Plant Diagnostic Clinic End of Year Summary for Agronomic Crops

Published: December 4, 2015

As of November 30th, the Plant Diagnostic Clinic (PDC) had a total of 400 samples submitted in 2015.  Most samples were submitted for disease diagnosis, though some were for insect or plant/weed identification (Figure 1). Despite the excessive rain and the many acres of production fields that were not planted, agronomic crops were the most frequently submitted for disease diagnosis. Soybean samples were the most numerous, however corn, wheat, alfalfa and lespedeza were also submitted (Figure 2).

Due to the rainy spring and early summer, it is no surprise that Pythium diseases were the most numerous.  Pythium is an oomycete, or a water mold, meaning it loves water and takes advantage of it by producing a motile spore called a zoospore that can ‘swim’ from root to root or plant to plant.  Eleven corn and eleven soybean samples were diagnosed with Pythiumdiseases such as root rot and seedling damping off.  An additional sorghum sample was also positive for Pythium root rot. Diagnosis of Pythium diseases is based on the observation of oospores (non-swimming spores) in plant tissues or via a serological assay.  There are many species of Pythium that can be pathogenic, with each having a range of preferred temperatures for growth and infection.

Other confirmed soybean diseases in 2015 included:

• Phytophthorastem rot (Phytophthora spp.) 4 samples
• Charcoal rot (Macrophomina phaseolina) 2 samples
• Cercosporaleaf bligh2t (Cercospora spp.) 2 samples  
• Sudden death syndrome (Fusarium virguliforme) 2 samples  
• Soybean stem borer (Dectes texanus) 2 samples
• Frogeye leaf spot (Cercospora sojina) 1 sample
• Phyllostictaleaf spot (Phyllosticta spp. ) 1 sample
• Anthracnose (Colletotrichum truncatum) 1 sample
• Brown stem rot (Cadophora gregata) 1 sample  
• Rhizoctonia crown and stem rot  (Rhizoctonia spp.) 1 sample 

Other confirmed corn diseases in 2015 included:

• Gray leaf spot (Cercospora zeae-maydis) 7 samples
• Northern corn leaf blight (Exserohilum turcicum) 4 samples
• Diplodiaear rot (Diplodia maydis) 2 samples  
• Anthracnose (Colletotrichum graminicola) 1 sample
• Blue mold rot (Penicillium spp.) 1 sample
• Physodermabrown spot (Physoderma maydis) 1 sample
• Southern corn rust (Puccinia polysora)1 sample
• Thrips damage (unidentified thrips) 1 sample    

Confirmed wheat diseases in 2015 included:

• Bacterial leaf streak (Xanthamonas spp.) 4 samples
• Loose smut (Ustilago tritici) 1 sample
• Scab (Fusarium spp.) 1 sample
• Wheat soil-borne mosaic (Wheat soil-borne mosaic virus) 1 sample
• Glume blotch (Septoria tritici) 1 sample
• Sharp eyespot (Rhizoctonia cerealis) 1 sample
• Stripe rust (Puccinia striiformis f.sp. poae) 1 sample

Forage crop issues included a sample of lespedeza with tar spot, and two alfalfa samples, one with a root and crown rot complex and the other with with suspected insect damage from the Clover root curculio (Sitona hispidulus). The most diagnosed issues were abiotic, including chemical injuries and environmental issues such as soil compaction or drought stress (Figure 3).

The PDC is open year round for sample submission.  The typical turn around is 48 hours, depending on the day of the week the sample is submitted.  If special testing is required, such as an ELISA or culture plating, turn around time varies.  A general diagnosis is $15, additional services are $10 each.  For agronomic crops, additional services may include culture plating, wheat virus ELISA assays, Goss’s wilt serological testing, Pythium spp. serological testing, Phytophthora spp. serological testing or other miscellaneous molecular testing methods.  Please see the PDC website http://plantclinic.missouri.edu/ or call (573-882-3019) for more information.

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