Ramularia Leaf Spot

What do artichokes, barley, beets, patience dock, rhubarb, and strawberries have in common?

Besides being delicious, they are all susceptible to a fungal disease called Ramularia leaf spot (RLS). Cotton, daffodils, jonquils, and narcissus are also vulnerable, along with several other wild plants, such as cowslip.

Severe Ramularia infection of strawberry (Jerzy Opioła) CC BY-SA 4.0

Ramularia leaf spot symptoms

Like most other leaf spot diseases, this one is characterized by, you guessed it, leaf spots. Reddish-brown spots occur on both upper and lower leaf surfaces. Those lesions often have a yellow halo but can be angular, circular, or rectangular, making this disease difficult to identify. Some even call Ramularia the master of disguise. To get a clear identification, growers refer to the five R's of Ramularia infection:

1. Red dots turn into reddish-brown spots [purplish on strawberry leaves, yellowish-green on rhubarb stalks].
2. Rectangular more often than not.
3. Restricted to the space between leaf veins.
4. Ringed with yellow halos [purple on rhubarb].
5. Right through the leaf.

Brown ulcers may also occur on flower bracts. Eventually, those bracts will curl up and dry out. Growers believe this disease is spreading because it is difficult to identify with certainty. But you can always assume that spots warrant a closer look.

Ramularia on patience dock (Tristram Brelstaff) CC BY-SA 3.0

In the case of Ramularia leaf spot, entire leaves will eventually shrivel up and die, taking millions of white fungal spores with them. Then those spores are splashed onto neighboring plants through rain and overhead watering.

Ramularia leaf spot lifecycle

Ramularia fungi have a rather complicated life cycle. There are several varieties with slightly different symptoms, but let's keep it simple, shall we? Most importantly, this disease spreads through infected seeds and plant debris and on the wind. Once spores come into contact with a plant, lesions form on lower leaves, spreading to upper leaves, then flowers. Those flowers produce infected seeds that continue the cycle.

Ramularia lesions (James Lindsey) CC BY-SA 3.0

Ramularia leaf spot management

Infected commercial crops are sprayed with fungicides up to eight times a year with limited success. Of course, you must wear protective clothing and limit the time spent around these chemicals to stay safe, so you might want to think twice before applying them to your groceries.

Since stressed plants are more likely to become infected, keeping your plants healthy with these tips can prevent many problems.

• Avoid overhead watering or water early in the day.
• Dispose of infected plants in the trash, not the compost pile.
• Employ crop rotation.
• Invest in certified disease-free seeds and seedlings.
• Quarantine new plants.

Figuring out what leaf spots are telling you can be tricky, but it's worth the effort to find out.