Rhizome rot: identify, prevent, control

Updated October 2026

Worst in hot, wet weather from December to March in South East Queensland, northern NSW and the tropics, especially after heavy rain.

Rhizome rot, often called Pythium soft rot, is caused by Pythium water moulds that live in soil and attack ginger and turmeric through the roots and the base of the shoots. Queensland research found Pythium myriotylum causing the serious outbreaks in the ginger industry since 2007 and 2008, with some growers losing whole blocks. The disease spreads in infected seed rhizomes, soil and water, so clean planting material and good drainage are the main defences.

Pythium myriotylum and other Pythium species

How to identify it

The lower leaves of the shoots turn yellow, starting at the leaf tips and edges, while the upper leaves may still look green.
Shoots wilt and fall over, and the base of the shoot, where it joins the rhizome, looks water soaked and pulls away easily.
When you dig up the plant, the rhizome is soft, brown and watery inside and can be squeezed like a wet sponge, often leaving only the fibrous skin.
The roots are brown and rotted, and affected rhizomes may have a sour smell as other organisms move in.
Plants die in patches that often follow the lowest, wettest part of the bed or the line of a watering pipe.

What it is often confused with

Bacterial wilt

Bacterial wilt of ginger makes shoots wilt suddenly while still green, and a cut rhizome oozes milky bacterial slime when squeezed. Pythium rot yellows leaves first and turns the rhizome watery without milky ooze.

Root rot

Our root rot page covers Pythium and Phytophthora root rots on other plants. In ginger and turmeric the same kind of water mould attacks the rhizome itself.

Nematodes

Root knot and burrowing nematodes leave rhizomes lumpy, cracked or with brown, dry lesions, and plants are stunted rather than collapsing in a soft rot.

When and where it is worst

Ginger and turmeric are grown in warm, humid gardens from Darwin and Cairns down through South East Queensland and northern NSW, and that is where rhizome rot causes most trouble. Pythium myriotylum is active in soil from about 20 to 35 degrees, so the risk peaks in the wet season from about December to March, especially when heavy rain leaves the soil saturated for days.

The water mould is carried into new beds on infected seed rhizomes and in soil and water. Its swimming spores spread through waterlogged soil and runoff, which is why low spots and poorly drained beds fail first. In cooler gardens grown in pots, overwatering through summer can trigger the same problem.

Plants it affects

These plants in our library list it as a problem to watch for.

Ginger Turmeric

How to prevent it

Plant only firm, clean seed rhizomes from a reputable supplier, and cut off and discard any piece with soft, brown or water soaked areas.
Grow ginger and turmeric in raised beds or mounds at least 20 to 30 cm high, in free draining soil rich in compost.
Water deeply but not every day, and let the top few centimetres of soil dry a little between waterings.
Rotate ginger and turmeric to a fresh bed every year or two, and do not plant them where either crop has rotted before.
Keep potted ginger and turmeric in free draining mix with plenty of drainage holes, and never let pots sit in saucers of water.

Organic control, step by step

Dig out affected clumps as soon as you see yellowing and wilting, and bin them along with the soil immediately around them.
Check the rest of the patch and harvest any healthy rhizomes early if the rot is spreading through the bed.
Rebuild the bed higher with fresh compost and coarse material before replanting, so water drains away quickly after storms.
Rest an infected bed from ginger and turmeric for several years, and grow crops that tolerate wet summers, such as sweet potato or taro, in a different spot.

Conventional control

No fungicide is registered in Australia for home gardeners to control rhizome rot in ginger or turmeric, and none will save a rhizome that is already soft.
Clean seed rhizomes, raised beds, rotation and careful watering are the practical controls for home gardeners.
If you use any garden product, always read the label, check that your crop is listed, and keep to the withholding period before you harvest.

Frequently asked questions

Can I eat ginger that has started to rot?

Cut away and discard any soft, discoloured part, along with a margin of healthy tissue, and use the firm remainder quickly. Throw out pieces that are watery all through or smell sour.

Can I plant supermarket ginger?

You can, but you have no way of knowing whether it carries the rot. Seed ginger and turmeric sold for planting from a reputable supplier is the safer choice, and it is usually less likely to have been treated to stop sprouting.

Why did my ginger rot after a week of rain?

Pythium needs waterlogged, warm soil to spread, and a week of heavy rain on a flat bed gives it exactly that. Raising the bed and improving drainage before next season is the best fix.