Plant height impact on wheat yield

As wheat begins to move into the flag leaf (Feekes 9) and boot (Feekes 10) growth stages many growers and consultants are commenting on the short stature of the 2010 wheat crop. We must first address the cause of the short wheat before we can assign yield estimates. Let's first address planting date. Late-planted wheat will generally be shorter than on-time planted wheat. The yield loss attributed to late-planted wheat is not merely a function of height but reduced tiller number and biomass capacity (planting date impact on wheat yield).

For our on-time planted wheat, development and in this case height is governed by many factors including water, temperature, as well as light quality and quantity. Data from our 2002-2007 winter wheat variety trials show only one year (2005) where there was a positive relationship between yield and plant height (Chart 1.). This suggests that height alone has no direct influence on wheat yield. As long as the minimum threshold for LAI (leaf area index) is reached wheat yield will then be determined by head number, head size, kernel number per spikelet, and kernel size. Since head number, head size, and kernel number per spikelet are already determined we are just waiting on the grain fill period to finalize our 2010 yield.

Chart 1. Relationship between plant height and grain yield.

Powdery Mildew Update

As noted in Shawn's previous posting, the wheat growth stage is mostly around Feekes 7. Karen Lackermann, graduate student in plant pathology, continues to collect disease data in the winter wheat variety trials and has been paying particular to the powdery mildew situation this year. The levels of powdery mildew have been variable across trial locations, with the highest disease incidence being observed at Chilton. Even within sites, there is high variation in disease incidence and severity. For example, at Chilton, some varieties have 0% incidence and severity, whereas other varieties have higher levels with severity ranging from 5 to 20% on the flag-3 (three leaves below the flag leaf). On the flag-2 leaf (two leaves below the flag leaf), severity has been moderate in these varieties, ranging from 1 to 5%. No symptoms of powdery mildew were observed on the flag-1 (one leaf below the flag leaf) leaf.

As we move into flag leaf emergence at Feekes 8, pay particular attention to symptom severity on the flag-2, flag-1, and flag leaf. If the average number of pustules on the flag-2 leaf and the leaves above it is 5 or greater, a foliar fungicide may be warranted for control of powdery mildew. If symptoms are only being observed in the lower canopy, below the flag-2 leaf, it may not be economic to apply a foliar fungicide.

Predicted Cold Temperatures Should not Impact Wheat

Cold temperatures (30 to 32 degrees F) are predicted across the state of WI for Friday and Saturday mornings. Our winter wheat plots at Arlington and Lancaster WI are arguably the most advanced in the state. Last night (5/5/10) the most advanced winter wheat varieties were in the late Feekes 7 (2-3 detectable nodes and just prior to flag leaf emergence) growth stage. Based on these grow stages the winter wheat crop should be safe down to 28 degrees F. For more detailed information please see "Know Your Wheat Growth Stage to Predict Cold Injury".

Fusarium Head Blight Alerts Available

If you are interested in receiving real-time alerts for Fusarium head blight updates or field reports, the U.S. Wheat & Barley Scab Initiative is offering a free subscription service in 2010. To sign up for these alerts, please click here. The alerts are a summary of commentary made by wheat disease specialists throughout the country as part of the Fusarium Head Blight Prediction Center. You can receive alerts in email and/or text message form. You can also sign up for different types of reports, whether just a national summary or specific regions. For example, if you just want to see a summary from Wisconsin and the corresponding soft winter wheat region, you should mark the "Mid West/Northern Region, Soft Winter Wheat".

If you have any questions about this service, please free to contact me.

Fusarium Head Blight Prediction Online for 2010

The Fusarium Head Blight Prediction Center is again up and running for the 2010 wheat growing season. I will be providing commentary on this site for Wisconsin similar to the previous growing seasons and this commentary often focuses on observations of all diseases we have noted around the state, and more importantly the current range of growth stages we have observed. Also, the U.S. Wheat and Barley Scab Initiative will be providing resources to help in communicating the current risk and situation across the wheat growing region. Some additional resources that may be of help as you access this site as well as determine the need for foliar fungicides for control of Fusarium head scab include:

1) Understanding the Fusarium Head Blight Prediction Center

2) Check Your Wheat Closely

Feel free to contact us with any questions and we will provide further updates as the conditions warrant.

Management of Small Grains - Fungicide Efficacy for Control of Wheat Diseases, Updated

We have been receiving several questions about the use of foliar fungicides for wheat. To provide further information regarding relative efficacy of foliar fungicides in wheat, the NCERA 184 (North Central Regional Committee on Management of Small Grain Diseases) recently updated their information of fungicide efficacy for control of certain foliar diseases of wheat. Efficacy ratings were based on field testing of materials over multiple years and locations by members of the committee. Efficacy is based on proper application timing to achieve optimum effectiveness of the fungicide as determined by labeled instructions and overall level of disease in the field at the time of application. Differences in efficacy among fungicide products were determined by direct comparisons among products in field tests and are based on a single application of the labeled rate as listed in the table. The Table lists the most widely marketed labeled products and is not intended to be a list of all products. The information in the table is provided only as a guide and does not provide an endorsement for any product.

Any questions about the table can be addressed to Paul: esker@wisc.edu

Early Season Wheat Diseases

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.