Dryland Foot Rot

Washington State University Bulletin

SP0004 -- 1993

Diseases of Washington Crops.

Otis C. Maloy and Debra Ann Inglis

Small Grains Home

Cause

Hosts

Symptoms and Signs

Disease Cycle

Control

1997 PNW Pesticide

Recommendations

This disease is also called Fusarium foot and root rot, common foot rot, brown root rot, and crown rot.

Cause
Dryland foot rot is caused primarily by the fungi, Fusarium culmorum and F. graminearum, which in some situations cause other diseases of wheat, such as head blight and scab. Neither F. culmorum nor the form of F. graminearum causing foot rot in the Pacific Northwest have known sexual stages. Both Fusarium species produce sickle-shaped macroconidia and chlamydospores in the macroconidia and/or mycelium. Microconidia are absent.

Hosts
These Fusarium species can invade a wide range of cereals and grasses. They are efficient saprophytes that survive and multiply on many crop residues.

Symptoms and Signs
Foot rot tends to be most severe on ridges and slopes where soils are drier than in low pots and draws. Infected crowns and roots are brown and rotted, and a brown to reddish brown discoloration of the stem may extend up several internodes (Photo 4). Leaf sheaths look normal; so peel these away to see the discolored culm. Water stress during the final stages of plant development promotes premature ripening, and "white heads" result even though adjoining healthy plants still may be green. In the early stages of disease development and under the right conditions, a pinkish crustlike discoloration (the sporulating fungus) may appear inside the leaf sheaths. Later on, split the stem longitudinally to observe pink or red mycelium inside.

Disease Cycle
The pathogens survive as chlamydospores in the soil or in infested plant debris. They are good saprophytes in tissues they previously parasitized, and can multiply rapidly on infested cereal and grass residues. Oats cut green for hay serve as an excellent substrate for sporulation, if the plants were colonized before they were cut. Chlamydospores formed in conidia or mycelium may persist in soil for months. These germinate and produce hyphae, which infect mainly through crown roots and through wounds sustained during crown root emergence. The pathogen then invades internodal tissues.

Moisture is essential for infection, but moisture stress during the late boot phase and heading enhances the disease, hence the name dryland foot and root rot. The disease can be severe in wheat receiving too much fertilizer for the amount of rainfall available, especially in areas receiving less than 16-18 inches per year.

Control
Cultural. Avoid early seeding. This practice promotes large plants that more often become water stressed later on. Establish nitrogen application rates on soil tests for residual nitrogen, and avoid excessive use of nitrogen fertilizer. In a dryland area receiving 10 inches of average annual precipitation, do not apply more than 50-60 pounds of anhydrous ammonia per acre. Clean cultivation discourages development of grass weeds and speeds breakdown of infested crop residues. However in low-to-intermediate rainfall areas, leaving crop residue on the soil surface allows colonization by competing saprophytic fungi which exclude the pathogen. Moisture conserving practices, such as chisel plowing to improve infiltration and to reduce runoff, and establishing a dust or stubble mulch to protect against water loss are beneficial. Crop rotation to nonhost crops and avoiding oats, help limit the buildup of pathogen populations in the soil.

Reference
Inglis, D.A., and R.J. Cook. 1986. The persistence of endoconidial and mycelial chlamydospores of Fusarium culmorum in wheat and wheat field soils of eastern Washington.
Phytopathology 76:1205-1208.