Using Plant Growth Regulators in Cereal Grains

• A lodged cereal grain crop not only suffers from lost yield potential and reductions in grain quality, but also from slowed harvest equipment and lost time.
• Reducing the potential for lodging while maintaining yield potential can be complicated for cereal growers.
• Including plant growth regulators in cereal crop management may help reduce lodging in high yield environments.

Causes of Lodging in Wheat

Environmental conditions and wheat variety selection have a large impact on lodging potential. Adverse weather conditions like strong winds and heavy rain can result in lodged wheat, especially for taller wheat varieties or those with poor stem strength. Prolonged wet conditions can increase disease pressure and allow fungal pathogens such as sharp eyespot to break the stems of infected tillers above the soil line. Applying more nitrogen (N) than the crop requires can result in increased vegetative growth and cell elongation, which can reduce plant strength in windy conditions. Too much N uptake may also occur as organic N from sources like manure is mineralized. High plant populations can also increase the potential for lodging, as more plants in the field lead to taller plants and weakened stems.¹

How to Avoid Wheat Lodging

There are several wheat management practices that can help reduce the likelihood of lodging. Managing lodging begins with selecting shorter wheat varieties with higher stem strength. Short and strong stems are less prone to lodging. Planting the appropriate plant population for your conditions and avoiding over-application of N fertilizer can also help reduce lodging.

Additionally, the application of plant growth regulators (PGRs) to a wheat crop may help reduce lodging. Plant growth regulators have the ability to modify the growth and development of a plant by either imitating plant hormones or preventing the synthesis of hormones within the plant.³

Applying Plant Growth Regulators to Wheat

There are several PGR options available to wheat growers in the United States.

• Ethephon – releases ethylene into cell tissue, which reduces cell elongation and crop height, potentially reducing lodging. Products containing ethephon should be applied between the flag leaf becoming visible and the boot growth stages. If 10% of the awns have emerged, it is too late to apply ethephon and crop damage could occur.
• Chlormequat chloride – inhibits the early stages of gibberellin production, resulting in reduced plant height and thickening stems. Applications should be made during stem elongation through jointing, to the first or second internode. This product is currently not labeled for use in the United States but has been under review with the EPA since 2023.
• Trinexapac-ethyl – also inhibits gibberellin production. It has a similar application timing to chlormequat-chloride.
• Gibberellic acid – promotes early growth rather than hindering it, which may result in larger plants that can withstand stressed growing conditions. The most beneficial time to apply is in the fall, to promote early growth of the crop.⁴

A study conducted in 2013 by Oklahoma State University investigated the effects of Palisade^® EC plant growth regulator—a product containing trinexapac-ethyl—on wheat and found an average reduction of one to two inches in plant height with one application. Only one of the three trial locations measured in the trial produced a higher yield. The researchers also observed that any reduction in lodging was limited by the stem strength of the wheat variety.²

Michigan State University also conducted a study in 2012 and 2013 to observe the effect of Palisade^® EC on wheat and found that, on average, lodging was significantly reduced in 2012. However, in 2013 the trial resulted in no significant yield gain. The Michigan State University study found that the effects of Palisade^® EC were more evident with higher application rates and earlier application timings.⁵

Applying a plant growth regulator to wheat may be most beneficial on fields with high yield potential, in early planted fields with vigorous growth, when planting a variety prone to lodging, if excess fertility is present from manure applications, or when implementing intensive wheat management practices.⁴ Applying a PGR to a wheat crop cannot increase yield potential but can help maintain yield potential by lowering the risk of lodging.

Plant Growth Regulator Application to Barley

Products containing chlormequat chloride or trinexapac-ethyl are labeled for use in barley. Manipulator™ 620 is registered for use in Canada, though not for use in the US, and contains chlormequat chloride, while Moddus^® contains trinexapac-ethyl as its active ingredient.

Lodging may contribute to malting barley failing to meet yield and quality standards. A research project in western Canada testing three PGRs on CDC Copeland, a two-row malting barley, took place over three years at five locations. Plant growth regulator products containing either chlormequat chloride or trinexapac-ethyl were applied at Zadoks growth stage (GS) 30 to 33, when the first through third nodes are detectable during stem elongation. This timing is similar to Feekes 6 to 7 on the Feekes growth scale. Ethephon was applied at Zadoks GS 37 to 39 (similar to Feekes 9) corresponding to flag leaf emergence. Three seeding rates were used to increase the likelihood of lodging. All PGR products tested in the study reduced plant height; however, the reduction in lodging was generally inconsistent across PGR products and testing locations, though trinexapac-ethyl showed the most promise based on the study’s results. None of the products tested affected yield or grain protein.⁶

Research conducted in Alberta found that trinexapac-ethyl provided improved standability for CDC Copeland compared to the untreated control. The research findings concluded that PGRs are meant to manage the risk of lodging in highly productive environments with high yield goals, or in cases where genetic resistance to lodging is not adequate. Growers should not apply PGRs to barley that is stressed due to environmental conditions.⁶

Ethephon applied to spring barley may shorten the last two or three internodes, particularly the peduncle, reducing the tendency to lodge while also reducing the loss of grain yield and quality. Application should take place while the barley is in the flag leaf to boot stage of growth and before awns appear. If ethephon is applied prior to or after the recommended growth stages, yield loss may occur. Barley heads should never be exposed to the product due to the potential for flower sterility. Research in irrigated trials by the University of Idaho found that ethephon applied to various barley varieties consistently reduced lodging, with most varieties having a positive yield response.⁷

Sources

¹Boring, T. and Nagelkirk, M. 2011. Contributing factors and harvest concerns for lodged wheat. Michigan State University Extension. https://www.canr.msu.edu/news/contributing_factors_and_harvest_concerns_for_lodged_wheat

²De Oliveira Silva, A. 2014. Plant growth regulators for wheat. Oklahoma State University. https://osuwheat.com/2015/02/19/plant-growth-regulators-for-wheat-2/

³VanDerZanden, A.M. 2014. How hormones and growth regulators affect your plants. Oregon State University Extension Service, Botany Basics. https://extension.oregonstate.edu/gardening/techniques/how-hormones-growth-regulators-affect-your-plants

⁴Follings, J. 2019. Plant growth regulators – the why, where and when. FieldCropNews. https://fieldcropnews.com/2019/06/plant-growth-regulators/

⁵Nagelkirk, M. 2014. Using Palisade plant growth regulator to improve wheat performance. Michigan State University Extension. https://www.canr.msu.edu/news/using_palisade_plant_growth_regulator_to_improve_wheat_performance

⁶Tidemann, B. D., O’Donovan, J. T., Izydorczyk, M. et al. 2020 Effects of plant growth regulator applications on malting barley in western Canada. Canadian Journal of Plant Science. 100(6):653–665. https://cdnsciencepub.com/doi/10.1139/cjps-2019-0200

⁷Robertson, L.D. and Stark, J.C. (Eds.) 2003. Idaho spring barley production guide. University of Idaho Extension. BUL 742. https://agresearch.montana.edu/wtarc/producerinfo/agronomy-nutrient-management/Barley/IdahoSpringBarleyProdGuide.pdf

Web sources verified 09/19/2024. 1726_444075