What’s Wrong With Your Black-Eyed Susans? (Keep Your Plant Healthy)

If your black-eyed Susans have discolored leaves, signs of mildew, or black spots, determining what is wrong with them sooner than later can help you save your plants. 

When determining what is wrong with your black-eyed Susans, identifying the symptoms and the root cause of the issue is critical. Most problems with these flowers, such as black spots, brown or yellow leaves, or mildew, result from inadequate light, aeration, and water conditions. 

In this article, I will give you a comprehensive guide to help you determine the root cause of any issues with your black-eyed Susans. I will also provide solutions for every issue so you can keep your flowers bright, healthy, and happy. 

Black-eyed Susan diseases and health problems: an overview

Symptom	Potential Causes	Natural Solution
Damaged leaves	Grasshoppers	Remove manually Backyard chickens
	Slugs/snails	Remove manually Set traps Backyard chickens
Brown leaves	Under or Overwatering	Provide ample drainage
	Root rot	Maintain soil moisture
	Leafhoppers	Keep planted areas clear of debris Attract beneficial insects
Yellow leaves	Overwatering	Provide ample drainage
	Nitrogen deficiency	Supplement with compost or organic fertilizer
	Insufficient sunlight	Plant in full sun
	Cold damage	Plant after risk of frost in spring
	Mites	Use biological controls such as ladybugs
	Verticillium wilt	Prune dead leaves Solarize soil
Yellow, white, or red spots	Rust	Prune infected plant matter
	White smut	Increase airflow and sun exposure Water at the base of the plant
Black spots	Septoria Leaf Spot	Plant black-eyed Susan in full sun Prune and aerate plants Water at the base of the plant
White fuzz	Powdery mildew	Apply proper irrigation, plant spacing, and soil drainage practices Remove infected plant matter
	Downy mildew	Apply neem oil to infected parts Increase airflow and sun exposure Remove infected plant matter
	Stem rot	Increase airflow and sun exposure Remove infected plant matter

Why black-eyed Susan leaves are damaged

Sometimes you’ll notice the leaves of your black-eyed Susan sporting shiny streaks or large holes in the middle or edge of the leaves. In this case, there are probably larger pests, such as grasshoppers, snails, or slugs eating away at your plants.

Grasshoppers

Grasshoppers, in particular, can do a lot of damage to black-eyed Susans since they are such voracious eaters. They will eat large holes through the leaves and even eat down the petals of your black-eyed Susan flowers.

The best way to deal with these pests is to handpick them off your plants and dispose of them.

A less conventional method to control grasshoppers is to get some backyard chickens to help with pest control. It may seem extreme to get chickens just for some grasshopper help, but they can also help with fall garden cleanup, produce manure, and they’re just plain entertaining to watch.

Just keep an eye on your chickens when you set them loose in the garden since they love to scratch at plant roots. A thick layer of mulch will help, but don’t leave them in one area of the garden for too long.

Slugs and snails

A shiny trail along the plant leaves is a surefire indication of slugs and snails in your garden, two of the most common garden pests, along with aphids.

Slugs and snails will also chew on the leaves of your black-eyed Susans but usually do not cause enough damage to kill the plant. Young black-eyed Susan seedlings are another matter, though. I’ve had snails eat an entire black-eyed Susan seedlings to the ground overnight, taking it beyond the point of recovery.

These pests are best controlled by setting out traps baited with beer, using an organic bait like Sluggo, or handpicking them off your plants.

Why black-eyed Susan leaves turn yellow

Yellow leaves in black-eyed Susan are often the result of overwatering, improper fertilization practices, inadequate sunlight, cold damage, or mites. 

Overwatering

Drainage is critical for black-eyed Susans, which are native prairie plants acclimated to hot, dry climates. Overwatering them can lead to yellowing leaves and more severe issues such as root rot, fungal infections, and pest infestations. 

When watering these plants, only apply the water at the base of the stem and avoid letting water collect on the foliage or flowers. Stick to watering once or twice a week instead of daily to ensure that the soil never becomes soggy. 

Too much or too little fertilizer

Black-eyed Susans prefer soils with moderate levels of nitrogen and phosphorus and may experience yellowing leaves if the soil fertility is too high or low. 

Plant black-eyed Susan in areas with naturally fertile soil or supplement the soil with organic compost. Fertilizing annually can ensure that the soil does not become depleted, but it’s a good idea to do an annual soil test to keep an eye on your soil’s fertility (or lack thereof). 

If your soil needs a boost, here are some resources that have served me well in my garden:

Inadequate light

Black-eyed Susans tolerate shade, but they prefer full sun. Most health problems found in these flowers result from inadequate warmth and sunlight. Thus, yellowing leaves due to insufficient light may indicate that a more severe issue, such as a fungal infection, could be just around the corner. 

