Preventing and controlling plant diseases is key to growing healthy plants. In this section, find information on plant disease identification and control, including rot, freeze damage, rust, blight, mold, scales, bacteria, viruses, fungus, wilt, mildew, gall, mites, moths, and cankers. You’ll also find tips on integrated pest management and herbicide summaries.
The vibrant yellow blooms of the Argentine senna shrub (Senna corymbosa) are a beautiful addition to any garden. However, like all plants, these shrubs can fall victim to diseases that impact their health and appearance. As an avid gardener, I’ve dealt with my fair share of senna shrub diseases over the years. In this article, I’ll cover how to identify the most common diseases affecting Argentine sennas and provide tips on treating them effectively.
Powdery Mildew
One of the most prevalent diseases you may encounter on your Argentine senna is powdery mildew. This fungal disease presents as a white or gray powdery coating on the leaves, stems and flowers. While not fatal, it can weaken the plant and detract from its beauty.
To treat powdery mildew, prune off any affected parts of the plant. Be sure to disinfect your pruning shears between each cut to avoid spreading the disease. You can also apply fungicides labeled for use on ornamentals to prevent its recurrence. Improve air circulation around the shrub through proper spacing and pruning to keep mildew at bay.
Root Rot
Excess moisture around the roots promotes fungal diseases like root rot Watch for wilting leaves, stunted growth, and yellowing foliage as signs of root rot Dig up the plant to examine the roots – healthy ones will be firm and white, while rotten roots appear brown, mushy and easily damaged.
Severely infected plants may need to be discarded. For mild cases, trim off the damaged roots and re-plant in well-draining soil amended with compost. Allow the soil to partially dry between waterings to prevent reinfection. Drenching the roots with fungicides can also help control root rot.
Leaf Spot
Small, dark spots or lesions on the foliage point to a leaf spot infection. These spots may start out small but can expand, killing the leaf tissue and causing defoliation
Prune off and destroy affected leaves to limit the disease’s spread. Disinfect your pruning tools after each cut. Apply copper-based fungicidal sprays as a preventative measure and continue monitoring for new leaf spots.
Anthracnose
The fungus that causes anthracnose thrives in warm, humid conditions. It manifests as dark, sunken lesions on leaves, stems and flowers. Heavy defoliation may occur in severe cases.
Improve air circulation through proper spacing and pruning. Remove and destroy fallen leaves and infected plant parts. Apply fungicides containing ingredients like chlorothalonil or myclobutanil to protect healthy tissue from infection.
Bacterial Leaf Blight
Despite its name, bacterial leaf blight on Argentine senna is caused by the fungal pathogen Pseudocercospora plectranthi. It leads to water-soaked spots that turn brown or black on leaves.
Prune off and discard affected leaves. Disinfect tools after each cut to prevent spreading the bacteria. Apply copper-based bactericides to protect healthy foliage from infection. Destroying fallen plant debris also helps minimize reinfection next season.
Leaf Spots
This disease causes small brown or black spots on senna leaves. The spots may be surrounded by a yellow halo. They start out small but can expand to kill larger sections of leaf tissue.
Remove any diseased leaves and dispose of them promptly. Improve air circulation around the shrub through proper spacing and pruning. Apply fungicides containing chlorothalonil, mancozeb or copper hydroxide directed at the foliage.
Preventing Argentine Senna Diseases
While diseases can arise even in the best cared for shrubs, following proper growing practices can help avoid many issues:
- Space shrubs at least 2-3 feet apart for adequate air circulation
- Water at the base to keep foliage dry
- Prune regularly to open up the canopy
- Disinfect tools between plants
- Remove fallen leaves and debris
- Avoid overhead watering late in the day
Types of Plant Diseases
Plant disease is “anything that prevents the plant from performing to its maximum potential.” We classify plant diseases as either abiotic or non-infectious diseases and biotic or infectious diseases.
Abiotic diseases are those caused by external conditions rather than living agents. These diseases are not infectious and include nutritional deficiencies, salt injury, ice, sun scorch, or soil compaction.
Biotic diseases are caused by living organisms, otherwise known as plant pathogens. These pathogens can spread from plant to plant and affect all parts of the plant, including roots, tubers, leaves, shoots, stems, crowns, fruit, and vascular tissue. Plant pathogens include fungi, fungal organisms, viruses, bacteria, phytoplasmas, viroids, parasitic higher plants, and nematodes.
Being able to quickly and accurately diagnose plant health gives you the best possible chance to solve any issues before losing the plant.
Field Crop and Forage Plant Diseases
A wide variety of diseases attack field and agronomic crops and forages. Successful disease control requires correct identification and knowledge of the cause and life cycle of the disease. It’s also essential to have control procedures available. There is plenty of information available for producers to increase their knowledge base, such as the Penn State Agronomy Guide. You can also turn to professional crop advisers or agronomy scouts for further guidance.
To make the right decisions about the controls to use, you need to have first-hand knowledge of the condition of the crops or forages in the field. Some common diseases to look for in corn include gray leaf spot and corn ear rot. Mycotoxins can cause moldy corn. Yield-limiting plant diseases do not become problematic until the reproductive stages of development, which means there is little benefit to early season fungicide applications.
Forage grasses are susceptible to a variety of leaf, stem, floral, and root diseases. Recent developments have led to improved management practices, such as using disease resistance species.
Small grains such as wheat may display symptoms of diseases such as head scab, black chaff, and Stagonospora glume. The quality and size of your yield depend on the severity of the disease.
There are some late-season diseases to look out for in soybean crops. Stem canker doesn’t show symptoms until well into the reproductive stages of growth. Soybean sudden death syndrome has pretty striking symptoms, but other diseases, such as brown stem rot or injury from chemicals can mimic it.
How To Identify Common Shrub & Tree Diseases
Can a landscape professional diagnose sick shrubs?
Similar to humans, when the needs of shrubs are not met, a decline in health will result. A landscape professional, trained and knowledgeable about plant health, can inspect and diagnose sick shrubs but for those determined to do a little self-diagnosing, here are some fundamentals to get you started.
What is the prognosis of shrub disease?
Depending on the specific type of shrub affected, the disease, diagnosis and treatment will all vary. Similar to humans, when the needs of shrubs are not met, a decline in health will result. You can begin by narrowing your prognosis by eliminating improper growing conditions or shrub pests.
Are there common shrub diseases in Atlanta?
Fortunately, many of these can be prevented if you know what to look for and how to treat it. Check out these tips from our lawn care experts to help you identify common shrub diseases, or call us at 770-923-0387 for a free estimate and landscape analysis. One of the most common afflictions Atlanta shrubs face is a fungus, Powdery Mildew Fungus.