Control of stripe rust of winter wheat with foliar fungicides, 2007

Authors: Chen, Xianming; Wood, David

Submitted to: Plant Disease Management Reports
Publication Type: Research Notes
Publication Acceptance Date: 1/22/2008
Publication Date: 4/1/2008
Citation: Chen, X., Wood, D.A. 2008. Control of stripe rust of winter wheat with foliar fungicides, 2007. Plant Disease Management Reports 2:CF015.

Interpretive Summary: A total of nine foliar fungicide treatments were tested for efficacy to control stripe rust on spring wheat at Pullman, Washington during the 2006-2007 growth season. Stripe rust severity was assessed in each plot four times during the rust development season. Test weight of kernels and grain yield were measured for each plot at harvest. All fungicide treatments significantly reduced stripe rust severity seven days after the last application. Differences in stripe rust severity between most fungicide treatments and non-treated control remained significant thereafter. Stripe rust severity values of all fungicide treatments were significantly lower than the non-treated control (100%), but varied significantly because of differences in the duration of efficacy and timing, rate, and number of applications. All treatments significantly increased grain yield, ranging from 38.9 to 59.8% on Hatton and from 58.5 to 111.8% on PS 279, compared to the non-treated control. The yield increase by fungicide applications could be valued at from $136 to $306/A depending upon the cultivar and treatment.

Technical Abstract: A total of nine foliar fungicide treatments were tested for efficacy to control stripe rust on spring wheat at Pullman, Washington during the 2006-2007 growth season using a randomized completed block design experiment with non-treated plots as the experimental control. Susceptible winter wheat varieties ‘Hatton’ (hard red) and ‘PS 279’ (Soft white club) were seeded on 16 Oct 06. Fungicides were applied in 16 gal water/A on different dates and stages depending upon the treatments. The first applications of Topguard for the two-application treatments were done on 6 Jun at early heading stage when stripe rust was 10-20% on PS 279 and 20-30% on Hatton. The one-time applications of Headline, Tilt, Quilt, Stratego, Topguard, and Quadris were done on 12 Jun when plants were at late heading stage. The second applications of Topguard for the two-application treatments were done on 20 Jun when plants were at flowering stage. Plots, ranging from 79.6 to 85.4 sq ft., were individually measured at the time of harvest and individual plots areas were used to calculate yields. Stripe rust severity (percentage of diseased foliage) was assessed in each plot on 6 Jun just before the first fungicide application and 27 Jun (flowering), 5 Jul (milk), and 13 Jul (soft dough) or 7, 15, and 23 days after the last fungicide spray, respectively. Plots were harvested on 11 Aug when kernels were naturally dry, and test weight of kernels was measured for each plot. Area under disease progress curve (AUDPC) was calculated for each plot using the four sets of severity data. Relative AUDPC was calculated as percent of the non-treated control. Rust severity, relative AUDPC, test weight, and yield data were subjected to analysis of variance and means were separated by Fisher’s protected LSD test. Mean stripe rust severity in non-treated control plots of Hatton was 23.8, 100, 100, and 100% on 6 Jun, 27 Jun, 5 Jul, and 13 Jul, respectively; and that of PS 279 was 15, 100, 100, and 100% on these dates, respectively. All fungicide treatments significantly reduced stripe rust severity 7 days after the last application. Differences in stripe rust severity between the fungicide treatments and non-treated control remained significant thereafter, except for PS 279 plots spayed with Headline that had a mean of 87.5% rust. Relative AUDPC values of all fungicide treatments were significantly lower than the non-treated control (100%), but varied significantly (11.9 to 41.9% on Hatton and 7.2-22.0% on PS 279) because of differences in the duration of efficacy and timing, rate, and number of applications. Only the treatment with Tilt significantly increased grain test weight of Hatton and only treatments of Tilt and two- application of Topguard at the rate of 14 fl oz/A increased grain test weight of PS 279. All treatments significantly increased grain yield, ranging from 38.9 to 59.8% on Hatton and from 58.5 to 111.8% on PS 279, compared to the non-treated control. The yield increase by fungicide applications could be valued at from $136 to $306/A depending upon the cultivar and treatment.