Corn stalk rots can cause yield losses through premature plant death, which leads to reduced grain fill, plant lodging which results in harvest problems, and lodged plants may develop ear molds if the ears touch the soil. Scouting for corn stalk rots may help to determine the type and extent of stalk rots meanwhile, this information can be used in future disease management decisions. For instance, plants infected with Goss’s wilt may die and may look like plants killed by stalk rots (Figure 1).
Nothing can be done about stalk rots affecting corn at this time, but changes can be made for the next growing season. Scouting may also help determine which fields need to be harvested early before heavy lodging occurs in those fields which have corn plants affected with stalk rots.
Figure 1. Corn plants killed by Goss’s wilt. Credit: E. Byamukama
Scouting for stalk rots can be done by using a push method. The push method is performed on 10 corn stalks with a minimum of at least five random stops in the field (in this case a minimum of 50 corn stalks would be push tested). A push method is accomplished by gently pushing the corn stalk to an angle about 45o. Corn stalks with rot will crumple at the first or second node above the soil or may fail to regain the erect position. Fields with 10% or more incidence of stalk rot should be harvested early.
Causes & Symptoms
Several pathogens cause stalk rots in corn but the most common stalk rots are caused by Gibberella zeae, Fusarium spp, and Colletotricum graminocola (this pathogen also causes Anthracnose leaf blight). Gibberella stalk rot is characterized by reddish discoloration which can be noticed when the infected stalk is split near the soil surface (Figure 2). Stalks with advanced symptoms may develop small black perithecia around the internode. Anthracnose stalk rot is recognized by a shiny black color on the outer surface of the stalk when the leaf sheath is peeled off (Figure 3). When split, stalks infected with anthracnose stalk rot, reveal the discolored pith. Fusarium stalk rot is not easy to diagnose but corn stalks with disintegrated pith (Figure 4) and without obvious discoloration on the stalk may indicate Fusarium stalk rot.
|Fig. 2. Corn stalk infected with Gibberella zea. Notice the pink discoloration of the pith, the diagnostic sign of the pathogen.
Credit: E. Byamukama
|Fig. 3. Shiny black spots on corn stalk caused by Anthracnose stalk rot.
Credit: Alison Robertson, ISU
Stalk rot pathogens survive in infected crop residues making the corn on corn rotation more of a risk for stalk rot development versus rotated corn. Therefore, the initial stalk rot management recommendation is crop rotation. Another effective stalk rot management strategy is planting resistant hybrids. Fields with a history of stalk rot and lodging should plant corn hybrids with resistance to stalk rots. Other good agronomic practices like fertility management, appropriate plant population per acre, and improved drainage may reduce chances of stalk rot development.
Figure 4. A healthy corn stalk (left) contrasted with a Fusarium stalk rot (right).
Credit: E. Byamukama