© 2006 Plant Management Network.
Assessing Fungicide Efficacies for the Management of Fusarium Head Blight on Spring Wheat and Barley
Charla R. Hollingsworth, Assistant Professor, Northwest Research & Outreach Center and Department of Plant Pathology, Christopher D. Motteberg, Research Assistant, and W. Galen Thompson, Research Fellow, Northwest Research & Outreach Center, University of Minnesota, Crookston 56716
Hollingsworth, C. R., Motteberg, C. D., and Thompson, W. G. 2006. Assessing fungicide efficacies for the management of Fusarium head blight on spring wheat and barley. Online. Plant Health Progress doi:10.1094/PHP-2006-0906-01-RS.
Small grains crop yield and quality losses resulting from Fusarium head blight (FHB) continue to threaten the economic sustainability of many small grains producers in Minnesota. Spring wheat breeders have made some progress in developing cultivars with moderate levels of disease resistance, but increased resistance in barley has not been achieved. Crop rotation and a timely application of fungicide remain the most important disease management strategies for managing the disease on both cropping species. Fungicide efficacy trials were conducted during 2003 and 2004 to compare the current industry standard (tebuconazole) efficacy with those of two experimental fungicides. Experimental products with active ingredients of metconazole or tebuconazole + prothioconazole significantly reduced percent FHB severity of spring wheat. Disease severity means with these experimentals averaged 28.5% less than tebuconazole, and percent visually scabby kernel means were 47% less with the experimentals compared with tebuconazole. Results were not as definitive for spring barley. Numerical trends from fungicide treatments were similar to those in spring wheat, but data were not statistically significant. These data indicate increased FHB management in Minnesota can be expected when experimental fungicides with active ingredients of metconazole or prothioconazole are registered for use on spring wheat by the EPA. The results for spring barley emphasize the urgency of achieving an effective disease management strategy for FHB and underscore the need for additional research on the disease in Upper Midwest states.
Fusarium head blight (FHB, scab) of wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) is caused primarily by Fusarium graminearum Schwabe [teleomorph Gibberella zeae (Schwein) Petch] in the US. The pathogen is known to cause widespread and repeated disease epidemics in regions with extended periods of rain, fog, or high humidity during critical plant growth stages (8,10). Wheat is known to be most susceptible to infection during and immediately following flowering (1,8,10), while barley is most susceptible to infection following spike emergence. Typically, culms of wheat are fully extended and spikes are emerged when plants flower (Feekes growth stage 10.51), but barley plants flower within the ‘boot,’ prior to spike emergence (Feekes growth stage 10.5).
Fusarium head blight has consistently reduced spring sown small grain yields and kernel quality in Minnesota and North Dakota since the early 1990s. Nganje, et al. (9) estimate disease-related losses at $5.2 billion from the two states between 1993 and 2001. During 2005, Minnesota and North Dakota experienced yet another FHB epidemic, resulting in estimated losses of $248 million.
A moderately resistant hard red spring wheat cultivar, ‘Alsen,’ is widely grown in northwest Minnesota and eastern North Dakota, but it has inherently lower yields than FHB-susceptible cultivars in the absence of a FHB epidemic. Currently, a small number of newly developed spring wheat cultivars with moderate disease resistance are being made available commercially. Barley breeders have been unable to duplicate the successes of wheat breeders. Resistance levels of commercial malting barley cultivars remain inadequate for use as a disease management tool.
Employing a number of disease management strategies has been shown to enhance FHB management during years when the disease is not severe. Small grains producers routinely: (i) rotate with a broadleaf crop; (ii) grow varieties with resistance; and (iii) track weather conditions as crops approach susceptible growth stages for determining whether fungicide application is needed. Since 1998, many Minnesota and North Dakota wheat producers have applied tebuconazole (Folicur) at 126 g/ha during the early flowering crop growth stage. Some states annually submit federal specific exemption requests to the US Environmental Protection Agency (EPA) for emergency use registrations (Section 18s) to annually permit use of tebuconazole on wheat and barley. A second generation of experimental triazole fungicides appear to offer superior disease management of FHB compared with tebuconazole. The object of this study was to compare disease management efficacies of systemic, experimental fungicides with the efficacy of tebuconazole, the current industry standard. This data will establish whether the next generation of products can significantly and consistently increase the level of FHB management for spring wheat and barley crops in Minnesota.
Protocol for Producing F. graminearum Corn Grain Inoculum
Four kg of corn kernels and approximately 4 liters of reverse-osmoses-treated water were placed into each of two stainless steel pans (30 cm × 51 cm × 10 cm). Pans were covered with aluminum foil and autoclaved twice for 120 min each cycle. Ten F. graminearum isolates (Fg1 - Fg10), collected from diseased grain harvested between 1996-1997 in Minnesota and North Dakota, were stored at -80°C on silica gels. Isolates were grown on Difco potato dextrose agar (Becton-Dickson and Co., Sparks, MD) in Petri dishes (100-mm diameter) on a laboratory bench for 7 to 10 days with a 12-h photoperiod under cool white fluorescent lighting. Half the growth medium and fungal mycelium from one dish of all 10 isolates was subdivided into smaller pieces and placed, fungal side down, into each pan containing sterile, room-temperature corn grain. Pans were recovered with aluminum foil and maintained on a laboratory bench until grain was completely colonized by isolates (approximately 14 days). Colonized grain was mixed by hand and transferred to burlap bags (Fig. 1). Bags were placed in an oven and maintained at 33 to 38°C from 48 to 72 h until dry. Dried inoculum was stored in burlap bags for 8 to 10 weeks at room temperature until trials were inoculated.
