Northern Corn Leaf Blight, Eyespot And Holcus Spot Appearing In Corn

 

Corn is mainly between VT (tasseling) and R1 (first silk). This is when we start to see fungal disease development. Recently scouted corn fields contained northern corn leaf blight, eyespot, Holcus spot, common rust, and common smut at very low incidence and severity.

 

 

Northern corn leaf blight (NCLB), caused by Exserohilum turcium, forms tan elliptical or cigar-shaped lesions that are parallel to the leaf margins (Figure 1). The NCBL pathogen overwinters on leaf debris and spread is through rain splash, but the spores can also be carried long distances by wind. Warm, humid weather and at least 6 hours of leaf wetness are ideal for infection. NCLB can reduce yield under favorable weather conditions. There have been reports of moderate levels of NCBL in Nebraska and Iowa this growing season. If lesions are seen on leaves below ear leaf at tasseling, fungicide application may be justified especially for no-till corn on corn. A list of fungicides that are effective against NCLB is maintained by the Corn Diseases Working Group.

 

 

 

 

 

Eyespot is caused by a fungal pathogen (Kabatiella zeae). This disease is characterized by translucent, circular to oval lesions with a yellow halo (Figure 2). The eyespot pathogen overwinters in crop debris and spores are disseminated by rain splashing to nearby plants. Eyespot is favored by cool, humid weather and is most common in no-till corn on corn fields. For fields with the history of eyespot, selecting a resistant hybrid, using tillage, and crop rotation will reduce the disease risk.

 

 

 

 

 

Holcus spot is caused by the bacteria Pseudomonas syringae pv. syringae. This disease causes round to elliptical spots that usually appear towards the tips of lower leaves (Figure 4.). The lesions start as dark green and water soaked but later become creamy white to tan. Older lesions may turn brown with a reddish brown margin. The holcus spot bacteria overwinters on crop residue and enters the plant through the stomata (natural openings in the leaf). Warm, rainy and windy weather (which we have had in many parts of the state) encourage infection. Holcus spot is usually not severe but for fields with a history of this disease, rotation and tillage may reduce the inoculum.

 

 

 

 

 

Common rust, caused by Puccinia sorghi, can be found in almost every corn field (Figure 4). However this disease rarely causes significant yield losses. The rust spores are blown from southern states and can infect corn as early as V6 growth stage. Field edges may have corn plants covered with rust pustules when corn is around R5 (dent) growth stage. Cultural practices like crop rotation or residue management are not effective, but most corn hybrids have general resistance to common rust.

 

 

 

 

 

Common smut, caused by the fungus Ustilago maydis, can be found in corn fields on plants usually injured by insects, farm machinery or hail. The galls contain millions of spores (teliospores) that overwinter in the soil and on crop debris (Figure 5). Spores germinate with moisture and when air temperatures are between 50-95° F. They can infect any part of the corn plant, and common smut is most severe when young, actively growing plant tissues are wounded.