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The late growth stage of peanuts refers to the period from the formation of the first full fruit pod until harvest, commonly known as the ripening phase. This stage typically lasts between 45 to 55 days. During this time, new leaves stop appearing, and the lower and middle leaves start to drop. The main goal of field management during this period is to prevent early leaf loss, especially in the upper leaves, to maintain a large green leaf area and extend the functional life of the leaves. This helps increase the number of effective pods, improve pod filling, and ultimately boost yield.
Early leaf drop in peanuts can be caused by several factors, including premature aging, excessive use of plant growth regulators, and poor soil conditions, particularly in sandy areas. Another major cause is leaf spot diseases, such as black spot and brown spot, which spread quickly and can lead to rapid defoliation within just a few days. Overuse or improper application of growth regulators like paclobutrazol can also accelerate leaf senescence. To prevent early leaf fall, it's crucial to focus on disease prevention and proper nutrient management.
One key strategy is to control leaf spot diseases effectively. These diseases, primarily black spot and brown spot, start from the lower leaves and gradually move upward. Early symptoms include small brown spots that develop into irregular lesions. Brown spot lesions are larger with yellow halos, while black spot lesions are smaller, lighter in color, and have neat edges without noticeable halos. In wet conditions, these lesions can merge into large, scorched areas that severely impact photosynthesis. If the infection spreads to the petioles, stems, or fruiting pegs, it can cause dark, dead tissues that significantly reduce yields. To manage these diseases, timely spraying with effective fungicides is essential. Recommended sprays include 80% mancozeb diluted at 800 times, 70% methyl thiophanate at 800–1000 times, agricultural anti-120 water agent at 200 times, 50% colloidal sulfur at 200 times, and a 1:2:200 Bordeaux mixture. Spraying should be done thoroughly every 8–10 days, with up to 3–4 applications needed for effective control.
Another important practice is foliar feeding, especially during the late growth stage when root nutrient uptake declines. At this point, leaves become more efficient at absorbing nutrients. Foliar sprays offer quick absorption, fast results, and high efficiency, making them an excellent way to prevent premature aging and leaf yellowing. For sandy soils or weak plants with insufficient base fertilizer, a 1% urea solution can be applied. However, for vigorous plants, urea may not be necessary. Phosphorus absorption by peanut leaves is strong, so applying a 2–3% superphosphate leaching solution (prepared by soaking for 14–16 hours) at 60 kg per acre every 7–10 days can increase yields by 7–10%. Alternatively, 100–150 g of potassium dihydrogen phosphate per acre dissolved in 50 kg of water can be sprayed in the evening or on cloudy afternoons. It's best to spray 3 times, every 7 days, and if rain occurs within 8 hours, reapplication is necessary.
Peanuts are also highly sensitive to iron deficiency, especially on alkaline soils. Symptoms include yellowing and whitening of leaves. Applying a 0.2% ferrous sulfate solution every 5–6 days for 2–3 times can quickly restore leaf color. Proper management during the late growth stage is essential for maximizing yield and quality. By focusing on disease control, nutrient supplementation, and leaf health, farmers can ensure better productivity and healthier crops.
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