Keeping black-eyed Susan in full sunlight is the best way to keep the leaves healthy and prevent most health issues that affect these plants. 

To learn more about finding the ideal spot for black-eyed Susan, you may find this article on Sun Or Shade For Black-Eyed Susan? (Plus tips for success) helpful. 

Cold damage

Cold weather may induce leaf yellowing in black-eyed Susan. Although black-eyed Susan is a biennial or perennial plant that comes back after winter, the foliage cannot survive temperatures below freezing. 

Cold damage is typical during fall and winter when the weather cools for the season. If you live in a warmer climate that doesn’t freeze, you might be able to avoid this altogether. 

For more information on this topic, check out this article on Are Black-Eyed Susans Annual Or Perennial Flowers?

Mites

Mites like the two-spotted spider mite may suck the sap from black-eyed Susan leaves, resulting in white, yellow, or light brown, crispy spots on the leaves. 

Spider mites are distinct since they produce webs, like spiders. These arachnids primarily infest unhealthy plants, so proper care of the Black-eyed Susan is critical for mite prevention. A stressed plant is much more vulnerable to pest pressure, so keep your flowers stress-free with full sun, regular water, and a layer of compost. 

Predatory mites and ladybugs prey on spider mites, so encouraging these species to inhabit the garden may eliminate unwanted pests. 

You can purchase packaged lady beetles or predatory mites to control spider mites or focus on planting various flowers in and around your garden to catch the eye of passing beneficial insects. 

Why black-eyed Susan leaves turn brown

Many factors may cause browning leaves in black-eyed Susan, including minor issues such as underwatering and more severe problems like root rot, verticillium wilt, and leafhopper infestations. 

Underwatering

The leading cause of brown leaves in most plants is underwatering. Black-eyed Susans are slightly drought-tolerant but still prefer consistently moist soil to thrive. Mulching black-eyed Susans can lessen the need for watering in hot or dry climates. 

Root rot

Black-eyed Susan plants thrive in moist soil, but the roots may die and become infected if you overwater them or if the soil does not drain well. 

Although root rot predominantly affects the plant’s roots, the leaves will suffer necrosis and turn brown if the infection progresses. 

When detected, removing infected roots, applying an antifungal treatment such as hydrogen peroxide or neem oil, and replanting the black-eyed Susan in fresh soil are critical. 

Irrigating and providing drainage to a black-eyed Susan patch will prevent root rot. Although black-eyed Susan plants tolerate partial shade, planting them in full sun may lessen the risk of root rot since the sun will keep the soil warm and drier, lessening the chances of fungal infections. 

Verticillium wilt

Verticillium wilt is a fungal infection that affects and clogs the circulatory system in plants. Once the plant is infected, the fungus prevents water and nutrient uptake through the stems and leaves, effectively starving the plant and causing the leaves to turn yellow. Eventually, the whole plant will wither and die. 

The fungus lives in the soil, but the infection spreads by insects as they move from plant to plant, feeding. It is also virtually impossible to eliminate. 

Disposing of infected black-eyed Susans and avoiding planting anything in the infected soil is the only treatment for this disease. 

You can try to speed the removal of the verticillium wilt through solarization, which essentially cooks the soil. 

To solarize your soil, lay a sheet of clear plastic over the infected ground, weighing down the edges to keep the plastic in place. Leave it in place for at least six weeks. It’s not a cure-all, but if you follow up the solarization with plants resistant to verticillium wilt, you have a greater chance of seeing your plants thrive the following season. 

Leafhoppers

Leafhoppers are small, green insects that target black-eyed Susan flowers, consuming the leaf edges and leaving brown, crispy edges along the foliage. 

Eliminating leafhoppers’ habitat, namely lawn debris such as fallen leaves, twigs, and dead plants, can ward off these insects. That’s a tricky thing to do in a garden where you mulch and leave old plants to overwinter, so you could also try encouraging beneficial insects, such as ladybugs, to come in and clear out the leafhoppers. 

White, yellow, or orange spots in black-eyed Susans

White, yellow, and orange spots on black-eyed Susan Susan leaves are usually the result of a fungal infection such as rust or white smut. 

Rust

Rust infections are common in flower gardens, and they can only thrive on plants that have water on the surface of their leaves. This infection results in surface spots ranging from off-white to yellowish orange to rust-red. 

Rust is rarely fatal to black-eyed Susans and other plants, but it may stunt that plant’s growth if left untreated. 

Pruning is an effective method to eliminate rust. Toss the pruned leaves into the garbage instead of the compost since rust is a fungal infection that can easily spread throughout the compost pile. 

