Plant and Insect Diagnostic Clinic Update - March 25, 2016

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.


The following are highlights of the winter months of 2016 in the Plant and Insect Diagnostic Clinic. Winter is typically slower in the clinic. However, a couple of interesting cases have reached us.

Phytophthora Rot on Spruce. Phytophthora is a genus of watermold pathogens that causes root rot in a variety of hosts. Typically symptoms are browning, yellowing or wilting of the entire plant. In some cases, dark zones can be found under the bark of tree crowns. There is no cure for this type of problem.  Avoid planting susceptible trees on heavy clay soil or low areas where drainage is suboptimal.

Diplodia Tip Blight on Austrian Pine. This disease is frequently seen in Austrian pine. Diploidia tip blight is caused by the pathogen Diplodia (=Sphaeropsis) sapinea. Symptoms originate at the tips of infected branches causing browning, stunting and needle drop. Minimizing stress on trees by watering and fertilizing them is all you can do for this disease. If caught early, infected branches can be trimmed and destroyed. In severe situations involving valuable trees, fungicides may be applied to protect new growth, but it will not eradicate the pathogen or cure the tree.

Pine Wilt on Scotch Pine. Pine wilt is caused by the Pine wood nematode Bursaphelenchus xylophilus. The nematode is spread from tree to tree by the pine sawyer beetle (a type of longhorned beetle). Typical symptoms of pine wilt are wilting, discoloration needle drop and death of the infected trees. The best management for pine wilt is prevention. Avoid planting susceptible pines (Scotch pine, Japanese red or black pines), and before deciding what tree to plant keep in mind the site characteristics (soil type and microclimate). If your tree has tested positive for pine wilt, remove infected trees to prevent the spread of the nematode to healthy trees. Removal should be done when the sawyer beetle is inactive and destroyed (winter- spring months).

Anthracnose on Sunflower. Anthracnose caused by various Colletotrichum species is common on a variety of hosts. Symptoms are typically sunken spots on leaves. In this case, spots were found on the cotyledon of sunflower plants and were caused by Colletotrichum acutatum.   This pathogen produces enormous amounts of conidia (seeds of the pathogen) under moist and warm greenhouse conditions. Conidia can be readily dispersed to healthy plants by water splashing at watering.

Nutrient Deficiency/Environmental Damage. We received samples of Avocado, Coffee, and Kumquat grown as indoor plants. These tropical plants were suffering from nutritional imbalances and environmental stress mainly related with seasonality (environmental light and temperatures differences typical of winter and spring months in the Midwest). Careful nutrient supplementation should be considered, including slow release fertilizer.



Example of diplodia tip blight. Shows pine needles turning brown
Diplodia overwinters as small, black spore-producing pycnidia on 2-year old pine cones.


Another example of diplodia tip blight. Shows pine needles turning brown, but less dramatic than last example

Diplodia fungus causes dead, brown needles at the tips of pine branches.



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 Net...