Occurrence: Occurs in all wheat-growing areas. Seed and soilborne, windborne.
Key symptoms:
· Kernels in heads of affected wheat plants are replaced with grayish-brown sori that produce a fishy odor; the outer hull of infected wheat kernels may remain intact ("bunt balls").
· Teliospores contain trimethylamine, a volatile, malodorous ‘fishy’ smelling chemical that is the basis for the term "stinking smut". Trimethylamine production varies among the different strains of this fungus.
· The pericarp (fragile outer covering) of infected wheat kernels remains intact until the infested field is harvested, at which time the pericarp ruptures, and powdery spores are released. Spores contaminate healthy seed at this time.
· Common bunt spore clouds are flammable and can combust during threshing.
· Plants infected by common bunt fungi may be stunted, but generally appear to be healthy until heads emerge.
· Diseased heads are slender and stay green longer than healthy heads, appear ‘greasy’.
· The glumes of infected heads spread apart.
· Formerly common, now controlled with seed certification
programs and seed treatments.
Pathogen information:
· Teliospores persist for 10 years or more on the surface of seeds and in the soil, and spores are wind dispersed.
· Spores germinate in response to moisture, producing infectious hyphae that penetrate germinating wheat seeds before seedling emergence.
· The pathogen grows within the host and eventually invades the head and developing ovaries, replacing host tissue with fungus.
· Reduces both grain yield and quality.
· The pathogen also infects rye (Secale cereale), triticale (Triticale hexaploide, Triticum secale or Triticosecale spp.), barley (Hordeum spp.) and grassy weeds including goat grass (Aegilops spp.), ryegrass (Lolium spp.), wild rye (Elymus spp.), and wheatgrass (Agropyron spp.).
· Because the pathogen requires cool moist soil conditions, the disease is generally less frequent and less damaging on spring-sown wheat than on fall-sown wheat.
· Moisture and cool soil temperature (40 to 60ºF) favor spore germination and growth of infectious hyphae that penetrate seed before seedling emergence.
Management Approaches:
Cultural management practices:
· Cultivar resistance
· Clean seed
· Winter
wheat sown early in autumn, when soil temperatures are still warm (>15°C /
~60°F) may escape infection, but this is not advised because it can increase
some other disease and insect problems.
See seed treatment list below; most common seed treatments except imazalil are effective against these organisms
|
Pesticide |
Product per 100 lbs seed |
Remarks |
|
Carboxin: various formulations and mixtures available |
||
|
Carboxin + Thiram |
3-4 fl oz |
|
|
RTU-Vitavax-Extra |
5 fl oz |
Wheat |
|
RTU-Vitavax-Thiram |
5-6.8 fl oz |
|
|
Difenoconazole |
||
|
Dividend Extreme |
1-4 fl oz |
55 day PHI |
|
Dividend XL |
1-2 fl oz |
55 day PHI |
|
Dividend XL RTA |
2.5 fl oz |
55 day PHI |
|
Incentive RTA |
2.5-10 fl oz |
Wheat; sec 24(c) barley ND, MN, MT, CO; 55 day
PHI |
|
Mancozeb: not all formulations are listed |
||
|
Manzate 75DF |
2.2-3.3 oz |
|
|
Tebuconazole: various formulations and mixtures available; not reg.
for rye |
||
|
Raxil-Thiram Flowable |
3.5-4.6 fl oz |
31 day PHI |
|
Raxil MD |
5-6.5 fl oz |
31 day PHI |
|
Raxil MD-W |
5 fl oz |
45 day PHI |
|
Raxil MD Extra |
5 fl oz |
42 day PHI |
|
Raxil XT |
0.16-0.20 oz |
31 day PHI |
|
Triticonazole |
||
|
Charter |
3.1 fl oz |
Wheat and barley |
|
Charter PB |
5.5 fl oz |
Wheat and barley |
|
Thiram |
||
|
42S-Thiram |
2 fl oz |
|
|
Thiram 50WP |
3.3-4.1 oz |
|
|
Triadimenol |
||
|
Baytan 30 |
0.75-1.5 fl oz |
|
|
Azoxystrobin |
||
|
Dynasty |
0.153-0.382 fl oz |
|
|
Protege |
0.153-.382 fl oz |
|
|
Thiabendazole |
|
|
|
LSP |
4-6 fl oz |
|
|
The information herein is supplied with the understanding
that no discrimination is intended and that listing of commercial products,
necessary to this guide, implies no endorsement by the authors or the
Extension Services of Nebraska, Colorado, Wyoming, Montana or South Dakota.
Criticism of products or equipment not listed is neither implied nor
intended. Due to constantly changing labels, laws and regulations, the
Extension Services can assume no liability for the suggested use of chemicals
contained herein. Pesticides must be applied legally complying with all label
directions and precautions on the pesticide container and any supplemental
labeling and rules of state and federal pesticide regulatory agencies. State
rules and regulations and special pesticide use allowances may vary from
state to state: contact your State Department of Agriculture for the rules,
regulations and allowances applicable in your state and locality. |
||
Categories: Small grains, Wheat, Triticale, Disease, Common bunt, Covered smut, Stinking smut
Date: 2/6/08