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.

Freeze Damage on Winter Wheat

Chad Lee and Jim Herbek, Extension Agronomists, University of Kentucky

The cold temperatures experienced yesterday in many areas and the cold temperatures expected tonight could damage the wheat crop. Wheat in the boot or heading stages generally needs temperatures at or below 30 F (-1.1 C) for at least two hours to cause severe damage. The Kentucky Mesonet reported lows of 45.1 F for Fulton County, 38.0 F for Graves County, 41.1 for Hopkins County, 42.7 F for Simpson County, and 39.6 F in Mercer County) for Sunday, May 12, 2013. None of these temperatures are low enough to severely damage wheat, but localized temperatures across fields may have been lower. 

Bleached wheat head exhibiting freeze

damage symptoms. Photo taken in 2012.

Usually, a week to ten days of warm, sunny weather is needed before the full extent of a freeze damage becomes evident. So, while we all want to scout fields today and tomorrow, a true assessment of freeze damage should not occur for about a week. Cool, cloudy days will slow wheat growth and slow the development of freeze symptoms.

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.

Armyworm Moth Flight Increases in Princeton and Lexington Traps.

Doug Johnson, Extension Entomologist

The capture of armyworm moths in the UK-IPM traps increased significantly in both the Lexington and Princeton traps for the trap week ending Friday May 3^rd. See the Graphics at:

http://www.uky.edu/Ag/IPMPrinceton/counts/taw/tawgraph.htm


In both cases the increase is large and is probably related to the warm weather over this period. Nevertheless, these captures will just bring us back to about average (Lexington) and a bit above average at Princeton. It is too soon to know if these increases point us to an outbreak population.


Even though trap captures have been reduced, and late this year compared to last, we need to remember that these pests are out and about. Just because the trap captures are low and late does not mean that there will not be a problem in some fields. Corn planting and growth are behind as well, and we are (at this writing Fri 5/3/13) about to enter another wet cool period. This type of weather will once again slow down planting and corn growth, and tends to favor armyworm development. Even though the risk is not above average, there is some risk just the same, and corn and wheat should be scouted for this pest.

I have had one report from far west KY that sound like armyworm on struggling 1-2 leaf corn though the diagnosis is not definitive. Just the same, it is best to remain alert for this pest.

Stripe Rust found in west Kentucky

Stripe rust has been found at low levels in southern Christian County in west Kentucky. I am sure it is in other counties in the west as well. Levels do not appear to be high, meaning that scattered plants with symnptoms were found, but bonified hot spots were not seen. In any event, it would be prudent to check your fields for the presence of stripe rust. If you find hot spots (not just single plants) you probably should  not wait to spray until early flowering, the typical time of application targeting head scab. However, if you just see a few scattered leaves here and there, I believe you could wait until flowering to spray with little risk that stripe rust will get ahead of you.

The greatest risk is in varieties that are known to be highly susceptible to stripe rust, such as "R35". However, if you find a hot spot in any variety, that would be cause for alarm since the fungus can overcome know resistance.