Stem Rot on Phalaenopsis Orchids

A few weeks ago, a Phalaenopsis orchid began showing signs it had stem rot. Although it had been given some treatment, it was unclear whether it would pull through. Sadly, the stem rot was more advanced than I thought, and it gave up. I came home from work to find this…

Phalaenopsis with stem rot
Phalaenopsis with stem rot…very advanced!

Today, I wanted to discuss stem rot, share some observations and suggest some ways to help prevent it.

Stem rot (or collar rot as it is sometimes known) is caused when water accumulates between the leaves of a monopodial orchid and does not evaporate because of poor ventilation. This begins to break down the tissue of the orchid, causing it to rot. Stem rot is more likely to occur if water accumulation is not removed immediately, or if the orchid is potted too low into the growing media. Poor ventilation is also a contributing factor.

What are the symptoms to look out for?

As with most rots on orchids, a tell-tale sign are black or brown patches. These patches spread rapidly, so you need to act fast if you notice them. The rot normally appears at the base of the orchid stem, where you may also find the area above this turns a creamy yellow colour (as seen in the photograph above). If left untreated, the rot spreads up the orchid in a short space of time, eventually killing it.

I noticed that the leaves on the affected orchid in my collection dropped several of its lower leaves that had yellowed, and its newest leaf also turned yellow. Given how slow orchids are to do anything, the decline of the orchid was rather fast, perhaps a few days.

You can see from this photograph how much of the stem was affected…

IMG_1995

How do you treat stem rot?

This depends on how early you notice the rot. If you catch it early, you may find that hydrogen peroxide 3% and cinnamon can treat it. Alternatively you could use a fungicidal treatment.

I found that un-potting the affected orchid provided me with the opportunity to really see what was going on. It also meant that the orchid could have any dead tissue removed without being a fiddly job. The roots and stem were sprayed with hydrogen peroxide 3% until the fizzing stopped. The water left over was then mopped up with a piece of kitchen roll to help dry out the affected area before cinnamon was applied to it, taking care not to spill any on the roots.

The orchid was re-potted (sitting a little proud of the media) and left in a well ventilated area. The aim was to help limit the conditions that rot thrives on, i.e. warm environments with high humidity.

What can be done to reduce the likelihood of stem rot developing?

If you water your Phalaenopsis orchids from above, take care not to splash the stem of the orchid. Should this happen, I find using the corner of a piece of kitchen roll to be ideal because it can get into the crevices. You’d be surprised at how much water gets into the creases!

Allow the media to completely dry out before you next water your orchid. The roots should be a silvery green when the orchid requires more water. Also, try and provide good air movement to help water evaporate.

If you are repotting a Phalaenopsis, try placing it just above the top of the media so that no leaves are buried, and the stem is a little more exposed to the air. If the media is constantly moist, and the leaves are sitting in that media, it will do your orchid no favours.

So, my advice here is this – if you think you have stem rot, deal with it straight away. Do not leave it and think the orchid will recover without any intervention; they don’t. If you pay your orchids regular attention, you should notice stem rot early, which will increase your orchids’ chance of survival.

Happy growing!

Clare

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