When hollyhocks are healthy, they’re some of the most beautiful garden flowers. Tall stalks tower overhead and display large blooms that brighten summer gardens. However, diseases, pests, and improper environmental conditions can discolor the plants’ foliage and lead to ugly flowers.
Becoming familiar with common hollyhock problems is one of the best ways to keep your plants healthy. When you spot something wrong with your plant, you can properly diagnose and treat the problem. Keep reading to learn about some pests and diseases that threaten these cottage flowers and discover ways to treat and prevent these issues.
Rust
Are the spots tiny insects?
When gardeners spot the orange lesions on their garden foliage, many are unsure what they’re looking at. Are the spots tiny insects? Clusters of eggs? A type of nutrient deficiency? Nope! It’s a fungal disease known as rust.
Hollyhock rust is caused by the fungus Puccinia malvacearum. This disease infects all Alcea species as well as low mallow, a common weed.
The first symptoms of rust are small yellow spots on the undersides of leaves. However, since these spots are difficult to notice, gardeners often spot this fungus when rusty pustules appear. These spore-producing bumps can spread and cover the entire undersides of the leaves. Eventually, infected leaves may become discolored and fall off the plant.
The spores can arrive on plants via the wind and overwinter in plant debris. Therefore, the disease often remains in a garden for multiple years.
Unfortunately, it’s difficult to control and treat this pathogen. Even if you remove the infected leaves from the plant, the spores will likely remain in the environment and re-infect the plant. The best option for keeping the disease away is to catch it early, remove infected leaves, and spray the remaining parts of the plant with a fungicide. Remember that fungicides don’t treat already present fungi but rather prevent the fungi from infecting more of the plant.
Most fungicides recommended for treating this disease are synthetic and unsuitable for organic production. However, every gardener must weigh the pros and cons of using these materials in their garden. If you apply a fungicide, follow product directions and rotate products to prevent the fungi from becoming resistant.
You can also try to spray sulfur fungicides on the plant’s leaves after you remove infected tissue. However, you will likely need to reapply these products every 10-14 days to prevent infection.
Since this disease is challenging to treat, prevention is often the best strategy. First, look for rust-resistant varieties. Although resistant seeds may not be able to fight off all strains of the fungi, they are more likely to remain healthy than non-resistant varieties.
You should also widen spacing to encourage good airflow. Grow in full sun and ensure at least eighteen inches of space. You can even expand to two or three feet apart if you’re worried about disease.
Keep the area around your plants well weeded to encourage airflow and remove any weeds that harbor the fungus. Cut back plants as soon as flowering is finished. Remove any fallen debris and pruned foliage from the garden, and never place infected plant tissue in your compost pile. You should also water near the base of your plant or utilize drip irrigation to avoid wetting the leaves.
Finally, ensure that you properly sanitize any tools that you use in the garden, including pruning shears, rakes, and hand weeders. Dipping the tools in a 10% bleach solution is an easy way to sanitize.
Powdery Mildew
This fungal disease infects various garden species, including cucumbers, roses, and apples.
You may already be familiar with the white coating that’s a key symptom of powdery mildew. That’s because this disease infects various garden species, including cucumbers, roses, and apples. Regardless of whether or not you’re familiar with this group of fungi, it’s helpful to learn how this problem pathogen appears on hollyhocks.
The main symptom of powdery mildew is a light white growth that resembles talcum powder. It often appears on the leaf tops, but it can also impact stems, flower buds, and leaf undersides.
As the disease progresses, more of the plant becomes covered in the white powder. Eventually, infected portions of the plant turn yellow and then brown. In severe cases, the leaves can die, causing the entire plant to weaken.
Fortunately, not all cases of powdery mildew require treatment. If you spot infections early, you can prune the infected tissue and dispose of it. Avoid overhead watering, prune to increase airflow, and check your plants regularly for more infected leaves. If they are nearing the end of their life cycle, it often makes sense to let them die rather than treat the fungi.
With that said, more severe cases warrant treatment. It’s important to note that most fungicides won’t cure present infections and can promote disease resistance. However, they will prevent the fungi from spreading.
Some types of fungicides to try include sulfur-based and copper-based products, horticultural oil, and Bacillus subtilis. No matter which product you select, make sure to follow package instructions to avoid harming your plants and the environment.
The best way to prevent powdery mildew is to limit the environmental conditions that encourage this fungi’s development. Since these fungi thrive in high humidity and stagnant air, your goal is to limit these conditions. Utilize drip irrigation rather than overhead watering to keep the humidity low. You should also plant in full sun and provide wide spacing for adequate airflow.
Since powdery mildew spreads via spores, avoid letting the debris of infected plants fall in your garden’s pathways. You should also avoid composting infected plants. Instead, dispose of the plants in the garbage to avoid spreading the disease.
Finally, keep your plants well-watered and fertilized to keep them as healthy as possible. Nutrient-deficient and water-stressed plants have difficulty fighting diseases, but healthy plants can utilize their natural defenses to fend off diseases like powdery mildew. However, avoid applying too much nitrogen since this will lead to lush, new leaves prone to attack.
Slugs and Snails
If you spot irregular holes on seedlings or lower leaves, slimy slugs and snails are likely culprits.
Although hollyhock plants don’t often have pest problems, a few critters will still take advantage of tender new leaves. If you spot irregular holes on seedlings or lower foliage, slimy slugs and snails are likely culprits.
Slugs and snails are types of mollusks that feed indiscriminately on plants. They use their mouths to eat irregular holes in leaves. This results in a series of small holes or a few larger, oddly-shaped holes.
