Unlike its robust counterparts like sage, rosemary, or thyme, cultivated parsley sometimes falls victim to disease issues. One of the most common problems is leaf spots on parsley. But what exactly causes these unsightly spots? Let’s delve into the two major parsley leaf spot diseases and how to combat them.
Understanding Parsley Leaf Spot Problems
One possible cause of leaf spots on parsley is powdery mildew, a fungal disease that thrives in low soil moisture and high humidity. This ailment initially appears as blister-like lesions on young leaves, often accompanied by leaf curling. As the infection progresses, the affected leaves become covered in a white to gray powdery substance. In severe cases, the plants may even experience leaf drop, especially among the younger leaves. Powdery mildew is favored by a combination of low soil moisture and high humidity levels around the plant surface.
Another culprit behind leaf spots on parsley is bacterial leaf spot. This disease manifests itself in different ways. With parsley leaf spot resulting from bacterial infection, you may observe angular tan to brown spots on the top, bottom, or edge of the leaf. These spots lack mycelia growth or fungal structure and may cause the infected leaves to become papery and easily crushed. Typically, older leaves are more susceptible to this type of infection than newer ones.
While both powdery mildew and bacterial leaf spot are concerning, they can be effectively treated with copper fungicide at the first sign of infection. Additionally, planting resistant strains and practicing good garden sanitation can help prevent the diseases from taking hold.
Other Diseases that Lead to Leaf Spots on Parsley
Septoria
Another common leaf spot disease affecting parsley is septoria leaf spot. This disease is introduced through infected seeds and can survive on dead or dried leaf detritus for several years. Early symptoms typically include small, depressed, angular tan to brown lesions, often surrounded by red or brown margins. As the infection progresses, the interior of the lesion darkens and becomes dotted with black pycnidia.
Neighboring plants, overwintered plants, or volunteer plants can also serve as sources of infection. The disease spreads during rainy periods or under overhead irrigation, as well as through contact with wet plants via people or equipment. Mild temperatures and high humidity provide favorable conditions for spore growth and increased infection.
To control septoria leaf spot, use disease-resistant seeds whenever possible or opt for seeds that have been treated to reduce seed-borne diseases. Drip irrigation is preferable to overhead irrigation. Additionally, rotating to non-host crops for at least four years in areas where the disease has been present can be helpful. Providing ample space between susceptible plants to promote air circulation, practicing good garden sanitation, and removing or deeply burying any crop detritus are also essential. Applying a fungicide early on according to the manufacturer’s instructions is advisable. For organic cultivation, a combination of cultural controls and potassium bicarbonate can be used on certified crops.
Stemphylium
In recent times, another fungal leaf spot disease caused by Stemphylium vesicarium has been observed in parsley. This particular disease is more commonly associated with garlic, leek, onion, asparagus, and alfalfa crops. The symptoms begin as small circular to oval leaf spots, initially yellow in color. Over time, the spots enlarge and turn tan to dark brown, with a yellow corona. In severe cases, the spots merge, causing the foliage to yellow, dry up, and eventually die. Although older foliage is more susceptible, this disease can affect leaves at any stage.
As with septoria leaf spot, Stemphylium leaf spot is introduced through infected seeds and spreads through splashing water from overhead irrigation or rainfall, as well as through activity around the plants.
To control this disease, it is advisable to use disease-resistant seeds or seeds treated to reduce seed-borne diseases. Drip irrigation is preferred over overhead irrigation. Rotating to non-host crops for at least four years in affected areas is recommended. Providing adequate space between susceptible plants to allow for air circulation, practicing good garden sanitation, and removing or deeply burying any crop detritus are also crucial steps. Applying a fungicide at the first sign of symptoms, following the manufacturer’s instructions, is essential. For organic crops, a combination of cultural controls and potassium bicarbonate can be used.
Understanding the various diseases that cause leaf spots on parsley and implementing the appropriate preventive measures and treatments is crucial for maintaining healthy and robust parsley plants. By adopting a proactive approach, you can ensure that your parsley thrives, adding flavor and vitality to your culinary endeavors.