August 8, 2008

Wet weather during the 2008 growing season favored many wheat diseases. Notable among them were seed-transmitted diseases caused by fungi, including the smuts (Figures 1 and 2).

Wheat grain used as seed this fall should be treated with fungicide to reduce losses from these diseases. If seed is not fungicide-treated, disease losses may increase in 2009 if seed is from areas affected by Fusarium head blight (scab) (Figure 3).

Figure 3. Scabby wheat with kernels infected by the Fusarium head blight (scab) fungus. Severe seedling blight can result if this grain is used as seed and not treated with a fungicide.

Importance of Treating Seed

In addition to controlling seed-transmitted fungal diseases, seed treatments also control many soilborne fungi such as Pythium and Rhizoctonia that cause damping off and root and crown rots. Thus, a good stand establishment and healthy and vigorous seedlings result, which optimizes the chances of obtaining high yields. Seeds treated with systemic fungicides provide additional protection from foliar diseases in the fall.

It is best to buy certified treated seed or use a commercial seed conditioner to clean and treat seed. Seed treated on-farm should be cleaned before treatment. Thorough coverage maximizes effectiveness of the seed treatment.

Seed that is internally infected by pathogens such as the smut and scab fungi should be treated with a systemic fungicide. Contact fungicides will have no effect on fungi that are already inside the seed.

Table I provides a partial list of seed treatment fungicides.

Stephen Wegulo
Extension Plant Pathologist

Table I. Wheat seed treatment fungicides.

Trade Name

Active Ingredient/s

Rate
(fl oz /100 lbs of seed)

Application Method

Fungi/Diseases Controlled

Allegiance -FL

metalaxyl

0.75

water-based slurry

Pythium damping off

Apron XL LS

mefenoxam

0.0425 - 0.085

slurry

Pythium damping off

Baytan 30  For use
only by commercial seed treaters

Triadimenol

0.75 -  1.5

slurry

Smuts, foot rot, take-all, powdery mildew, leaf rust, stripe rust

Captan

captan

1.5 - 4

slurry

Seed and seedling rots, not bunt or smut

Charter

triticonazole

3.1

slurry

Smut, bunt, seedling blights, Fusarium crown and root rot, seed-borne Fusarium

Cruiser Extreme

thiamethoxam
fludioxonil
mefenoxam
azoxystrobin

See labels for Maxim XL, Apron XL, and Dynasty

See labels for Maxim XL, Apron XL, and Dynasty

Broad spectrum

Dividend Extreme

difenoconazole
mefenoxam

1 - 4

slurry

Broad spectrum

Dividend XL RTA

difenoconazole
mefenoxam

2.5 - 10

slurry

Broad spectrum

Dynasty

Azoxystrobin

0.153 - 0.382

slurry

Damping off, bunt

Kodiak biological fungicide

Bacillus subtilis

0.05 - 0.1 oz

slurry

Rhizoctonia, Fusarium

Maxim 4 FS

fludioxonil

0.08 - 0.16

slurry

Fusarium, Rhizoctonia, Helminthosporium, Aspergillus, Penicillium

Maxim XL

fludioxonil
mefenoxam

0.167 - 0.334

slurry

Fusarium, Rhizoctonia, Pythium, Aspergillus, Penicillium, bunt

Raxil MD

tebuconazole
metalaxyl

5 - 6.5

slurry

Broad spectrum

Raxil MD Extra

tebuconazole
metalaxyl
imazalil

5

slurry

Broad spectrum

Raxil MD Extra W

imidacloprid
tebuconazole
metalaxyl
imazalil

5.14

slurry

Broad spectrum, includes the insecticide imidacloprid

Raxil MD_W

imidacloprid
tebuconazole
metalaxyl

5

slurry

Broad spectrum

Raxil-Thiram

tebuconazole
thiram

3.5 - 4.6

slurry

Broad spectrum

Raxil XT

tebuconazole
metalaxyl

0.5 lb pouch/40-50 hundredweights of seed; add 0.5 lb pouch of colorant

slurry

Broad spectrum

42-S Thiram

thiram

2

slurry

Broad spectrum

Vitavax -34

carboxin

2 - 3

slurry

Loose smut, common bunt

RTU-Vitavax-Thiram

carboxin
thiram

5 – 6.8

Commercial seed treatment or pour-on hopper-box application

Broad spectrum

Fungicides listed represent the best information available. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by the University of Nebraska–Lincoln Extension is implied.