Citrus foot rot, also known as skirt rot, is a serious disease that primarily affects the roots and lower trunk of citrus trees. The infection typically starts at the root neck and spreads downward, causing decay in the main and lateral roots. Initially, the cortex of the root and neck becomes brown with water-soaked spots, emitting a distinct fermented grain-like odor and exuding a sticky substance. When dry, this exudate hardens into granules. During wet and rainy seasons, the disease can rapidly progress, forming layers and eventually reaching the xylem. In severe cases, the bark of the root rots away, exposing the inner wood. However, if the disease progresses slowly or stops, the surrounding healthy tissue may naturally heal. In dry conditions, the affected area’s cortex dries out, hardens, and may crack or peel off. Under favorable conditions, the disease can reappear and expand again.
The primary pathogens responsible for this disease are species of *Phytophthora*, particularly *Phytophthora parasitica* and *Phytophthora citrophthora*. In some regions, such as Hunan and Sichuan, *Fusarium* spp. are also implicated. The disease thrives in warm, humid conditions and is most commonly observed in sweet oranges, lemons, and similar varieties. Oranges, grapefruits, and Satsuma mandarins are less severely affected, while wolfberry and limes show high resistance. Older trees tend to suffer more from the disease. Factors such as deep planting, poor soil management, excessive fertilization, insect damage, low-lying orchards, heavy clay soils, poor drainage, and weak plant growth can all contribute to the development of this disease.
To manage citrus foot rot effectively, it is essential to implement proper cultural practices. First, select disease-resistant rootstocks such as trifoliate orange, sour orange, taro orange, or perfume orange. Avoid using citrus as a rootstock in low-lying areas and raise the grafting point appropriately. Plant trees at the correct depth, ensuring the root neck remains exposed. Avoid damaging the bark during cultivation, and ensure proper drainage after rain. Do not apply uncomposted manure, and control pests like root borers.
For infected trees, early intervention is crucial. Carefully remove the soil around the affected area and gently scrape away the diseased tissue, including a 0.5–1 cm margin of healthy tissue. Dispose of the removed material properly. Apply a fungicide treatment, such as 843 Recovery Agent, 72% Precoce, 70% Pak Dewet, or 25% Metalaxyl, diluted to 150–200 times the concentration. Treat the wound two to three times, spaced seven days apart. After healing, fill the area with fresh, sterilized soil or treat the soil with a 0.5–1% solution of the fungicide. Alternatively, apply 30% soil bacteria solution at 500–1000 times dilution, using 3–5 liters per tree. These measures can significantly reduce the spread and impact of the disease.
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