Diseases on Black-eyed Susan leaves and Solutions

Diseases on Black-eyed Susan leaves and Solutions

With many vivid flowers, Black-eyed Susans bring a splash of stunning yellow and black color to your garden. This article from gardenhow.net will provide information about this flower and the methods to protect them, especially from the problems of Black-eyed Susan leaves.

Black-eyed Susan leaves

Black-eyed Susan blooms belong to the daisy family as Gloriosa daisy or brown eyed Susan. The Black-eyed Susan is a big wildflower that grows to a height of 30-90 cm. 

The leaves of the Black-eyed Susan are quite long, ranging from 5 to 17.5 cm in length. They have a lanceolate to ovate form and are thin. Winged petioles, strong veining, rough texture, and sparse toothing characterize the leaves. The leaves are many and develop in an irregular pattern along the stalk’s length.

Moreover, the leaves vary in form and size, but are normally 2 to 7 inches long and up to 2 inches broad, with the lowest leaves being lance-oblong, lance-elliptic, or spatula-shaped on long stalks, and the top leaves being stalkless. Surfaces are thickly coated in short stiff hairs; edges are toothless or have a few shallow teeth. The upper half of the stems are unbranched or few-branched, with long, white, stiff, spreading hairs.

Black-eyed Susan leaves

What are the problems related to Black-eyed Susan leaves? 

When planting Black-eyed Susan, you can confront some difficulties related to diseases like Black Eyed leaves. Therefore, you need to find some symptoms and set up the solutions for growing them successfully. 

Leaf spots

  • Causes Black-eyed Susan leaves spot

Bacteria or fungus can create black spots on Black-eyed Susan leaves.  The bacteria pseudomonas and xanthomonads can cause leaf spots, can kill Black-eyed Susan leaves. 

  • Symptoms of Black-eyed Susan leaves spot

The fungus Septoria rudbeckia causes Septoria leaf spot, which forms small 1/8 – 1/4 inch dots on the leaves. Fruiting bodies (pycnidia) of small, black, pinpoint size form in the center of the spots. The lower leaves are the first to be impacted. The illness then splashes water up the plant, moving it up the plant. The rudbeckia cultivar ‘Goldsturm’ has the most angular leaf spot. 

It starts as small dark angular spots on lower leaves that appear to be wet but soon spread to cover the entire leaf. It starts from the bottom and works its way up the plant. A bacteria causes angular leaf spot. 

The fungus Septoria rudbeckia causes Septoria leaf spot, which forms small 1/8 - 1/4 inch dots on the leaves
The fungus Septoria rudbeckia causes Septoria leaf spot, which forms small 1/8 – 1/4 inch dots on the leaves

Leaf spots


Black-eyed Susan leaves spot
Black-eyed Susan leaves spot
  • Solutions for Black-eyed Susan leaves spot

Fall cleaning is the first step in treating this disease. Ensure that diseased foliage is removed and destroyed. Plantings should be pruned in the spring to allow for better air circulation and to prevent disease-spreading overhead irrigation. Rudbeckia’s leaves and stems develop irregular black spots because of several fungal leaf spot diseases.
Moreover, Chlorothalonil or a copper fungicide may be used if cultural measures (sanitation, thinning, and appropriate watering) are unsuccessful in controlling the problem. Before the symptoms start, use it in the spring. 

Downy mildew

  • Causes Downy mildew

This is the most common disease of Black-eyed Susan. Fungi can cause downy mildew. 

  • Solutions

Leaf spots with downy white or gray patches under the leaves are common symptoms of this disease. The downy growth is caused by the development of sporangia, which are spread by the wind between plants. Cool, rainy weather is frequently conducive to disease.

Downy mildew on Black-eyed Susan leaves

Downy mildew on Black-eyed Susan leaves

Downy mildew on Black-eyed Susan leaves
Downy mildew on Black-eyed Susan leaves
  • Solutions

You can use some methods to control downy mildew such as reducing humidity and leaf wetness. Fungicides can also be used to control the disease if they are used as soon as symptoms appear. Mancozeb is one of the chemicals approved for usage in Connecticut. For dose rates, safety considerations, and usage instructions, see the label. 

