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Plant growth regulators for wheat

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David Marburger

David Marburger

Since April 2016, I have served as the Small Grains Extension Specialist at Oklahoma State University. My research and extension efforts focus on delivering science-based recommendations in order to increase small grains production and profitability for stakeholders throughout Oklahoma and the southern Great Plains.

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Many Oklahoma wheat farmers battled lodged wheat in 2013 and are looking to plant growth regulators to help reduce lodging in 2014. Lodging occurs due to a variety of factors, and as shown in the figure below, the timing of lodging will determine the final impact on grain yield. Lodging at head emergence can cause as little as 30 or as much as 80% yield reduction. The numbers in the figure do not account for harvest losses, which can exceed losses associated with lower photosynthetic capacity shown in the figure.

Slide05

Freeze injury or disease can cause lodging due to stem failure, which is characterized by plant stems breaking near the base. I the absence of weakened stems due to freeze or disease, most lodging in wheat is caused by failure of the root anchorage system (root lodging). Root lodging occurs when the anchorage system of a top-heavy wheat plant is weakened due to moist soil and wind provides sufficient force to overcome the rotational stiffness of the root/soil complex. Research has shown that increasing the soil water content from 17 to 26% reduced the force required for anchorage failure by 33%, and as little as 0.25 inches of water plus 11 mph winds were enough to cause lodging. The thicker the wheat crop and/or the taller the wheat crop, the more force that winds exert on the root anchorage system and the greater the likelihood of lodging.

Severe lodging in an Oklahoma wheat field in 2013

In 2013 we evaluated the plant growth regulator trinexapac-ethyl, which is sold under the trade name Palisade®. Palisade is a giberellic acid inhibitor and works primarily by reducing plant height. In our study we evaluated 12 oz/ac of Palisade with and without 4 oz/ac of Tilt (propiconazole) applied at Feekes GS 7 (two nodes visible above the soil surface). We included an untreated check and ALL plots, including the check, received 10.5 oz/ac of Quilt Xcel at Feekes GS 10.5 (heading). We conducted the trial at Stillwater (Irr), Perkins (Irr), and Chickasha (Non-Irr).

Slide11

While application of Palisade resulted in numeric reductions in plant height at Chickasha and Stillwater, differences among treatments were not statistically significant.

Slide14

We rated plots for lodging at harvest using a 1 – 10 scale with 0 equaling no lodging and 10 equaling complete lodging.  Application of Palisade plus Tilt reduced lodging over Palisade alone at Chickasha. Application of Palidsade or Palisade plus Tilt resulted in numeric reductions in lodging scores at Stillwater, but the result were too variable to result in statistical significance. Palisade did not affect lodging at Perkins.

Slide18Application of Palisade or Palisade plus Tilt increased grain yield at Chickasha and had no effect on grain yield at Stillwater or Perkins. It is interesting to note that the Palisade treatment increased grain yield at Perkins even though the plots lodged at comparable levels as the non treated check. My best hypothesis is that the treated plots lodged later than the non treated plots, as all plots were standing at anthesis (see picture below).Lodging occurred at Chickasha, but occurred later in the season.

Slide19Palisade and Palisade plus Tilt increased test weight at Chickasha and had no effect on test weight at Perkins or Stillwater

To summarize this first year of work with plant growth regulators, we found a trend for one to two inch reductions in plant height when Palisade or Palisade plus Tilt were applied, but this only translated to increased grain yield at one site. Our results are consistent with other wheat plant growth regulator research, which has reported similar variation in response among sites and years.  The literature also shows that reduction in lodging is relative to the straw strength of the variety. That is, a plant growth regulator will not make a lodging prone variety stand like one with excellent straw strength, rather they will make it less prone to lodging relative to the same variety non treated.

Based on current evidence, plant growth regulators in Oklahoma are best kept on acres with high (> 80 bu/ac) yield potential that may have greater propensity for lodging due to variety or fertility.  If these high yield potential acres are being sprayed with a growth regulator at GS 7, the addition of a foliar fungicide might be prudent if it can be included at a relatively low cost. This early-season fungicide application will not, however, substitute for a fungicide application at flag leaf.

Full disclosure: Syngenta donated the product for this trial, but the only funding for the research was provided by the Oklahoma Agricultural Experiment Station and the Oklahoma Cooperative Extension Service. We are conducting the same trial in 2014 along with a separate trial evaluating Palisade in drought stress environments that is partially funded by Syngenta. The analysis and recommendations made in this blog post are preliminary and based on research findings from 2013. Recommendations may change as further research is conducted and new information is obtained.


3 Comments

  1. Daryl Strouts says:

    I’d be interested to see if there was an effect on seed quality. Since Certified seed is of higher value, often times seed producers are willing to invest more in their crop. While fungicides may not always produce an economical gain in yield, they often improve seed quality by producing a higher percentage of larger and/or heavier test weight seed. The reduced cleanout means more high-quality, saleable seed wheat for the Certified seed grower. Do growth regulators provide an improvement in seed size or TKW?

    • osuwheat says:

      Daryl, in the absence of lodging I would not expect growth regulators to have any effect on seed size or quality. Seed quality generally goes down as lodging increases, so I would expect plant growth regulators to increase seed size and quality if they prevent or delay lodging. We did not look at seed size, but the improved test weights observed in our study would certainly point towards increased seed size and less clean out. I agree on the fungicides regarding seed size. We have observed a solid 1 to 1.5 lb/bu increase with the application of foliar fungicides at flag leaf.

  2. […] provided 2013 results in a blog post last year, and this post provides an update including our 2014 findings. While application of Palisade […]

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