Plant Growth Regulator and Early-Season Foliar Fungicide Effects on Hard Red Winter Wheat Yield.

Plant growth regulators have been used in intensive wheat management systems to reduce plant height and reduce lodging, but plant growth regulators for wheat have not been studied extensively in the southern Great Plains. The objective of this study was to evaluate the use of plant growth regulators and early-season foliar fungicide applications in hard red winter wheat in Oklahoma. Irrigated and non-irrigated studies were conducted in central Oklahoma during the 2012-2013 and 2013-2014 wheat production seasons. The hard red winter wheat variety Iba was seeded at 60 kg ha^-1 using conventional tillage methods each year. A combination of pre-plant and topdress nitrogen were applied on a yearly basis to ensure that 200 kg ha^-1 N, including soil test NO3-N, was available for plant growth. Experimental design was a randomized complete block with four replications, and treatments were no growth regulator, 105 g ha^-1 trinexapac-ethyl (12 oz ac^-1 Pallisade EC) applied at Feekes GS 7, or 105 g ha^-1 trinexapac-ethyl tank-mixed with 126 g ha^-1 propiconazole (4 oz ac^-1 Tilt 3.6 EC) applied at Feekes GS 7.  All treatments received 93 g ha^-1 propiconazole plus 108 g ha^-1 azoxystrobin (10.5 oz ac^-1 Quilt Xcel) at Feekes GS 10.1. Application of a growth regulator plus foliar fungicide reduced wheat lodging at one of three sites during the 2012-2013 wheat production season, but no significant reductions in plant height were observed. No lodging was present in any of the treatments in 2013-2014, but growth regulators reduced final plant height by approximately 5 – 10 cm. Application of a growth regulator or growth regulator plus fungicide increased wheat grain yield in two of six site years, but increased grain yield did not always coincide with reduced lodging or reduced plant height.