2003 Field Trials of Spring Wheat and Barley
Hard red spring wheat cultivar ‘Oxen’ (FHB susceptible to moderately susceptible), and spring barley cultivar ‘Robust’ (FHB susceptible), were planted into a Wheatville loam soil with oat residue present on 28 April at the Northwest Research and Outreach Center (NWROC) near Crookston, MN. Each trial was a randomized complete block design with four replicates. Plots were 1.5 m × 4.6 m with rows 19 cm apart. Weeds were controlled by hand labor and a 29 May tank-mixed application of Puma (fenoxaprop-p-ethyl) at 585 ml/ha and Bronate Advanced (bromoxynil) at 1.2 liter/ha. On 4 June, five weeks after planting, dried F. graminearum inoculum was spread evenly throughout the test and bordering areas at a rate of 370 kg/ha. Full-canopy, night cycle mist irrigation was initiated following inoculation. Rondo mini-sprinkler misting heads with 0.8 mm nozzle orifice size and 40 liter/h nominal flow rate (Bowsmith, Inc., Exeter, CA) were situated atop fiberglass dowels at 3-m intervals and supplied water via plastic feeder pipe. Fiberglass poles were used in both trials as well as the nontreated border plots to ensure a uniform misting canopy throughout the test area. Beginning June 5, trials were misted at 15-min intervals each night at 10:00 pm, 11:35 pm, 1:10 am, 2:45 am, 4:20 am, 5:55 am, and 7:30 am. Misting was temporarily discontinued if rain events caused saturated soil in the test area. Fungicide applications were made on barley test plots at the Feekes 10.5 plant growth stage (27 June) and on wheat plots at the Feekes 10.51 plant growth stage (1 July) with a CO2 backpack-type applicator with XR Teejet flat fan 8001VS nozzles spaced 51 cm apart on a 1.5-m boom angled 60° from vertical positioned forward and backward to the direction of travel at 187 liter/ha and 276 kPa (Table 1).
Table 1. Fungicide treatments applied to hard red spring wheat
x Each fungicide treatment included Induce, a nonionic
2004: Field Trials of Spring Wheat and Barley
Oxen spring wheat and Robust spring barley were planted into a Wheatville loam soil with wheat residue present on 4 May at the NWROC. Each trial was a randomized complete block design with four replicates. Plots were 2.4 m × 4.6 m with rows 15.2 cm apart. Weeds and early foliar diseases were controlled with a 8 June tank-mixed application of MCPA (2-ethylhexyl ester of 2-methyl-4-chlorophenoxyacetic acid) at 585 ml/ha, Harmony GT (thifensulfuron-methyl) at 24 ml/ha, Puma (fenoxaprop-p-ethyl) at 775 ml/ha, and Tilt (propiconazole) at 292 ml/ha. On 11 June, F. graminearum inoculum was spread at a rate of 112 kg/ha. Inoculum rate was reduced from the 2003 level because the test was situated within a much larger F. graminearum inoculated, misted disease nursery. Mist irrigation design was as before. The same disease nursery misting schedule was used for these trials. Trials were misted for 7 min at 56 min intervals each night from midnight through 8:00 am. Plant growth stage fungicide application timing and equipment remained the same as in 2003. Fungicide was applied to barley plots on 7 July and to wheat plots on 14 July (Table 1).
Assessment of Fusarium Head Blight Symptoms, Grain Yield and Quality, and Statistical Analyses
A total of 50 spikes per plot were arbitrarily collected when FHB symptoms became apparent prior to plant senescence. Spikes were maintained in short-term cold storage (approximately -23°C) until symptoms were rated. Fusarium head blight severity (percent spikelets per spike with symptoms) of wheat data were recorded based on a visual scale where each effected spikelet accounted for 7% of the total spike (11). Disease severity was assessed in much the same manner for barley, however a visual guide had not yet been developed. Fusarium head blight incidence (percent spikes with symptoms) and FHB index [(severity × incidence)/100] were also recorded. Visually scabby kernels (VSK) of wheat was estimated using a set of grain standards (7). Mycotoxin analyses were conducted at the University of Minnesota Department of Plant Pathology Mycotoxin Laboratory using gas chromatography/mass spectrometry. Also recorded were moisture content, thousand-kernel weight (TKW), percent protein, test weight, and yield. Yield data were normalized at a moisture value of 13.5%.
