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I spotted my first soybean flower yesterday at the Janesville, WI variety trial site which was planted May 4th. As we enter the soybean reproductive growth phase there are a few things to keep in mind. The first is that soybean will produce flowers for ~3 to five weeks, depending upon planting date and environment. Soybean will abort anywhere from 20 to 80% of the flowers that they produce. Generally it is the first and last flush of flowers produced that are most likely to be aborted.

Second of all the timing window for our glyphosate applications in soybean are quickly closing.

“Monsanto has clarified the definition of “throughout flowering” in regard to the latest stage that glyphosate can be applied to glyphosate-resistant soybean. Soybean flowering is defined as the R2 growth stage. The R3 growth stage begins when one of the four top nodes with a fully developed leaf has a 3/16 inch long pod. With this definition, glyphosate can be applied through the R2 growth stage, but not after the R3 stage begins. Applications made after the R3 stage are off-label applications.”

On average it takes ~ 4 days to move from R1 (beginning flower) to R2 (full flower) and ~10 days from R2 to the start of R3 (beginning pod). That means we have ~2 weeks for glyphosate applications to occur.

Next, wheel track damage made from ground applications may start to reduce yield. Sprayer wheel traffic from first flower (R1) through harvest can damage soybean plants and reduce yield (Hanna et al. 2008). Our research suggests that an adequate soybean stand (more than 100,000 plants per acre) planted in late April though mid-May can compensate for wheel tracks made when a field is sprayed at R1. Yield loss can occur, however, when wheel tracks are made at R1 or later in thin soybean stands (less than 100,000 plants per acre) or late planted soybeans. Regardless of stand, plants could not compensate for wheel tracks made at R3 (early pod development) or R5 (early seed development). The average yield loss per acre is based on sprayer boom width (distance between wheel track passes). In our trials yield losses averaged 2.5, 1.9, and 1.3% when sprayer boom widths measured 60, 90, and 120 foot, respectively. Multiple trips along the same wheel tracks did not increase yield loss over the first trip.

Lastly, for white mold questions please refer to the following information: White Mold in Soybean in 2010: Factors to Consider

Image 1. Soybean crop beginning to bloom.

While most of the wheat in Wisconsin has flowered, there are still areas where flowering will occur over the next few days to week. I just spoke with Mike Ballweg in Sheboygan County and wheat closest to the lake is in the Feekes 10.2 to 10.4 range, meaning 1/4 to 3/4 of the inflorescence are visible. A check of the Fusarium head blight forecast from June 12 indicated that there were a few pockets around the state where the risk was higher than we have seen earlier in the week. In particular, along Lake Michigan, there is a moderate to high risk and this risk remains moderate to high over the next 24-48 hours. Forecast temperatures indicate cool conditions in this area and there are scattered chances of rain over the next few days. Another factor to consider is that in this part of the state over the past few years, we have heard many reports of dockage or rejection of grain due to Fusarium head blight. This is an area where much of the wheat has followed corn silage, so noting what your previous crop was can also help determine if the risk of infection may be higher. Make sure, however, to check closely the wheat growth stage before making a decision to apply a foliar fungicide since timing is critical for suppression of the FHB and fields may vary greatly in terms of flowering especially as you move inland from the lake. Please see our earlier postings and articles about different foliar fungicides for suppression of FHB as well as pre-harvest intervals based on products.

Currently, wheat in many areas of Wisconsin is starting to flowering or will be over the next few days. The current risk for Fusarium head blight is low based on the Fusarium Head Blight Prediction Center. Rainfall has been rather light the past 7 days, although some locations received rainfalls upwards of 0.30 inches or more this morning (6/6) in thunderstorms that are passing through the state. The next 2-3 days will be extremely hot with temperatures in the low to mid 90s. From the National Weather Service, it looks like the next chance for rain is Wednesday into Thursday, when air temperatures are also suppose to cool off. Based on these factors, the recommendation for using a foliar fungicide for suppression of FHB is not recommended. We will continue to monitor conditions as the week progresses and provide any updates as necessary.

