Update on NDSU Studies for Optimizing Fungicide Application for Scab Control

By Marcia McMullen, Jim Jordahl, and Scott Meyer, NDSU Plant Pathology Dept.; John Lukach, Langdon Research Extension Center; Terry Gregoire, Devils Lake Area Office

NDSU researchers have continued to look at methods to improve control of head scab (Fusarium head blight) with fungicides. Included is the evaluation of application techniques for improving fungicide efficacy. Field research in 2000 and greenhouse studies in 2001 have substantiated previous recommended practices and have provided some new information for maximizing efficiency of fungicides used.  The following is a summary of some of the key findings.

Timing of Infection Events and Treatments:  
Accurate timing of fungicide application is critical for success.  In the field, multiple infections may occur if weather is favorable for infection. However, producers most often look for a single application timing to provide good control. 

Conclusion: 
Field studies at Fargo in 2000 reaffirmed that if only a single application of the recommended rate of fungicide is going to be applied, the best timing for maximum reduction in scab severity is at early heading for barley and early flowering for wheat (Table 1).

Table 1. Effect of Timing of Treatment on % Reduction in Scab in Russ Wheat and Robust Barley, Field Studies, Fargo 2000.

Treatment	Feekes Growth State Applies **	% Reduction in Scab *** Russ HRS           Robust Barley
Folicur*	10.30	52.1	59.8
Folicur*	10.51	73.1	54.0
Folicur*	10.54	62.4	48.3
LSD	0.05	19.7	32.2
* Folicur applied once at 4 fl oz/acre + 0.06% Induce with ground sprayer, forward/backward X R8001 nozzles, 18 gpa ** Feekes 10.3 = head half emerged; Feekes 10.51 = early flowering in wheat, early head emergence in barley; Feekes 10.54 = kernel watery ripe *** Multiple infection events may have occured in the fields; range of scab severities were: 6.3 - 23.4% in Russ wheat; 3.4 - 8.7% in Robust barley.

Greenhouse studies in 2001 looked at single full-rate or multiple split-rate fungicide treatments at various growth stages, with either a single fungal inoculation event at flowering or with multiple inoculation events. All inoculations in the greenhouse were followed by a 24-hour period in a mist chamber.

Studies with Munich durum showed that all single or split applications that included a treatment at early flowering significantly reduced scab severity over the untreated check and over a late application at kernel watery ripe stage (Table 2).   Multiple applications did not significantly improve control over a single application at flowering. 

Table 2. Effect ot Timimg of Fungicide Treatment on % Reduction of Scab in Munich Durum, Greenhouse Trial, 2001 Treatment * Rate/Acre Feekes Growth State Growth State Applied G % Reduction in Scab** Folicur 2 fl oz + 2 fl oz 10.3 + 10.51 92.3 Folicur 1 fl oz+ 2 fl oz+ 1 fl oz 10.3+ 10.51+10.54 93.1 Folicur 4 fl oz 10.3 59.1 Folicur 4 fl oz 10.5 75.8 Folicur 4 fl oz 10.51 81.0 Folicur 4 fl oz 10.54 24.7 Folicur 2 fl oz + 2 fl oz 10.5 + 10.51 93.7 Folicur 2 fl oz + 2 fl oz 10.51 + 10.54 81.0 LDS 0.05     40.1 * Folicur applied with 0.06% Induce, forward/backward XR8001 nozzles ** Inoculation only applied at Feekes 10.51; range of scab severities: 2.3 - 36.4%

In a similar study with Grandin wheat (data not shown), single applications at full label rate or multiple, split rate applications of Folicur fungicide significantly reduced disease over the untreated checks, except for single applications at half head emergence or at kernel watery ripe. 

Conclusions from greenhouse studies on wheat:
Multiple applications with split rates of Folicur provided slightly greater reduction in percent scab than did a single application at flowering, but differences among the treatments that included any treatment at early flowering were non-significant. Under weather conditions favoring infection, single fungicide applications done too early (head half emerged) or too late (kernel watery ripe) are not effective.

Adjuvants:
A number of traditional adjuvants and some experimental adjuvants have been tested in combination with Folicur fungicide and Tilt fungicide for control of scab. The results indicate that Folicur performs much better with a non-ionic surfactant than without. The manufacturer of Folicur, Bayer Corp., recommends 0.12% v/v rate of Induce; most of our experiments were done with a 0.06% v/v rate of Induce. NDSU has done only a few tests with the 0.12% v/v rate of Induce, and these tests generally showed a slightly better reduction of scab with the 0.12% v/v rate over the 0.06% rate of Induce. Tilt fungicide also performed better with a non-ionic surfactant (0.06% v/v rate), or a silicone based adjuvant (0.03% v/v). Several experimental adjuvants also looked very good for reducing percent scab.

Conclusion:
Use appropriate adjuvant with Folicur or Tilt to get optimum performance against scab.

Nozzle orientation for ground application:
Field and greenhouse studies reaffirmed that angled sprays directed forward and backward toward the grain head consistently result in the lowest scab severity when fungicides are applied with conventional-type ground sprayers (Table 3). Leaf diseases (data not shown) also were reduced more with the forward/backward orientation of nozzles than forward or backward alone. Conclusion: Angled sprays of fungicide, directed both forward and backward, consistently result in greatest reduction in scab field severity with conventional-type ground sprayers.

Table 3. Nozzle orientation effects of reduction of scab in field and greenhouse.     % Reduction in Scab Field Severity ***     Field 2000, Fargo Greenhouse 2001 Treatment Nozzle ** Orientation Grandin HRSW Robust Barley Grandin HRSW Robust Barley Folicur* F + B 74.4 52.4 95.1 80.3 Foicur * F 62.6 34.4 92.2 67.9 Folicur * B -- 29.5 84.8 54.2 LSD 0.05   11.3 24.6 NS 25.6 * All Folicur treatments at 4 fl oz/acre + 0.06% Induce, applied at early flowering ** XR 8001 nozzles at 30o angle from the horizontal; 19 gpa field; 9 gpa greenhouse *** Range of scab field severities were: Grandin field, 1.3 - 22%; Robust field, 2.8-6.1%; Grandin greenhouse, 1.2 - 24.3%; Robust greenhouse, 6.6 - 33.6%