As temperatures drop and days shorten in fall, new opportunities emerge with the start of a new season. Unfortunately, that change also means new threats emerge. Garden diseases aren’t only prevalent in the warmer months – they can strike in fall and winter, too.
Whether you’re looking for an impressive winter harvest or want to keep your fall perennials happy, it’s important to stay vigilant for both pests and diseases in fall. Regular monitoring, correct watering techniques, and intervention as needed can keep your garden free of fall plant diseases. Catching these problems early stops a small problem from becoming an overwhelming one.
Powdery Mildew
The descriptive name of this fungal disease makes identification easy. Powdery mildew shows up as a white or gray powdery coating on the leaves (or stems and flowers) of a variety of species. It pops up toward the end of summer and can remain throughout fall, especially on leafy vines like cucumbers and squash.
Powdery mildew is not highly damaging, but it does weaken plants by interfering with photosynthesis. Over time, leaves begin to yellow and may even die off if the problem is severe and left unchecked.
This disease spreads quickly in overcrowded environments with little airflow and high humidity. To prevent it, prune any overcrowded areas and space your fall plants carefully. If you notice the early signs of infection, remove the affected parts of the plant to prevent spread. While some choose to leave their plants, powdery mildew can survive the winter in plant debris, so it’s best to discard any major problem areas.
Downy Mildew
While powdery mildew typically spreads through gardens in dry conditions, downy mildew prefers damp and cool environments in the spring and fall. Different species prefer different host plants, but it is common on leafy greens and herbs in fall, especially after periods of heavy rain.
The first signs typically appear on the surface of leaves as small yellow spots. Leaf undersides will have mold corresponding to the spots on the upper surface. The affected leaves eventually wilt and die, impacting overall health. As the disease spreads, growth problems become more severe, particularly in fruiting plants.
Prevention is key to tackling this disease. To prevent downy mildew, avoid overhead watering or install drip irrigation to focus the moisture on the soil. Mulching around the base of the plants can also help by reducing the splash of water from the soil onto the leaves.
If downy mildew does appear, remove and destroy the infected parts of the plant immediately. Using neem oil can also help control its spread, but it does not remove the problem.
Early Blight
If you’re growing tomatoes or potatoes, you need to be aware of early blight. This disease produces dark rings on the lower leaves of the plant that slowly spread over time. The signs usually appear around mid-summer but can continue into fall if not effectively managed.
When left unchecked, early blight can cause significant defoliation, reducing the plant’s ability to produce fruit. It can also remain in plant debris over the cooler months, ready to attack again when the conditions are right.
Remove any infected plant material immediately, and avoid watering the leaves directly. Focus the water stream on the soil only and try to limit any splashing water from transferring problems from the soil to the foliage. A mulch barrier can also help here.
Luckily, there are several prevention methods you can adopt to stop early blight from becoming a major problem in the first place. One of the best options is choosing resistant varieties like the ‘Indigo Rose’ cherry tomato. Also rotate crops so susceptible plants are not infected the following year.
Leaf Spot
Dreaded leaf spot is not one specific disease but a group with a common symptom. You guessed it, leaf spots. Leaf spots are caused by fungi (or sometimes bacteria) and can be brown, black, or yellow, depending on the species. Like the previous entries on this list, they typically begin in late summer and continue into fall.
There are specific measures of control for different types, but preventing leaf spot (and other diseases) starts with keeping your garden tidy. Remove any fallen leaves or plant debris, as these are avenues pathogens use to overwinter and spread. Again, water the base of the plants rather than the leaves to help keep the foliage dry and less susceptible to infection.
If leaf spot appears, remove the affected leaves as soon as you spot them. Dispose of them properly, and never add these leaves to your compost pile. If you have trees affected in fall, rake up the leaves often to discard them before the issue spreads.
Black Spot
Rose growers will know the struggle of black spot, a common fungal disease in rose gardens. As the name suggests, it produces easily identifiable black spots on the leaves, which eventually drop off the plant.
Cooler evenings create the perfect environment for black spot to spread, particularly in humid regions. Watering in the evenings and watering overhead or periods of rainfall exacerbate symptoms.
To manage black spot and other rose diseases, ensure your roses are planted in a sunny location with good air circulation. Keep the foliage dry year-round and prune regularly to remove any overcrowded canes that can trap moisture.
While black spot is almost inevitable on roses, it’s still important to remove the affected leaves immediately. Clean up fallen leaves around the base of the plant to prevent the fungus from overwintering. A layer of mulch is a good deterrent as well.
Rust
Rust is a fungal disease that typically produces rust-colored pustules on the underside of leaves, although different types produce slightly different symptoms. It doesn’t always start in fall but continues to spread this season, with the previously bright pustules turning dark brown as they age.
Rust weakens plants, causing stunted growth and poor overall health. It’s also more likely on stressed or unhealthy plants, making growth issues that much worse. While it won’t kill a plant instantly, it can cause defoliation and harvesting issues in vegetable gardens.
Although there are different types of rust, prevention methods are the same. Start by removing any infected leaves and improving air circulation around your plants. Don’t compost these leaves – discard or destroy them. Continue cleaning any debris and fallen leaves throughout the season to remove spots where rust might like to overwinter. Rotate your crops from season to season.
Scab
Scab is a damaging disease that affects a wide range of garden fruits and vegetables in the fall, including apples, pears, and potatoes. The rough and scabby lesions pop up on the fruit (or tubers in the case of potatoes), not something you want to see when you’re looking forward to your harvest.
Scab is an issue from early spring and into summer but continues into fall until trees drop their leaves. Fruit trees become more susceptible if they’ve been stressed by drought or other factors earlier in the season.
Choose resistant varieties whenever possible, such as the ‘Honeycrisp’ apple tree. Rotate smaller crops like potatoes every season. Also, avoid over or underwatering and make sure your plants have good air circulation to reduce humidity around the foliage.
Although fruits with signs of scab are generally considered safe to eat, they don’t look particularly tasty. Use pruning and preventative measures to avoid the spread of this issue.
Anthracnose
Anthracnose appreciates the cool temperatures of early fall, especially after periods of wet weather.
It is one of the most common garden diseases, resulting in issues with leaf spots (as discussed earlier) and various blights. It affects a variety of plants and causes dark, sunken lesions on foliage and fruits. Specific symptoms differ depending on the species and host plant.
The management of this disease is the same as other fungal diseases. Correctly space plants at planting time to avoid overcrowding and prune as needed to increase airflow. Mulching can help prevent the fungus from splashing onto the plants from the soil, and removing any infected plant material will reduce the spread of the disease.
Black Rot
Black rot is a bacterial disease that is found on brassicas in fall and winter, caused by the bacterium Xanthomonas campestris pv. campestris. Other garden diseases have the common name black rot, but this is one of the more likely types to appear in fall.
Infected plants develop v-shaped marks on the foliage with significant discoloration. These marks slowly spread throughout the leaf, causing wilting and leaf drop. You may also spot black markings that indicate a disease issue.
This bacterial disease spreads quickly in wet, warm conditions. Watch your watering and clean up any infected debris or plants to limit spread. Since the issue can spread via infected seed, only purchase seeds from a reputable supplier.
