Controlling Wheat Leaf Diseases, FHB: Fungicides Can Make a Difference

Wheat growers today have a number of fungicide products to choose from for disease control.  Over 15 different trade name products are federally registered for wheat today, unlike the early 1990s, when only a few fungicide products were available. The addition of strobilurin fungicides also has brought a new fungicide chemistry to the market. Today’s registrations include:

• Coppers (Champ, Cuprofix, Kocide)
• Mancozebs (Dithane, Manex II,
• Manzate 75, Penncozeb)
• Mancozebs + copper (ManKocide)
• Triazoles
  -- Propiconazoles (Tilt, PropiMax,
• Contend, Bumper)
  -- Tebuconazole (Folicur) A Sec. 18 emergency exemption has allowed use of Folicur by the region’s producers for Fusarium head blight control.  
• Strobilurins
  -- Azoxystrobin (Quadris)
  -- Pyraclostrobin (Headline)
  -- Trifloxystrobin + propiconazole (Stratego)
• Triadimefon (Bayleton)
• Sulfur (Sulfur DF)

Leaf Disease Control
Recent studies through North Dakota State University and the Research Extension Centers compared the efficacy of some of these products for leaf disease control. The products Folicur, Tilt, Stratego, and Headline all performed very similarly in reducing the severity of fungal leaf spots and rust on flag leaves of spring wheat and durum in 2002 (Table 1). All gave excellent control when applied at full heading to early flowering. In one trial (Fargo3) the fungicides were applied at Feekes 10 (late boot).

Product	Rate/acre	*Fargo 1 HRSW	*Fargo 2 HRSW	**Fargo 3 HRSW	*CREC HRSW	*CREC Durum	* Langdon on REC HRSW
	-	---%severity of leaf diseases on flag leaf at soft dough stage-----
Untreated	---	25.5	18.3	18.7	78	73	65
Folicur	4 fl oz/a	7.0	3.5	10.5	37	28	35
Tilt	4 fl oz/a	---	3.3	12.5	35	35	35
Stratego	10 fl oz/a	---	---	8.0	31	25	33
Headline	6 fl oz/a	5.8	---	---	28	26	30

Fusarium head blight (scab) control
Uniform Fusarium head blight (FHB) control trials in 2002 examined the efficacy of Folicur fungicide and two experimental fungicides for control of FHB.  These trials indicated that Folicur fungicide, on average,  reduced field severity of FHB by 60% and increased yield by 7 bu/a in hard red spring wheat and 8 bu/a in durum wheat, with 1 to 1.5 lb/bu test weight increases. Two experimental products, AMS21619 from Bayer CropScience, and BAS505 from BASF performed slightly better than Folicur in these tests.  Trials were located at the Fargo Experiment Station, the Carrington Research Extension Center, the Langdon Research Extension Center, and the North Central Research Extension Center.  Trials were supported by funds from the National Wheat and Barley Scab Initiative.

In separate, industry-sponsored FHB control trials at these locations, Folicur averaged 58.2% reduction in FHB field severity, while Tilt averaged 41.1% reduction in scab field severity. Headline fungicide was also tested in some of these studies, and although its application at flowering often produced a reduction in FHB similar to Folicur and Tilt, Headline also increased DON (vomitoxin) content is some cases, while Folicur and Tilt reduced DON. 

This phenomenon of increasing DON has been observed in previous trials with fungicides containing strobilurins, including Headline, Stratego and Quadris.  Therefore, fungicides containing strobilurins are NOT recommended for flowering time application for FHB control, because of their potential to increase DON.  The triazole fungicides, Folicur and Tilt, are the recommended fungicides for this use.

Full Rate, One time Application vs. Split Rate, Split Timing Application of Folicur for FHB Control
Greenhouse evaluations of split applications of fungicide to control FHB continued this past year at NDSU.  Oxen spring wheat, Munich durum, and Robust barley were included in the tests.  Folicur fungicide treatments were evaluated with one, two or three inoculations of the plants to simulate possible single or multiple infection events in the field.  Single inoculations and fungicide treatments were at flowering (Feekes 10.51) in wheat and at early heading (Feekes 10.5) in barley.  Multiple inoculations were at head half emergence, flowering, and 4 days following flowering; split treatments were applied at Feekes 10.3 and Feekes 10.5 or Feekes 10.51.

Results in spring wheat and durum: Results (Table 2) indicated that two split applications of 2 fl. oz. of Folicur had little advantage over a single application of the full label rate (4 fl. oz.), regardless of whether the single application was tested with a single inoculation or with three inoculations.  The similar control achieved under multiple infections with a split application or a full rate single application at flowering would indicate little economic advantage to using two half-rate applications in wheat.

Results in barley: Multiple inoculation events in barley overwhelmed the single application of Folicur (Table 2, bottom row). Therefore, if multiple infection events occurred following heading in barley, split applications of reduced rates of Folicur may have an advantage over only one application.  The data also indicates that the disease is harder to control in barley than in spring wheat and durum if weather is very favorable for continued infection.

Treatment1	Rate/acre	# Fungicide Applications2	# Fusarium graminearum Inoculations3	% FHB Field Severity 4
				(Oxen)	(Munich)	(Robust)
Untreated	---	---	1	64	45	13
Untreated	---	---	2	88	77	44
Untreated	---	---	3	90	81	75
Folicur	4 fl oz	1	1	5	8	1.4
Folicur	2 fl oz, 2 fl oz	2	2	28	20	12
Folicur	4 fl oz	1	3	22	27	69
1Folicur applied with 0.25% v/v Induce 2Fungicide applications at Feekes 10.3, Feekes 10.5 or 10.51 3Inoculations at Feekes 10.3, Feekes 10.5 or 10.51, 10.54 4Field severity=Incidence (% heads infected) x Head severity (% of head with symptoms) at soft dough.