G1998

Common Root Rot and Fusarium Foot Rot of Wheat

Common root rot and Fusarium foot rot are fungal diseases common in dryland winter wheat and in no-till and continuous cropping systems.


Stephen N. Wegulo, Extension Plant Pathologist
Robert N. Klein, Extension Cropping Specialist


Cause and Occurrence

Common root rot is caused by the fungus Bipolaris sorokiniana. Fusarium foot rot, also known as dryland foot rot, is caused by fungi in the genus Fusarium. These diseases are most common in dryland winter wheat and in no-till and continuous wheat cropping systems. The most common Fusarium species causing foot rot are Fusarium graminearum and F. culmorum. These fungi are abundant and occur in the soil and on cereals and other grass hosts, and some literature sources refer to an interrelated disease complex involving both fungi known as root and crown rot. Infection of wheat heads results in infection or contamination of grain. If such grain is used as seed, seedling blights occur. The fungi also cause leaf spots and/or blotches. In winter wheat, the diseases caused by these fungi occur throughout the growing season.

Symptoms

Symptoms of common root rot include dark brown to black lesions on roots, subcrown internodes, and stem bases. Lesions may coalesce, forming large areas of dead tissue in the crown. Discoloration of the subcrown internode (Figure 1) is diagnostic of common root rot. Infected plants may be stunted and/or chlorotic and occur randomly or may be seen in irregular patches in the field (Figure 2). Primary or secondary roots may appear brown or blackened.

The most common symptom of Fusarium foot rot is a dark brown lesion around the node of mature plants. In dry areas, the whole stem base may become girdled by a dark brown lesion (Figure 3). A cottony pink mycelium may appear on affected stem bases and is diagnostic of Fusarium foot rot. If disease is severe, plants may mature early, produce shriveled grain, have white heads which may be void of kernels, and appear bronze or bleached or die prematurely. Occasionally one or more tillers on a plant or usually entire plants may die. Scattered pockets of dead and dying plants (Figure 2) may be seen in affected wheat fields. Poor tillering and yellowing of plants (Figure 4) may occur.

Figure 1. Common root rot. Note the discoloration on the subcrown internodes (arrows).
  Figure 2. Scattered pockets of dead and dying plants is a symptom of common root rot and/or Fusarium foot rot.
Figure 1. Common root rot. Note the discoloration on the subcrown internodes (arrows).   Figure 2. Scattered pockets of dead and dying plants is a symptom of common root rot and/or Fusarium foot rot.
     
Figure 3. Fusarium foot rot on a wheat stem base. Note the dark brown discoloration (arrow).
  Figure 4. Yellowing caused by common root rot and/or Fusarium foot rot.
Figure 3. Fusarium foot rot on a wheat stem base. Note the dark brown discoloration (arrow).   Figure 4. Yellowing caused by common root rot and/or Fusarium foot rot.

Disease Cycle

B. sorokiniana overwinters mainly as mycelium in infested host debris and as conidia (asexual spores) in the soil. Mycelium (pl. mycelia) consists of strands of interwoven, largely microscopic, tubular hyphae (filaments) that make up the vegetative body of a fungus. Fusarium spp. overwinter as perithecia (sexual fruiting structures) and chlamydospores (thick- or double-walled asexual spores) in host debris. Initial infections occur on coleoptiles, subcrown internodes, and primary and secondary roots. Only these initial infections are responsible for root and foot rotting during the growing season. If infections caused by B. sorokiniana progress above the soil line, secondary conidia are produced and dispersed by wind. They land and initiate lesions on leaves and tillers, causing a disease known as spot blotch, characterized by distinct, elongate brown-black lesions that are most frequent on lower leaves and most noticeable after heading. During wet weather, Fusarium spp. also can cause ash-colored or brown lesions on leaves.

Favorable Environmental Conditions

Common root rot and Fusarium foot rot are favored by drought and intermediate to warm temperatures. Stress caused by dry seedbeds, loose seedbeds, wind, freezing, or damage from Hessian flies also predisposes wheat plants to the two diseases. Disease severity is higher in no-till and continuous wheat cropping systems. In contrast to common root rot and Fusarium foot rot, which are favored by dry conditions, take-all, a disease which also affects roots, is favored by wet and poorly drained soils.

