Plant and Insect Diagnostic Clinic Update - September 11, 2015

News Article

 The following are highlights and updates about samples and questions recently received in the Plant and Insect Diagnostic Clinic. Visit the PIDC's Facebook page to ask questions and for updates and more pictures.

 

Diseases

 

Plentiful rainfall, flash floods and excessive soil moisture have caused a tough year for trees and shrubs.  Some trees (oak, ashes, lilacs among others) are suffering from leaf yellowing and off-green color. A change in the pH of the soil may be of the many factors that contribute to the unthrifty look of the foliage. In some instances, roots may not be able to uptake nutrient readily available in the soil (due to inadequate soil moisture or/and pH), and nutritional deficiencies develop.  The yellow leaves turn necrotic (brown) at the edges, a symptom known as abiotic or environmental leaf scorch. Factors associated with abiotic scorch include winds, salt or toxic metals in the soil, extreme soil nutrient imbalance, and soil moisture extremes. This type of scorch appears uniformly distributed on the canopy and can be observed shortly after environmental stress occurred. It is important to differentiate environmental leaf scorch to the bacterial leaf scorch.  For more information see the article on Bacterial Leaf Scorch Testing elsewhere in this issue.

 

Sycamore anthracnose. When have received some samples of a very common disease of sycamore trees called sycamore anthracnose For more information visit the Clinic website.

 

Bur Oak Blight: How to Submit a Sample.  It has been a year of high incidence for Bur Oak Blight (B.O.B). If you suspect your tree is suffering from B.O.B, keep the following in mind when submitting a sample for confirmation:

  • Select a couple of branches with leaves attached to a twig
  • Look for green leaves that have red veins and necrotic petioles. 
  • Look for black pustules on dried out leaves attached to the twig.

See our Facebook page for examples of B.O.B. symptoms! 

 

Sooty Blotch and Fly Speck on Apples has been particularly difficult to control this year. Heavy rains and excess moisture have contributed to these fungal pathogens being particularly aggressive. In a year like this, fungicide treatments become a challenge.  Always remember to select the most effective fungicides, alternate FRAC (Fungicide Resistance Action Committee) groups with a different mode of action every week and keep spray intervals every 7 to 10 days. 

 

Insects

This is a great time of the year to check out oak trees for a variety of insects. We have noted oak blotch leafminer on white oaks, oak lace bug, and a wide variety of galls. Oak leaves are also looking a bit off-color due to mites and lace bugs that feed on the surface of the leaves. This late in the year there is no need to be concerned about leaf feeding insects or mites. Just enjoy the diversity on your oaks!  We did!  See the photos below.

 

Large, dark and "triangular-shaped" moth common in the yard or at the porch light the past few weeks are probably green cloverworm moths.  The dark moths with the extended "snout" are common in late summer after the caterpillars have spent the summer feeding on the foliage of a wide variety of plants. The caterpillars are not pests except for very rare infestations in soybean fields.  According to BugGuide, the caterpillars feed on leaves of alfalfa, beans, clover, ragweed, raspberries, and strawberries.  The moths are harmless and no control is needed. It is not practical to kill moths that are coming to porch lights, etc. from a large variety of locations.  It’s too late to control caterpillars.  Any feeding that happened in crops is past.

 

Stippling discoloration typical of mites feeding on oak foliage.

Stippling discoloration typical of mites feeding on oak foliage.

 

"Can't we all just get along?"  A multicolored lady beetle and a yellowjacket wasp share space on a oak gall to feed.

"Can't we all just get along?" A multicolored Asian lady beetle and a yellowjacket wasp share space on a oak gall to feed.

 

Oak lace bug adult.

Oak lace bug adult.

 

The markings on the green cloverworm moth are not always distinct; Moths may be tan to solid black.

The markings on the green cloverworm moth are not always distinct; Moths may be tan to solid black.

 

Three common orb-weaver spiders present in Iowa this fall.

Three common orb-weaver spiders present in Iowa this fall.

Authors: 

Lina Rodriguez Salamanca Extension Plant Pathologist and Diagnostician (Program Specialist II)

Dr. Lina Rodriguez Salamanca is an extension plant pathologist and diagnostician with the Iowa State University Plant and Insect Diagnostic Clinic, a member of the North Central Plant Diagnostic Network (NCPDN) and National Plant Diagnostic Netw...