What About Soybean Rust?

I have been monitoring reports from the southern U.S. to determine what we might see as a risk for soybean rust in 2008. Also, thanks to a message from David Fischer, UW-Extension-Dane County, we know that growers are paying attention to the possible risk for soybean rust as they consider their planting options for switching from full-season corn hybrids to either soybean or shorter-season corn hybrids. As it stands right now, soybean rust activity in the south has been quiet. The last documented detections were in mid-April and conditions in southern Texas (which would be a primary source of inoculum for Wisconsin) has been dry. Questions have been raised regarding the situation in Mexico, and to the best of our knowledge, the last documented detections there were in January. Thus, the risk for soybean rust in Wisconsin remains low. We will continue to monitor the situation in the south, especially Texas and Louisiana over the next few weeks. Supported by check-off dollars and the USDA, Wisconsin will have 15 sentinel plots in 2008 to help us in our monitoring efforts for soybean rust. Updated information can also be found at www.sbrusa.net.

Early Season Soybean Diseases

As I stare out my window, watching rain fall, I write this short note to remind everyone to pay attention after planting for early-season seedling diseases in soybean. The cool and wet weather favors a disease like Pythium, but it is critical to make a good field assessment to determine which soybean seedling problems may be found. Often, the effects of seedling diseases is missed because symptoms are not expressed early in the season, but over the growing season, early-season soybean diseases can impact plant vigor during the reproductive stages. In the recent April 24, Wisconsin Crop Manager, Nancy Koval, Craig Grau, and I discuss the differences between seedling diseases and how to accurately diagnose them. Furthermore, updated information is now available at www.planthealth.info/seedlings_basics.html regarding soybean seedling diseases, which has information summarized across a multi-state area.

Aphid Numbers in Wheat are Low

Spring aphid treatments were applied to our Barley Yellow Dwarf Virus experiment on 5/6/08 at our Arlington, Lancaster, and Janesville sites. Wheat growth stage varied among our planting dates and ranged from Zadoks 14,22,30 (Feekes 4-5) “pseudostem erection” to Zadoks 16, 29, 31 (Feekes 6) “1st detectable node”. Across all of our plots we found only one Oat Bird Cherry aphid. The established spring threshold for this pest is 50 aphids per linear foot of row.

Oat Bird Cherry Aphid

Drawing by Dennis Murphy – MU

Scouting for Wheat Diseases

Winter wheat in much of Wisconsin is around the jointing stage.  This is an excellent time to start scouting for wheat diseases, especially those that are known to overwinter in Wisconsin like Septoria and Powdery mildew.  We have detected those two diseases in our initial scouting around the state, but their presence is highly dependent on the wheat variety.  In our scouting efforts, we have found these diseases in more susceptible varieties.  Severity of Septoria and Powder mildew is still very low at the moment.  Have a look through the April 10 Wisconsin Crop Manager for two articles that describe scouting for wheat diseases and also the decision process for understanding the risk for a disease outbreak and the use of foliar fungicides.

Wheat Stands at Chilton and Lancaster

On Monday April 21st we assessed winter injury at our Chilton WI variety test site. Some ice damage was present, however the damage was isolated to low lying areas. Wheat stand and tiller counts were excellent outside of these areas. The growth stage was a Feekes growth stage 3 or Zadoks growth stage 15 (five leaves unfolded) 29 (main shoot and 9 tillers). At our Lancaster plots (4/23/08) wheat stands were excellent across the board. This included our planting date and variety trial plots. The growth stage in our variety trial planted late September was a Feekes growth stage 3 or Zadoks growth stage 16 (five leaves unfolded) 29 (main shoot and 9 tillers). Yield potential at both locations is excellent.

Weather dependent we are rapidly approaching jointing in southern WI so be cautious if you intend to apply 2,4-D for weed control.

Winterkill and Tiller Counts

The last two days have lead to some very interesting findings in our wheat research plots at Arlington WI. Winterkill for the most part was limited to areas where ice was standing for several weeks (>2.5 weeks). Winterkill damage was greater in our early (9/14/07) and “normal” (9/28/07) winter wheat planting dates than in our late planted wheat (10/23/07). We hypothesize that this was due to differences in respiration rates. Growth in our early and normal planting dates was greater than we usually get in Wisconsin (main shoot and 2 to 8 tillers per plant); whereas late planted growth was about normal (main shoot emerged). Excessive fall growth would contribute to greater respiration rates thus the potential for increased winterkill under the ice.

One advantage of the winterkill this year for our program will be an assessment of variety tolerance to winterkill. In our variety trial we saw a range of 0 to 60% winterkill. This information will be reported in our 2008 Winter Wheat Variety Trials Results.

The wheat that survived (most of our research was unaffected by the winterkill) has a very good yield potential at this point in the season. Wheat planted on 9/28/07 has a tremendous tiller count. We averaged 7 tillers per plant with excellent stands. This would equate to a Feekes growth stage 3 or Zadoks growth stage 15 (five leaves unfolded) 27 (main shoot and 7 tillers). The delays in N application due to weather may prove beneficial to most WI wheat growers because our tiller counts are so high. Early N on these stands would promote lush growth on the main stem and tillers and would likely lead to higher disease incidence in this dense canopy.

FREE SOYBEAN CYST NEMATODE TESTING

Take the Test – Beat the Pest

Shawn Conley and John Gaska, UW Soybean Research and Extension

The UW-Madison Agronomy Department, in cooperation with the Wisconsin Soybean Marketing Board, is again offering free soybean cyst nematode (SCN) soil testing for Wisconsin growers. This program is intended for growers to sample several of their fields in order to identify if SCN is present and at what levels. Growers will be responsible for collecting soil from fields suspected to have SCN and then sending the sample to the SCN testing laboratory for analysis. They will receive a lab report back with the SCN egg count and a brochure to help plan future rotations and other cultural practices to lower SCN infestation if they exist.

We have a limited number of these free kits available and will furnish them on a first come – first served basis at up to four per farm. Crop consultants, advisors, and crop input retailers are encouraged to request kits for their client’s farms. Each kit has a bag and a prepaid mailer for one soil sample, which should represent about 10-15 acres. Both the postage and lab fees are prepaid. Anytime before, during, or right after the growing season are great times to collect soil samples for routine soil fertility analysis and for SCN monitoring.

Soil sample test kits are available now and can be requested from Colleen Smith at clsmith8@wisc.edu or at 608-262-7702.

For more information on SCN testing and management practices to help reduce the losses from this pest, please contact: Shawn Conley: spconley@wisc.edu; 608-262-7975