To avoid rust on your plants, do not use overhead sprinklers to water your black-eyed Susans, and plant them in sunny areas to reduce the water buildup on the leaves. 

Proper spacing will also increase airflow, encouraging drainage and reducing water buildup on the leaves. 

White smut

White smut is a fungal infection of black-eyed Susan leaves resulting in white spots and yellow to dark brown lesions on the foliage. 

White smut spores spread via the air, making it challenging to eradicate without cultural prevention. 

This fungus thrives in shady and humid areas and is most common in early spring and fall. Moving an infected black-eyed Susan to a warmer, sunnier, and drier spot may slow or stop the spread of this fungus. 

Proper placement and watering of black-eyed Susan are also critical for preventing white smut. 

Black spots on black-eyed Susan leaves

Black spots are most commonly a symptom of septoria leaf spot, one of the most common problems you’ll see with black-eyed Susans. 

Septoria leaf spot

Septoria rudbeckiae is a fungal infection that predominantly targets black-eyed Susan or black-eyed Susan. This infection causes tiny black to purple spots on black-eyed Susan leaves and does not affect the flowers. 

A minor infection will not harm the black-eyed Susan, but leaf loss and necrosis could prove fatal if left untreated. 

This fungal infection thrives in damp, cool conditions, so reducing watering frequency and regularly pruning and dividing black-eyed Susan to provide more ventilation may eliminate it. 

Avoid pouring water over the leaves of black-eyed Susan as the moisture may attract or spread septoria infections.

Organic treatments with antifungal products such as neem oil will also prevent the spread of this disease. 

White fuzzy mildew on black-eyed Susans

All fungal infections of black-eyed Susan flowers result from excess moisture on the leaves or soil. 

Proper irrigation practices, ample plant spacing, and adequate soil drainage prevent these diseases. 

Powdery mildew

Powdery mildew is a prevalent fungal infection that spreads via the air. This non-toxic fungus covers leaves in a film of powdery spores, eventually suffocating and dehydrating the plant. 

Antifungal treatments such as neem oil or hydrogen peroxide soaks and antifungal soil treatments are the only way to eradicate powdery mildew once it infects the plants. Unfortunately, it’s a common sight in gardens by the end of the season.

Prevention is the best method to keep this fungus from a black-eyed Susan Suan or any other flower. Aeration, adequate sunlight, and avoiding overwatering will keep it away as long as possible. Still, chances are high that, eventually it will set in as part of the gardening season. 

Downy mildew

Downy mildew is a pervasive fungal infection. Symptoms include fuzzy white, gray, or blue fungal growth on the underside of black-eyed Susan leaves and yellowed lesions on the leaf tops. 

Downy mildew spreads rapidly via air and water. Any attempts to wash or blow spores off of the leaves will result in the spread of this disease. 

To effectively control downy mildew, dispose of affected foliage and plant matter, increase aeration, and reduce water buildup on the plants’ leaves. 

Pruning and ensuring that black-eyed Susan plants are at least 18 inches (45.7 cm) from each other will help prevent the spread of downy mildew. 

More space between plants increases airflow and reduces the buildup of water droplets on the leaves, especially if you’re planting your black-eyed Susan flowers in the shade, where the leaves may stay damp from the morning dew. 

Stem rot

Sclerotium and Sclerotinia infection, known as southern blight or stem rot, are among black-eyed Susan’s most common diseases. 

This fungal infection results in yellowing and browning leaves and a ring of white mycelial growth (the fungus’ roots) around the base of the plant. Small brown and white bumps, called sclerotia, may emerge around a blackening stem with fuzzy, white fungal growth in severe infections. 

Good airflow and full sun exposure are critical for the prevention of stem rot, but once this rot has infected a black-eyed Susan, the only way to remove it is to discard the plants. 

This fungus can survive in uninhabited soil for up to four years, so avoid planting anything else in the area after diagnosing black-eyed Susan with stem rot. 

Avoid problems with your black eyed Susan flowers from the start

Although many issues may affect black-eyed Susan, it’s infrequent. If problems do occur, these steps can be a big help to get your flowers back on track:

• Plant your black eyed Susan in full sun from the beginning. Transplant to a sunnier spot if necessary.
• Use drip irrigation or hand water at the base of the plant. Avoid overhead watering.
• Plant black eyed Susans in well-draining soil.
• Provide adequate spacing between plants to allow for good airflow.
• Remove plant matter with any sign of fungal disease to prevent it from spreading.

If you monitor the sun exposure, moisture levels, and airflow of your black-eyed Susan Susans, you can effectively prevent all of the issues on this list.