Phytophthora blight
Damping-off, stem/collar rot and wilting, and leaf/fruit blight in wet, waterlogged conditions — a fast, water-driven disease stopped mainly by drainage.
- Pathogen
- Phytophthora (soil/water-borne, fungus-like)
- Spreads by
- Water, splashing & soil; debris
- Favoured by
- Heavy rain, waterlogging, poor drainage
- Main risk
- Damping-off, stem rot & wilt, leaf/fruit blight
Overview
Phytophthora blight, caused by soil- and water-borne Phytophthora, is a serious, fast-moving disease of chilli, pigeonpea (arhar) and several other crops, especially in wet, waterlogged conditions. It attacks in several ways: it damps off seedlings; it rots the stem base, collar and roots so the plant suddenly wilts and collapses (a dark, water-soaked lesion often girdles the stem at soil level); and it blights the leaves, shoots and fruit with dark, water-soaked, rapidly-spreading rots, especially where soil splashes onto the plant.
It is strongly driven by water — heavy rain, waterlogging, poor drainage and splashing spread it fast, and it can race through a low-lying, poorly-drained field in a wet spell, appearing as expanding patches of wilted, blighted plants. It carries over in the soil and on debris. Because it is so tightly tied to wet conditions, management leans heavily on drainage and water management (raised beds, no waterlogging), along with resistant varieties, clean seed/seedlings, rotation, and protective fungicides in wet weather.
How to identify it
- Damping-off of seedlings in wet nurseries, and sudden wilting and collapse of older plants.
- A dark, water-soaked rot of the stem base/collar and roots, often girdling the stem at soil level.
- Dark, water-soaked, rapidly-spreading blight of leaves, shoots and fruit, especially where soil splashes up.
- Expanding patches of wilted, blighted plants racing through a wet, low-lying, poorly-drained field.
What causes it and when
- Soil- and water-borne Phytophthora, which attacks roots, stem base and above-ground parts.
- Spread by water, splashing and soil, and strongly driven by heavy rain, waterlogging and poor drainage.
- Carries over in the soil and on infected debris to start the next outbreak.
- Races through low-lying, poorly-drained fields in a wet spell, in expanding patches.
Cultural & organic control
- Ensure excellent drainage and avoid waterlogging — grow on raised beds/ridges, never in low-lying, water-holding land.
- Use clean, disease-free seed and seedlings and grow resistant/tolerant varieties where available.
- Rotate away from susceptible hosts, avoid soil splashing onto the plants (mulch), and give good spacing.
- Rogue out and remove affected plants with the surrounding soil, and destroy infected debris.
Chemical control
- Treat seed/seedlings and, at the first appearance, drench the base and spray with a CIB&RC-registered Phytophthora fungicide (e.g. metalaxyl+mancozeb, or copper/other recommended products).
- Time protective sprays and drenches to wet, high-risk spells, and improve drainage at the same time.
- Chemicals will not overcome a waterlogged field — fixing drainage matters more.
- Confirm the current fungicide and package for your crop with your local KVK.
Prevent it coming back
- Make excellent drainage, raised beds and no waterlogging the routine — the single most important factor.
- Use resistant varieties, clean seed/seedlings and rotation, and mulch to stop soil splashing.
- Plan protective drenches/sprays for wet spells and rogue affected plants with their soil.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Frequently asked questions
My chilli/pigeonpea plants are suddenly wilting and rotting at the stem base in wet weather. What is it?
Sudden wilting and collapse with a dark, water-soaked rot of the stem base/collar and roots, plus dark spreading blight on leaves and fruit in wet, waterlogged conditions, is Phytophthora blight. It races through a poorly-drained field in the rain. Improve drainage at once and grow on raised beds, use resistant varieties and clean seedlings, mulch to stop soil splash, and drench/spray with a registered Phytophthora fungicide, roguing affected plants with their soil.
Why is drainage the most important thing against Phytophthora blight?
Because Phytophthora is a water-loving, water-borne organism — it needs wet, waterlogged soil and splashing water to spread and infect, and it races fastest exactly where water stands. A low-lying, poorly-drained field in a wet spell is ideal for it, while a well-drained, raised-bed crop denies it the standing water it needs. That is why fixing drainage and avoiding waterlogging do more than any spray; fungicides support but cannot overcome a constantly wet, waterlogged field.
How is Phytophthora blight different from a Fusarium wilt?
Both can wilt the plant, but the drivers and signs differ. Phytophthora blight is water-driven — it strikes in wet, waterlogged conditions, damps off seedlings, causes a dark water-soaked rot of the stem base and roots, and also blights leaves and fruit, racing through in wet weather. Fusarium wilt is a soil fungus that plugs the vascular tissue and wilts the plant with browned internal stem tissue, often in warm conditions, without the water-soaked blight. Phytophthora is managed above all by drainage; Fusarium wilt by resistant varieties and soil health.
Symptoms and control measures follow ICAR, KVK and state agricultural-university package-of-practices; any named chemical is a registered use. Always read the product label and confirm the dose for your crop and zone. editorial policy.