The effects of chlormequat chloride and ethephon on selected small grain cereals in South Africa.
Lodging poses a serious limitation to successful economic production of small grain cereals and can lead to extensive yield and quality losses. Plant growth regulators (PGR's) that reduce plant height and lodging have been employed in management systems in Europe and the United States, however, these compounds have not been evaluated on commercial cultivars of wheat, barley and oats in South Africa. Current recommendations to reduce lodging include limiting N inputs, seeding rates and critical irrigations, all of which may also limit yield potential and grain quality. The objectives of this study were to assess the effects of two common stem-elongation-inhibiting PGR's (chlormequat chloride and ethephon) on the growth, development, and agronomic characteristics of wheat, barley and oats. The aim of the study was to introduce an additional component of intensive cereal management in the form of PGR's, and to allow producers to implement intensive production practices without incurring losses due to lodging. Field trials were conducted with each of the three cereal crops in the 2003 and 2004 seasons at Vaalharts and Bethlehem. The PGR's were applied separately and in combination with each other to lodging-tolerant and -susceptible cultivars (wheat and oats) at different stages of development (tillering, elongation, flag leaf stage). The PGR's were also tested in combination with different levels of N (barley) applied at the haulm elongation stage, the flag leaf stage, or both. The PGR chlormequat produced negligible effects on plant height, lodging, yield, or quality components in all of the tested cultivars . Ethephon and the PGR combination successfully reduced plant height (by 120 to 150mm) and lodging (by 25 to 94%) when applied to the lodging susceptible cultivars of wheat and oats at the flag leaf stage or as a split application to the barley cultivar "Puma" (plant height and lodging reduced by 180 to 230mm and 83 to 92% respectively). Effects on grain yield were variable, ranging from occasional reductions (by 3 t ha(-1) and improvements (by 1 t ha(-1) with the barley, and no effects with the wheat and oats. Wheat quality parameters such as protein content and hectolitre mass were improved by 2 and 4% respectively. However, the nature of the responses was highly dependent on the times of application with later applications producing the greatest positive effects on quality, yield and lodging reductions. Additionally, ethephon and the PGR combination allowed higher levels of N to be employed without increases in lodging of barley. Generally, ethephon and the PGR combination applied at the flag leaf stage of growth are suitable anti-lodging tools for small grain cereal production and should be employed as an insurance measure against lodging in intensive management systems.
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