By: Mary H. Dyer, Credentialed Garden Writer
Carnation septoria leaf spot is a common, yet highlydestructive, disease that spreads rapidly from plant to plant. The good news isthat septoria leaf spot of carnations, which shows up in warm, damp conditions,is relatively easy to manage if caught soon after symptoms first appear. Readon to learn more about carnation septoria symptoms and what you can do aboutthis pesky disease.
Septoria on carnations is easy to spot by the development ofpale brown patches with purple or violet edges. These show up first on thelower part of the plant. Most likely, you’ll also notice tiny black spores inthe center of the rings.
As the spots enlarge and grow together, the leaves may die.Carnation septoria symptoms may include leaves that bend downward or sideways.
Septoria on carnations is favored by warm, damp conditionsand spreads by splashing water and windborne rain. Mitigating these conditionsas much as possible is the key in carnation leaf spot control.
Don’t crowd carnationplants. Allow plenty of space for air to circulate, especially during damp,rainy weather or periods of high humidity. Water at the base of the plant andavoid overhead sprinklers. Although you can’t control the weather, it helps tokeep the foliage as dry as possible. Apply a layer of mulchunder the plants to keep water from splashing on the leaves.
Sanitation is major in controlling septoria on carnations.Remove infected leaves on and around the plant and dispose of them properly.Keep the area free of weeds and debris; the disease can overwinter on diseasedplant matter. Never put infected plant matter in your compostbin.
If carnation septoria leaf spot is severe, spray the plantswith a fungicidalproduct as soon as symptoms appear. The next year, consider plantingcarnations in a different, unaffected location in your garden.
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Every gardener with a shady corner loves rhodies. A rhododendron (Rhobodendron spp.) is called the queen of the shade garden since these flowering shrubs not only tolerate some shade but crave it. Since they also like moist soil, it is no wonder that the majority of the serious diseases these plants face involve fungi.
If you believe that your rhododendron has fungus on its foliage, then you need to take action, including reviewing the plant's cultural care. Unstressed rhodies usually do not get attacked by fungal diseases, so keeping the shrubs happy is a good way to keep them healthy. That why, before you begin to treat a fungal disease, it is a good idea to get a solid overview of your rhodie's cultural needs and growth requirements.
Lesions on Sweet William caused by Heterosporium.
OSU Extension Plant Pathology Slide Collection, 1987.
These spots were due to Pseudomonas sp. on these Dianthus Star Double 'Starlette' plants.
OSU Plant Clinic Image, 2016.
Leaf spots on this Dianthus 'Scent First Passion' was due to Alternaria sp.
OSU Plant Clinic Image, 2018.
Cause Septoria dianthi and Cladosporium echinulatum ( sexual Mycosphaerella dianthi) , fungi, have been found by the OSU Plant Clinic Phyllosticta sp. has been reported in Washington. All are favored by wet conditions that keep leaves wet for extended periods of time. Cladosporium requires 15 to 20 hours of leaf wetness at 64°F.
Leaf spots due to the bacteria Pseudomonas sp. has also been found by the OSU Plant Clinic.
Symptoms Septoria produces roughly circular, light brown spots with a purplish brown border. Spots tend to be more numerous on lower leaves but are randomly scattered on the leaf. Spots continue to enlarge and eventually cause the leaf to die. Small, black, fruiting bodies (pycnidia) may be near the spots' centers. As the disease progresses, entire leaves and stems become necrotic. The whole plant develops a scorched appearance.
Leaf spots from Cladosporium have a light grayish center surrounded by a dark-reddish-to-black zone. This darker zone may extend lengthwise along the leaf. Leaves may be deformed or kinked if spots are near the margin. Spots can coalesce.
Chemical control Fungicides work best when applied during active plant growth but before symptoms develop and before wet weather is expected.
Black Spot: Black spot is a fungus that is very common during humid weather because it is a waterborne disease. As its name implies, small black spots form on leaves and stems, eventually weakening the plant and causing the leaves to drop.
Treatment: Choose black spot-resistant varieties and be meticulous about sanitation. Water the roots of the rose, avoiding the foliage. Water in the morning, so that splashed leaves have time to dry off. If black spot is an annual problem, try a dormant spray of lime sulfur at the end of the season and again in early summer. Once black spot appears, it is hard to stop. Neem oil and sprays containing potassium bicarbonate are somewhat effective.
Downy Mildew: Downy mildew is a very serious disease that spreads rapidly and can defoliate a rose plant in days. It is not as common as black spot and favors cool, wet weather. Purple spots with yellow edges form, often on the veins on the top side of the leaves and along the stems. Pale gray fuzz can form on the underside of the leaves. The leaves will eventually become brittle and fall.
Treatment: The good news is that downy mildew often clears up with the weather. To reduce the chance of downy mildew, practice good garden sanitation and keep the rose plants well pruned for air circulation. As with other diseases, a dormant spray may help.
Rust: A rust infection is easy to spot. Small orange pustules spots form on the undersides of the leaves. This fungus can also cause defoliation. Rust is most prevalent when nights are cool.
