Brief Weather and Disease Update - June 23-29, 2009

Weather conditions last week were rather hot and humid early in the week, as temperatures were in the low 90s throughout many our research project areas. Late in the week, temperatures did fall back into the 80s and now into the 70s and 80s. Rainfall was light, in particular at our winter wheat variety trial locations. Weekly rainfall totals were:

• Arlington: 0.01 inches
• Chilton: 0.11 inches
• Janesville: 0.01 inches
• Lancaster: 0 inches

Winter wheat is past flowering for the state - the risk window for Fusarium head blight. To determine if FHB was a problem in your field, assess fields during the soft dough growth stage. We are currently taking field notes and will update you shortly on the preliminary results.

Soybean diseases to date have been low, primarily bacterial blight and brown spot. Remember though, this is an excellent time to scout for early season stress that may be caused by soilborne pathogens. Also, take advantage of the free SCN testing program, sponsored by the Wisconsin Soybean Marketing Board. For further information, please contact Colleen Smith at clsmith8@wisc.edu or 608-262-7702.

Fusarium Head Blight Status - June 24

While much of the winter wheat crop is well past flowering, there are still pockets of the state, especially near Lake Michigan with wheat heading into flowering this week. The current Fusarium head blight forecast shows a low risk for the majority of the state, however, there are some pockets in west central and southwest with a medium risk for infection, and pockets along Lake Michigan and the northwestern portion of the state in the high risk category (Figure 1). The one to three day risk maps show a reduce area under risk for Fusarium head blight each day.

Figure 1. Risk map for Fusarium head blight in Wisconsin on June 24, 2009. The 1-3 day forecast map shows a reduction in the area under a medium to high risk. Much of the wheat crop in the state is past flowering, however, we have received some reports of crops just now into the flowering growth stage.

Current FHB Status: Today (June 24), both Shawn and I were at the Winter Wheat Variety Trial site at Lancaster. Low levels of FHB were noted in the trial (See images below). Our preliminary observations indicate the highest level of incidence level (i.e., the number of infected heads) is around 9% in only a few plots and that the severity of infected kernels is very low (meaning that index values that are a measure of incidence and severity are less than 1% at the moment). We will be taking our more detailed field notes for FHB over the next week as we move into the soft dough growth stage. This is our recommended timing for FHB assessments for growers and others as well. Assessments for FHB can be made in the field by assessing 100 consecutive heads, noting the number of heads with symptoms of FHB and also the severity of infected heads (the number of kernels infected on a head).

Rainfall over the past week at the winter wheat variety trial locations (June 17 to June 24):

Arlington = 1.7 inches (temperatures ranged from the 60s into the 90s)

Chilton = 0.2 inches (temperatures ranged from the 50s to around 90)

Janesville = 2.64 inches (temperatures similar to Arlington)

Lancaster = 1.38 inches (temperatures similar to Arlington and Janesville)

Yellow Soybeans and Nitrogen Fixation

Several questions have arisen over the last few days related to the "yellow" or "N deficient" appearance of many soybean fields across Wisconsin (Image 1). This symptomology is typical given the cool environmental conditions and slow growth that has plagued much of our soybean crop. In soybean, active N-fixtion does not begin until the V2-V3 (2 to 3 open trifoliates) growth stages. Even if you were to properly dig a soybean plant, identify and split a nodule, the red apperarance does not necessarily mean that fixation has fully begun (Image 2). Given our rainfall pattern over the last 24 hours and projected temperatures these yellow beans will likley recover in the next 3-5 days if not sooner.

Image 1. Yellow soybean crop.

Image 2. Soybean nodulation.

Weather: 8-15 June 2009

Arlington:

Chilton:

Janesville:

Lancaster:

Fusarium Head Blight Update - June 11

Currently, wheat is still ranging from early heading to well past flowering growth stages around the state. We are still receiving questions regarding disease management decisions, especially if we should be concerned for Fusarium head blight. Recall the critical period for infection by the pathogen that causes FHB (Fusarium graminearum) is during flowering and requires warm and humid conditions (i.e., moisture). This period lasts approximately 7 days.

To look at the current risk, I examined the FHB forecast from Penn State (http://www.wheatscab.psu.edu) for June 11 and it shows a low risk across the state (green color = low risk; yellow = medium risk; red = high risk). Also, examining the 24-48 hour forecast risk map, Wisconsin remains at a low risk for FHB.

