Cerospora is known as both Leaf Blight and Leaf Spot. It’s a common fungus that infects many food crops including carrots, grain legumes, peppers, corn, soybeans, and coffee. Many gardeners and farmers are familiar with this disease and with how its sudden appearance can spell doom for a crop.
There are many host plants in the cornucopia to which Cercospora can attach. Those listed above, especially carrots and legumes, are the most common. Eggplants, tomatoes, rice, sorghum, cotton, and others are also susceptible to this blight. It can infect plants at any stage of development, usually targeting leaves, stems, fruits, pods and seeds.
It manifests in much the same way on every plant infected, though some nuances for individual species are also possible. In carrots and other thin-leafed plants, it will cause the leaf margins to curl and move towards the withers and stems. On broader leaves, it will manifest as pale-tan to gray spots in semi-round shape and spread to connect those dots into one large blight.
In darker leaves, it can appear as a purplish color with a lighter-colored center.
In all cases, as the spots elongate and spread to infect most of the leaf and/or stem, they will become gray and “fuzzy” as spores are formed. Plants with a large portion of their leaves covered in gray are considered completely infested and “blighted.” Destruction is often the only recourse.
Like most fungi, Cercospora will infect a host plant and grow until spores form. These will be transferred to seeds, the ground, mulch, compost, etc. and lie dormant until conditions are ripe (usually late spring) for infestation.
Infected plants can seem perfectly healthy until the right humid, damp, warm conditions occur and then the spores and infection can begin quickly and within days have infested much of the host.
How This Leaf Fungus Impacts the Plant
On most plants, it will spread quickly under good conditions and can severely maim or kill the plant within a week or two. Mild infections can lead to infected seeds and fruits, which spreads the spores of the blight to the next generation.
Fruit production will be stunted as will plant and foliage growth. Some plants, if infected early, will die.
How to Prevent Leaf Spot Diseases
As with most fungi, prevention means allowing good aeration around the plants, proper spacing between plants, hygienic conduct such as using only clean seeds, and careful management of moisture and watering.
Damp, humid conditions are the Cercospora’s preferred habitat, so watering at ground level is a must.
Treating Cercospora Leaf Spot
Once infected, plants can be treated if it’s done early. Fungicides work well with this blight at this stage. If the plant is more than 20% infested, then destruction may be the only choice to keep other plants from succumbing.