Finishing the two-day trip to check on our wheat studies, today I visited the Lancaster and Janesville locations. Wheat at both of these locations is rapidly advancing, with Lancaster being at a very solid Feekes 10.5 (inflorescence completely emerged), while at Janesville, the growth stage ranged from Feekes 10.1 (first inflorescence spikelet visible) to 10.5 (inflorescence completely emerged).

With where the wheat growth stages are in the southern part of the state, this means we should be paying critical attention to the weather and risk of Fusarium head blight infection. A check of the Fusarium Head Blight Prediction Center today for the southern third of Wisconsin indicated that the risk of FHB infection was low, except for a few pockets along the Illinois border that were in the moderate range. However, looking at the one to three day forecast, the risk of FHB infection is predicted to be low. A foliar fungicide would not be recommended at the current moment. We will continue to monitor conditions during this week as well as over the next couple of weeks to provide updates for the risk of FHB as well as management recommendations. For information regarding products that can be effective at suppressing FHB (with well-timed applications), please check here. Pay close attention to individual fungicide labels especially in regards to the latest growth stage that a product can be applied as well as any pre-harvest intervals for applications.

What about other diseases? As I scouted at both locations today, there were three main diseases noted including BYDV, Septoria lead blotch, and powdery mildew. Across the four locations assessed the past two days, the BYDV at Lancaster had the highest incidence and the incidence of this disease at Janesville was similar to what we observed at Arlington yesterday. Powdery mildew also appeared to be slightly more severe at Lancaster than at the other locations, although symptoms were still mostly in the lower canopy to the flag-3 or flag-2 leaf, depending on variety. The two videos below provide some pictorial evidence of what was being seen for both diseases at Lancaster.

With some warmer weather last week, wheat growth stages moved along from what we had seen in previous weeks. A check of some of our research studies found that the wheat was at the Feekes 6 and 7 growth stages (first and second nodes ). This is an important time to be out in the wheat and scouting to determine if the use of a foliar fungicide will be needed as we move into flag leaf emergence (Feekes 8). The flag leaf is the most important leaf, accounting for upwards of 50% or more of the final yield and a goal with the use of a foliar fungicide is to protect this leaf. While we have received a few questions about powdery mildew and also noted a little bit of Septoria leaf blotch in some of our trials, we have not had widespread reports of wheat diseases so far this growing season.

Looking ahead, there exist some thresholds as you scout at Feekes 7 and 8 to determine if a foliar fungicide may be warranted.

At Feekes 7, the thresholds are:

Powdery mildew: check the uppermost leaf – the threshold is an average of five pustules per leaf.

Wheat leaf rust: check any leaf – the threshold is an average of one pustule per leaf.

Septoria leaf blotch: check the uppermost leaf – the threshold is 25% of the leaves having expanding blotches

At Feekes 8, the thresholds are:

Powdery mildew: check from the flag-2 leaf (2nd leaf below the flag leaf) and upward – the threshold is an average of five pustules per leaf on the flag-2 leaf.

Wheat leaf rust: check from the flag-3 (3rd leaf below the flag leaf) and upward – the threshold is an average of one pustule per leaf on the flag-3 leaf.

Septoria leaf blotch: check from the flag-2 and upward – the threshold is 25% of the leaves having blotches

If you note disease in the lower canopy but not on any of the leaves discussed above, consider increasing the frequency of your scouting to determine if there is evidence of new pustules or blotches moving into the upper canopy.

For further information regarding factors to consider for determining the need for a foliar fungicide recommendation, please check here.

For information regarding the efficacy of several foliar fungicides against different wheat diseases, please check here.

Results across our different studies the past few years have indicated that the best response to a foliar fungicide application has occurred when powdery mildew was the target and the wheat variety was susceptible. When the wheat variety was resistant to powdery mildew, we have not seen a consistent response, if at all.