Root rot is caused by soilborne pathogens such as Phytophthora, Pythium, or Rhizoctonia. The fungi blacken and decay the root tissue, destroying its ability to take up water and leading to a gradual decline of the plant.
When the root system is compromised by rot, the plant's ability to absorb water and nutrients is severely diminished. This can manifest as leaf scorch, as the foliage cannot receive enough water to compensate for transpirational losses.
When roots are infected by pathogenic fungi and begin to rot, the xylem vessels become blocked, preventing water and nutrient transport to the foliage. The leaf cells lose water and turgor pressure collapses. Due to the heavier structure of the upper palisade mesophyll, the entire leaf blade sags and curls downward.
Roots turning black, soft, and foul-smelling.
Yellowing spreads across the whole plant rather than only old or new leaves
Leaf edges scorch brown or dry out as fungal root damage restricts water and mineral uptake
Entire shoots, stems, and young leaves wilt and droop rapidly despite the growing medium being wet or damp, caused by decayed roots failing to absorb water.
A distinctive musty, fungal odour from the rotting roots — distinguishable from waterlogging, which smells anaerobic but lacks the fungal note.
Stunted, slow-growing plants.
Leaves lose turgor pressure completely, becoming soft and causing the entire leaf blade to droop and curl downward.
Midrib yellowing along the main axis while the blade remains green — a mid-to-late sign of root rot when damaged xylem can no longer transport water and minerals adequately. Typically accompanied by wilting, which distinguishes it from Rose Mosaic Virus vein yellowing (no wilt).
Phosphorous acid 400 g/L SL (FRAC P07), applied as a drench or foliar spray to prevent Phytophthora root rot. 50–100 ml per 10 L every 7–14 days (rate converted from pepper labels). Preventive only; good drainage matters most. Do not mix with mineral oil or copper.
