Why Your Sweet Corn Plant Leaves Are Turning Brown

Sweetcorn is a true crowd-pleaser. It is fun and relatively easy to grow at home and the delicious kernels of corn form a colourful addition to many family meal times. I am a particular fan as it is one of the vegetables my children will willingly eat without a fuss! 

Notwithstanding the pleasures that come with eating and growing sweetcorn, it is not without its issues and gardeners often report their corn plant leaves turning brown. Let’s investigate the various reasons why this can happen and how it can be remedied.

Why Do Sweetcorn Plant Leaves, Turn Brown

There are multiple reasons why sweetcorn plant leaves turn brown, from insufficient light, too much or too little water and even the amount of fertilizer in the soil. 

All of these can impact photosynthesis which depletes leaves of chlorophyll and causes them to discolour, a process known as chlorosis. 

Pests and diseases can also result in brown leaves. If you can identify the issues early enough to intervene, then your corn ears should be salvageable.

What Causes Brown Leaves on Sweetcorn

Understanding what has caused the leaves of your sweet corn plant to turn brown and knowing how to remedy the issue requires an initial deep dive look into the symptoms. Once established, fixing the problem can begin. 

Inadequate Watering 

Sweet corn needs ample water to produce ears, but inadequate watering, either too much or too little will impact the leaves. Here is a detailed look at what that can look like when growing corn.

Underwatering 

Underwatering sweetcorn causes the cells near the leaf margin to become dehydrated and turn brown and crack. Corn plants require at least 1 inch of water per week, and ample water is essential during the hot months of July, August and September and when silks appear. 

Once the leaves turn brown from lack of water there is no way to salvage them as the leaf has dried out to the point it is dying. You can gently remove the brown part of the leaf. 

Sweetcorn is a clever plant and if some water has been applied the actual corn ear will take the water available as the priority over the leaves, so if it is early enough in the season you can use the brown leaves as an indicator to get back on top of the watering schedule to ensure it does not impact the corn production.

Overwatering 

Sadly, it is not a simple case of just liberally watering your plants as overwatering can lead to brown leaf tips in sweetcorn plants. 

This is because excess water will fill up the airspaces in the soil, depriving the roots of oxygen. Without oxygen, the roots will die and adversely affect the plant’s ability to take up water.

The first sign of overwatering is the yellowing of leaves, and as it continues, brown and sloppy leaves. Over-watering will also wash away essential nutrients from the soil causing chlorosis. 

According to Utah State University, overwatering can be more stressful than drought to plants and harder to remedy as it often causes root damage which is much trickier to solve.

Lack of Nutrients

Healthy soil is critical in all vegetable production but is particularly key with sweetcorn as it prefers a well-rounded, slightly acidic soil which rarely occurs naturally. These are some of the key signs to look out for that will help to identify a deficiency in your soil.  

Magnesium Deficiency

Yellowing between the veins, otherwise known as chlorosis, generally indicates a deficiency of manganese, iron or magnesium. A lack of any of these minerals will impact the chlorophyll in the plant which is responsible for its green colour. 

Iron deficiency affects the youngest leaves first, whereas the symptoms of manganese and magnesium deficiency tend to start in older leaves.

Nitrogen Deficiency

Lack of nitrogen causes a more general yellowing or reddening, starting with the older leaves, and is often accompanied by a lack of vigour.

With many of these nutrient problems, the yellow tissue can turn brown if the deficiency becomes more pronounced.

Corn plants are heavy feeders so applying a balanced nutrient-rich fertilizer for corn to the soil before planting can prevent many of these issues. In addition, you will need to maintain a regular fertilizing schedule as the growth cycle progresses.

Nitrogen Deficiency in Corn Plant
Nitrogen deficiency in corn plant

Potassium Deficiencies

Potassium is critical for sweetcorn and often there is just not enough naturally occurring in the soil. Similar to other nutrients, potassium helps to regulate growth and metabolism and a deficiency can adversely hamper all the functions of the sweetcorn plant and interfere with photosynthesis.

The first signs of potassium deficiency would show in the form of yellowing of the young leaves. Older leaves will start withering around the edges and will show brown scorch marks on them, despite being kept in the shade and watered regularly.

If you turn the leaves over and take a closer look at the undersides, you may also see purple spots appearing there.

Adding potash, to the soil before planting, can help to alleviate this issue. 

