Fungicide application for protection against scab – what do I do when I can’t hit the “perfect” timing?

Carl A. Bradley, Extension Plant Pathologist, University of Kentucky

Just like the porridge in the “Goldilocks and the Three Bears” story, there is a “just right” timing for when to apply a fungicide for protection against Fusarium head blight (a.k.a. scab) of wheat. That “just right” timing is the Feekes 10.5.1 growth stage (beginning flowering), when anthers are just beginning to extrude from the middle part of the wheat head. Unfortunately, not all main stems and tillers will be at this stage at the exact same time, but when 50% of the wheat heads are at this Feekes 10.5.1 growth stage, that is considered the “just right” timing for applying a fungicide for protection against Fusarium head blight.

2016 UNIVERSITY OF KENTUCKY WHEAT FIELD DAY

Colette Laurent, UK Grain Crops Coordinator

The annual UK WHEAT FIELD DAY is slated for Tuesday May 10, 2016 at the UK Research and Education Center in Princeton, KY.
Registration will begin at 8:00 am (CDT).  The tours will end at noon and field day will conclude with a lunch sponsored by the Kentucky Small Grain Growers Association.


Field Day Topics Include:

FHB Prediction Tool Upgrade

Don Hershman, Extension Plant Pathologist, University of Kentucky

Heads up! The new FHB (Head Scab) forecasting tool has a new feature.You can select the FHB susceptibility level of the variety you have planted.

Wheat Disease Management for 2015 Starts Now

Don Hershman, Extension Plant Pathologist, University of Kentucky

Wheat diseases reduce grain yield and/or quality in most years. Many wheat producers rely on foliar fungicides as their primary disease management weapon. Foliar fungicides are certainly an important disease management tool. However, pre-plant decisions made – that is, decisions being made right now for the 2015 wheat crop - have the greatest impact on which diseases develop during the season and to what extent. Thus, it is critical to make as many of the “right” decisions as possible to reduce the potential for diseases to reduce both grain yield and quality next spring.

For more on how pre-plant decisions impact disease potential, go to this link:
http://www2.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/ppfsagsg6.pdf

FHB Risk Low, But Will This Last?

Don Hershman, Extension Plant Pathologist, University of Kentucky

Early wheat varieties are now headed out and some are flowering in southern Kentucky. In many other fields, wheat is in or entering the head emergence stages. FHB fungicides will begin to be applied about the middle of next week and will continue for about 2 weeks. Presently the risk is low across Kentucky, but rains being forecast for this weekend and mid next week suggest to me that the FHB risk could change rapidly. Recent warm conditions with adequate soil moisture have likely encouraged the FHB fungus to become active in residue and I sense that any significant rainy period over a 2-3 day period could prompt spores to be released. If this occurs in the vicinity of or downwind to a fully headed wheat crop, the FHB risk could be considerable. If I had a decent wheat crop and it would be fully headed by this weekend to mid next week, I would seriously consider spraying an FHB fungicide, such as Caramba or Prosaro just before, at or up to five days after the target 10.51, early flowering timing. The risk map is green for now across KY, but I do not think that status will hold. I hope I am wrong.

Wheat Disease Update

Don Hershman, Extension Plant Pathologist, University of Kentucky

The FHB situation in west and southern KY is good. Most fields have 1% FHB or less. Occasionally a field will be seen with 5% incidence and rarely one with 10-20% incidence can be found. In any event, it appears as though the FHB predictive models worked very well (again) this season. In terms of other diseases, the rusts are fairly low at this time. Speckled leaf blotch has made its way to the flag leaf in many fields due to the cooler than normal temps. Nodorum blotch is also present in many fields, but the dry weather the last week has not helped its cause. Hits of BYD are present in most fields, but overall the disease is very limited. Overall, it looks like fungicide sprays made at early anthesis, targeting FHB, will do an excellent job of keeping fungal diseases on the flag leaf in check until dry-down begins.

