Wednesday, May 27, 2009

Flag Emergence and Foliar Fungicides for Wheat

In the past week, wheat development has moved into flag leaf emergence (Feekes 8-9, Zadoks 37-39) and in parts of the state past flag leaf and into the boot growth stage (Feekes 10, Zadoks 40).  This is a critical period for making assessments for the need for foliar fungicides.  Over the past few years, while we have seen yield responses of 7-10 bushels per acre with a well-timed foliar fungicide application during this period, we have typically seen this response for a susceptible wheat variety.  In particular, this response has been due to control of powdery mildew (Figure 1).  

Current Observations Across the State and in the Winter Wheat Variety Trials:

Note: special thanks to Karen Lackermann for this information and update.

We have started to receive some reports of powdery mildew on wheat, primarily in the northeastern part of the state and on susceptible varieties.  We have also noted this disease at the Lancaster and Chilton variety trial locations. Overall, the level of powdery mildew (both incidence and severity) has been low and not necessarily on the most critical leaves like flag leaf, flag-1 leaf, or flag-2.  The dry weather the past week or so seems to have limited disease development at this point in the growing season.

In observations for other diseases that can be controlled by foliar fungicides, we have noted the following at the winter wheat variety trials locations: septoria leaf blotch (Figure 2), wheat leaf rust (Figure 3), and wheat stripe rust (Figure 4).  Overall, the severity of these diseases has been rather low (1-2%).  In stems where the disease severity has been higher, the symptoms have been  observed mostly in the lower canopy.  Across the locations, we have noted wheat leaf rust at all four variety trial sites, however, the highest frequency of these observations have been from Janesville.  We have seen septoria leaf blotch at all of our trial locations except the Chilton.  


Figure 1. Powdery mildew of wheat.

Figure 2. Septoria leaf blotch of wheat.

Figure 3. Wheat leaf rust.

Figure 4. Wheat stripe rust.

As a reminder, in the March 26, 2009, Wisconsin Crop Manager article entitled, "Do I Need to Spray a Foliar Fungicide in Wheat in 2009?", we provide information regarding thresholds for powdery mildew, septoria leaf blotch, and wheat leaf rust.  Current thresholds are also provided here to help guide decisions specific to Feekes 8 and post-Feekes 8 until Feekes 10.51 (flowering; Zadoks 60):

Powdery mildew, Feekes 8: check from the flag-2 leaf upward; the threshold is 5 pustules per leaf on the flag-2 leaf, on average.

Septoria leaf blocth, Feekes 8: check from the flag-2 leaf upward; the threshold is 25% of leaves with blotches.

Wheat leaf rust, Feekes 8: check from the flag-3 leaf upward; the threshold is 1 pustule per leaf, on average.

If wheat is already beyond Feekes 8, the recommendations up through Feekes 10.51 (flowering; Zadoks 60) are:

Powdery mildew, Feekes 8 until Feekes 10.51: check from the flag-1 leaf upward; the threshold is 5 pustules per leaf on the flag-2 leaf, on average.

Septoria leaf blocth, > Feekes 8 until Feekes 10.51: check from the flag-2 leaf upward; the threshold is 25% of leaves with blotches.

Wheat leaf rust, > Feekes 8 until Feekes 10.51: check from the flag-2 leaf upward; the threshold is 1 pustule per leaf, on average.

Making the decisions to spray a foliar fungicide during this time requires knowledge of the wheat variety, active scouting of multiple locations in a field, proper identification of diseases, and an accurate assessment of the most critical leaves.  For further information, this information is also discussed in a recent video available at the UW-Extension YouTube website:


Monday, May 25, 2009

Weather - May 18-25, 2009




Arlington:



Chilton:




Janesville:




Lancaster:



Monday, May 18, 2009

Weather 10-17 May 2009



Arlington:


Chilton:


Janesville:


Lancaster:
Add Image

Thursday, May 14, 2009

Early Season Wheat Disease Assessments

Updated: 15 May

We have begun our early season wheat disease assessments at the winter wheat variety trials in Wisconsin. Our approach for disease assessments follows the recommendations we made in the March 26, 2009 Wisconsin Crop Manager article, entitled, "
Do I Need to Spray a Foliar Fungicide in Wheat in 2009?" These assessments are also a part of the thesis research for Karen Lackermann, Plant Pathology, to improve the decision management system for controlling wheat diseases in Wisconsin.

At Janesville and Lancaster, wheat growth and development currently ranges from Feekes 4-5 (pseudostem erection; Zadoks 30) to Feekes 6 (1st detectable node; Zadoks 31). In our assessments at those two locations, we have found symptoms of the Septoria leaf blotch complex, leaf rust, and stripe rust. The level of disease is relatively low and specifically, we have only noted symptoms in the lower canopy and nothing on the newest emerged leaf. At this range of growth stages, we do not recommend the use of foliar fungicides for Septoria or the rust diseases. Scouting over the next two weeks, however, will help to determine if these diseases are increasing in the canopy. Furthermore, the use of the thresholds we outlined in our Wisconsin Crop Manager article can help determine the need for a foliar fungicide as we move into flag leaf emergence.    

We have also completed our first assessments at the Chilton variety trial location.  Wheat was at Feekes 4-5.  Similar to the other locations, we observed Septoria leaf blotch, leaf rust, and stripe rust.  Of all the samples we have assessed, only 1 had symptoms of leaf rust on the newest leaf. Our recommendation is similar to Janesville and Lancaster at the moment. 

We will continue our assessments for the rest of the growing season including Feekes 7 (2nd detectable node; Zadoks 32), Feekes 8-9 (flag leaf emergence; Zadoks 37-38), and Feekes 10.51-11.1 (flowering to soft dough; Zadoks 60-75) at all of the variety trial locations and will continue to update you all on how wheat diseases are progressing around the state.   

Wednesday, May 13, 2009

Weather, 3-9 May 2009



Arlington:




Chilton:




Janesville:




Lancaster:


Wednesday, May 6, 2009

Verify Wheat Growth Stage Before Applying Growth Regulator Herbicides

Poor wheat stands caused by late planting, decreased tillering, and winterkill have many growers contemplating herbicides in 2009. Make sure you properly growth stage your wheat before applying dicamba or 2,4-D. The mid September and early October planted wheat crop is at or nearing the Feekes 4-5 or Zadoks 30 growth stage (pseudostem erection or hollow stem) (Image 1.). After this stage and when wheat has a visible joint (Feekes 6), wheat can be very sensitive to dicamba and 2,4-D herbicides. Last year we had several reports of 80 bushel wheat dropping to 20 bushel wheat when dicamba was applied at Feekes 6. After jointing there are several other herbicides that can be safely used. Please refer to Pest Management in WI Field Crops Bulletin A3646 for these options.

Image 1. Feekes 4-5 or Zadoks 30 growth stage in wheat

Chris Boerboom

Sunday, May 3, 2009

A New Feature - Weather Updates from Winter Wheat Variety Trials

During the winter period, we were able to purchase four new weather stations for use at the winter wheat variety trial locations. To help provide information from those weather stations to growers, we will posting on a near-weekly basis graphs for temperature, relative humidity, and rainfall. We hope you find these useful.

PERIOD: 26 APRIL TO 2 MAY 2009


Location: Arlington



Location: Chilton



Location: Janesville



Location: Lancaster