Nathan Kleczewski, Extension Specialist – Plant Pathology; nkleczew@udel.edu
Over the past 1-2 weeks several growers have asked about the black/brown spots they are seeing on their corn stalks (Figure 1). In many instances these spots may be a result of Purple leaf sheath or Physoderma brown spot. In both cases, the black spots do not affect the stalk. Check this out for yourself by removing a sheath with brown spots. The discoloration is limited to the inside of the leaf sheath and the stalk should be healthy.
Purple leaf sheath develops when weak bacterial or fungal parasites grow underneath the leaf sheath. Here the microbes grow on pollen and other particulate matter lodged between the stalk and the leaf sheath. Eventually they grow into the leaf sheath, resulting in a purple/brown/black spot. Lesions are darker on the inside of the leaf sheath and this should make sense because this is where infection occurs. Insect damage may contribute to occurrence of purple leaf sheath.
Figure 1. Brown spots on corn stalks commonly seen in Delaware corn fields this year.
Physoderma Brown Spot is caused by Physoderma maydis, a fungal like organism. Unlike purple leaf sheath, Physoderma infection results in brown to black “pinhead” spots on leaf midribs and leaf sheaths (Figure 2). Small, oblong, yellow spots may occur on the leaf blade (Figure 3). The organism overwinters in infected tissue and infects corn in the whorl under warm, wet conditions. Because of this, Physoderma lesions often occur as bands of disease, not independent spots as in Purple leaf sheath.
Figure 2. Close up of pin head black/purple spots caused by Physoderma maydis.
Photo: Clemson University –USDA Cooperative Extension Slide Series, Bugwood.org
Figure 3. Symptoms of Physoderma maydis on the leaf.
Photo: Clemson University –USDA Cooperative Extension Slide Series, Bugwood.org
A third spot you may come across looks different than Purple leaf sheath and Physoderma. These spots are large, oval, tan to gray, and often have a black border. These spots are likely caused by Gray leaf spot. Gray leaf spot lesions on leaf sheaths are not rectangular as they appear on foliage because leaf sheaths are more succulent, so the veins do not impede fungal growth. The presence of Gray leaf spot lesions on the sheaths should not cause any direct issues with stalk health.
FAQs
The black tar spots form after the flecking or yellowing. These spots are the fungal structures called stromata, which are embedded in the plant tissue. They are elongated, raised, and cannot be removed by rubbing them.
How to treat black spots on corn stalks? ›
In most instances, a fungicide application between the VT growth stage (tassel emergence) and R2 growth stage (blister) is the most effective for controlling tar spot. Furthermore, a mixed-mode-of-action fungicide product is often more effective than a single-mode-of-action product.
What is the black mold on corn stalks? ›
The black mold is saprophytic fungi — microorganisms that feed on dead plant material. The wet weather over the weekend followed by warm, humid weather and morning dews have favored growth of these organisms. They are not known to produce toxins, and the harvested grain should look relatively clean.
What is the best fungicide for tar spot in corn? ›
What is the best fungicide for Tar Spot? If conditions are favorable for Tar Spot development early in the season, consider a twopass fungicide program using Trivapro® or Miravis® Neo fungicide at the V4-V8 corn growth stage and the VT/R1 growth stage.
What are the brown spots on corn stalks? ›
Physoderma brown spot (PBS) and physoderma stalk rot (PSR) are fungal diseases caused by the Physoderma maydis pathogen. PBS was not previously considered an economically important disease in the Midwest.
Can you eat corn with black spots? ›
Do not use corn with obvious mold or rot on the corn itself. If the edible portion of the corn is slimy or the majority is black or molded, throw it away.
Are black spots on corn bad? ›
Over the past 1-2 weeks several growers have asked about the black/brown spots they are seeing on their corn stalks (Figure 1). In many instances these spots may be a result of Purple leaf sheath or Physoderma brown spot. In both cases, the black spots do not affect the stalk.
What is the black stuff on my corn? ›
Growth of fungi feeding on dead/decaying tissue and their black spores on corn husks (a) (and other plant parts) may give it a dark, dusty appearance, especially during harvest. The ear itself is usually unaffected by these fungi (b).
Is corn mold toxic? ›
Aflatoxin is a toxin produced by two fungi that can cause cancer. They typically grow near food crops and enter the corn through pollen tubes or through damage caused by insects. Aflatoxins are the most prevalent natural liver carcinogen. Chronic levels of exposure can hinder child growth and nutrition, the study said.
What is corn stalk rot? ›
Stalk rots leave stalks weak and unable to support the weight of the ear. Yield losses occur when stalk and pith. tissue degrade below the main ear, which. leaves the stalk brittle and prone to. lodging close to harvest (Figure 1).
Tar spot pathogens toxins that can hurt your cattle, etc.
-Many plant pathogens (e.g. bacteria, fungi) produce toxins that help the pathogen trick plant defense responses or kill plant tissues. This does not mean that the toxin has an effect on humans, cattle, swine, etc.
How do you get rid of tar spot fungus? ›
When infected leaves drop, they should be removed and disposed of immediately to reduce the number of fungal spores that can spread to other trees. Raking leaves is traditionally a fall activity but Maple Tar Spot management requires summer leaf raking in synch with the fungus's damage and your tree's leaf drop.
When should you spray for a tar spot? ›
Be ready to spray between the VT and R3 growth stages if you plan to use just one fungicide application and you are seeing tar spot increase. If you spray between the V8 and VT growth stages, be ready to monitor the smartphone apps and do more scouting as you might have to pull the trigger again later in the season.
What does corn fungus look like? ›
What is huitlacoche? Huitlacoche is a fungal disease caused by the fungus Ustilago maydis which affects certain variations of corn plants. It grows on the ears, surrounding and ultimately consuming the kernels, and looks similar to pebbles. The outside is a bluish grey, but the inside is very dark, almost black.
Why does my corn stalk plant have brown spots on the leaves? ›
Banish brown spots 🍂 from your Cornstalk Dracaena and restore its lush, green glory with these expert tips! Over/underwatering and light/heat stress cause brown spots on Cornstalk Dracaena. Pests contribute to spotting; control with insecticidal soap or neem oil.
What does corn blight look like? ›
Symptoms. Typical symptoms of northern corn leaf blight are canoe-shaped lesions 1 inch to 6 inches long. The lesions are initially bordered by gray-green margins. They eventually turn tan colored and may contain dark areas of fungal sporulation.
How do you control corn stalk rot? ›
Minimize stress on plants: Common stresses that lead to stalk rot include; high nitrogen, low potassium fertility, high moisture in the mid to late season after a dry early season, moisture stress early in the season and during grain fill, high leaf disease incidence.
When to spray for a tar spot? ›
Be ready to spray between the VT and R3 growth stages if you plan to use just one fungicide application and you are seeing tar spot increase. If you spray between the V8 and VT growth stages, be ready to monitor the smartphone apps and do more scouting as you might have to pull the trigger again later in the season.
How do you treat maize stalk rot? ›
Chlorination of irrigation water or soil drenching with bleaching powder (33% chlorin @ 10 kg/ha) at pre flowering stage is recommended. Formulations containing copper oxychloride can also be effectively applied against the disease.
Figure 1. Brown spots on corn stalks commonly seen in Delaware corn fields this year.
Figure 2. Close up of pin head black/purple spots caused by Physoderma maydis.
Figure 3. Symptoms of Physoderma maydis on the leaf.