Current Statewide Findings for SDS and BSR

With additional reports of sudden death syndrome (SDS) in soybean fields including areas of the state we have not previously detected SDS, we are receiving increased numbers of questions if we have detected brown stem rot (BSR) as well in these fields. First off, not every field will have SDS as we have seen several other diseases in 2010 that might have similar looking symptoms to SDS or BSR. One of the general things we are noting, however, is the following sort of statement: "we are seeing yellow patches in some of the fields." Given our own observations from research trials both on our UW research farms as well as our on-farm locations, when you see the yellow patch, stop and take a closer look at the symptoms.

In regards to the question about BSR, to date, the samples we have received into the Field Crops Plant Pathology lab and tested have had only SDS. We use a molecular approach to our diagnostics to differentiate SDS from BSR and the results have been very clear when examining these samples. As an additional piece of information, we are also working to isolate the respective pathogen(s). We will continue to monitor the situation for both diseases as the season progresses. Lastly, we want to emphasize that if you have a positive field for SDS take a soil sample to look for the presence of Soybean cyst nematode.

Get Your Wheat Seed Order in Early

Local cash and futures prices topping $6.10 and $7.00 per bushel, respectively coupled with the strong likelihood of early corn and soybean harvest have many growers considering winter wheat in 2010. Seed availability of elite varieties will begin to tighten so it is imperative to get your seed orders in early. To date, all of the wheat seed samples that have come into the Wisconsin Crop Improvement Association have been blue tag certified (>85% germ). This is good news to growers as certain areas of the state had difficulties with harvest and sprouting. It is still premature however to fully know the total amount of certified wheat seed from the 2010 crop available for planting in 2010. I strongly caution growers from planting bin run seed in 2010 given the sprouting issues and low test weights, both of which can negatively impact germination, tillering, and overwintering.

Reports of Frogeye Leaf Spot in Soybean

Over the past week, we have had reports of Frogeye leaf spot in soybean. Frogeye leaf spot is caused by the fungus Cercospora sojina. DATCP noted finds of this disease in some fields in the southern part of the state. While Frogeye leaf spot has been documented in Wisconsin, it is still a disease that for many is a relative unknown. As you scout soybean fields late in the growing season, symptoms of Frogeye leaf spot can be recognized as angular, brown to reddish brown spots that are irregularly shaped and have a light brown to gray center. While lesions on stems and pod can occur later in the season they are less common and distinctive than lesions on the leaves. If there are pod infections, seeds near those lesions can be infected and develop conspcuous light to dark gray or brown areas.

Why 2010? The prolonged warmer, more humid and rainy periods we have seen this year are very favorable to development of this disease. Management recommendations for Frogeye Leaf Spot include the use of resistant soybean varieties, crop rotation that is 2 years or longer (the pathogen overwinters in soybean debris). Foliar fungicides can be effective for control of this disease, but timing of application is important.

For more information about Frogeye Leaf Spot, there are several good fact sheets like:

http://www.ces.purdue.edu/extmedia/BP/BP-131-W.pdf

http://www.soydiseases.illinois.edu/index.cfm?category=diseases&disease=119

http://www.planthealth.info/frogeye_basics.htm

Late Season Stem Diseases - Look Closely...

We are receiving questions and also samples this year that are similar to fields we visited during the 2007 and 2008 growing seasons. As a reminder, the focus for many of those field visits were specifically if there was a breakdown in the Rps 1K gene for Phytophthora. A summary of that information is available here.

Similar to those two years, samples we have looked at this year have not necessarily been typical and it has not been easy to identify a primary disease of interest (i.e., the primary cause). Samples submitted to the Plant Disease Diagnostic Clinic have often yielded evidence of multiple pathogen species in a given sample. Recent results from the Wisconsin DATCP Phytophthora root rot survey of 45 fields between 16 June and 9 July indicated presence of Phytophthora in 15 fields (33%), which was an increase from the previous two years (20% in 2008 and 18% in 2009, respectively). In spite of the increase, the results still indicate that it is important to make sure you have a proper diagnosis of suspect soybean plants. Two diseases that can often be confused during the later stages of soybean development are Northern stem canker and Phytophtora. Below are a description of the two diseases and associated symptoms/signs:

Northern stem canker (Diaporthe phaseolorum var. caulivora): reddish brown to black discoloration on stems and petioles that can first appear around flowering. Lesions originate at the nodes and appear sunken and may girdle the stem. There can be a yellow and brown discoloration of leaves around the veins and plant death is associated with petiole and leaf retention.

Phytophthora stem and root rot (focus is on symptoms after V4): brown to black lesion that extends above and below the soil surface. A root rot can be found. Leaves turn yellow and petioles will droop. Wilting where tip of the plant forms a shephard's hook. Plant death associated with petiole and leaf retention.

For further information about soybean diseases, please consult Soyhealth.

For a field diagnostic guide of common soybean diseases in Wisconsin, please click here.