There’s always something after your corn.

Whether it’s diseases or insects, you can count on an annual, epic struggle to produce an impressive corn crop.

And one enemy is Physoderma maydis.

Although this fungus doesn’t usually cause major, widespread economic issues, it is found across the Corn Belt and can cause problems on some farms. The fungus was first described in India back in 1910, and over the past 100 years, there have been sporadic outbreaks of Physoderma-related problems in the U.S.

So, what’s the issue? Physoderma is the causal agent of both Physoderma brown spot (PBS) and Physoderma stalk rot (PSR). Experts used to think PBS led to the development of PSR. But we now know each disease is introduced to the plant at different stages of development.

Let’s break it down.

Physoderma Brown Spot

First showing up on the leaves as round/oblong, yellowish spots, the “brown spot” lesions also appear on the stalk and leaf sheath. The spots form bands across the leaf. Over time, the lesions turn brown, form together, and dissolve into brown pustules. 

These pustules contain the reproductive structures of the Physoderma fungus that can overwinter in the soil and cause reinfections.

Weather plays a key role in spreading this disease. The Physoderma sporangia require around three days of standing water (i.e., lots of heavy rains) and relatively high temperatures (73°F to 90°F) to burst and release infection-causing zoospores. The tiny buggers get into the whorl of the corn plant and inflect it—usually in the V3-V9 range.

How big of an issue does it cause? Research varies, but some studies show that yield loss can be over 20% due to a lack of leaf area and thus less photosynthesis. 

Keep this in mind: It’s important to correctly identify the disease so you can handle any issues. Physoderma brown spot can resemble other diseases, especially southern rust. However, unlike rust, PBS usually creates more distinct lesion bands and darker-colored leaf midribs.

Physoderma Stalk Rot

Stalk rot is caused by the same fungus, but PBS doesn’t necessarily lead to PSR. 

Unlike Physoderma Brown Spot, PSR isn’t as easy to spot. That is, until you hear it: the unmistakable “snap” of a breaking corn stalk.

Usually attacking the V6 or V7 node, the disease creates a black ring around the lower node, which destabilizes the plant, especially when the wind picks up.

For PSR, the big issue is obviously keeping your plants upright. Rotten stems and windy days don’t exactly mix, and your yield will take a dive if your plants are on the ground.

Management and Prevention

If you and your LG Seeds agronomist identify disease pressure from Physoderma, here are a few ideas to help deal with the issue:

Crop rotation: Soybeans are not a host plant for Physoderma. Although the fungus can hang out in the soil for several years, keeping beans in the rotation and avoiding corn-on-corn can manage the disease cycle by trying to starve it out.

Tillage: Shredding and burying those corn stalks can help reduce disease occurrence. Be sure to balance this option with your soil conservation needs.

Resistant hybrids: Choosing the right hybrid is crucial, and LG Seeds offers corn hybrids that have shown tolerance to Physoderma diseases. Work with your LG Seeds agronomist and see if our more Physoderma-tolerant hybrids—like LG6420, LG62C07, LG52C42, LG47C77 and LG66C44—are a good fit for your operation.

By Your Side

Whether you’re selecting top-notch hybrids or identifying yield-robbing diseases, your reliable partner is right by your side and ready to help. Reach out to your LG Seeds agronomist for support you can take to the field.