Phlebitis, also known as Phytophthora, is a major disease that affects the production of squash. Proper prevention and control are crucial for increasing yield and improving farmers' income. This disease is a serious soil-borne infection caused by *Phytophthora capsici* and *P. bergii*. It can occur throughout the entire growth cycle of the plant, affecting roots, stems, leaves, and fruits. The disease typically appears in July and August, especially during hot and rainy periods or after irrigation. Infected plants show symptoms such as water-soaked lesions on the roots and stems, which gradually turn dark green, then yellowish-brown, and eventually rot or collapse. In severe cases, the whole plant dies.
The initial signs on the stem include water-stained spots that expand over time, leading to sunken, gray-brown areas. When vines are affected, the damage often starts near the tip, with dark green, waterlogged depressions that later cause wilting of the upper parts. On the leaves, large round or irregular water spots appear, followed by discoloration and eventual wilting. Fruit infections begin with dark green water spots, which grow larger and lead to full rot. In wet conditions, a white or gray mold layer forms, often accompanied by a foul odor.
The primary source of infection is oospores present in the soil and on infected plant debris. These spores become active after winter, spreading through wind, rain, or irrigation. The disease thrives in temperatures between 10°C and 37°C, with an optimal range of 28–30°C and soil moisture above 85%. Heavy rains followed by sudden dry weather increase the risk of outbreaks. Flood irrigation or excessive watering (soil moisture over 95% for 4–6 hours) allows rapid infection, with one generation occurring within 2–3 days. Clay soils tend to have more severe cases than sandy or loamy soils. Continuous planting of cucurbits without proper crop rotation increases disease severity. Mulched cultivation reduces incidence compared to open fields, and high ridges are better than flat beds. Drip irrigation is more effective than flood or furrow irrigation, and watering in the early morning or evening is preferable to midday irrigation. Overuse of undecomposed organic fertilizers can also promote disease development.
To manage this disease effectively, several strategies should be implemented. First, implement a rational crop rotation system. Since pathogens survive in the soil, rotating crops every four years helps reduce their buildup. Avoid planting melons in the same area repeatedly, and instead rotate with non-cucurbit crops like wheat, corn, or legumes. Choose well-drained, fertile soils with good aeration and drainage.
Second, use high-quality seeds with strong germination and purity, such as varieties like Xinsheng No. 1 or Minmelon No. 1. Before sowing, dry the seeds for 2–3 days, then treat them with 2.5% Clarion seed dressing. Mix 10 ml of the solution with 150–200 ml of water and apply it to 5–10 kg of seeds.
Third, adopt proper cultivation techniques, such as drip irrigation under mulch or raised bed planting. Drip irrigation systems help maintain even moisture levels and reduce the risk of waterlogging. Plant at appropriate densities (3,000–3,500 plants per acre) to avoid overcrowding and ensure good air circulation.
Fourth, practice scientific irrigation. Water only when necessary, avoiding overwatering. Use drip or trickle irrigation rather than flood or furrow methods. Ensure that water reaches the root zone without flooding the base of the plant. Irrigate in the early morning or late evening to minimize evaporation and stress on the plants.
Finally, apply fungicides promptly. Since the disease spreads quickly, preventive spraying before symptoms appear is essential. After heavy rains, spray the field once, then repeat every 5–7 days. Recommended fungicides include 64% Oxadixyl WP at 500 times dilution, 58% Metalaxyl WP at 500 times, 72% DuPont Kocide WP at 500 times, or 69% Mancozeb at 800 mg/liter. Combining foliar sprays with fertilizer can help lower costs while maintaining plant health.
By following these integrated management practices, farmers can significantly reduce the impact of Phlebitis and improve the sustainability of squash production.
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