Cultural Management

 

Figure 5. Suggested seeding dates for winter wheat in Nebraska.
Figure 5. Suggested seeding dates for winter wheat in Nebraska.

 

Management with Seed Treatment Fungicides

Seed treatment fungicides (Table I) provide an early window of protection in the fall against common root rot and seedling blights caused by Fusarium spp. When selecting a seed treatment product, pick one that has activity against common bunt and loose smut as well as common root rot and Fusarium spp. Uniformly coat the seed when applying the seed treatment product. It is best to have the seed treatment applied with commercial seed treating equipment. For drill box application, fill the drill box one-third full of seed, sprinkle one-third of the fungicide over the seed and mix with a paint paddle. Repeat until the proper amount of fungicide has been added and mixed. Read and follow all label directions for mixing and application.

Table I. A partial list of wheat seed treatment fungicides1 for control of seed- and soilborne fungal diseases
Fungicide Trade Name2 Active Ingredient Rate per 100 lbs
Allegiance® Dry metalaxyl 1.5-2.0 oz
Allegiance®-FL metalaxyl 0.75 fl oz
Allegiance® LS metalaxyl 1.2 fl oz
Apron XL® LS mefenoxam 0.32-0.64 fl oz
Captan 400 captan 1.5-4.0 fl oz
Captan 400-C captan 1.5-4.0 fl oz
Charter® triticonazole 3.1 fl oz
Charter® PB triticonazole + thiram 5.5 fl oz
CruiserMaxx® thiamethoxam + mefenoxam + difenoconazole 5.0 fl oz
Dithane® DF Rainshield™ mancozeb 2.3-3.5 fl oz
Dithane™ M45 mancozeb 2.2-3.3 fl oz
Dividend® difenoconazole 0.5-1.0 fl oz
Dividend Extreme® difenoconazole + mefenoxam 1.0 fl oz
Dividend® XL difenoconazole + mefenoxam 1.0-2.0 fl oz
Dividend® XL RTA difenoconazole + mefenoxam 2.5 fl oz
Dynasty® azoxystrobin 0.153-0.382 fl oz
Grain Guard® mancozeb 2.0 oz per bushel
Incentive™ RTA® difenoconazole + mefenoxam 2.5-10.0 fl oz
LSP thiabendazole 2.0-4.0 fl oz
Manex® maneb 6.5-5.2 fl oz
ManKocide® mancozeb + copper hydroxide 4.0 fl oz
Manzate® Flowable mancozeb 3.5-5.2 fl oz
Manzate® Pro-Stick™ mancozeb 2.2-3.3 fl oz
Maxim® 4FS fludioxonil 0.08-0.16 fl oz
Maxim® XL fludioxonil + mefenoxam 0.167-0.334 fl oz
Penncozeb® mancozeb 2.3-3.5 fl oz
Prevail® carboxin + PCNB + metalaxyl 1.5-3.0 fl oz
Proceed™ tebuconazole + metalaxyl + prothioconazole 5.0-7.5 fl oz
Raxil® MD tebuconazole + metalaxyl 5.0-6.5 fl oz
Raxil® MD Extra tebuconazole + metalaxyl + imazalil 5.0 fl oz
Raxil® MD W imidacloprid + tebuconazole + metalaxyl 5.0 fl oz
Raxil®-Thiram tebuconazole + thiram 3.5-4.6 fl oz
Raxil® XT Wettable Powder tebuconazole + metalaxyl 0.16-0.20 oz
RTU-Vitavax-Thiram carboxin + thiram 5.0-6.8 fl oz
Vitavax-200 carboxin 3.0-4.0 fl oz
Vitavax®-34 carboxin 2.0-3.0 oz
1Read the label to ensure the fungicide has activity against the target disease/s.
2Fungicides 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.

Acknowledgments

The authors would like to recognize the contributions of John E. Watkins, Extension Plant Pathologist, the original author of the material presented in this publication.

This publication has been peer reviewed.

Disclaimer

Reference to commercial products or trade names is made with the understanding that no discrimination is intended of those not mentioned and no endorsement by University of Nebraska–Lincoln Extension is implied for those mentioned.

 


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