The dark spots appearing in the centers of the leaves of your plants increase in size as time goes by and eventually cause the leaves to die? This may have been a fungus disease caused by some species of cercospora that develop during damp and rainy summers. Cercospora leaf spots are one form of th e leaf spot disease.
This particular genus contains over 1200 species, each of which is specialized towards a particular plant species it tends to attack. Most common among these is Cercospora beticola. Small spots on leaves of all species eventually multiply into lesions, turning leaves brown and eventually causing “full leaf collapse” or defoliation. Some species are particularly susceptible to this fungal infection, while others have natural resistance to it.
At this point, gardeners need a good strategy to overcome cercospora on leaves. Allowing a crop to fall victim to this disease is not a good option, so it’s important to have a plan in place. It’s better to catch these lesions early and utilize successful management methods so that your neighbors won’t have the same problems you’re facing. By utilizing the right resources and taking the right steps, you will be able to prevent the infection from spreading beyond the point of resistance and prevent cercospora fungus from infecting other plants you love to grow.
What is Cercospora Leaf Spot (CLS)?
All species of cercospora prefer humid, warm environmental conditions (especially warmth and humidity at night). In order to prevent spore growth, the temperature must be between 77 and 95 degrees Fahrenheit in early summer or late spring. Proper irrigation management is essential in this regard. Leaf spots infected with cercospora appear as small dark circular lesions less than an inch in diameter on the leaf. These lesions are purple to maroon in color and have a gray or brown interior. If left untreated, the lesions will spread to younger leaves if not treated. You will first notice these lesions on mature leaves, but they will also move to younger leaves if left untreated.
Lesions form near the mouth of the plant or the perimeter and expand upwards and inwards through the plant’s life. During the progression of the disease, these lesions cause nutrients to divert from fruits, vegetables, and flowers to leaves, making the development of non-leaf elements impossible. This disease can cause your crop’s yield to decrease by a significant percentage; you may lose more than half your harvest.
The susceptibility of plants to leaf collapse varies by species; certain cultivars are resistant to the condition more so than others. Agricultural scientists have undertaken research into naturally resistant varieties. It is best to avoid cultivating those species in traditionally warm and humid climates so that you stop spreading the disease or lose 50% of your crop to severe CLS-affected plants.
The beta species of plants are susceptible to cercospora leaf spot: swiss chard, sugar beets, spinach. The pathogen is spread by weeds, which are often the source of the infection. Even remaining seeds and plant debris can compromise the disease management process, which is easy, but requires attention to detail.
Types Of Cercospora Fungi
Farmers and gardeners commonly encounter Cercospora beticola, which attacks the beta group of plants (sugar beets and leafy greens). Cercospora leaf spots occur on a wide range of other plants as well. Roses are susceptible to Cercospora rosicola. This fungus is susceptible to Cercospora hydrangea on Hydrangea plants, and Cercospora melongenae on Eggplants. The variety of species shows how adaptable it is and how quickly the spores can spread. The health and safety of your garden as well as those around you depends on proper management and control of the spread.
There are various cercospora species in the world and not all are associated with cercospora leaf spot (CLS) on plants; for instance, cercospora blight occurs on soybeans. The same term is used for cercospora damage on junipers, celery, and carrots. Cyclosporic leaf spot is the outcome of infection with a particular cercospora pathogen. Cercospora on corn is called gray leaf spot.
Life Cycle Of The Cercospora Fungus
Generally, Cercospora species reproduce by spreading from infected leaves, seeds, or other plant debris, usually by wind and rain. They then attach themselves to healthy leaves and invade their cellular structure. A fungus causes the plant to develop lesions, which allow further asexual reproduction of spores, ultimately causing the plant to die. Infestations of this fungus can be spread by infected garden beds, tools, or weeds. They can be made worse by infected seeds, as well as when debris is left in garden soil. When temperatures and humidity are warm at night, and temperatures remain between 77 and 95 degrees, the conditions are optimal for CLS.
