Friday, August 20, 2010
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.
Thursday, August 19, 2010
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.
Sunday, August 8, 2010
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:
Sunday, August 1, 2010
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.