Powdery mildew 

  • Cause Powdery mildew

High humidity or overwatering can cause powdery mildew in Black-eyed Susan leaves. 

  • Symptoms

These fungi are obligate plant parasites that develop vegetatively on the leaf surface of the plant, delivering haustoria into epidermal cells to receive nutrients from the host. Vegetative mycelium and spores carried in chains on upright conidiophores make up the white mildew on the leaf. Under high humidity, wind-dispersed mildew spores can germinate without free water, and the disease is typically severe when conditions are humid but dry. In powdery mildew-affected areas, small black overwintering structures known as perithecia are common.

Downy mildew
Downy mildew
Leaf spots with downy white or gray patches under the leaves are common symptoms of this disease
Leaf spots with downy white or gray patches under the leaves are common symptoms of this disease
  • Solutions

You can use fungicides to control the disease as soon as symptoms appear. Potassium bicarbonate, ultrafine oil, sulfur, triadimefon, and thiophanate-methyl fungicides are among the chemicals approved for use in Connecticut. For dose rates, safety considerations, and usage instructions, see the label.


  • Causes rust 

Rust refers to both the disease and the bacterium that causes it. 

  • Symptoms of rust

Rusts are obligate parasites with the ability to infect either one (monoecious) or two (heteroecious) host species. Rust infection causes powdery pustules on leaves or stems with rust-colored spores or gelatinous horns. Plants are generally stunted, and the surrounding tissue is damaged and yellowed.

  • Solutions

You can remove the alternate host to control heteroecious rusts, but with most perennials, you can use fungicides administered to control as soon as symptoms appear. Sulfur and mancozeb are two of the compounds that have been approved for usage in Connecticut. For dosage rates, safety considerations, and usage instructions, see the label. 

When the Black-eyed Susan leaves are wet, foliar diseases become more common, which is why you don’t need to water Black-eyed Susans above. Preventative fungicides, as well as removing infected Black-eyed Susan leaves and allowing proper air circulation to plants, can help prevent certain diseases from forming. To prevent disease transmission, severely you need to remove infected plants. 

Other Black-eyed Susan diseases

Besides some diseases related to Black-eyed Susan leaves, here are other problems:

Stem rot

  • Causes and symptoms

Sclerotinia sclerotiorum is a fungus that forms hard, black sclerotia that may live in the soil for many years. Sclerotia germinate best when the soil temperature is between 55 and 60 degrees Fahrenheit. The fungus may grow and live for many years on dead organic plant matter. 

Near the root collar, off-color lesions appear. On the stem, a white, cottony fungal growth occurs later. The white growth may form hard, black sclerotia. The roots stay healthy, but the plant wilts and finally dies above the stem lesion.

Stem rot
Stem rot
  • Solutions

The first method we should mention is cultural control. You need to provide the space for good air circulation. Moreover, overhead watering should be avoided or applied in such a way that the plants are not moist for long periods. Besides, avoid extremes of too wet or too dry by watering moderately yet consistently. Maintain a pH of 5.8 to 6.2. Besides, you can remove infected plants as soon as possible. At the end of the growing season, you can also remove and destroy crop remains. Plant less susceptible plants such as alyssum, daffodil, salvia, pansy, or decorative grasses in the planting bed. Rushes, sedges, and the fountain grass Pennisetum glaucum are all resistant crops.  

The next method is chemical control. The following materials may offer protection; however, there have been few decorative experiments to show the ideal time. 


  • Causes and symptoms 

This disease affects plants’ vascular or water-conducting tissues, causing wilt symptoms by obstructing water flow. As a result, symptomatic plants may flag or wilt on one side, with twisted and yellow leaves that become brown and hang down before drying. Despite ample soil moisture, the plant displays drought signs. The vascular tissues are often dark or discolored when the stem is sliced open at the base. 