Symptoms of Leaf Spot
There are differences among species of CLS or cercospora blight, with some showing symptoms that appear as maroon spots on sugar beets. Infections of eggplants that are caused by CLS have light brown, irregular spots with no border, the color of caterpillars. Fruits can also be infected with spots that resemble caterpillars eating the fruit.
The symptoms of Cercospora rosicola are very distinct purple necrotic lesions surrounded by light tan or grey centers whereas those of Cercospora hydrangea are more light grey to white in color. The symptoms of Kale CLS are varied, but typically show light brown discolouration. Sometimes the lesions have a purple border. Spinach cercospora leaf spot symptoms are similar, though it doesn’t always have a dark maroon border. Even plants suffering from severe symptoms have the same general symptoms: brown leaves and dead stems grow where the leaves were once alive.
There are, however, other pathogens that may be confused with cercospora leaf spot. One potential example is black leaf spot on roses, which is characterized by clusters of leaves without necrosis. Black leaf spots will not look as round as CLS. It is possible to discern a fungal infection from a bacterial infection by inspecting the spots with a magnifying glass. Light gray or light purple hairs suggest a fungal infection, not a bacterial infection. Being aware of the differences between diseases is useful when trying to control and prevent a problem. In the process of identifying diseases, you can take advantage of many resources available. Your local agricultural extension office is a terrific source of information.
Controlling Cercospora Fungi
Although cercospora species can be controlled with fungicide, good garden hygiene is the best way to prevent cercospora leaf spot from spreading. Cercospora leaf spot is most common in humid summer weather, which lasts through the night. This environment is favorable for cercospora spores, which can lead to further disease development, making management especially crucial during high temperatures. Understanding this environment is the first step in understanding how to control CLS.
Even though organic treatment methods are slightly less effective than chemical treatment methods, they are still viable. The home gardener also has much more access to these methods than to most chemical methods, so that’s great!
Researchers found that organic fungicides versus chemicals were the most effective treatments for Cercospora beticola in beet crops. They required both a liquid copper fungicide and Bacillus amyloliquefaciens. The former is a fungicide produced by bacteria, while the latter is copper dissolved in a gel and subsequently injected into the target. Both have high fungicidal properties, however their combined action was extremely effective against cercospora species.
A fungicide that protects against CLS disease should be applied in advance of conditions where CLS is expected to appear. Neem oil is also effective in treating CLS disease, but more as a preventative than as a treatment. As a preventive measure, use fungicides to protect your crops if you know that summer temperatures will be high and humidity will be high.
To control CLS or cercospora leaf blight, there are two types of fungicides: fungicides applied to leaves and systemic agents. One popular plant treatment is triphenyl tin hydroxide (Super Tin). These are applied to the leaves of beticola, and other varieties susceptible to disease development. Other systemic fungicides that are applied to leaves include Benlate and Topsin M.
If you have noticed the development of cercospora leaf spots resistant to many fungicides, contact your local agricultural extension office to determine whether an additional application of systemic fungicide will worsen the outbreak of resistant strains of cercospora disease. A reliable resource is your local agriculture extension service to find out about common diseases in your region and when to apply fungicides.
Preventing Leaf Spots
Managing the site where you grow for cercospora leaf spot is the only surefire way to prevent it. Make sure your garden is properly irrigated, your beds are free of dirt, and contact with infected plants and areas should be limited. If you are imitating irrigation, your crop will become humid and moist, which encourages cercospora growth. Avoid leaf-to-leaf contact with infected crops, and don’t let plants that have CLS go to seed. In a similar vein, do not plant seeds infected with cercospora leaf spot, as this will just prolong its life cycle and give it more time to develop resistance to treatments.
If you have a sugar beet plant, a rose, or another vegetable susceptible to cercospora leaf spot, review all of its leaves regularly, especially in humid hot summers when the disease is more likely.
Environmental and cultural preventative measures are the best way to manage CLS. Use clean tools after every use. Remove infected plants from your vegetable beds and compost piles. Don’t plant near an infection area since the spores usually stick around there. Rotate your crops and plant away from previously infected areas. Agricultural and horticultural scientists have identified some strains of plants that can withstand defoliation caused by CLS. These strains can withstand leaf defoliation.