Cercospora Leaf Spot – Symptoms and Damage Prevention

Family:Mycosphaerellaceae

This is a fungus disease that affects crops like eggplant, hot pepper, sweet pepper, carrots, okro, Sugar beet, beet root, roses, shrubs.This fungus symptoms can occur primarily on foliage, petiole and stem lesions develop when conditions are highly favorable. It can be stored in crop residues and spread by wind, insects , water etc.

LifeCycle

Cercospora leaf spotcan be caused by many different Cercospora fungal pathogen speciesdepending on the plant type infected. For example, Cercosporabeticola infects sugar beets whereas Cercospora rosicola infects roseplants.

This is considered afoliar disease and can be especially devastating to sugar beet cropsin North Dakota and Minnesota. This disease is sometimes misdiagnosedas black spot. Infection will begin at the bottom of the plant andwill work up toward leaves with new growth.

This happens when thefungal spores germinate and enter through natural openings of leaveswhen conditions are optimal. If leaves do not have high moisturelevels on their outside tissue for at least 11 hours, new spores areunlikely to enter the plant.

While infection ismost commonly found on leaves, sometimes stems, bracts, or fruit canalso be affected. Once spores infect a plant, it will take 5 to 21days for symptoms to appear. This fungus has the ability tooverwinter in plant debris that remains in a field after harvest.

Cercospora Leaf Spot

Symptoms and Damage

One of the most common symptoms of this disease attack on crops is when you notice round spots with a light grey center and a deep brown margin surrounded by a yellow ring. The leaves later turns yellow then wilt and fall.

Onstems, elongated spots can be seen as they appear.

Identificationand Habitat

Identification

As the name suggests,this disease causes spots on foliage. The circular blemishestypically have an average diameter of 3 millimeters that is betweenbrown and reddish-purple in color, bordering a gray center.

However, if spots havejust developed, the gray center will not yet be visible. When thisfungus experiences favorable conditions, it may progress through 4 or5 cycles in one season.

Each progressive cycleis often more severe than the previous one, with spots sometimesgrowing to have a diameter of 10 millimeters. As these spots kill theplant cells, leaves will begin to fall from the plant, causingdefoliation.

A plant’s yield willbe reduced from the limited photosynthetic capacity and can alsoresult in more juice impurities and less sucrose extraction for sugarbeets.

Habitat

Cercospora leaf spotfavors weather that is wet, warm, and humid; often most prevalentfollowing canopy closure. During the day this fungus thrives whentemperatures are between 80 and 90 degrees Fahrenheit and at nightwhen temperatures exceed 60 degrees Fahrenheit.

The disease will notdevelop well if temperatures reach 93 degrees or higher. Humiditylevels are preferred between 90 and 100 percent. More susceptibleconditions for Cercospora involve areas near waterways, plants closeto other fields that were infected in the past, and those nearshelter-belts.

Managementand Control Methods

CulturalControl

Since infection growsworse with time, early control is essential for effective managementof this disease. In order to do this, scout fields frequently tocatch any infection early, especially in highly susceptible areas.Also, whenever possible keep vulnerable plants away from areas thatare most commonly affected by this disease.

For example, plantsugar beets no closer than 100 yards from other previously infectedareas. Practice fall tillage to bury infected plant debris that couldbe a possible overwintering site for Cercospora spores. Rotate crops,giving sugar beets a 2 year break in-between and replacing them witha crop type that is less susceptible.

It is important tonote that having satisfactory control is often dependent on using anintegrated management system that includes the use of both culturaland chemical methods.

ChemicalControl

Fungicides should beapplied once first symptoms appear. Most often, additionalapplications will be needed to continue effective control, especiallywhen conditions are favorable for this fungus; however, if usingTopsin with a protectant (e.g., Supertin), this application shouldonly be used once per season.

Other fungicides withthe following active ingredients have also shown to be effective forthe control of Cercospora: copper oxychloride, sulfur, maneb,mancozeb, chlorothalonil, propiconazole, and neem oil. Always be sureto carefully read the fungicides label for cautions and properapplication before use.

In order to avoid thisfungi building a resistance to a certain chemical, ensure the samefungicide is not being used back-to-back. Additionally, if only oneapplication type is being used annually, do not use the same type ofapplication.

High spray pressure isbest, often 100 psi, and also high water volume. Using both of thesemethods can create more effective control. On average, fungicides canprovide protection for 2 weeks. Also, treatment methods in place forpowdery mildew and black spot have also helped in the management ofCercospora.

cercospora leaf spot

Damage Prevention

Someof the ways by which these fungus disease can be managed or preventedis through the following measures:

  1. Always use healthy seeds.
  2. Remove all crop residues, weeds and infested plants.
  3. Avoid overhead watering otherwise water early in the morning.
  4. Apply fungicides on the foliage in case of early symptoms.
  5. Implement crop rotation by alternating with plants such as sorghum, corn or fodder plants.

Refrences:

https://www.ag.ndsu.edu/cpr/plant-pathology/controlling-cercospora-leaf-spot-with-fungicides-8-11-11

https://edis.ifas.ufl.edu/pp267

https://www.ag.ndsu.edu/pubs/plantsci/rowcrops/pp1244.pdf

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