Scout For Stalk Rots & Top Dieback In Corn

 

 

 

A number of corn fields are showing top dieback symptoms (Figure 1). Top dieback is when two or more of the topmost corn leaves die prematurely. This can be caused by a number of factors including fungal infection, hybrid (senescence starts from the top leaves), and insect damage. Usually fungal infection is the top culprit. While it is normal to see the top corn leaves dry due to natural senescence around this time of the season, premature death of top leaves before black layer can lead to yield loss.

 

 

Determining whether the top dieback is due to natural senescence or disease can be done by looking at the distribution of affected plants in the field. If all of the plants in the field have the 2-3 top leaves dying, this may be due to natural senescence. However, if random plants in the field have the top leaves dying, this may be due to anthracnose top dieback disease caused by the fungal pathogen, Colletotricum graminicola. Plants infected with anthracnose top dieback have black spots on the stalk that can be seen when the leaf sheath is peeled away (Figure 2). A closer look at the black spots with a hand lens may reveal the survival structures of the fungus.

 

Anthracnose top dieback can be managed through selection of resistant hybrids. Fungicides applied at flowering may help in reducing top dieback. Tillage to bury residue will also reduce the pathogen inoculum.

 

 

 

Another set of corn diseases being seen at this time are the stalk rots. Corn stalk rots are caused by several pathogens but the most common stalk rots are caused by Colletotricum graminocola (anthracnose stalk rot), Fusarium spp. and Gibberella zea. Stalks with anthracnose stalk rot have black spots on the lower nodes (Figure 3). Fusarium stalk rot is not easy to diagnose but usually the plant dies prematurely and may not have black spots (Figure 4). For Gibberella stalk rot, splitting the stem may reveal pinkish discoloration of the pith.

 

 

 

 

Nothing can be done about the stalk rots developing in corn at this time, but management decisions can be made for the next growing season. Scouting corn fields at this time to determine which fields have high stalk rot incidence can inform producers which fields may need early harvesting before heavy lodging can occur.