Wheat Updates-May 2016


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May 27: Wheat is in the milk to soft dough stages of filling with later heads still pollinating in Clay/Nuckolls county fields.  Stripe rust greatly increased in severity, particularly on susceptible varieties. This photo is showing progression on Overland.  I haven’t seen stripe rust yet in fields planted to Wolf.  Barley yellow dwarf is appearing in small amounts in more fields, but is limited to field corners/borders thus far.

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May 23: (Photo: barley yellow dwarf in wheat-characterized by yellow-purple flag leaves.  It is vectored by aphids). Wheat is in the late flowering to beginning milk stage in many Clay/Nuckolls county fields.  Stripe rust increased in severity this past week in more susceptible varieties and barley yellow dwarf is also appearing more often in patchy areas of fields.

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May 15: Rain is falling this morning in parts of our area and wheat is in a variety of heading and flowering stages.  While the risk management tool at:  http://www.wheatscab.psu.edu/ still says “low risk” I’ve been concerned it had the potential to be higher with our growth stage and weather conditions.  Last week I received numerous wheat fungicide questions.  Caramba and Prosaro are the two products you can apply legally once your wheat is flowering.  Twinline is off-label once flowering begins.  Yes, it has metconazole in it (also active ingredient in Caramba) in addition to a strobilurin, but it only legally can be applied to Feekes 10.5 which is full heading and is off-label once flowering occurs.  Caramba and Prosaro will help prevent scab in addition to kill the rust already occurring in your plants.  Unfortunately, I was also starting to see barley yellow dwarf appearing in Nuckolls County fields.  This virus is vectored by a number of aphid species.  We’d been seeing aphids and stripe rust for a month at this point but both remained below threshold levels/low incidence.  Barley yellow dwarf can be identified by the flag leaf turning a bright yellow-purple color.  With 80% of wheat yield coming from the flag leaf and there being nothing you can do about barley yellow dwarf, this also needs to be part of your decision making process if you were planning on applying a fungicide for preventing scab/controlling stripe rust.

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May 9: We’ve been seeing stripe rust in wheat for over a month now, but the amount of rust has remained low.  Some have chosen to spray wheat at this point; however I’m also concerned about the potential for Fusarium Head Blight (scab) in wheat.  Fusarium head blight is caused primarily by Fusarium graminearum, the same fungus causing Fusarium stalk, root, and ear rot in corn.  The fungus survives the winter in corn and other small grain residue and then releases spores in the spring.  However, wheat planted into soybean ground can still be affected by scab because the fungal spores can be wind-blown in addition to being water-splashed to wheat that is in the flowering stage.

According to research, wheat is susceptible from flowering through soft dough development stage.    “Typical” fungicides used for control of fungal leaf diseases are off-label thus illegal to apply once the wheat has flowered and they do not have activity on the Fusarium fungus causing scab of wheat.  Management for scab includes the use of the preventive fungicides Caramba or Prosaro.  Both are labeled for headed and flowering wheat.  There’s a 30 day pre-harvest restriction for both.  Rainfast varies from ¼ hour to 2 hours or when dry depending on environmental conditions.  Both fungicides can help prevent scab and control rust on the plant.

Research from the US Wheat and Barley Scab Initiative (which is a combined effort of several Universities in the U.S. and Canada) has found that the best prevention using these products occurs when wheat is headed and 30% of the plants are in the beginning flower stage.  Application within five days of these criteria still showed positive results.  This research also showed that application before or after this time period greatly reduced effectiveness of preventing scab.  Understandably, the economics of fungicide application are difficult in wheat, yet, if you are aiming to make one application, this could be your best option for both scab prevention and controlling rust in your plants.  The risk map for scab can be found at:  http://www.wheatscab.psu.edu/.  With wheat at heading to beginning flower and rain/humidity this risk in reality could be higher for us.

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May 1: Wheat progressed quickly in one week!  Wheat in Clay and Nuckolls counties have flag leaves emerged even though wheat is really short.  The color is getting better thanks to moisture, root establishment, and nitrogen uptake.  I also didn’t see an increase in rust incidence this past week and aphid numbers were holding steady.  For those asking about fungicides, I’m still hoping we can hold off a little longer with current wheat economics, especially since in those counties rust wasn’t increasing due to the colder temps.  With warmer temperatures this coming week, please be checking your wheat.  If possible, one option that could be more economical in non-irrigated situations would be to consider treating your wheat once during flowering with either Caramba or Prosaro (as these products both prevent scab at the proper application timing and also kill fungal diseases including rust already present on the leaves).  We’ll have to see what happens with rust development and with how long it takes for heads to emerge.  There’s also been consistency with some varieties rated high for rust resistance where I have yet to find rust in them-so that’s a good thing!

About jenreesources

I'm the Crops and Water Extension Educator for York and Seward counties in Nebraska with a focus in irrigated crop production and plant pathology.

Posted on May 31, 2016, in Crop Updates, Diseases and tagged , , , , , . Bookmark the permalink. Leave a comment.

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