Terry Gregoire, Extension Area Cropping System Specialist, Devils Lake, ND

Marcia McMullen, Extension Plant Pathologist Fargo. ND

John Lukach, Superintendent Langdon Research and Extension Center Langdon, ND

Fusarium head blight has over the years caused billions of dollars in damage to small grain crops in the U.S. and Canada. Genetic resistance is a few years away and cultural control methods of rotation , residue management and choosing tolerant varieties will not prevent disease occurrence. Fungicide use has been shown to significantly reduce fusarium infection when weather conditions are favorable to disease development. Fungicides have shown effectiveness in lab and greenhouse and field situations but fusarium control is often disappointing. Much research has been done since 1993 to improve the effectiveness of fungicides. New fungicides have been labeled for heading application and application techniques have examined in detail. Application parameters studied have included the following variables for ground application of fungicides.

A. Application timing including split application

B. Spray application angle

C. Spray pressure: 30 psi to 90 psi in 10 psi increments.

D. Spray nozzles: Various nozzles studied. Generally smaller gallonage nozzles have better coverage than nozzles providing coarse sprays.

E. Gallons of water per acre (gpa); 9 to 54 gpa.

F. Effects of dew

H. Adjuvants

Many experiments have shown that the flowering stage is the optimum time to apply fungicides to wheat (fig.1). Application timing for barley is at about 50% head emergence.( Figure 2 ) A timing-of-inoculation study showed that head scab did not develop substantially when barley was inoculated when awns were just showing but became severe when fully emerged heads were inoculated. Fungicide application also was more effective when the fungicide was applied before inoculation than after inoculation. These results indicate that application of a fungicide should be in early head emergence or very soon after head emergence, when environment is favorable for the disease and when there is reasonable chance to get fungicide on the emerging head.

Split application of fungicide applied during flowering appears to be most effective for reducing scab effects, however, most control is provided with a single application at flowering time. Treatments before heading or after flowering do not provide any additional benefits compared to a single mid flowering application. (Figure 3)

Spray application angle, Pressures, Nozzles, GPA

Studies among a team of researchers in North Dakota has shown that fungicide treatments are most effective if sprays are directed at an angle toward the wheat and barley heads, rather than directed straight down (Figure 4).

Single nozzles oriented at an angle to the grain improves coverage compared to straight down nozzle orientation but only one side of the head is covered well. Using a twin nozzle arrangement (Figure 5) improves uniformity of coverage. Hard red spring wheat, Durum wheat and Barley differ in coverage with different nozzle arrangements. Although the TwinJet TJ8002 nozzle costs less than the forward/backward arrangements, this nozzle generally provided less head coverage as compared to the forward/backward orientations of the XR8001 flat fans or the forward/backward oriented TD01s. For the XR8001 nozzles, the best coverage occurred at 30-40 psi, or at 80-90 psi at 18 gpa, and lowest head coverage occurred at 50-60 psi at 9 gpa. TD01 nozzles performed optimally at 60 psi at 18 gpa in these tests.

Durum wheat — Increased water volume (Figure 6) improved head coverage of both the XR8001 and the TD01 nozzles on Munich durum. The XR8001 with 18gpa at 40 psi provided the best percent head coverage in this trial. For Munich durum, increased water volume was essential for improved head coverage and disease control. Head coverage increased steadily with increased gpa, but disease severity decreased only up to the 36 gpa volume. The percent head coverage on barley was consistently better with the forward/backward XR8001 flat fans than the forward/backward TD01 nozzles at both 9 and 18 gpa and across psi's, with 30-40 psi giving the best coverage. Increased gpa also improved head coverage, but in an inoculation experiment, increased gpa only slightly reduced disease severity.

Effect of Dew

The volume of water present on a grain head covered by dew appears, by visually estimate, to be many times greater than the water applied during a fungicide application. The potential to manage the presence of dew to increase spike coverage or uptake of fungicide on the head offers small grain producers a technique to increase the efficacy of fungicides. Spray solution volume and adjuvant are important parts of fungicide application techniques which producers can easily adjust during the day to accommodate the environmental conditions at time of application.

Five unpublished experiments in ND have included dew as a variable. Two experiments on barley to evaluate dew effect on FHB control were conducted by J. Pederson in 1998. Head coverage by fungicide and dye solution increased from 8 to 21% when spraying dew-covered heads compared to dry heads later in the day. Not enough FHB occurred for evaluation. The second experiment had head coverage by fungicide and dye of 5.8 and 1.4% for dry and rain wet heads, respectively. FHB levels were low with no difference detected. Field severity of FHB on durum was reduced from 3.4% on dew-covered heads in the morning to 1.3% when spraying dry heads in the afternoon, T. Gregoire 1998. Dew effect in another trial was non-significant for FHB head severity on durum, T. Gregoire 2000. A greenhouse study found no significant differences in FHB field severity between fungicide applied to dripping wet heads and dry heads, M. McMullen 2001. FHB levels, field severity, when using 0.06% v/v Induce non-ionic surfactant were 3.5 and 1.5% for wet and dry heads, respectively, compared to levels with 0.125% v/v Induce of 1.1 and 1.3% for wet and dry heads, respectively.

Trends from trials with dew treatments indicate the spraying of fungicide in very wet conditions may reduce efficacy. Measured effects of fungicide application in light morning dew, mid-day and evening conditions were small and variable between experiments. Time-of-day for fungicide application appears to be a minor factor for crop producers. Use of recommended adjuvant rates and high spray solution volumes when dew is present was supported by trends in this work.

Adjuvants

Tests with Folicur and Tilt fungicides indicated that the addition of an appropriate adjuvant generally increased head coverage and decreased fusarium field severity. .