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Winter wheat in Wisconsin is looking very good across the majority of our field trials. In some of these trials, we are already at the Feekes 4 (Zadoks 30, pseudostem erection) growth stage. This week, it was noted that there is some evidence of powdery mildew (see photos below courtesy of John Gaska) in some of these trials. This is an important period for some early-season management decisions (not just for foliar fungicides also). Specifically for decisions for disease management, it really starts with knowledge of the relative susceptibility of your wheat variety against powdery mildew. With that knowledge, a second step is to then determine how severe and where in the wheat canopy are symptoms of powdery mildew being noted. At Feekes 4-5, the recommendation for the use of a foliar fungicide is based on the appearance of symptoms of powdery mildew on the newest (i.e., upper) leaf. Scouting by examining approximately 100 leaves in a field from different locations. Assess the severity for each leaf by counting the number of powdery mildew pustules. If the average number of pustules is 10 or greater, this may indicate the need for use of a foliar fungicide. In most years, we often see symptoms of powdery mildew in the wheat canopy, but typically only in the lower canopy due to the microclimate and varietal differences. Disease management decisions at these earlier growth stages need to take into account the assessment of the most appropriate leaf material that may impact the flag leaf later in the growing season.

Photos from Arlington, WI (Courtesy of John Gaska, Dept. Agronomy). Notice that the primary location of symptoms are in the lower canopy. As discussed earlier, guidelines for the use of foliar fungicides are based on examination of the uppermost leaf.

Late soybean and field corn harvest caused a significant drop in WI winter wheat acres in 2010. Many growers, including myself, still decided to move forward with late winter wheat plantings. To answer late-planted wheat questions we published the following article on November 23rd 2009.

Late Planted Winter Wheat: Growing Slowly But Surely

As with many growers we had a difficult time getting all of our winter wheat planted in the “Optimal” planting date window in 2009. A significant number of winter wheat acres across Wisconsin were planted under the full knowledge of reduced crop insurance coverage as well as reduced yield. Given that the 10-day weather outlook calls for reduced temperatures as well as potential flurries I was interested in the “state” of our November 13th planted winter wheat in Janesville WI. In Image 1. we see that the radicle, seminal roots, and coleoptile have all emerged. In wheat the radicle and seminal roots will be the first structures to appear. Only after the seminal roots and radicle begin to imbibe water will the coleoptile begin to elongate.

For those winter wheat acres that were planted in the last few days remember that winter wheat will vernalize once the radicle emerges from the seed as fall growth will continue as temperatures fall to zero. Literature referenced: R.J. Cook and R.J. V

Today (3/18/10) I revisited our Janesville winter wheat site that was planted on Friday November 13th 2009. The wheat crop has emerged relatively uniformly and appears to have made it through the winter with very little crop loss (Image 2).

At this juncture the most critical decision facing growers is “Do I invest money into this crop?” Though I have no data that directly mimics this years situation we can use our 2009 planting date study as a starting point. In Figure 1 below we see that our late planted wheat (planted Oct 17th) suffered a 28% yield loss when compared to our early planted wheat (planted Sept 18th). Though our 2010 crop was planted 27 days later than the 2009 data what we can guesstimate is that your late planted wheat will likely yield at least 28% less than normal production levels. So your decision is “Can I still make money off of a wheat crop that is expected to yield ~30% less than normal production levels.” If the answer to that question is yes than it is critical to get across that wheat as quickly as possible with an early N application to stimulate tiller formation. It will also be important to scout early and often as weeds will likely be a greater issue in 2010 than in “normal” years.

We have recently completed the development of a Winter Wheat Variety by Disease Database (version 1.0) based on results from the 2009 Winter Wheat Performance Trials in Wisconsin. The goal of this database is to assist growers in variety selection, especially regarding how these varieties compared against different diseases commonly seen in Wisconsin. This database will continue to be updated annually.

Within this database, varieties can be sorted based on their combination of disease response and yield performance. At each location, every variety has been given a score from 1-4 for each disease:

– 1 = high yield, low disease
– 2 = high yield, high disease
– 3 = low yield, low disease
– 4 = low yield, high disease

These scores are based on rankings of yield and disease response. Each variety was ranked as either high yield (top 50% of varieties for that location) or low yield (bottom 50% of varieties for that location) and low disease (top 50% of varieties for that location) or high disease (bottom 50% of varieties for that location). A word of caution…the use of “high” and “low” in this context are relative terms. These are meant to describe a variety in the top or bottom half of varieties within a given location. These designations should be interpreted carefully; if the overall level of a disease was low at a location, then even the variety ranked worst for that disease might not have had very high levels of disease.

Before using the database, read “Using the Excel Database: Background and Instructions,” which describes the presentation of the data and the use of the “sort” function in Excel.

After looking at the instruction file, open the Winter Wheat Variety-Disease Database. The “sort” feature described in the instructions can be used to look at which varieties perform best against certain diseases, or to look at the performance of specific varieties.

