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Plant Growth Regulators to Reduce Lodging in Small Grains (06/06/19)

Most of the small grain crop has now emerged and with the warmer weather is developing rapidly; winter wheat is already jointing.

Most of the small grain crop has now emerged and with the warmer weather is developing rapidly; winter wheat is already jointing. There has been growing interest in the use of plant growth regulators (PGR) as a means to reduce lodging in small grains, particularly in the high yielding environments where lodging is more problematic and when growing two-row barley varieties.

PGRs are commonly used in Europe and other regions of the Americas (Chile, for example) where yields are considerably higher than ours. PGRs are synthetic compounds that either mimic plant hormones or interrupt biosynthesis of plant hormones thereby altering the growth and development of the plant. They can reduce plant height and/or thicken basal stems thereby making the plant less prone to lodging. PGRs are not intended to increase yield potential but protect yield potential by reducing the risk of lodging. PGRs will be profitable only if they reduce yield losses that might occur from lodging. They will most likely be profitable when applied to a variety known to be prone to lodging and to crops that seem likely to have high yield (i.e. early planted and no moisture or other stresses by the time of application).

The effectiveness of PGRs in shortening crops depends on the rate used, the timing of application and the environment. The Minnesota On-Farm Research Group conducted on-farm trials using the PGR trinexapac-ethyl (Palisade®) in spring wheat in 2016-2018 (their annual reports can be found at https://mnwheat.org/farm-research-network/ ). In only a few of their trial sites did the treatment substantially reduce plant height and improved yield to the point that the treatment was considered profitable. We have conducted small plot research over the last two years. In 2017, height reduction was minimal with Palisade®. Last year, however, plant height was reduced substantially and lodging was significantly reduced in sites where there was lodging (see following table). Ethephon (Cerone®) also reduced plant height and lodging in 2018 trials (data not shown), but since it is only labeled for use in irrigated wheat and barley in North Dakota, I did not include those data. Applying a PGR with herbicides and/or fungicides can reduce the application cost if the timing of the PRG application corresponds with the timing of the other chemicals. Mixing currently available PGRs is allowed with most commonly used herbicides and fungicides, but it is not recommended when plants are stressed. Check the label for information about chemical compatibility.

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Early emerged wheat and barley crops will soon reach the stage when PGRs may be applied. Palisade® can be applied as a single application any time between Feekes growth stage 4 and before Feekes 8, or as a split application with the first application at Feekes 4 to 5 and the second at Feekes 7. Feekes 4 occurs as the plant is completing tillering, the leaf sheaths begin to thicken and the plant begins to grow upright. Since the growing point is below the soil surface at this point, the stem of the plant is just a pseudo-stem formed by the leaf sheaves holding the plant upright. At Feekes 5 the pseudo-stem becomes more erect and at Feekes 6 the first node appears (see Figure 1 of winter wheat with its first node visible), and the true stem begins to elongate. Feekes 7 occurs when there are two visible nodes above ground, and Feekes 8 when the flag leaf (the last leaf) begins to emerge from the whorl.

 

Joel Ransom

Extension Agronomist, Small Grains and Corn

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