Yearly data from each trial were analyzed separately using ANOVA. Only those categorical data with homogenous variances in both test years were combined. For this reason, different data parameters are used for wheat (e.g., FHB severity, visually scabby kernels, test weight, TKW) compared with barley (e.g., protein, DON, yield). Fisher’s protected least significant difference mean separation tests were performed with SAS (SAS Institute Inc., Cary, NC) using PROC GLM. ‘Year’ was determined to be a random affect while ‘fungicide’ was a fixed affect. Data from single year results are available (4,5,6).
Wheat: Fungicide Efficacies
Fusarium head blight disease pressure was moderate and consistent across years. Yearly FHB index means from nontreated control treatment plots were similar (e.g., 2003, 36.3% and 2004, 41.2%), as were DON grain concentration means from the nontreated treatment (e.g., 2003, 15.0 ppm; 2004, 15.2 ppm). Single year results for 2003 and 2004 are published (4,5).
Interactions for ‘year × treatment’ were not significant for FHB severity, test weight, TKW, or VSK; while ‘treatment’ affects were significant (Table 2). Simple affects of ‘year’ were significant for parameters measuring disease (e.g., FHB severity and VSK), largely due to increased FHB disease pressure in 2004 compared with 2003. Increased disease did not effect those kernel quality parameters reported (e.g.: test weight and TKW) (Table 2).
Table 2. Hard red spring wheat: Effect of fungicides, averaged over two years, on crop health and kernel quality following inoculation with Fusarium graminearum.
x Each fungicide treatment included Induce, a nonionic surfactant, at 0.125%.
y Column abbreviations: FHB Severity = Fusarium head blight severity; VSK = visually scabby kernels; TKW = thousand kernel weight.
z Treatment data in columns with the same letter designator are not significantly different at P = 0.05.
Tebuconazole application resulted in nonsignificant disease control when compared to the nontreated control treatment for VSK, test weight, and TKW (Table 2). Tebuconazole significantly reduced FHB severity over the nontreated control treatment, but was less effective at reducing severity symptoms than either metconazole or the tebuconazole + prothioconazole (mixed) treatment. Metconazole resulted in increased control of FHB severity over tebuconazole, but did not reduce severity significantly compared with the mixed product treatment. Metconazole was not significantly different from tebuconazole or the mixed product in the remaining categories reported (e.g., VSK, test weight, TKW). The mixed treatment had increased control over tebuconazole (e.g.: FHB severity, test weight, TKW), but was not significantly different from metconazole.
Barley: Fungicide Efficacies for Managing Fusarium Head Blight
Yearly FHB index mean results from the nontreated control treatments were similar across years (e.g., 2003, 35.7% and 2004, 37.4%), while DON grain concentration means for the nontreated treatment were slightly greater during 2004 (e.g., 2003, 15.0 ppm and 2004, 18.6 ppm). Single test year results for 2004 are published (6).
Interactions for ‘year × treatment’ were not significant for DON, protein, or yield (Table 3). Affects of fungicide ‘treatment’ were not significant at P < 0.05, while ‘year’ affects were significant for protein and DON, but not for yield (Table 3).
Fungicide application did not significantly increase or decrease grain protein, DON concentration, or yield compared with the nontreated control treatment. While numerical trends are similar to those reported for spring wheat, treatment differences are not significant.
Table 3. Spring barley: Effect of fungicides, averaged over two years, on kernel quality and grain production following inoculation with Fusarium graminearum.
x Each fungicide treatment included Induce, a nonionic surfactant, at 0.125%.
y Column abbreviation: DON = deoxynivalenol.
z Treatment data in columns are not significantly different at P = 0.1.
Disease Management Implications
Tebuconazole is routinely recommended by upper Midwest extension plant pathologists for use on small grains to manage FHB (3). Application of tebuconazole at the early flowering growth stage (Feekes 10.51 growth stage) results in greater disease management compared with propiconazole, the other triazole product currently available for use against FHB (data not shown). Propiconazole (e.g., Tilt) is registered via a Section 3 for application on wheat up through full head emergence (Feekes 10.5 growth stage) an application timing too early to apply fungicide to susceptible floret tissues (2). Both of the experimental fungicide products (e.g., metconazole, tebuconazole + prothioconazole) demonstrated increased control of FHB in hard red spring wheat when compared with tebuconazole. Increased disease management by these products is promising for hard red spring wheat producers in that fungicides with greater FHB management efficacy may be available for use in the near future. Chemical companies are working with the EPA to obtain product registrations for use of their experimental products against FHB. A decision by the Agency is expected during 2007.
Used alone, tested fungicides offer little hope for managing FHB of barley in locations with moderate to severe disease epidemics. Effective disease management on barley remains elusive in production areas with weather events that promote F. graminearum infection and disease development. In the future, a combination of increasingly resistant barley cultivars with improved fungicides may aid in reducing crop losses.
This research was supported, in part, by the US Wheat and Barley Scab Initiative, University of Minnesota Department of Plant Pathology Mycotoxin Laboratory, the Northwest Research and Outreach Center, Bayer CropScience, and Valent USA. The authors thank Drs. Marcia McMullen and Carlyle Holen for their critical reviews of the manuscript.
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