leaf scorch (Xylella fastidiosa)? 

Oak suspect to be affected by environmental scorch.
Scorch may be of the noninfectious or infectious type. Environmental stress, root injury, drought, and many other factors may cause leaf margin necrosis, a condition we call scorch. It is usually widespread in a tree and is fairly uniform. Such a condition is not necessarily repeated in following years and is noninfectious.  I have seen this symptom occur recently on trees that have been found to have girdling roots or some obstruction of nutrients under ground. Basically, I suspect that something may be restricting root growth. Symptoms such as this can also occur if trees are growing in an unfavorable site, near obstructions, or in an exposed location.  If this tree is showing these symptoms every year, this stress may gradually weaken the plant and make it more susceptible to diseases or secondary pests, winter injury, or other environmental issues.

There is also an infectious leaf scorch is caused by the bacterium Xylella fastidiosa. The most frequent hosts of this disease include elm, oak, sycamore, mulberry, sweetgum, sugar maple, and red maple. Look for scorch symptoms that occur in early summer to midsummer and then intensify in late summer. The scorched leaf edges or tissue between veins may be bordered by a yellow or reddish-brown color.

The symptoms occur first on one branch or section of branches and slowly spread in the tree from year to year. It is one of those situations that you hope will be better next year but only gets worse. Symptoms will often show on oldest leaves first, distinguishing this disease from environmental scorch that first appears on newest leaves. Of course, diagnosis is never that simple. We did not observe this pattern on pin oaks in Illinois. In fact, most references say that oaks show symptoms on an entire branch at once. Bacterial scorch often allows infected leaves to remain on the tree until the fall. Oaks are again the exception. They will drop leaves early. If you have seen a slow decline in your oak, leaf scorch symptoms showing each July to August, and fall leaf drop about a month ahead of healthy oaks, BLS may be present.
The bacterial pathogen is found only in xylem tissue. Xylem-feeding leafhoppers and spittlebugs are thought to spread the bacterium in landscape trees. It can also be transmitted between trees through root grafts. The transmission methods must not be very effective, though, because we do not see rapid spread of the disease from tree to tree.   We will be testing for this bacterium at the U of I Plant Clinic. There is a fee of $25. It is suggested that you call ahead to be certain you have prepared the correct sample and avoid resampling at your expense.  Leaf petiole tissue is preferred for this test, so leaves with green petioles are the usual request. Please send your samples in the next several weeks. We will collect samples, store them, and then run ONE test on all the submitted samples in August, 2013.

Thyronectia canker of Honeylocust

Honey locust infected with Thyronectria canker.
Fungal canker diseases are fairly common on stressed honey locust trees. One of the most common canker diseases found on Honeylocust at the U of I Plant Clinic is Thyronectria.  Research has shown that honey locust cultivars vary in susceptibility to the canker fungi. Look for resistance ratings when purchasing new honey locust trees. The disease has been linked to drought stress in many cases. Where tree selection is not a choice, avoid injury, provide water in periods of drought stress, and help tree vitality by removing dead wood and fertilizing. As with most canker diseases, there is no rescue treatment that can be sprayed on the tree. When you see a canker problem, try to determine the cause of stress and take measures to alleviate that stress.

Iron chlorosis of trees
Chlorosis or yellow leaves with green veins of trees such as maples, pin oaks, and river birches has been quite evident in the last few weeks.  Illinois soils typically have a high (alkaline) pH level. These higher pH soils may cause problems such as nutrient deficiency chlorosis. In alkaline soil types, minor nutrients are often “tied up” within the soil chemistry making them unavailable to the tree. Iron deficiency is often more a problem on new leaves first. Cultural and environmental growing conditions can also influence iron deficiency and chlorosis by creating an environment unfavorable for root growth. Compacted soils, poor drainage, root damage and drought all can affect root growth. Last summer’s drought may have contributed to many of the trees currently showing iron chlorosis.  For more information on Iron Chlorosis, please read the following reports:

Thanks to the perfect weather conditions, there continues to be many reports across Illinois of tree diseases such as Anthracnose leaf blights, Fireblight (Erwinia amylovora), Apple scab (Venturia inaequalis), Common Cedar Rusts of Illinois, Taphrina Diseases.  Luckily, most of these diseases are not considered to be major diseases. You can read more about some of these diseases at the following links:
Common Cedar Rust Disease of Illinois http://hyg.ipm.illinois.edu/article.php?id=482
Callery Pear Blights (Bacterial Blast or Fire Blight) http://hyg.ipm.illinois.edu/article.php?id=490

Many plants including trees have been diagnosed with Phytophthora root rot.  You can learn more by reading the Phytophthora root and crown rot ALERT blog: http://universityofillinoisplantclinic.blogspot.com/2013/06/phytophthora-root-and-crown-rot-alert.html

Dr. Phil Nixon, U of I Extension Entomologist has reported infestations of many insect pests on trees and shrubs in Illinois this past month and updates on these pests can be found at the following Home, Yard, and Garden article links:

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