What Is Causing Hibiscus Leaf Spots: How To Fix It?

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Leaf spots on the hibiscus may be caused by bacteria or fungus. This condition usually happens in the wintertime when cool temperatures and extended damp conditions set up the ideal circumstances for bacteria and fungus to grow. 

Hibiscus in the landscape may experience damp leaves on an ongoing basis, leading to fungus and bacteria problems and leaf spots. 

Hibiscus Leaf SpotPin

If you live in an area where dew forms on the plants’ leaves regularly (especially during the cool winter and early spring months) and does not evaporate for many hours, fungus and bacteria will multiply on the leaves. 

This is also a problem on very cool, rainy days, which is exacerbated if your plants are poorly pruned or planted too close together, so there is little airflow. 

Luckily, even though leaf spots look ugly on your Hibiscus plant, they are not usually life-threatening. 

If you can cleanly remove the affected leaves and resolve the problem that allowed the fungus or bacteria to grow, your problem should be solved. Your plant may look a bit bare for a while, but new leaves will soon grow. 

So what causes hibiscus leaf spots, and how to fix it? Read on to learn more.

What Happens If You Don’t Treat Leaf Spot? 

It’s never a good idea to leave any bacterial or fungal infection to its own devices. If you don’t clear away the affected leaves, the spotting may spread over the leaves and affect photosynthesis. This could weaken your plant. 

Luckily, the leaf spot doesn’t usually affect the entire Hibiscus plant. Therefore, you should be able to eradicate it by pruning away a fairly minor portion of the plant’s leaves. Generally speaking, leaf spot disease in Hibiscus is not usually fatal to the plant. 

If your Hibiscus experiences a leaf spot over a large area, or if the leaf spot returns year after year, you should take the situation seriously. 

Carefully examine your growing area and plant care habits to determine why leaf spot is an ongoing problem. 

What Plant Care Problems Contribute To Leaf Spot?

A cool, wet, shady setting provides the perfect environment for fungal and/or bacterial growth. 

Be sure to provide your Hibiscus with ample amounts of bright, direct morning sun and some shelter from the harshest midday and afternoon sun. 

Provide a warm environment. The best temperatures for Hibiscus are 65° to 75° degrees Fahrenheit. Be sure not to allow the temperature to drop below 55° degrees Fahrenheit.

Be sure to keep the soil consistently moist but never soggy. It’s also important to protect your outdoor plants against extended downpours. 

Moreover, move container plants to a sheltered area and ensure plants in the landscape have excellent drainage.

How Can You Get Pruned Leaves To Grow Back Faster? 

After pruning away damaged and infected leaves, give your plant a good feeding with a high-quality, water-soluble fertilizer containing micronutrients (e.g., iron, magnesium, and copper). The best NPK ratio to encourage foliage growth is 6-4-4 or 12-6-6.

Note that you should take care when using fertilizer. Don’t overdo it, or you may run the risk of causing fertilizer leaf burn. This is browning that starts at the leaf tips and eventually “burns up” the whole leaf. 

Be sure to follow packaging instructions carefully when applying fertilizer or anti-fungal products. 

Use half-strength fertilizer solutions in hot weather (95° to 100° degrees Fahrenheit). In temperatures greater than 100° degrees Fahrenheit, don’t fertilize. 

How Can You Keep Leaf Spots From Returning?

You may wish to use an anti-fungal spray on your plants’ remaining foliage and stems to kill off any fungal infection that may remain. 

Make changes to your plants’ environment to discourage bacterial and fungal growth. 

Be sure your plants are properly pruned to allow airflow. For plants in the landscape, prune surrounding plants to allow in more light and improve airflow. 

Hibiscus in containers and/or those kept indoors should be moved to areas where they will get ample sunlight. Space your container plants to allow room for growth and airflow. 

Be sure to keep your plants warm enough. For outdoor plants, you may have little control, but don’t despair. 

You may have leaf spot problems early in the spring when the temperature is still cool, and the weather is still wet. 

However, if all other conditions are correct, these problems will likely resolve on their own as summer approaches, and the weather becomes warmer and drier. 

Is Rust Disease The Same As Leaf Spot Disease? 

Rust disease, also known as Hollyhock rust, is always caused by a fungal infection (Puccinia malvacearum). This type of disease is very common in members of the mallow plant family, including Hibiscus. 

The pathogens that cause rust disease are blown about by the wind, especially during rainy weather in springtime. When the pathogen comes in contact with a likely host plant, it takes hold of the new leaf growth. 

If your marred leaves present rusty spots on the leaves’ tops and small yellow bumps on the underside, the problem is rust disease. 

Unlike simple leaf spots, Hollyhock rust can be fatal to Hibiscus and should be treated promptly. In addition to making sure your plants have a healthy environment, you should also treat your unaffected plants with an anti-fungal solution such as: 

  • Chlorothalonil as a preventative on new growth. 
  • Neem Oil Spray and soil drench can be used any time of year as a preventative.
  • Sulfur-based fungicides can be used in temperatures lower than 85° degrees Fahrenheit as a treatment. 

While you might successfully treat an isolated plant with a sulfur-based fungicide, your chances of success are low. Instead, you are best off removing and destroying infected plants (along with any possibly infected garden debris). 

Treat remaining plants, first with a sulfur-based fungicide and then (when new growth emerges) with a chlorothalonil product. Once the problem is resolved, use a neem oil spray weekly as a preventative measure. 

TIP: Never spray any product when the sun is high and hot. Apply pesticides, fungicides, and other foliar sprays early in the morning. 

Are Brown Spots The Same As Rust Spots? 

Hibiscus may exhibit brown spots that spread to encompass entire leaves when they go through a growth or re-leafing cycle early in the spring. 

When this happens, the plant simply diverts resources to fresh, new growth so that older foliage dies, falls, and makes way. Therefore, this is not a cause for concern. 

What If The Leaves Are Spotted And Curled? 

Insect pests may cause leaf spots accompanied by curling or deforming. If your plants’ environment and care are correct, suspect a pest infestation. 

Healthy Hibiscus Resist Leaf Spots

By providing the right environment for your Hibiscus plants, you can prevent problems with leaf spots. 

Be sure to give your plants lots of warmth and sunlight, along with the right amount of water and fertilizer. Prune regularly, provide ample space, and pay close attention to your plants to ward off problems before they get out of hand. 

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