Bald cypress trees are stunning landscape specimens known for their graceful, feathery foliage. However various diseases can affect these trees, including downy mildew. This fungal disease results in unsightly foliage damage and potential defoliation when left unchecked. If you notice signs of downy mildew on your bald cypress, prompt action is needed to treat the issue and protect your tree.
What Causes Downy Mildew?
Downy mildew on bald cypress is caused by the fungus Peronospora taxa. It thrives in cool, wet conditions. The fungal spores can easily spread between trees via wind or rain splash. Once infection occurs, the fungus penetrates the leaves, consuming nutrients and causing spotting, discoloration, and defoliation. Stressed, damaged, or overcrowded cypress trees are most susceptible.
Identifying Downy Mildew
Be on the lookout for these common symptoms
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Pale green patches on upper leaf surfaces
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Grayish, fuzzy fungal growth on leaf undersides
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Yellowing or browning of foliage
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Premature leaf drop
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Stunted spring growth
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Dieback of shoots and twigs
Carefully inspect both sides of leaves, especially after wet weather. Check inside the canopy for internal symptoms. Early detection and treatment is key to combatting downy mildew successfully.
Treating Downy Mildew
If downy mildew is identified early, treatment can help restore tree health. Recommended control methods include:
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Improve air circulation and light penetration through proper spacing, pruning, and thinning of canopy.
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Rake up and dispose of fallen leaves to remove spore source.
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Apply fungicidal sprays containing chlorothalonil, mancozeb, or copper sulfate during early stages of infection. Repeat per label instructions.
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Water in early morning to allow foliage to dry out during the day. Avoid overhead irrigation.
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Mulch around tree to prevent spore splash from soil onto leaves.
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Fertilize appropriately to maintain tree vigor. Avoid over-fertilization.
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Monitor weekly and treat promptly at the first sign of infection.
With aggressive treatment, downy mildew can be controlled before severe defoliation and dieback occurs. But prevention is better than cure when it comes to protecting your bald cypress.
Preventing Downy Mildew
Here are some tips to avoid downy mildew problems in the future:
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Select resistant bald cypress varieties like Shawnee Brave, Berryville, and Emerald Sentinel.
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Prune branches regularly to open up interior canopy and increase sunlight and airflow.
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Water early in the day at soil level to keep foliage dry.
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Space trees properly to prevent overcrowding.
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Clean up and dispose of leaf litter and debris around trees.
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Sterilize tools after pruning infected trees to avoid spreading spores.
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Apply preventative fungicide spray after new spring growth emerges.
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Monitor weekly and treat any issues promptly.
With diligence and proper care, you can help prevent downy mildew from taking hold in your landscape. Keep your bald cypress healthy and continue enjoying its graceful beauty for years to come.
Powdery Mildew versus Downy Mildews
Powdery mildew (Podosphaera xanthii or Erysiphe cichoracearum) is one of a number of other fungal diseases often confused with downy mildew. Mixing them up is a problem because the treatments for each are different. Powdery mildew is a whitish growth that looks like a powder. The spots start as circles on the surface of the leaf and then grow to cover the whole leaf, including the veins. The leaves only turn yellow after they have had powdery mildew for a while. Powdery mildew can kill plants by blocking the chlorophyll in the leaves from sunlight. The plant starves to death as a result.
Stopping downy mildew is much easier than controlling it. Help prevent downy mildew in your landscape by following these tips.
Scientists have bred some resistant cultivars of plants that are susceptible to this disease. While every type of plant does not have a choice that is resistant, use resistant cultivars wherever possible. Make sure that you do not get any infected seed by buying from a reputable nursery.
It is important to scout your plants often. If you see symptoms, remove that plant immediately, put it in a plastic bag, and put it in the trash. Do not compost diseased plants as most home compost piles are not hot enough to kill the downy mildew pathogen.
Wet leaves are necessary for this type of mildew to invade plants. Eliminate moisture by pruning plants to improve air circulation. In row crops, make sure to space plants to allow for good air circulation even after they are mature. Make sure the rows are far enough apart, as well.
One of the worst things you can do is water plants from the top. A whole host of diseases must have wet leaves to infect the plant. Overhead irrigation wets the leaves. If you must water from the top, water in the early morning hours, before 10:00 a.m. so the leaves will dry before nightfall.
The best way to water plants is using drip irrigation. The water comes out at the emitters at ground level and sinks right to the roots. Drip irrigation also saves money because it takes less water.
Mulching helps keep soil off your plant’s leaves so mildews don’t get a foothold. Mulch conserves water and keeps roots warm in winter and cool in summer. Three inches of mulch around your ornamental plant repays the cost of replacing plants many times over.
Sanitation is key to controlling downy mildew. The spores overwinter in plant debris. Infected leaves have spores on them that can get splashed on uninfected leaf surfaces. After your crops are done, rake up all leaves and plant debris and discard them. If you are dealing with ornamental plants, make sure all the leaves are off the mulch when they have finished falling.
Quarantine new plants for a while before putting them in the ground or the greenhouse. Since a plant can be infected up to 10 days without showing symptoms, a regular 14-day quarantine is helpful in reducing plant disease.
Important Strains of Downy Mildews
These types of downy mildew are economically important. They often attack home gardens as well as commercial growers.
Cucurbit downy mildew infects cucumber, melon, gourds, pumpkin, and squash. In watermelons, the leaves curl more than on other crops as well as displaying the rest of the symptoms.
These include cabbage, broccoli, Brussel sprouts, kale, kohlrabi, Chinese cabbage, turnip, radish, cauliflower, and mustard.
This infects the leaf, stem, flowers, and fruit and kills off the vines.
Kill Powdery Mildew With This Natural Garden Remedy: Hydrogen Peroxide
FAQ
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