Wednesday, May 1, 2013

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

Monthly Summary  

(Courtesy of Kelly Estes, State Survey Coordinator) 

Average Temperature and Precipitation

Modified Growing Degree Days (Base 50⁰ F, starting March 1

Station Location
Actual Temperature
One- Week Projection
Two-Week Projection
St. Charles
Rend Lake
Dixon Springs

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:
U of I Plant Clinic Facebook Page:
Follow Stephanie Porter on Twitter @skporter

It has been evergreen, or should I say “ever-brown” mania at the U of I Plant Clinic, thanks in part to last year’s drought.  We have received many spruce, pine, yew, and arborvitae samples with browning attributed to abiotic problems such as drought, sunscald, winter burn, or salt injury.   Abiotic means that the browning symptoms were not caused by a disease pathogen, insect or mite. 

Stressed spruce that likely declined due to drought

Many clients and homeowners have reported that their evergreen has appeared to have died almost overnight. For most cases, it is highly unlikely that their trees died “overnight”. Clients don’t always see the early symptoms of a disease. Also, diseased evergreens may not show a sudden change like you would see with a deciduous tree. This may especially be the case for evergreen killed during fall and winter months. For example, we can cut a branch off of an evergreen to use for a wreath or winter outdoor container. Cutting the branch disrupts the physiology or the branch. Yet, many wreaths and evergreen decorations can last several months outdoors in cold to cool temperatures with minimal loss of color and appearance.  
They also question why only one tree or shrub died while others besides it remain healthy. The answer may not be simple and straight forward, and may be the result of a combination of factors. The affected tree could have been stressed for some other reason and the drought may have taken them “over the edge”, so to speak.  The trees pictured above were likely planted at the same time, yet the dead trees look shorter than the nearby living trees. That could indicate they were stressed for number of years prior to the drought. Individual plant genetics may have predisposed one tree over another. Also specific planting sites (soil, exposure, etc.) could influence the trees health.

So, why are people submitting these “ever-brown” samples to the U of I Plant Clinic?  They are ruling out disease pathogens, insects, or mites as a possibility for the observed, browning symptoms.  For more information on submitting samples to the U of I Plant Clinic, please refer to the following link:

We have received a few Blue Colorado spruces with signs of Rhizosphaera needlecast and, as most know, this is something that can be managed with a protective fungicide, at the correct timings, early in the spring.  Thanks to the drought stress, we have also been observing fungal canker diseases on trees.  In a “normal” year, we see a lot of Cytospora canker on spruce; however, now we have been finding  Eastern white pine and Douglas fir infected with canker that is suspected to be due to Cytospora.  For additional information of other secondary pests of Eastern white pine, please refer to the following ACES press release:

Fungal root and butt rots on deciduous trees are on the rise as well, due to drought stress.

Suspected Cytospora canker on Eastern White Pine

We have also received spruce with signs of spruce spider mites.  For additional information on spruce spider mites, you can refer to the following link:  Before a miticide application is made, it is important to determine that active mite stages are present and that the population is sufficiently large enough to warrant control. It is common with spruce spider mite for an infestation to suddenly disappear, probably due to predation, weather changes, or other factors. Sometimes, the mite infestation does not return for decades.” – Phil Nixon, Extension Specialist, Pesticide Safety Education Program/Ornamental Household Insects

For additional information on spruce problems, you can refer to the new Spruce Problem Factsheet:

Reports of pine wilt disease have been received as well.  Trees infected with pine wilt should have been removed by late winter. The pine sawyer beetle vector will be emerging soon and will spread the nematodes. To test a pine for the presence of pinewood nematodes, take sample branches that are 2" in diameter and about 12" long. The branches should be from an area having brown needles.   The samples can be submitted to the U of I Plant Clinic for a fee of $20.

For additional information on the stress of drought on trees or shrub, please refer to the following Home, Yard, and Garden Article:

Invasive Species News from the Illinois Cooperative Agriculture Pest Survey (CAPS) Program 

(Courtesy of Kelly Estes, State Survey Coordinator)


The CAPS program is a joint effort between several state and federal agencies that focuses on the early detection of exotic, invasive plant pests, diseases, and weeds. This year our surveys will be focusing on Thousand Cankers Disease of Walnut. Trapping for the walnut twig beetle will be beginning in May. Questions or concerns about TCD? Have a potential trapping location? Please contact Kelly Estes, State Survey Coordinator- or 217-333-1005. Other invasive species surveys across the state will be getting started as well. Gypsy moth and emerald ash borer traps will soon been seen. Remember, gypsy moth egg hatch begins around 145-200 DD and emerald ash borer adult emergence begins around 450-500 GDD.  You can keep up to date with invasive species news at the CAPS Blog.
May is Illinois Invasive Species Awareness Month! The goal of Illinois Invasive Species Awareness Month (ISAM) is to provide resources and opportunities to help stop the spread of invasive species in Illinois. There are dozens of educational events and volunteer opportunities that focus on invasives species hosted by ISAM partners – find an event in your area on the calendar

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