  • Solutions

Wilt control includes removing infected plants, as well as their roots and soil. Because pathogens may live for extended periods in soil and plant waste, proper disposal of plants and soil is critical.

How to prevent mold, rust, and Mildew without chemicals?

These strategies for avoiding mildew, gray mold, and rust on Rudbeckia hirta plants work by reducing the amount of moisture around the plant (mold, fungus, and rust all love moisture) and limiting the distribution of infection-causing spores.

Space your plant

Remember that mature plants often have a spread of one to two feet when planting, especially if you’re conducting a mass planting.

Furthermore, there should be adequate space around each plant for air to circulate. The possibility of moisture build-up that causes mold and mildew will be reduced with good airflow.

Cut plants back

After the first bloom, cut back the plants to improve airflow, and your flowers will blossom again! We can let your flowers go to seed in the fall. 

Divide the Plants

 plants if you divide Rudbeckia hirta on a regular schedule, you can get a lot of small Black-eyed Susan

Weed Regularly

Also, keep the weeds at home. They not only retain moisture but also attract bugs. 

Water from the bottom

Watering your Rudbeckia hirta from the bottom is as simple as turning a spigot with a soaker hose linked to a spigot or rain barrel, or an in-ground watering system. 

Select a good location

Rust and mildew may thrive in an improper environment. Avoid growing your Black-eyed Susan in a shaded place instead of a full-sun spot, and don’t put it in soil that doesn’t drain properly. 

Select a good location for your Black-eyed Susan
Select a good location for your Black-eyed Susan

Benefits of Black-eyed Susan

Black-eyed Susans Susan has several benefits in your life, not only in terms of creating a beautiful landscape, but also in terms of bringing values such as medicine, food, and drink, as well as decorative reasons.

Benefits of Black-eyed Susan leaves

Black-eyed Susan leaves can provide some benefits related to health. You’ve probably heard about the health advantages of drinking herbal tea before going to bed or in the morning. There are several herbal teas available in the shape of ready-to-drink goods right now, but brewing it yourself is still far superior. However, one key point to remember is that you can utilize all components of the Black-eyed Susan blooming plant except the deadly seeds.  

Other benefits

  • Medicine 

Black-eyed Susan root extracts may improve the immune system, according to recent findings. 

Moreover, another study found that Black-eyed Susan had antibacterial capabilities against the bacteria that cause diseases.

One of the numerous health benefits of Black-eyed Susan is its antioxidant concentration. As a result, this flower is an excellent immune enhancer. The research shows the effectiveness of Black-eyed Susan as a cold cure

The medicinal ingredients in Black-eyed Susan’s stem may aid in the management of high blood pressure and the prevention of severe ailments such as stroke and heart attack.

  • Ornamental purposes

Most people use Black-eyed Susan in floral arrangements. They’ll look excellent as garden border flowers and you can use them to fill in gaps between plants by using complementary hues.

Q & A

Why are your Black-eyed Susan leaves curling?

These signs suggest that the plants are having difficulty bringing water up via their roots. Check the roots of one plant to determine whether they are healthy. 

Why are there holes on your Black-eyed Susan leaves?

Your Black-eyed Susans appear to have mildew or fungus. This fall, make sure to carefully clean the bed and dispose of all of the materials. In the meanwhile, use an all-purpose fungicide on your plants. 

Final Thoughts

In conclusion, Black-eyed Susan will be a vibrant addition to your garden with a splash of colorful flowers. This article from gardenhow.net provided detailed information related to Black-eyed Susan leaves. Hopefully, through it, you can find and solve difficult problems when planting Black-eyed Susan. Thank you for reading!  

Related posts:
Overview: Great varieties of Rudbeckia: Black-eyed Susans, Coneflowers
When, Where and How to plant Black-eyed Susan seedlings?
Lists of Black-eyed Susan companion plants
What are the methods for caring for Black-eyed Susans?

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