Rhubarb Leaf Spots: Causes and Treatment
Introduction
Rhubarb is a popular vegetable that is often used in pies and sauces. It is easy to grow and generally pest-free. However, rhubarb can be susceptible to leaf spots, which can affect the appearance of the plant and, in severe cases, reduce its yield.
What Causes Rhubarb Leaf Spots?
Rhubarb leaf spots are typically caused by fungal diseases, such as Ascochyta and Ramularia. These fungi spread through spores that are carried by wind and splashing water. The spores can infect rhubarb plants through small wounds or openings in the leaves.
Symptoms of Rhubarb Leaf Spots
Ascochyta Leaf Spot:
- Small, greenish-yellow blotches on the upper surface of the leaves
- Blotches develop white centers surrounded by a reddish border and a grayish-green area
- Infected areas turn brown, die, and fall out, creating holes in the leaves
Ramularia Leaf Spot:
- Small, red dots that enlarge to become round lesions
- Lesions become white, then tan with a purple border
- Stalks may develop a white fungus that gradually turns brown as the tissue dies
Cultural Factors Contributing to Rhubarb Leaf Spots
In addition to fungal diseases, cultural conditions can also contribute to the development of brown spots on rhubarb leaves. These include:
- Pesticide residue: Pesticides can cause yellow patches on the leaves that gradually turn reddish-brown.
- Salts: Excess salts in the soil can also cause brown spots on rhubarb leaves.
- Overcrowding: Rhubarb plants that are too close together can create a humid environment that favors the growth of fungi.
- Lack of dividing: Rhubarb plants should be divided every 10 years to prevent overcrowding and promote healthy growth.
Treatment and Prevention of Rhubarb Leaf Spots
Cultural Practices:
- Practice good sanitation by removing and destroying infected leaves and stems.
- Plant rhubarb in a sunny, well-drained location with fertile soil.
- Keep the area around rhubarb plants weed-free and free of debris.
- Divide rhubarb plants every 10 years to prevent overcrowding.
- Fertilize rhubarb plants regularly to improve their overall health and resistance to diseases.
Fungicides:
In severe cases, a copper compound fungicide may be applied to control leaf spot. However, it is important to follow the instructions on the fungicide label carefully and to avoid overuse.
How to Get Rid of Brown Spots on Rhubarb Leaves Caused by Cultural Conditions
- Pesticide residue: Avoid using pesticides on rhubarb plants. If pesticide residue is suspected, rinse the leaves thoroughly with water.
- Salts: Leach excess salts from the soil by watering the rhubarb plants deeply and frequently.
- Overcrowding: Divide rhubarb plants every 10 years to prevent overcrowding.
- Lack of dividing: Dig up and divide rhubarb plants that have not been divided in over 10 years.
Conclusion
Rhubarb leaf spots are a common problem that can affect the appearance and health of rhubarb plants. By understanding the causes and symptoms of these diseases, as well as implementing proper cultural practices, you can prevent and treat rhubarb leaf spots and ensure a healthy and productive rhubarb harvest.
