Assessing the utility of the growth regulator trinexapac-ethyl and fungicides in mid-Atlantic soft red winter wheat production systems

Soft red winter wheat (SRWW) is an important crop in the mid-Atlantic. The use of growth regulators such as trinexapac-ethyl (TE) applied with nitrogen applications at pseudo-stem erection [Zadocks (ZGS) 30] has gained more interest in the region as a means to reduce lodging and potentially improve yields. Fungicide use has also increased, with many growers applying fungicides at ZGS 30 and again at ZGS 37 or ZGS 60. The safety and utility of TE in SRWW production systems, used alone or in combination with fungicides, is unknown. We evaluated the utility and safety of TE, applied alone, tank mixed with a fungicide at ZGS 30, and in combination with a foliar fungicide at ZGS 37 or ZGS 60 for utility and safety in mid-Atlantic SRWW. Three replicated field experiments were conducted over two growing seasons in Delaware, and yield, test weight, and disease severity on the flag leaf, were assessed. No phytotoxicity was noted in any of the TE or TE x fungicide treatments tested. TE applied alone reduced plant height by nearly 7 cm, but the application of fungicide at ZGS 37 or 60 slightly negated this effect. No lodging was observed. The addition of a fungicide at ZGS 30 followed by Prosaro (prothioconazole + tebuconazole) at ZGS 60 resulted in the greatest yields and test weights. All fungicide programs significantly reduced leaf blotch complex on the flag leaves relative to untreated controls; however, no difference was detected between ZGS 37 and ZGS 60 treatments. These results indicate that TE can be used safely in SRWW production when applied alone or when tank mixed with a fungicide; however, the effect on plant height reduction and potential impact on lodging may be reduced in situations where fungicides are used.