Since both pests are active at night, spotting what’s causing the damage is often difficult. You see the holes, but where are the pests? One way to check for slugs and snails is to lift rocks, landscape fabric, pieces of wood, and plant debris surrounding the affected plant. Oftentimes, you’ll see the slimy gastropods sheltering under these structures to protect themselves from the hot sun and daytime predators. You’ll also see their trails on the ground around your plants.
Although these pests can eat any foliage, they pose the biggest threat to young plants. The pests prefer these tender young leaves over tough older ones, and the small plants are less likely to rebound from damage.
Some caterpillars also find hollyhock leaves a delicious food source and cause the foliage to become ridden with holes. However, you can often spot caterpillars chewing on the leaves during the day. Additionally, these pests often feed on leaves a few inches above the soil surface, while slugs and snails typically remain close to the ground.
Fortunately, these pests are easy to control. If you think they’re eating your young plants, take action ASAP to avoid serious damage.
Although many gardeners swear by beer traps, these aren’t the only way to deal with slugs and snails. Another common treatment method involves laying a wooden board or metal sheet on the ground and checking it each day. The critters will crawl under the structure during the day, making it easy for you to find the mollusks and dispose of them in soapy water.
However, I’ve found the easiest and most effective way to control these pests is to use a specialized organic slug bait. This attracts slugs and snails and entices them to feed. The iron phosphate in the bait kills the slugs and snails. However, it’s not harmful to humans, pets, or wildlife. The best way to apply this bait is to sprinkle a handful of the granules around the infected plant.
The best way to prevent these pests is to create an unfavorable environment. Remove any debris that may serve as a hiding spot and keep tall weeds away.
You can also sprinkle diatomaceous earth in a ring around the base of your hollyhock plants. This material irritates and cuts the pests, encouraging them to stay away from your plants. However, you’ll have to reapply the material each time it rains. Humid weather can also require reapplications over time.
Hollyhock Weevils
Knowing what they look like can help you keep your flower stalks looking flawless.
Although they rarely kill plants, hollyhock weevils munch on leaves and flower buds, leading to undesirable damage. Knowing what they look like can help you keep your flower stalks looking flawless.
These weevils are one-eighth to one-fourth of an inch long with a black body and light brown legs. They have a hard exoskeleton and elongated snouts.
The pests typically appear in the early summer and begin feeding on hollyhock leaves. The damage appears as a series of small holes. As the flower buds emerge, the weevils work their way up the plant and begin eating the buds. This damage appears as small brown holes on the buds. When the pests cause enough damage, the flower buds may drop, or the resulting foliage may appear disfigured.
Once the flowers mature and turn into seed pods, the female weevils lay eggs in the developing seeds. The emerging grubs feed on the seeds and prevent them from forming properly.
Luckily, these pests are easy to treat. One of the easiest ways to remove them involves placing a sheet or towel underneath your plants and then shaking them. The weevils will fall from the plants, and you can easily dispose of them by placing them in soapy water.
Although the shaking method is almost always the best approach, you can also implement other treatment strategies. Organic insecticides like neem oil and pyrethrins will help kill the weevils and prevent them from continuing to damage your flowers. If you opt to use insecticides, make sure to follow the product instructions.
The best way to prevent these weevils from entering your garden is by removing old debris from the ground. The pests often overwinter in plant debris, so taking it out of your garden will prevent the weevils from emerging the following spring.
Anthracnose
Damage can range from a few brown spots to entirely discolored foliage.
A common garden problem, anthracnose is a fungal disease caused by species in the Colletotrichum genus, which can attack hollyhocks. Damage can range from a few brown spots to entirely discolored foliage.
The symptoms of anthracnose vary depending on the type of plant that’s infected. Therefore, the fungal disease that occurs on your hollyhocks may look quite different from that which infects your oak trees or squash plants.
Hollyhock leaves infected with anthracnose often develop brown irregular spots that spread over time. Unlike hollyhock rust, these spots appear on the tops and bottoms of leaves and are flat rather than raised. If the disease is left untreated and cool, wet conditions persist, the entire leaf may turn brown and drop prematurely. The infection eventually spreads to stems, petioles, and roots.
As cool, wet spring conditions give way to warmer temperatures and drier weather, anthracnose often decreases. However, you can also take steps to limit the severity of the disease.
Since a fungus causes anthracnose, look at options meant to treat fungi. Although synthetic fungicides are an option, they can also harm the environment. Fortunately, people have been looking at a variety of environmentally-friendly ways to treat anthracnose. These include essential oils, beneficial bacteria and fungi, and plant extracts. While bacteria like Bacillus subtilis and Bacillus thuringiensis have been shown to slow the spread of some types of anthracnose, there hasn’t been much research completed on testing them against the various species.
Sulfur and copper based fungicides can also help spread the spread of anthracnose. However, they will not kill the fungi that are already present. Therefore, you should remove infected leaves and spray the remaining foliage with the fungicide.
Anthracnose prefers cool, damp environments, so avoiding these conditions is key to prevention. While you can’t alter outdoor temperatures or natural rainfall, you can take steps to keep your plants’ leaves dry. Avoid sprinklers and other types of overhead irrigation. Instead, install drip irrigation or water the soil around the base of the plants.
You should also implement practices that allow for good airflow. These include planting your hollyhock plants at least 18 inches apart, keeping weeds out of the garden, and pruning leaves to encourage airflow.
Finally, remove fallen plant debris from your garden. This fungus can overwinter on twigs, leaves, and branches, so removing old material can help prevent future infections.
