2018 Soybean Official Variety Trial Phytotoxicity Evaluations

Phytotoxicity following the application of a fungicide known to produce injury.

One of the questions over the past few seasons has to do with the presence of phytotoxicity and how varieties may differ in sensitivity following a fungicide application.  One entire set of the Official Variety Trial (OVT) was planted in Stoneville, MS (MG IV and V: Conventional, early, late, LibertyLink) planted as single rows of each variety and replicated four times.  Plots measured 12 feet in length and received an application of 4 fl oz of Stratego YLD at R4.  Stratego YLD was selected since the product had previously been observed to produce a moderate level of phytotoxicity on some varieties.  A single evaluation was made 18 days post-application for the purposes of observing the incidence (0-100%; percentage of the plot exhibiting phytotoxicity) and severity (0-9; severity of the leaf tissue exhibiting phytotoxicity) for each variety.  The tables presented should provide information as to the potential response of each of the varieties included in the OVT and the level of phytotoxicity that may occur as a result of a fungicide that is likely to produce a moderate level of phytotoxicity.

Numerous fungicide products can produce a phytotoxic response post-application.  In general, products that contain a demethylation inhibitor (DMI; triazole) are the most commonly associated with phytotoxicity.  However, to date, a yield reduction as a result of phytotoxicity has not been documented in any of the trials conducted in Stoneville, MS as a result of applying a commercially labeled product for soybean over the last 5+ years.

Maturity group IV:

Maturity group IV Conventional: MG IV Conventional

Maturity group IV Early: MG IV early

Maturity group IV Late: MG IV late

Maturity group IV LibertyLink: MG IV LL

Maturity group V:

Maturity group V Conventional: MG V Conventional

Maturity group V Early: MG V early

Maturity group V Late: MG V late

Maturity group V LibertyLink: MG V LL