June 11, 2009 risk map:

1-day forecast map:

2-day forecast map:

Short Wheat Does Not Necessarily Mean Reduced Straw Yield

As most wheat across Wisconsin has headed, county agents as well as crop scouts alike are commenting on the overall "shortness" of the 2009 winter wheat crop. It has been well documented that plant height alone is a poor predictor of straw yield. However, Morrison et al. (2007) found a strong relationship among plant height, grain yield, and straw yield in high yielding wheat varieties in Northern Illinois (Predicting Wheat Straw Yields in Northern Illinois). A more critical factor for Wisconsin growers in 2009 would be their planting date. Donalson et al. (2001) found that planting date proved to be a strong driver in increasing straw yield (earlier planting date increased straw yield). In Wisconsin many acres of wheat were planted later than normal due to delayed corn and soybean harvest. Wisconsin growers also experienced significant winter-kill that thinned wheat stands. Though these thin wheat fields did compensate somewhat through increased tillering, straw yields may be reduced.

Edwin Donaldson, William F. Schillinger and Stephen M. Dofing. 2001. S traw Production and Grain Yield Relationships in Winter Wheat. Crop Science. 41:100-106

Weather: 2-8 June 2009

Arlington:

Chilton:

Janesville:

Lancaster:

Note: Discrepancies in rainfall and/or temperature data for June 8 are in part due to differences when data were downloaded.

Pay Attention to Wheat Growth Stages

The winter wheat is rapidly advancing around the state, based both on our observations in the field as well as from reports around the state.  It is very important that you closely examine the growth stage if considering the application of a foliar fungicide.  For example, when we examined the winter wheat variety trial at Lancaster today, wheat ranged from Feekes 10.4 (heads approximately 3/4 emerged) to Feekes 10.5.1 (anthesis) (Figure 1).  Many fungicides that are used for control of foliar diseases, including Headline, Quilt, Quadris, and Stratego, for example, are only labeled until Feekes 10.5 (full head emergence).  Applications made after this growth stage are considered off-label.  

Figure 1. Wheat head showing evidence of flowering. This image was obtained on 3 June at the Lancaster ARS Winter Wheat Variety Trial. Image courtesy of Karen Lackermann.

Furthermore, pay particular attention to the severity of the different wheat diseases and on which leaf symptoms are observed.  As we have recently discussed in the blog and the Wisconsin Crop Manager, the decision to consider a foliar fungicide at this point in the growing season for diseases like powdery mildew, septoria leaf blotch, and wheat leaf rust should be focused on the upper leaves. Also, make sure that you properly identify diseases, as we have seen some virus symptoms like Barley Yellow Dward Virus in plots (Figure 2). Foliar fungicides are not effective against viruses.

Figure 2. Symptom of Barley Yellow Dwarf Virus. Image couresty of Karen Lackermann.

Fusarium head blight update:

As we move into flowering, remember that this is the critical period for infection by the pathogen that caused Fusarium head blight.  From the initial phase of flowering to the end of flowering takes approximately seven days.  Based on recent weather conditions and the Fusarium head blight prediction center, the current risk for Fusarium head blight (as of June 3) is low across the state in Wisconsin.  

We have also received some questions as to the current situation around the U.S.  Our situation in Wisconsin is much better than other parts of the country, as the severity of Fusarium head blight further south, starting in southern Illinois and running into Arkansas and Kentucky, in particular, is high and there are concerns regarding the risk of high DON contamination.  

Cool Temperatures Causing Crooked and Broken Wheat Heads

Temperatures at our winter wheat variety testing sites (Janesville, Arlington, Lancaster, and Chilton) ranged from the mid 30's to the high 40's in the early morning hours of June 1st. Though these temperatures are generally not low enough to cause yield loss we are hearing initial reports of wheat heads being caught in the boot or in the extreme being tangled in the flag leaf (Images 1 and 2). This symptomology is most prone in awnletted wheat varieties (varieties with very short awns), but can also occur to awned wheat. If wheat heads are merely bent then yield loss is unlikely however if wheat heads are completely snapped off then yield loss has occured and growers should contact their crop insurance agent.

Image 1. Awnletted wheat head caught in auricles.

Image 2. Wheat head wrapped in flag leaf.

If entire fields are showing uniform injury or patterns appear check spray records and timings to ensure that head damage is environmetnal and not herbicidal as growth regulator herbicides such as dicamba and 2,4-D can cause epinasty (twisting) and head malformation.

Weather - 26 May to 1 June 2009

Arlington:

Chilton:

Janesville:

Lancaster: