Identification and Management of Anthracnose Leaf and Stalk Rot

There are many diseases a corn producer must be concerned with throughout the growing season. Foliar diseases and stalk rots can appear similar and can manifest themselves in similar ways. It is important to correctly identify the disease before preparing for management. 

Anthracnose can manifest itself as a leaf blight, top dieback, and/or a stalk rot. Seeing the leaf blight phase doesn’t mean the stalk rot phase will develop or vice versa.1 The leaf blight phase can be confused with other similar looking foliar diseases. Anthracnose leaf blight has irregular, water-soaked lesions that have no definitive shape (Figure 1). The lesions typically start at the bottom of the canopy and progress upwards. This is in part due to anthracnose overwintering in corn residue and spreading by splashing water. Keep a closer eye on fields that are corn-on-corn or no-till, as anthracnose can be more common in those settings due to the higher inoculum load.1

Anthracnose leaf blight lesions. Figure 1. Anthracnose leaf blight lesions. Note the irregular pattern to the lesions.

Foliar diseases that might be confused with anthracnose leaf blight are northern corn leaf blight which has long cigar shaped lesions and grey leaf spot which has long squared off lesions that run parallel with the leaf veins. The key thing to note is the irregular water-soaked lesions for anthracnose leaf blight. 

Anthracnose may also manifest itself later in the growing season as a stalk rot just before plants mature. With anthracnose stalk rot, the entire plant usually dies, and several lower nodes may have rotted by the time an issue is noticed. When looking for anthracnose stalk rot look for shiny, black blotches/streaks, or specks on the stalk rind (Figure 2). These symptoms are typically found on the lower internodes. The stalk vascular tissue, or pith, is usually discolored, soft, and shredded. Scouting for any type of stalk rot prior to harvest is very important, especially when one finds anthracnose. These fields should be put at the top of harvest priority to avoid stalk lodging issues.

Anthracnose stalk rot Figure 2. Anthracnose stalk rot. Note the black lesions on the stalk rind and rotted pith.

Sometimes top die-back can be observed in fields that have an anthracnose stalk rot infection. With the top die-back phase of anthracnose, the plant above the ear dies prematurely and the rest of the plant remains green (Figure 3). The top portion of the plant turns brown because the vascular system has been so compromised that water translocation to the top of the plant has been reduced or ceased. Death of the top leaves may also be due to one or more factors that include corn product characteristics, environmental stress, and corn borer damage.2

Anthracnose top die-back Figure 3. Anthracnose top die-back.

There are many other stalk rot diseases that may be mistaken for anthracnose stalk rot. Charcoal rot has small, black, microsclerotia throughout the vascular pith tissue with little visual symptoms on the rind. Fusarium stalk rot has dark brown water-soaked lesions on the rind along with the pith weakening and shredding. With anthracnose stalk rot, the tell-tale larger black lesions on the rind with the accompanying disintegrating pith are diagnostic characteristics. 

When it comes to management there are a few things that one can do to try to manage the onset of anthracnose in their fields. The best recommendation is to plant tolerant or resistant corn products. Choosing a product that is resistant to anthracnose is one of the easiest considerations when choosing seed for the next year. When placing those chosen products for planting, take into consideration crop rotation, residue levels, and previous history with anthracnose. Crop rotation to a non-host crop can help break up the disease cycle.  Labeled fungicides are available for anthracnose leaf blight; however, it is important to take into consideration corn product susceptibility and the amount of inoculum present in corn residue.

Lauren Botine

Sources:

1Wise, K., Mueller, D., Sisson, A., Smith, D., Bradley, C., Robertson, A. 2016. A farmer’s guide to corn diseases. APS Press. St. Paul, MN. Iowa State University.

2Robertson, A. 2019. Top dieback in corn: Is Anthracnose the Cause? Integrated Crop Management. Iowa State University. https://crops.extension.iastate.edu/encyclopedia/top-dieback-corn-anthracnose-cause/.

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