PREDICTING YIELD RESPONSES OF COTTON TO GROWTH REGULATORS
Mar 10, 2017

Uncategorized Agronomy & physiology WCRC Agro-physio-australia WCRC1
Abstract                                                                         Back to Table of contents
There have been some significant recent improvements in the understanding of vegetative growth management in cotton using growth regulators. Successful advisory programs have been implemented for cotton growers to monitor their crops and apply growth regulators to prevent excessive vegetative growth. In some instances vigour indices and height:node ratios can disregard conditions where a crop is moving from good conditions to bad, or from bad to good. For example, a crop may have short seedling internodes from cool weather or other stress, then have better conditions where subsequent vegetative growth may be excessive. Although the crop vigour index may still be ‘low’, it has a high current rate of vegetative growth and could still respond to a growth regulator.
This aspect of monitoring and managing cotton crop vegetative growth has been examined in Australia for five seasons. Treatments included sowing dates and varieties. The crops ranged in final plant height from 60 to 160 cm; and yields ranged from 1100 to 2500 kg lint/ha. In every experiment, the rate of increase in internode length was measured prior to applications of Mepiquat chloride (MC - Pix). Results showed that when internode length increased at less than 5.5 cm/node, no response or even negative yield responses to MC were obtained. When internode length was increasing at more than 6.5 cm/node, significant yield increases were obtained. This association was generally true across cultivars, although there were indications that some cultivars were more or less responsive to MC. Since it is usually too late to obtain yield responses to MC once a crop is already too tall, this procedure allows problem situations to be diagnosed before excessive vegetative growth occurs.

Conclusions
Regular monitoring of plant size is the only way to accurately determine the need to manage crop growth. These results have shown that there is a useful correlation between vegetative growth and yield response to MC. Cultivar differences appear to exist and should be considered in management decisions.

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