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
- Disease Cycle
- Favorable Environmental Conditions
- Cultural Management
- Management with Seed Treatment Fungicides
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 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 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.|
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.
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.
- Seed adapted cultivars for the geographic area.
- Seed into a firm, mellow seedbed (loose seedbeds promote disease).
- Maintain a balanced soil fertility (avoid excessive nitrogen fertilization particularly by reducing the amount of fall-applied nitrogen).
- Control weeds in summer fallow land (weeds deplete soil moisture which predisposes plant roots to infection in the fall).
- It is best to use certified, fungicide treated seed (bin-run seed is at higher risk).
- Seed at the recommended date (Figure 5) for your geographic area (early planting or extended, warm fall weather promotes disease).
|Figure 5. Suggested seeding dates for winter wheat in Nebraska.|
- Seed when soil temperature at seed depth is 55°-60°F.
- The above cultural practices recommended for crown and root rot also reduce the risk of winter injury.
- Rotate crops to reduce Fusarium foot rot inoculum (avoid planting wheat following corn or wheat).
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|
|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.
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.
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.
Visit the University of Nebraska–Lincoln Extension Publications Web site for more publications.
Index: Plant Diseases
Issued February 2010