Peanut leaf spot disease is caused by two distinct pathogens: Cercospora arachidicola (black spot) and Cercospora personata (brown spot). These two fungal species are different in their characteristics and symptoms. Brown spot typically appears earlier, during the early flowering stage of the plant, while black spot tends to develop later in the growing season. As a result, brown spots are commonly found on the lower leaves, whereas black spots appear more frequently on the upper leaves. In autumn-planted peanuts, black spot is more prevalent, while spring-planted peanuts tend to show more brown spots.
Both diseases can infect various parts of the peanut plant, including the leaves, petioles, stems, pegs, stalks, and pods. When the infection becomes severe, it can lead to premature defoliation, causing the plants to wither early. This not only affects nutrient accumulation but also reduces kernel yield and oil content. Additionally, the pods may become weak, leading to fruit drop during harvest and reduced seed viability.
The occurrence of peanut leaf spot is closely linked to several factors, such as short crop rotation cycles, high temperature and humidity conditions, low resistance in certain varieties, poor soil structure in sandy areas, and inadequate fertilization. To effectively manage this disease, farmers should adopt the following strategies:
Crop rotation is one of the most effective methods. Rotating peanuts with rice or other dryland crops like maize, sweet potato, or cassava for 2 to 3 years can significantly reduce disease pressure. Improving soil health through the use of organic manure and better cultivation practices helps enhance plant resilience.
Choosing resistant varieties is also crucial. Farmers should select peanut varieties that have strong resistance to leaf spot, especially when planting either spring or autumn crops. In addition to cultural practices, chemical control measures are often necessary. Commonly used fungicides include 50% wettable sulfur, a 0.5% to 1% Bordeaux mixture combined with soy flour (0.2%) or rosin extender (0.4%) as a sticker, 0.3% lime sulfur, and a 75% chlorothalonil solution diluted at 600 times. These treatments have proven effective in controlling leaf spot disease and protecting yield.
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