Current Head Scab (FHB) Risk Situation

Don Hershman, Extension Plant Pathologist, University of Kentucky

Below (in italics) is my current commentary off the FHB PREDICTION TOOL WEBSITE (www.wheatscab.psu.edu/).  The models on which the FHB risk assessments are based are considering spore production – not infection. So the models are basically saying that right now few Fusarium spores are being produced and if you don’t have the spores, you won’t have infection even if the conditions are right (which they are not).

Based on the map model, all of KY is currently at low risk (indicated as green). However, if you look at the other model in operation (click on a weather station {be sure to click on the red "Agnet" tab to see many more weather stations}), you will see that some areas are on the bubble (click on "probability" once you have clicked on a specific weather station), but the risk is still low for now. This status can change fast considering there is quite a bit of moisture in the soil. So if I were a farmer and had a good crop I would probably spray once my crop hit early flowering. I say this because other diseases will likely build up over the next month and you will also control any head scab infection that does occur.  Kind of a insurance approach knowing that the moisture levels will likely result in some disease over the next month.  But if FHB was the only consideration, the FHB risk is low for now.

The Current Wheat Crop and Risk for Head Scab

Chad Lee, Extension Agronomist, University of Kentucky

Weather in some parts of Kentucky dipped below 30 degrees Fahrenheit last night (April 10 into this morning April 11). These temperatures are low enough to damage wheat that is heading. About 10 days of good growing conditions are needed to assess damage to the wheat crop. Some of the wheat is flowering and farmers need to make decisions now on spraying the wheat with a fungicide. Should they spray these fields?

The following is a synopsis of a conversation with Don Hershman, extension plant pathologist.

Wheat FHB Risk Update for KY

Wheat is in the very early flowering stages to flag leaf Extension, depending upon where you are located. Casual observations in west KY indicate that most wheat is still in the process of heading, but will likely begin to flower early next week. We are two to three weeks ahead of where we
normally are for this time of year. The FHB risk is very low except for a very small pocket of moderate risk in extreme southwest KY. Generally we have been warm and dry, but there have been some isolated showers in some areas in recent days. The potential for rain to occur in the form of pop-up thunderstorms is fairly high for today (Wed, April 4) and tomorrow (Thursday, April 5). Then we should have mostly clear weather beginning Friday though most of next week when many fields will be flowering. This bodes well for low FHB risk, but this could change rapidly if conditions decline. Generally, the hot, dry weather has greatly limited foliar disease development in most fields up to this point.

Wheat Head Scab and Options for the Next Crop

Head scab (or Fusarium head blight) was a major problem across Kentucky in 2009. As farmers prepare for the 2009-2010 wheat crop, there are some things they can do.

The latest Wheat Science newsletter addresses some of the lessons about wheat and head scab in 2009. Options for seed wheat are also considered.

The pdf file is available at:

http://www.ca.uky.edu/ukrec/newsltrs/News09-3.pdf

The newsletter archives is available at: http://www.ca.uky.edu/ukrec/index.htm

Head Scab Newsletter

The Wheat Science IPM Group Newsletter was released on June 4, 2009 with the latest information for mangaing wheat with Fusarium head blight (or head scab) this season.

The newsletter is available as a pdf at: https://www.ca.uky.edu/ukrec/newsltrs/News09-FHB.pdf

FHB Risk, May 7, 2009

An email from Don Hershman had the following image. The image is from the FHB Risk Assessment Tool at Penn State. http://www.wheatscab.psu.edu/riskTool_2009.html
Much of the wheat-growing area is in red or yellow, meaning that we have high to medium risk for FHB, according to the model.

See Don's post from May 6, 2009 for more details about head scab and management options.

FHB May Be Severe in Kentucky this Year

Wheat across central and west Kentucky (which makes up the bulk of the wheat acres in the state) has been in various stanges of flowering since early last week. Many fields are currently at full anthesis or slightly beyond.

