Love My Roses, But Not Rose Diseases!

Do you love your roses, but hate seeing the diseases that can hurt them? I love making flower arrangements for myself and my friends throughout the summer and fall. I love all the different colors and varieties. But I hate diseases that threaten my lovely rose bushes! I hope the following information about Idaho’s 3 most common fungal rose diseases will help you to better understand how to keep your roses healthy. 

Rust

The symptoms of this fungal disease are small orange blisters on the underside of leaves. A small amount will not cause a lot of damage to the rose, but the spores can blow to other roses and infect those roses. This disease can survive the winter, so it's best to control it so it doesn't carry from one year to the next.

Black Spot
This fungal disease fungus looks like spots on the surface of the leaves and causes the leaves to drop off early. It can survive the winter and in the spring the rain will splash on to the rest of the plant and spread it. It is recommended to prune off the disease for winter, allowing plenty of air flow between the major branches. Additionally, water the bottom of the plant to avoid getting water on the leaves.

Powdery Mildew
This fungus looks like grey and white powder. It will show up anywhere on the plant. This does not need water to spread and can survive the summer. Remove any infected leaves that you see on the plant and prune for winter. Water to avoid leaves, as with Black Spot. Once into the summer weather you can give your rose a wash with the hose to remove mildew and aphids. 

The following fungicides and natural pesticides can be helpful in keeping your rose bushes healthy:

Potassium bicarbonate is a chemical relative of baking soda. We also see it as antacid in over-the-counter medications.  It will control Black Spot and Powdery Mildew.  A few of the names you can find it under in the garden center are: Bi-Carb Old Fashioned Fungicide, Kaligreen, and Bonide Remedy. 

Bacillus subtilis is a microbial pesticide. It is a bacteria found in air, water and soil.  According to the product label, it is effective in controlling all three important rose diseases. It is sold as “Serenade Garden Disease Control”.

Neem Oil is a naturally-occurring pesticide found in seeds from the neem tree. It kills a variety of insects, including aphids.

Along with the tips above, it is important to keep the ground area under roses clean, of leaves, rose buds, and debris. I hope this helps you to keep your roses looking beautiful and healthy all season!

Pictured above:
My 5 year old rose bush

Hollyhocks

It's easy to fall in love with the cheerful hollyhocks sprawled all over my elderly neighbor’s junk filled backyard. He was happy to share seeds with me and told me he remembered them from the 1950’s when his parents bought the farm.  

There are 1500 species and 27 genera in North America and grow in zones 2-10. The edible flowers are considered a delicacy in Turkey. Hollyhocks (Alcea rosea) are in the mallow family.

Hollyhocks require:

• Full sun
• Moist, well-drained soil
• Should be watered with drip irrigation or soaker hose
• Grow up to 8 feet tall
• Biennials -- take two years from seed to bloom
• Plants reseed themselves
• Companion plants are pansies and campanulas

They attract hummingbirds and butterflies. In the Victorian era, hollyhocks were a symbol of ambition and initially were plants for the wealthy. They were used medicinally for respiratory ailments and for cooking.

My hollyhock plants looked ragged, with bumpy reddish growths on the lower leaves. The spots became dry, brown, and left holes in the lovely green leaves. Initially I treated them with a detergent based wash, then applied insecticide per the research from my plant books. The problem continued, and I noted that other gardens’ hollyhock leaves were equally as unattractive as mine. It seemed we would need to co-exist. I just picked off the offensive leaves.

Before Google was available for research I had to rely on books. In my master gardening class, I learned how to use the Google search site (site:.edu hollyhocks). Using this educational search, I was able to find out what was causing problems. To my amazement, the culprit was a fungus! The mystery was solved as I perused the pictures and found the Puccinia malvacearum fungus.

One of the most common problems with hollyhock is Rust (Puccinia malvacearum). Rust causes the plant to look ragged, with bumpy reddish growths on the lower leaves. The fungus overwinters in infected plant debris. In the spring new infectious spores are formed on infected plant debris that cause infection on the newly emerging leaves.

Disease Control Strategies: 

• Cut infected plants at the soil line and remove debris as soon as the hollyhocks are done flowering. This prevents the rust disease from overwintering and infecting in the upcoming spring. 
• In addition, remove and destroy any mallow weeds growing near hollyhocks.
• Adding a layer of mulch around hollyhocks in the spring will hinder overwintering of spores within in plant debris. 
• Scout hollyhocks in early spring. Remove and destroy the first leaves that appear infected. 
• Proper location choice can be important to reduce the chance of infection. An ideal site will have adequate sunlight, good soil drainage, and sufficient air circulation.
• It is also recommended to water the plants early in the day, so that they dry relatively quickly.
• Consider purchasing more resistant varieties such as the Alcea rugosa and Alcea ficifolia.
• A preventative fungicide can be applied to plants BEFORE infection or as soon as infection is detected. Frequent treatments will need to be applied as new growth emerges.

My initial plants are a very old variety, I have secluded a few and removed most of the plants. We have a large area, and I hope to avoid infecting any new plants. I have new plants from the seed swap at the Canyon County U of I Extension Office. According to Wisconsin Horticulture these are fungicide treatments and usage that will help your hollyhocks.  

“If you decide to use fungicides for control, select products that are labeled for use on hollyhocks (or more generally on ornamental flowering plants) and contain the active ingredients chlorothalonil, mancozeb, myclobutanil, tebuconazole, or triticonazole. When making more than one application, DO NOT use the same active ingredient for all treatments. Instead, alternate the use of at least two active ingredients with different modes of action to help minimize problems with fungicide-resistant variants of the hollyhock rust fungus. Myclobutanil, tebuconazole and triticonazole have similar modes of action and should NOT be alternated with one another. Be sure to read and follow all label instructions of the fungicides that you select to ensure that you use products in the safest and most effective manner possible.”

I will also be purchasing new seeds in my quest for lovely, cheerful hollyhocks!