Plant and Insect Diagnostic Clinic Update - March 31, 2010

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


The clinic received its first termite swarmers last week. These are winged termites setting out to start a new colony. Termite swarmers inside a house indicate you should have a termite inspection. Please see this pamphlet for information on choosing a pest management professional. Please see this HHPN article for information on termite swarmers.

Larder beetles and carpet beetles continue to appear in homes. Most are probably feeding on dead insects in the walls of homes and no control is feasible or necessary.


Botrytis blight of geranium caused by the fungus Botrytis cinerea. Symptoms of this disease vary from distinct spots to large dead areas or V-shaped lesions. Symptoms on stems appear at the base of plants as light-to dark-brown lesions. To manage this disease remove and discard infected plant material to reduce amount of fungal inoculum, avoid overhead irrigation and promote good air circulation. Preventive fungicides application can also be considered.

Xanthomonas leaf spot and blight of begonia is caused by the bacterium Xanthomonas campestris pv. begoniae. Lesion on leaves, petioles, and stems may be the only symptoms, but plants may wilt and collapse if systemic infections occur. Removal of infected leaves is recommended in some cases to reduce bacterial inoculum, however there is a risk of systemic infection through the wounds. High relative humidity favors disease development, so it is important to avoid overhead irrigation to maintain dry foliage as well as to increase air circulation in the greenhouse to reduce dispersal of the pathogen. For more information about this disease:

Winter dessication in Concolor fir is being observed now. Most likely several other evergreen around Iowa are showing brown tips and/or needles, at this time of the year most likely is just winter dessication. Plants should recover and start producing new shoots later in the spring.

Rhizosphaera needle cast and Sudden needle drop (SNEED) on Colorado blue spruce. Early spring when needles are about 1/2 inch long is the best time to spray against Rhizosphaera needle cast to protect the new growth. Unfortunately it is not know if fungicides for Rhizosphaera will help stop infection by SNEED.


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