Pests

There are various pests that like sweetcorn but one of the most prevalent is the black corn flea beetle. These small oval beetle damages leave by spreading disease and feeding on the outer layer of leaf cells leaving brown stripes on the damaged leaves. 

Corn flea beetles become active when soil temperatures reach 65F. 

The best way to deter these notorious pests is to clear all debris from around your corn before planting as this is where the corn flea beetle can overwinter.

Other pests attracted to corn include cutworms, seed corn maggots and wireworms. These pests prefer to feed on the roots or the corn kernels rather than the leaves themselves.

Disease

Sweetcorn is rarely impacted by the disease in domestic gardens. Two slightly more common issues that can arise though are corn smut disease and pyoderma maydis.

Physoderma Maydis

Physoderma maydis is a pathogen that impacts corn and will cause small round or oblong yellow and brown spots across the leaves. The midrib of the leaf may also display clusters of dark purple to black oval spots. These may also be observed on the stalk, leaf sheath and husks. 

Some of these spots can form blister-like pustules of powdery sporangia which can survive in the soil for 2-7 years. It is not terminal for sweetcorn but may impact yields and can spread to other plants. 

If you believe your plant may be impacted by this, harvest what you can safely from your plants but then dig up, dispose of it carefully and ensure you turn the soil and let it breathe before planting anything else. There is limited evidence on whether the use of fungicides is effective in treating this issue. 

Corn Smut

Corn smut can be identified by large, fleshy, brown swellings containing a black sooty mass of spores appearing on the leaves, stems, ears, or silks. 

The fungus that causes this disease mostly occurs in the Southeastern States when temperatures are high (79 to 100F) and moisture is abundant.

The best treatment is to pick off and destroy all infection sites while they are immature and have not yet released spores. Be sure to do this carefully since spores can readily blow to nearby plants and cause more disease. Corn smut overwinters on plant debris in the soil, so do not turn infected crop residues back into the soil.

Corn smut is unmistakable
Corn smut is unmistakable

Common Rust

Puccinia sorghi or common rust is identified by linear elongated streaks of brown and orange. Sweetcorn plants already infected by a mosaic virus are more prone to infection with Puccinia sorghi. The airborne spores create this distinctive rusting that will come off in your fingers when rubbed. Unfortunately, if left untreated rust spores will develop to overwinter and potentially infect future crops.

The best line of defence again rust is to plant rust-resistant varieties of corn of which there are hundreds to choose from on this PDF datasheet.

Common rust on corn leaves Why Your Sweet Corn Plant Leaves Are Turning Brown
Common rust on corn leaves

Final Thoughts on Corn Plant Leaves Turning Brown

Sweetcorn is a plant that really does lend itself to growing at home as you get a maximum taste when it is freshly picked and eaten, and its sweet flavour makes it popular with even the most hardened vegetable avoiders! 

But it is not without its issues and brown leaves can be one indicator of those. Effective soil management before planting coupled with identifying causes as they occur and, in all cases, some quick intervention can turn around most problems, from feeding the plant to treating pests to re-establishing a good watering regime. 

Acting quickly if you spot any pesky brown leaves will ensure you are still enjoying delicious corn on your late summer barbecues!

For more facts and advise about sweetcorn plant cultivation, here’s a link to Sweetcorn Growth Stages.

FAQ Sweet Corn Plant Leaves Are Turning Brown

Can brown leaves turn green again?

Generally, once a leaf has turned brown it indicates it is dead or dying so cannot turn green again. But this does not necessarily mean the whole plant has died. Identifying the cause and addressing it whilst removing the brown areas will allow the green leaves to flourish.

Why are my sweetcorn seedlings turning brown?

Your seedling leaves are turning brown because you are overwatering or underwatering them. They can turn brown if the weather is too hot or too cold. Some other reasons include transplant shock, overfertilization, or poor soil. Some pests and diseases may also turn the leaves brown.

Citation

Utah State University – Overwatering

Clemson Cooperative Extension – Insect Pests of Sweet Corn

The University of Minnesota Extension – Spots of Corn Leaves

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Ben's horticultural interest grew when graduating from Hertfordshire University in 1997. Having contributed to numerous publications including Better Homes & Gardens, Garden Design Magazine, and The English Garden. He is also the author of Propagating Houseplants Made Easy.