Treatment: Treatment of rust is similar to treatment of black spot: good sanitation and a preventative dormant spray after pruning. Once infected, remove all infected leaves and try Neem oil for control.
Mosaic Virus: Once a rose is infected with Rose Mosaic Virus, there’s not much to be done except check with the nursery for a replacement. Rose Mosaic Virus shows up as yellow mottling on leaves and deformed new growth. It can stunt growth or it can be a mild infection.
Treatment: If there are only a few affected leaves, the plant may continue growing and blooming fine. The really good news is that it won’t spread to your other roses.
There's plenty of advice on avoiding these diseases and other problems, so make sure you arm yourself with plenty of knowledge so you can have full rose blooms in no time.
There are no chemical solutions for treating TMV after it infects your plants. Prevention through good biological practices and rapid response to infection is key to controlling this garden problem.
There are many ways to reduce your risk of battling TMV in your garden.
Plants that are highly susceptible to TMV such as non-resistant tomato varieties should not be planted in the same bed for at least 2 years.
If you grow plants at risk for TMV, even if you don’t believe they are infected, remove your crop residues from your garden beds to reduce risk. Rather than tilling in plant residues, hot compost them. Then, ensure the ideal moisture rate of 60% during decomposition, and age your compost for 1-2 years to prevent possible contact with infected undecomposed plant matter.
Non-smoking or chewing policies are not just great for your health, but also for the health of your garden. By keeping dried tobacco away from your garden, you can reduce your risk of transmission.
Use a bleach solution of nine parts water to one part bleach as a tool dip between plants. Allow the tools to soak for one minute. Alternatively, you can dip tools in a mix of one part nonfat milk to four parts water for one minute.
Wash your hands vigorously with soap and warm water for at least 30 seconds if you come into contact with infected plants.
Weeds that are prone to catching TMV should be kept under control in the garden to reduce the potential for plant-to-plant transmission.
If you plant lots of the susceptible plants in a patch, the virus can spread quickly from plant to plant. If you space plants out and interplant with non-susceptible varieties, you can reduce the risk for quick transmission.
Buy seeds or plants that are certified disease-free or TMV resistant. Disease-free seeds need to be fermented, dried at a temperature of 125º F, and preferably saved for 1-2 years before planting to ensure the virus is no longer viable in the seeds. Plants should come from certified seeds and be grown in sterile planting medium.
Consider choosing hybrid or naturally resistant plant varieties to plant if you might be at greater risk for TMV infection. For example, many tomato or tobacco farmers have shifted to TMV resistant seeds. Also, greenhouses seem to be particularly susceptible to TMV, so resistant plants are a good option for indoor growing.
Research has shown that skim milk washes or trisodium phosphate solution can inhibit the virus when applied to seeds and seedlings.
For treating seeds, soak them in a 10% solution of trisodium phosphate for at least 15 minutes. Trisodium phosphate ( (Na3PO4) is a very strong cleaning product additive that can be purchased from online retailers. Use caution when handling.
You can also use one part skim milk to four parts water and spray seedlings until they are saturated. This has been shown to inhibit the virus when used on young seedlings.
If you have identified or suspect you have TMV in plants consider the following options.
Entirely remove the plant and roots, placing them carefully inside a sealed plastic bag to avoid contaminating other plants. Send the sealed bag to the landfill or burn or hot compost the plant matter and disinfect the bag prior to re-use with nine parts water to one part bleach.
If your plants are still productive, it can be hard to remove them. Quite frankly, in many commercial environments, plants are allowed to produce at lower rates rather than lose the entire harvest as a standard practice. However, as long as infected plants remain in the garden, they are a potential risk for transmission to your other plants.
If you don’t plan to immediately remove the plants, then use extra sanitation measures to reduce the risk of spreading the virus. For example, wash your hands after you harvest or otherwise handle an infected plant. Use dedicated gloves for potentially infected plants. Sanitize not only blades but handles of garden tools.
Although TMV is not primarily transmitted by insects, unhealthy plants are more prone to pest pressure. Consider using row covers to prolong the life of your plants and eliminate the possible risk of pest cross-infection.
Do not save seeds from plants that might potentially be infected. Even with fermentation and appropriate drying and storing procedures, the seeds could be a source of future infection. Don’t risk it.
Many of us gardeners share our harvests and our overstock on plants. If you have issues with TMV in your garden, warn other gardeners before sharing. Even if they still want your extra tomatoes, at least they will be forewarned to take extra precautions in processing. Plus, they won’t be tempted to save the seeds.
If you have strains of TMV that are particularly bad for certain vegetables or plants, take a year off from those plants entirely. Then, add extra compost to your garden to speed the decomposition of any plant residues.
Once TMV is in your garden, you can reduce its long-term impact by switching your planting line-up to TMV-resistant varieties for two years to let the disease time-out in your garden.
Temporarily using gardening methods like square foot gardening where you start your garden with brand new soil, can give you a fresh start. By bringing in new soil that does not contain crop residues from TMV infected plants, you can better limit risks for reinfection.