Plants make our surroundings beautiful and lively. But, like all living organisms, they are also susceptible to diseases. While there are diseases that ravage entire plant systems, some of them target leaves, hindering their functions and overall health.
If you’re looking to protect your plants against debilitating diseases, the first step is identifying the disease. After properly identifying the pathogen, you can implement the right treatment.
In this article, we’ll look at common plant leaf diseases and the right treatments to treat them effectively.
Leaf Spot
Leaf spot is a common plant leaf disease caused by viruses, bacteria, or fungi like Xanthosoma, Cercospora, and Alternaria. Most of the leaf spot diseases, however, are caused by fungi. The pathogens are typically host-specific and will cause the disease in a specific family of plants.
Recognizing the Problem
Depending on the pathogen, spots may occur on the upper and lower surface of the leaves. They are, however, first observed in the inner and lower leaves where humidity is higher.
The leaf spots can be black, brown, or tan, rounded or angular, raised or sunken with smooth or fringed edges.
Other symptoms that can help identify the disease include curling and wilting leaves, deformed flowers, and overall poor plant growth. As the disease progresses, you can also observe fungal spores in the larger and older spots.
Management
Leaf spot tends to spread when leaves are wet or there is high humidity, therefore, reducing high levels of moisture is an important step in leaf spot management.
The first step is to prune the affected leaves and dispose of them in the trash. Do not throw them in the compost. Pruning promotes good air circulation, allowing plants to dry up quickly.
Also, as you water the plants, target the roots and keep the foliage as dry as possible. Fertilizing your plants on time also improves their ability to fight against leaf spot disease.
If the disease persists, use copper-based or broad-based spectrum fungicides like mancozeb, iprodione, or chlorothalonil.
Powdery Mildew
Powdery mildew is a group of diseases caused by a variety of fungi in the Erysiphales order. The most common ones include Erysiphe, Podosphaera, Sphaerotheca, and Uncinula. It tends to affect leaves in high humidity or shady conditions.
Recognizing the Problem
Powdery mildew is easy to identify as a white to gray powdery substance visible on the upper and lower leaf surfaces. The leaves also curl upwards, turn brown, and eventually fall prematurely.
Management
The first step is to trim the infected leaves and other affected plant parts and dispose of the debris properly. Do not throw the debris in the compost or till it in the soil as it may overwinter and cause new infestations.
Other management practices include spacing your plants to promote proper circulation and lower humidity levels. Irrigate your plants mid-morning to allow for rapid drying.
Fungicide applications can help kill present infections and prevent future reoccurrences. These include neem or jojoba oil, sulfur-based sprays, and baking soda solutions (1 tablespoon baking soda, ½ teaspoon liquid soap in 1 gallon of water).
A synthetic fungicide like myclobutanil applied in the early stages of the disease can also provide effective control.
Downy Mildew
Downy mildew is another common plant leaf disease that can affect landscape plants and vegetables like lettuce and cabbage. Unlike powdery mildew which is directly caused by fungi, downy mildew is typically caused by algae.
Recognizing the Problem
To identify the disease, look for yellow spots on the upper leaves and white to grayish fuzzy growth on the lower leaves.
Management
Downy mildew often appears during cool, wet weather, therefore, increasing air circulation, reducing humidity, and avoiding overhead watering can eradicate the disease and keep it away.
Once you prune the affected leaves, make sure to dispose of them responsibly to avoid recurrence in the following spring.
To prevent downy mildew disease in ornamental landscapes and vegetable gardens, apply a combination of preventive fungicides like mancozeb and chlorothalonil.
Rust
Rust is a common fungal disease that mostly affects plant leaves. Most rust fungi require specific plant hosts to complete their life cycle. The rust spores vary in color from orange, yellow, black, or brown.
Recognizing the Problem
On leaves, rust appears as ring-shaped orange, golden, or yellow spots. The spots resemble the brown iron rust, hence the name. The pustules are commonly found on the lower surface and can be numerous on a single leaf. In extreme cases, the leaves turn yellow and can fall prematurely.
Management
If it’s a small infestation, removing the affected leaves can stop the spread of the disease. Proper plant maintenance encourages vigorous growth that can overcome rust infestation.
If the infestation is severe, timely spraying of fungicides like mancozeb, cyproconazole, and azoxystrobin can treat the disease effectively.
Blight
Blight is a familiar name as we often associate it with potatoes or tomatoes. It is a fungal disease easily spread by wind, leading to devastating damage. Extended periods of warm and humid conditions accelerate the spread of the disease.
Recognizing the Problem
Blight damage initially appears as small spots and grows into irregular yellow-ringed lesions. The spots often appear along the veins or edges of the leaves. Since they grow close together, they cause quick premature death and defoliation of the leaves.
Management
The best defense against blight is prevention. Avoid sprinkler irrigation as it may create ideal conditions for the disease to develop.
A 2-3 year crop rotation between legumes and non-legume crops can help reduce pathogen buildup in the soil, minimizing an outbreak in the next crop rotation.
The fungicides that provide the best blight control results are mancozeb and chlorothalonil. However, persistent use of one product may lead to resistance, and interchanging is advised. Also, applying the fungicides as preventatives is more effective than using them to eradicate the disease.
Lead Editor for Insight Weeds.