As we all know, it has rained a lot over the past 5-8 days across much of the state. This wet weather, as well as temperature and humidty conditions, have resulted in a moderate to high FHB risk across most of central and west Kentucky. The windy weather before it started to rain, and now the rain, has greatly hindered fungicide applications aimed at Fusarium head blight suppression. Some spraying was probably possible on Monday and Tuesday of this week, but the current storm system moving through the state will effectively eliminate the possibility of ground spraying for today (Wed), probably tomorrow, and maybe into Friday-Saturday. Aerial application will also be challenged. The bottom line is that most wheat fields in the state will be highly vulnerable to FHB. By time spraying is possible again, it will be too late to spray most fields due to label restrictions. Plus, from a practical perspective, once infection has occurred, fungicides (which are not that good against FHB in the first place) are of little value.

I rarely prognosticate epidemics, but it seems that nothing is in our favor, and everything is pointing towards an significnat FHB episode in the state. Fields that were in full flower early last week may escape significant infection since they were beyond the most susceptible infection stage by the time the rains began. Likewise, crops that have yet to flower, may escape infection. But the acres that fit either of these two scenarios is rather small compared to the whole.

If it is any consolation, remember that when FHB pressure is high (such as I believe it is right now), fungicide-treated crops can still be severely impacted by both FHB and DON. That is, only 30-50% suppression can be expected when fungicides are applied under the best of scenarios. One final point. Some may be thinking that they wish they had sprayed while their crop while it was still heading out, but before flowering. Doing so would have provided little benefit against FHB due to the limitations of fungicides against FHB and the fact the new tissue that emerges after application would be (for all practical purposes), unprotected.

I am sorry to have to predict this gloomy situation. We will know how accurate my words are by mid-May. That is about how long it will take for FHB symptoms to be expressed.

Current Status of Fusarium Head Blight

Low temperatures and breaks between rain events (up until this past event) have kept the FHB predictive model from indicating even moderate FHB risk (up until now). The block of rain we have just experienced has changed that, so the FHB models are now showing moderate to high risk for spore release in much of central and west KY. I believe conditions will be ripe for spore release beginning Monday night. Spore release happens mostly happens at night and is actually favored more by high humidity than rain. Rain can give you splashing of spores, but it also washes spores out of the air and off of plants. Infection, on the other hand, requires free moisture, so infection generally is greater when spores have been released and transported to heads during dry, but humid, periods at night, followed by rain the next day or so to support infection. It is complicated and that is why we don't always have a lot of FHB. It is rather hard to get!

I encourage growers with decent crops that are just entering flowering to to spray as much as they can Monday and Tuesday and into Wed. I realize that getting sprayers into fields will be hard, so that is a complicating factor that may prevent many fields from being sprayed this year. It is what it is. More wet weather is anticipated beginning Wednesday. I have had several questions asking about how late one can spray and still get FHB suppression. That is pretty simple. Most labels restrict application to early flowering or at most 50% bloom. Thus, there is not much of a decision to make. The days to harvest restriction is very specific for all fungicides labeled for wheat.

The key thing to remember is that according to the FHB models, up to the present moment, not many spores have been available to spread to heads, let alone infect heads. But after today and the gloves come off unless it turns hot and dry fast. This could be a bad FHB year in light of the lack of spraying and/or difficulty in getting fields sprayed. But the timing of this rain coinciding with the completion of head emergence or flowering in many fields is hard to deal with. If fields had sprayed before the rain, it might have been too early to get good coverage on the heads.

Updated Wheat Scab Risk Management Tool

Our colleague, Don Hershman, said that the Fusarium Head Blight (Head scab) Risk Management Tool has been updated and is available at: http://www.wheatscab.psu.edu/riskTool_2009.html

The tool provides a general risk level for wheat in a given area.

Once into the tool, identify what date you want to select (such as today).
Then identify the wheat model (spring wheat or winter wheat).
Finally, select the state in the map that applies.

A color-coded map will appear with green being little risk, yellow being medium risk and red being high risk. This model can help when deciding to make a preventative fungicide application.