This may or may not shed some light on your situation and after readingit makes sense since your friend doesn't have the same prob with the same soil etc.
Link is here:
http://www.oisat.org/pests/diseases/fungal/cercospora_leaf_spot.html (same info)
Cercospora leaf spot
Scientific name:
Cercospora spp.
Causal organism:
Fungus
Important species:
Cercospora leaf spot on carrot (
C. carotae)
Cercospora leaf spot on grain legumes; Cercospora leaf blight (
C. canescens)
Frogeye leaf spot of pepper (
C. capsici)
Gray leaf spot on sorghum (
C. sorghi)
Gray leaf spot of corn (
C. zeaemaydis)
Cercospora leaf spot of soybeans (
C. kikuchii)
Frogeye leaf spot of soybean (
C. sojina)
Cercospora leaf spot or brown eyespot of coffee (
C. coffeicola)
Host plants
Grain legume, carrot, eggplant, pepper, tomato, tobacco, rice, corn, sorghum, oil palm, cotton, coffee, and other secondary host crops
Affected plant stages
All growth stages
Affected plant parts
Leaves, stems, fruits, pods, seeds
Symptoms
Cercospora leaf spot on carrot
Infested leaf has tan to brown spots with curled leaf margin and later on it withers. As the disease progresses, the leaflets turn yellow and also with curled margins. Spots on the leaf petioles, stems, and flower parts become elongated and have dark-brown color. On heavily infested plant, defoliation may occur.
Cercospora leaf spot on grain legumes; Cercospora leaf blight
Infected leaf has semi-round brown lesions with pale-tan to gray centers that are surrounded by dark-brown or reddish slightly depressed margins. A closer look shows white masses of spores growing on the dead tissues.
Frogeye leaf spot of pepper
Infected leaf has frogeye-shaped spots, about 0.2-1.5 cm in size. The center of the spots is grayish-brown colored dead tissues. Masses of small black dot-liked fungal spores are found scattered on the dead tissues. During severe infection, yellowing and defoliation occur.
Gray leaf spot on sorghum
Infected leaf has small circular to elliptical dark-purple or red spots with tan or brown center. Eventually, the spots elongate and are covered by gray spore masses. Heavily infested plant has a blighted appearance.
Gray leaf spot of corn
Initial leaf infestation appears as tiny to slightly elongated, roughly parallel-sided spots with yellow margins. The later stage of infestation shows rectangular tan to gray spots that remain evident on completely blighted leaves. The fungal growth on the lesions gave a characteristic grayish cast, hence the name.
Cercospora leaf spot of soybeans
Infected leaf has reddish-purple angular to irregular spots up to 1 cm in size. During heavy infestation, the leaves have leathery, dark-reddish-purple appearance.
Frogeye leaf spot of soybean
Infected leaf has circular to angular brown spots with narrow red or dark-reddish-brown margins that vary in size from less than 1 mm to 6 mm in diameter. Later, spots have ash-gray to light-brown centers with distinct purple to reddish margins. Eventually, the center becomes nearly white with small dark spots and the margins darken. During heavy infestation, the spots may appear uniformly over the foliage.
Cercospora leaf spot or brown eyespot of coffee
Infested leaf has small yellow eye-like spots that slowly expand up to 5mm in size. Later, the outer portion of the spot is brown while the center becomes gray-white. Infested cherry is dried, blackened, and has almost circular scar on the pulp which makes de-pulping difficult. Diseased berries have poor the bean quality.
Conditions that favor development
- Warm temperature, frequent rain, and high humidity
- Diseased-seeds and planting materials
- Over-crowded plants with poor air flow and low sunlight penetration among plants
- Improper soil nutrient and irrigation management
- Poor soil drainage
Prevention and control
- Rotate crops
- Heat water seed treatment
- Use diseased-free seeds or use resistant cultivars
- Proper observance of planting distances
- Proper field sanitation
- Removal and proper disposal of infected plants. Burn infected plant tissues when possible
- Clean contaminated equipment
- Avoid working when plants are wet
