Phytophthora root + stem rot of soybean

Symptoms

Damping-off of seedlings in wet cool soils, brown sunken stem cankers extending upward from soil line on older plants, yellowing + wilting of foliage progressing to whole-plant death, root system rotted + decayed, field patches in wet low spots.

Plants affected

• soybean

Easily confused with

• soybean cyst nematode

  How to tell them apart: On soybean (Glycine max), both Heterodera glycines (soybean cyst nematode) and Phytophthora sojae (Phytophthora root and stem rot) create the same patchy circular-to-oval areas of stunted, pale plants with interveinal yellowing and midday wilting, so the leaves alone cannot tell them apart. Dig plants and rinse the roots: Heterodera glycines reveals tiny lemon-shaped white-to-pale-yellow females (cysts), about the size of a pinhead, studding the fine roots, with a poorly nodulated, stubby root system. Phytophthora sojae instead shows a soft brown-to-chocolate rot of the taproot and lower stem, often with a darkened lesion creeping up from the soil line on the stem, and no white beads on the roots. P. sojae damage is worst in wet, poorly drained or compacted spots, whereas the cyst nematode patches do not track soil moisture in that way.

Common questions

How do I recognise Phytophthora root + stem rot of soybean on soybean?

Damping-off of seedlings in wet cool soils, brown sunken stem cankers extending upward from soil line on older plants, yellowing + wilting of foliage progressing to whole-plant death, root system rotted + decayed, field patches in wet low spots.

Do I have to report Phytophthora root + stem rot of soybean?

No. Phytophthora root + stem rot of soybean is not a notifiable organism, so there is nothing to report to an authority. Treat it as a normal garden problem.

How is Phytophthora root + stem rot of soybean treated?

Mainly with biological and cultural measures — removing affected material, changing the conditions that favour it, and treating with agents approved in your country. The exact steps and their timing depend on the plant, the season and where you live: Dr. Phyto works them out in a free diagnosis.