Questions about how to use the database can be addressed to either Paul (Email: esker@wisc.edu) or Karen Lackermann (lackermann@wisc.edu).

With the wide-spread reports of White mold (or Sclerotinia stem rot, SSR) this year in Wisconsin and across the region, we have been fielding many questions about control options. In particular, many of these questions have been about Contans WG. In this blog, Angie Peltier (Postdoctoral Research Associate in Plant Pathology) and I try to provide information that will help you understand more what biological control for white mold entails.

What is Contans WG?

Contans WG (SipcamAdvan; Durham, NC) is a commercial biocontrol agent and is a proprietary powder formulation that contains the fungus Coniothyrium minitans. Contans WG has been labeled for use in both conventional and organic soybean.

C. minitans was first described in California in 1947, and it is now known to have a world-wide distribution. The host range of C. minitans includes important plant pathogens such as Sclerotinia sclerotiorum, S. trifoliorum, S. minor, and some strains of Botrytis cinerea, B. fabae, and Sclerotium cepivorum (Turner and Tribe, 1976).

How does it work?

The fungus that causes white mold (Sclerotinia sclerotiorum) produces long-lived survival structures called sclerotia that many say resemble rat droppings. Sclerotia are important in the life cycle of Sclerotinia, allowing the fungus to survive in the soil until conditions are favorable for the disease cycle to begin: Upon canopy closure and during periods of cool and wet weather, sclerotia germinate to produce mushroom-like fruiting structures called apothecia. Apothecia produce ascospores that are wind-disseminated. If during a period of leaf wetness ascospores land on dying soybean flower tissue, they can use this food source to gain entry into susceptible soybean plants and cause disease. Many apothecia can emerge from one sclerotium, making each sclerotium an important inoculum source.

When a water suspension of Contans WG is incorporated into the soil, viable spores of C. minitans that come into direct contact with sclerotia, germinate, and then gain entry into the sclerotium by a chemical etching process, eventually causing the disintegration of the sclerotium. Degraded sclerotia cannot produce apothecia, and therefore, these sclerotia produce no inoculum to initiate infection of soybean.

What factors need to be considered for use?

Application timing. Application timing can influence efficacy. While the Contans WG label does not specifically indicate optimal application timing, the manufacturer’s “Directions for Use” (Prophyta, Germany) suggests a minimum of 3 months between application and when SSR disease is likely to develop, to allow adequate time for colonization of sclerotia. Some research suggests that there is a lag time between application and disease suppression. Important consideration: in fields with a high sclerotia load in the soil, enough sclerotia may survive to still cause a substantial level of disease.

Tillage. The “Directions for Use” states that after soil application, the product “should be incorporated as thoroughly and uniformly as possible to a depth of 5 to 20 cm”. An important consideration is also to avoid additional tillage after incorporation, as tillage can bring uncolonized sclerotia to the soil surface.

Some unanswered research questions:

Much of the published data has focused on both aerial and soil application of C. minitans (not Contans WG). Efficacy of C. minitans application has been shown through the reduction of disease in field trials for other crops susceptible to S. sclerotiorum, including dry and snap bean, sunflower and oilseed rape. To date, no research has been published on the use of Contans WG or C. minitans to control white mold in soybean. Therefore, further field research is needed to understand the efficacy of C. minitans in soybean.

In addition, the label directions state that the product must be incorporated into the soil. We are currently examining how efficacy of Contans WG may be impacted under no-till situations.

Lastly, although this issue has not yet been adequately researched, there is some indication that soil type may affect parasitism of sclerotia by C. minitans, which may reduce efficacy in some production situations.

Wisconsin growers are struggling to get their soybean crop harvested and we are no exception. As of today the WSRP (WI Soybean Research Program) have only harvested 18% of all of our plots and projected weather outlooks show no real extended harvest window in sight. One of our combine crews just called from Chippewa Falls, WI minutes ago. We opened up the field and were treated with soybean moisture’s in the low to mid 20’s. Nothing left for us to do but shut it down for the day and hope for some drying weather. As we continue to struggle through harvest soybean seed quality, drying, and storage issues will continue to arise. Below are a few sources of information that may prove useful as harvest pushes forward.

• Soybean seed quality: Be aware of the differences between sclerotinia, phomopsis, and purple seed stain. Please see Common Soybean Diseases in Wisconsin, Soybean Quality Issues in 2009, and Discolored Soybean Seed.
• Soybean Grain Drying, Conditioning and Aeration: Drying Soybeans in 2009, Harvesting, Drying and Storing Frost-Damaged Corn and Soybeans and, Drying Soybeans Requires Special Considerations
• More info on grain quality please see Chat n chew cafe and grain harvest.

Note of Interest: John Gaska called from the field after the initial post and indicated that all of the pods he inspected remain tightly sealed and no germination was occuring. Grain quality at the Arlington location still looked good to excellent.