Stalk Quality Concerns Going into Harvest • 9.23.16

Kris Young

Stalk Quality Concerns Going into Harvest

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As combines are making their way into corn fields, growers are noticing less than ideal plant health and intactness.  Stalk lodging is a concern since many of the plants have broken tops and stalks are brown and mushy.  Closer examination shows these plants have been infected with some form of stalk rot.  See guidelines below for information on stalk rot development, identification, scouting and management. 

Stalk Rot 101

Stalk rot typically occurs in a corn plant when some kind of stress disrupts the production of carbohydrate that is needed to fill kernels in the ear.  When the plant is no longer able to produce enough carbohydrate to fulfill kernel demand, it starts to translocate carbohydrate from the roots and stalk to satisfy the kernel demand.  As a result, roots begin to weaken and are not able to fight off root rot pathogens.  Root rot pathogens move up the stalk shutting down water and nutrient flow within the plant.  Root rot becomes stalk rot which leads to stalk cannibalization or death. 

Stalk rot can set in at any time.  We typically notice symptoms just after the R5 stage (dent).  Early symptoms of stalk rot include wilting, change from green to gray color, ear droops downward, ear becomes spongy when twisted and lesions present at the base of the stalk.  Plant eventually turns brown prematurely and the internal stalk pith disintegrates which makes the plant more susceptible to stalk breakage. 

 Likely Causes of Stalk Rot in 2016

·         Early crown and root damage stress during wet and very cool May

·         Nitrogen deficiency due to high N losses during a wet May

·         Heat stress during month of June and again in mid-July

·         Wind/hail damage from storms in June and July

·         Leaf diseases such as gray leaf spot and Southern Rust moving in July and August

·         Anthracnose top dieback expressing itself in late July and August

Stalk Rot Identification

There are many different types of stalk rot.  Weather conditions during the growing season dictate the kind of stalk rot present.  For 2016, anthracnose has been the most common stalk rot followed by diplodia, gibberella and fusarium.    

Anthracnose Stalk Rot

·         Typically starts out as anthracnose top dieback where the top 1/3rd of the plant dies back

·         Stalk lesions appear as shiny black blotches or streaks on the lower stalk

·         Internal stalk tissue may have tan to brown discoloration starting at nodes

·         Favored by extended periods of hot, cloudy and humid conditions

Diplodia Stalk Rot

·         Lower internodes become straw-brown and spongy

·         Stalk lesions appear as tiny, dark fungal specks called pycnidia that form just under the stalk surface near the base of the plant.  Pycnidia specks cannot be easily scraped off surface.

·         White fungal mycelium may appear on the stalk surface

·         Tan to brown internal stalk tissue discoloration

·         Favored by dry and warm conditions early followed by wet weather after silking 

Gibberella Stalk Rot

·         Black specks on lower stalks.  Larger than pycnidia specks and can be easily scraped on stalk surface.

·         Internal stalk tissue has a pink to red discoloration

·         Favored by dry and warm conditions early followed by wet weather after silking 

Fusarium Stalk Rot

·         White, fuzzy growth at nodes on lower stalk

·         Internal stalk tissue has a whitish-pink to salmon discoloration

·         Favored by dry and warm conditions early followed by wet weather after silking 

Scouting for Stalk Rot

By doing a quick survey in a field, a grower can determine the amount of stalk damage that is present to aid in harvest timing decisions.  By walking through the field and “pinching” the lower stalk, a grower can determine the strength of the stalks.  If the stalk crushes easily by hand, stalk rot has infected the plant.  Another good method is a simple “push” test which is done by pushing the stalks to a 45⁰ angle.  Stalks that easily kink over or fall to the ground are infected with stalk rot.  If more than 25% of the stalks are infected, early harvest should be considered to minimize harvest losses. 

Management of Stalk Rots

Nothing can be done to treat or prevent stalk rots in corn.  However, there are some general practices that can be implemented to help reduce the onset of stalk rot development.

·         Select hybrids with good resistance to stalk rot pathogens and/or high ratings for stalk strength and stay green

·         Use a plant population that matches up with the hybrid and the growing conditions.  Over-populating a hybrid with limited resources (water and nutrients) can stress a hybrid and make it susceptible to stalk rot pathogens.

·         Match a balanced fertility program with hybrid and growing environment.  For example, consider using side-dress N on fields prone to N loss and on hybrids that respond well to side-dress N.

·         Consider applying foliar fungicides to maintain plant leaf health and increase tolerance to other plant stresses

·         Schedule irrigation to minimize drought stress

A growing season full of weather extremes with warm, wet conditions during grain fill can predispose corn plants to stalk rot pathogens.  Take time to scout each field and identify which ones may develop lodging issues.  Schedule those fields for an early harvest to prevent potential harvest losses.  Have a safe and bountiful harvest!

Resources

1.   http://cropwatch.unl.edu/stalk-and-ear-rot-diseases-developing-early-few-fields

2.  http://crops.extension.iastate.edu/cropnews/2014/09/watch-stalk-and-ear-rots-corn

3.  http://extension.udel.edu/fieldcropdisease/2013/09/12/identification-of-stalk-rots-of-corn/

4.  https://webapp.agron.ksu.edu/agr_social/eu_article.throck?article_id=1119

Image 1

Anthracnose Stalk Rot

Image 2

Diplodia Stalk Rot

Image 3

Gibberella Stalk Rot

Image 4

Fusarium Stalk Rot

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