Plant and Insect Diagnostic Clinic Update - June 9, 2010

The following are highlights and updates about samples and questions recently received in the Clinic:


We have continued to receive many samples of larder beetle larvae that are probably feeding on insects in the walls of homes. Larder beetle larvae are about 1 cm long, brownish, covered with short tan hairs and have a pair of spines at the tip of the abdomen that are curved backwards. For more information on larder beetles please see our Insect Information Note.

We have received additional reports of cottony maple scale from Lyon, Union, Jones  and Bremer Counties in addition to the earlier report from Chickasaw County. Cottony maple scales produce honeydew and so often the first thing a homeowner notices is a sticky substance on anything underneath the tree. No treatments are recommended as they tend to be a sporadic problem in Iowa. Please see the picture below and this article from HHPN June 15, 2005.

Willow sawflies are doing a bit of defoliating in central Iowa. Sawflies are actually a type of wasp whose adults look more like flies. The larvae tend to feed in groups and sometimes defoliation can be noticeable. Once the larvae are nearly full grown (like those in the picture below) treatment is primarily only for revenge since the damage has already been done.

Little red bumps are on many maple leaves. This is a leaf gall caused by an eriophyid mite and called maple bladder galls or maple spindle galls (depending on their shape). Although it can look impressive they are harmless to the tree.  See below for a picture of maple spindle galls. Please see the picture below and our galls pamphlet.


Brand Canker of  rose caused by the fungus Coniothyrium werndsorffiae.  Management practices include avoiding injuring canes, removing and discarding cankered areas by pruning canes with a sharp knife just above the node. Try to maintain the soil well drain.  Chemicals controls are not needed if cultural controls are practiced.

Strawberry leaf blight or web blight caused by Rhizoctonia solani. Occasionally will cause severe leaf blight that destroy plants by defoliation if environmental conditions are favorable for the disease. The pathogen attacks older leaves and petioles first; later in some cases new leaves might become distorted and wrinkled. High levels of soil moisture and high relative humidity are favorable for this disease, so try to improve drainage, remove and discard infected plants part and provide more aeration. If cultural control do not work you might decide to spray.   The Midwest Small Fruit and Grape spray guide has information about fungicides and time of application. 

Iris bacterial soft rot is caused by the bacterium Erwinia carotovora. Dieback starts at leaf tips and progresses down to the base with leaves turning yellow and wilting. Bacteria infects plant through wounds caused by borers. Plant tissue decays into a foul-smelling mass and the plant dies as the inner parts of roots disintegrates. Bacterial spreads by infected plants, soil, insects or tools. There is no cure for this disease, infected plants must be removed and discarded. Also destroy infected rhizomes before planting, avoiding wounds to rhizomes when digging them up.  Chemical control with bactericides (streptomycin sulfate and cupric hydroxide) is not recommended, because due to the systemic nature of the pathogen it's known to have limited success. In the fall clean up all plant debris and control iris borers.

We are receiving several inquiries about “turf dying” in large areas in home lawns.   No disease pattern is present or has been detected. Most of the problems are believe to be related to drought and unusual warm temperatures part of the last 2-3 weeks.   If this is the problem turf should recover after some time with irrigation or the lawn can be re-seeded.   ISU extension turfgrass specialist Dave Minner continues to investigate if other factors are involved in the problem.  We will be sending information out later on.   

Cottony maple scales covering a branch.

Willow sawflies look like caterpillars, but are actually wasp larvae.

An impressive number of maple spindle galls.


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