The weather this year is similar to 2004. In years with cool, wet springs there have been a considerable number of reports of wheat crop injury following early season (4-5 leaf growth stage) applications of herbicide/fungicide tank mixes. During 2004, we conducted the first year test of a two-year study looking at crop injury resulting from applications of pesticide tank mixes during periods of extended cool weather. The research is being repeated in 2005.

Research plots were located at the Northwest Research and Outreach Center near Crookston. Alsen spring wheat was planted into wheat residue on April 30, 2004 and harvested on Sept. 2. The fungicides Tilt (Syngenta), Quilt (Syngenta), Headline (BASF) and Stratego (Bayer CropScience) were applied in combination (tank mixed) or sequentially with the herbicides Puma + Bronate Advanced. The experimental design was a randomized complete block with four replications.

The purpose of the 2004 study was to determine if there were detrimental yield and quality effects arising from plant injury resulting from applying half-rates of fungicides tank-mixed with herbicides at the 4-5 leaf growth stage.

There were no detrimental effects on yield when half -rates of fungicides ‘Tilt’, ‘Quilt’, or ‘Stratego’ were applied early (4-5 leaf growth stage) in a tank-mix with ‘Puma’ + ‘Bronate Advanced’ herbicides in a single application, compared to the control plot that didn’t receive fungicide, and a sequential fungicide application where the fungicide was applied separately from the herbicide on the same day. A tank-mix application of ‘Headline’, ‘Puma’, and ‘Bronate Advanced’ decreased grain yield 7% or 6.2 bu/ac, increased the vomitoxin levels (DON) in grain by 51% or 0.33 ppm, and increased the number of spikelets on heads exhibiting Fusarium head blight (FHB) symptoms by 71% when compared to a sequential application (Figure 1). Tank-mix applications of ‘Stratego’ also resulted in increased DON levels by 30% or 0.19 ppm. The tank-mix application of ‘Quilt’ decreased the number of FHB-infected heads across whole plots (FHB incidence) by 57%, but increased plant leaf injury six days after application by 30% over the sequential treatment (Figure 1).

Overall, DON levels were greatest when fungicide was not used with herbicide (Figure 2). A tank-mix application of fungicide reduced DON levels by 9% compared to the control treatment. But, applying fungicide sequentially resulted in a 25% reduction in DON levels when compared to the control. Compared to the control treatment, tank-mixing fungicide with herbicides increased grain protein by 2%, while the sequential treatment resulted in a 1% increase in protein. Grain test weight, thousand kernel weight, and FHB field severity (FHB head severity x FHB incidence/100) were not affected by fungicide application methods.