Plant and Insect Diagnostic Clinic Update – July 14, 2017

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. For more information on a particular disease or insect problem listed, follow the article cited.

Plant Identification

The following plant identification highlights represent recent sample submissions

Dodders, or Cuscuta species, are plants that specialize in parasitizing other plants. See information about dodder from University of California IPM   

Quackgrass is a perennial grass that is classified as a weed. Quackgrass in lawns can be difficult to control. For options to control this weed please see the publication "Weed Control in Home Lawns."

Birdsfoot trefoil has been obvious in lawns.  According to Richard Jauron part of the reason it is noticeable in some areas this year is because drought conditions reduced the need to mow and so the bright yellow flowers are not being cut off.  


The following plant disease highlights represent recent sample submissions from fruit, vegetables, and ornamentals.  

Faciation on spirea
Fasciation on spirea

Annual and Perennials

Spirea - Fasciation is a fascinating symptom caused by mutation or Phytoplasma.  See the University of Arkansas article on Fasciated Plants.

Broadleaf Trees

Oak - Anthracnose see our encyclopedia article

Lilac - Anthracnose see our encyclopedia article

Oak - Suspected physiological scorch

Birch - Birch Leaf Spot. See this great resource for common problems on birch from University of Maryland Extension IPM Series: Birch trees

Oak - Suspected Herbicide Injury or Exposure. In the Clinic our assessment for chemical injury is based on visual examination of the sample; we do not test for herbicide residue. We can provide a list of laboratories that test for herbicide residue upon request. It is important to note that growth regulator herbicides are commonly used for broadleaf weed control and are in both homeowner and professional products.


Cucumber, muskmelon broccoli, kale - Suspected Herbicide Injury or Exposure, read about herbicide sources at the home garden on our article on Chemical Injury in Vegetables.

Fruit (small and tree fruit, including hops)

Peach -  Bacterial spot.  See our encyclopedia article Bacterial Spot on Stonefruit Trees

Apple - Powdery mildew symptoms in fruit.  See Penn State article Powdery Mildew of Apple

Apple -  fruit cracking and russeting See University of Minnesota article on Apple russeting 


imported longhorned weevil
Imported Longhorned weevil, 3 mm long, crawling on notebook paper.

Japanese beetles have caused problems over much of the state.  Populations had been lower in recent years due to dry summer conditions and cold winter temperatures that reduced larval survival.   See the article elsewhere in this issue.

It's imported longhorned weevil time again.  These hardshelled, outdoor beetles are a common accidental invader went they crawl into the house by mistake.  The practical control is to vacuum or sweep and discard.  See our encyclopedia article on ILHW (which is what we call it since its name is longer than it is!).

If you notice lots of wasps flying around your magnolia you should check it for magnolia scale.  This now common pest feeds on the sap of magnolia trees and produces large amounts of sticky honeydew (excrement) that lands on the magnolia leaves and ground beneath the trees.  It is common for sooty mold to grow on the honeydew giving the leaves a dirty appearance. Wasps and other insects are attracted to the trees because they feed on the honeydew.  It is late to use systemic insecticide this year, but crawlers can be treated later this summer and systemic insecticides can be used after bloom next summer.

Magnolia scale
Large grayish female magnolia scales feeding on the branch.  They produce sticky honey dew that is shiny on the leaves below.  The black coloration is from sooty mold that grows on the honeydew.


Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Horticulture and Home Pest News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on July 14, 2017. The information contained within may not be the most current and accurate depending on when it is accessed.