Winter Wheat Yield and Profitability from Dividend and Vitavax Seed Treatments

Fungicide seed treatment is required to protect winter wheat (Triticum aestivum L.) from infection by smut fungi in the Pacific Northwest(PNW). Vitavax (carboxin—2,3-dihydro-5-carboxanilido-6-methyl-1,4-oxathiin) dominated this market for 25 yr before Dividend (difenoconazole—1-(2-[4-(4-chlorophenoxy)-2-chlorophenyl]-4-methyl-1,3-dioxolan-2-yl-methyl)-1H-1,2,4-triazole) was registered as a smut-control treatment in 1994. Relative effects of these fungicides on productivity and profitability of winter wheat are not known; therefore, the objectives of this study were to collect data relative to those factors under commercial conditions. Twenty four experiments that included these fungicides were performed over 5 yr at 12 locations, using seven cultivars. Up to 44 comparisons of cultivar × location × year were possible for some fungicide treatments and application rates. Grain yields were equivalent for Vitavax-treated and untreated seed. Dividend increased yield 5% (2.7 bu/acre) over the Vitavax treatment, for an $8.25 increase in net profit per acre. Profitability of Dividend was increased by reducing the application rate from the standard rate of 0.5 fl oz/cwt to 0.25 fl oz/cwt. Profitability of Dividend was higher in regions where wheat production is less than 40 bu/acre than in areas of higher productivity. Five winter wheat cultivars differed in yield response to Dividend. Neither fungicide affected test weight or kernel weight. This research demonstrated that, by using Dividend, producers can maintain profitability while reducing fungicide application rates by a factor of 10. Research QuestionFungicide seed treatments are required to protect winter wheat from infection by smut pathogens on about 5 million acres in the Pacific Northwest. Dividend seed treatment was recently registered to compete in a market dominated by Vitavax. This research determined comparative effects of Dividend and Vitavax on wheat yield, test weight, and profitability. Literature SummaryOur experience has been that Vitavax provided excellent control of smuts but did not improve grain yields when smuts were not limiting to yield. Early tests suggested that Dividend often led to slight yield advantages that were statistically insignificant for most individual experiments. Study DescriptionResults of 24 experiments were grouped to examine overall effects of Dividend and Vitavax seed treatments, or untreated seed, on grain yield, test weight, kernel weight, and profitability. Tests were performed at 12 eastern Oregon and Washington locations over 5 yr. Two or three cultivars in 16 of 24 tests provided an opportunity to make up to 44 comparisons among treatments, and to examine the possibility of different responses among cultivars. All tests except one were in nonirrigated winter wheat-summer fallow rotations in 10- to 20-in. precipitation zones. Plots measured 5 by 20 ft, contained five rows spaced at 12-in. intervals, and were replicated five to six times in a randomized complete block design. Planting dates (September and October) and depths (1.5–5 in.) and all tillage, fertilizer, and weed management procedures were in accordance with commercial practices. Applied QuestionsDo Vitavax and Dividend seed treatments increase wheat yields? In 39 comparisons, Vitavax (3–4 fl oz/cwt for Vitavax 200 or 4–5 fl oz/cwt for RTU Vitavax Thiram) did not improve winter wheat yield significantly (0.1 bu/acre) over that of untreated seed. In contrast, the yield of winter wheat was 5% (2.7 bu/acre) higher for the Dividend (0.5 fl oz/cwt) than Vitavax treatment. What is the comparative profitability for wheat treated with Vitavax or Dividend? The net profit for grain harvested from Dividend (0.5 fl oz/cwt) treated seed was $8.25/acre higher than for Vitavax-treated seed. Profitability of Dividend over Vitavax was improved to $11.24/acre when the Dividend application rate was reduced to 0.25 to 0.33 fl oz/cwt but remained at $8.24 when the rate of Dividend was increased to 1 fl oz/cwt. Compared with untreated seed, Vitavax reduced profitability by $0.92/acre. It must be stressed that critically important smut-controlling properties of these fungicides were not included in these calculations. As such, it is very important to indicate that Vitavax serves a highly profitable disease control requirement where it will continue to be used preferentially over Dividend. At the present time, it is not clear that low application rates for Dividend (0.25–0.33 fl oz/cwt) are adequate to protect winter wheat from infection by smut pathogens. All seed planted in the inland Pacific Northwest must continue to be treated with a smut-controlling fungicide. Do production areas differ with respect to relative yield or profitability advantages expected from seed treatments? Relative yield improvement and profitability from Dividend seed treatment (0.5 fl oz/cwt) were highest in areas that produced less than 40 bu/acre. While yield improvement was comparable for both production brackets (2.7–3.0 bu/acre), the relative increase was 13% in the low-yielding areas and 5% in high-yielding areas. In areas that produce less than 50 bu/acre, the yield was amplified another 4% (1.4 bu/acre) when the application rate for Dividend was increased from 0.5 to 1 fl oz/cwt. In production areas higher than 50 bu/acre, however, the higher rate of Dividend decreased yield by 2% (1.3 bu/acre), compared with the 0.5 fl oz rate. Do cultivars differ in responses to fungicide seed treatments? Five winter wheat cultivars appeared to differ in their response to treatment with Dividend. All cultivars had higher mean yields with Dividend than Vitavax treatment (0.6–4.2 bu/acre) or no treatment (0.6–5.2 bu/acre). Additional tests will be necessary to assure that relationships reported in this paper are accurate. Are test weights or kernel weights improved by fungicide seed treatments? Winter wheat test weights and kernel weights did not differ among treatments examined in these experiments, suggesting that the increase in yield associated with Dividend seed treatment is a response to production of more grain per unit area.