Plant Doctor Archive

Cycad turning brown

I HAVE a decent sized cycad that is in the ground and has done really well for the last few years. All of a sudden the outer leaves are turning brown and dying off at an alarming rate. I can't see any pests on it and other cycads close by are not affected. Any ideas?

IF your cycad is Cycas revoluta, the most common one available at present, there are a couple of points to consider. Shortly after producing a flush of new leaves (which usually appear all together from the of the top of the trunk) the old leaves start to deteriorate, generally turn yellow and die off. To keep the plant looking good, you eventually need to cut these old leaves off and in good conditions with a healthy cycad this can become an annual event.

However, if your plant has not produced any new leaves for some time and the old ones are dying off, it's a signal all is not well and the most likely problem is root rot or rot in the base of the trunk which, with palms and cycads, is often referred to as the caudex. A good way to check if there may be a root problem is to gently put pressure on the caudex and try to rock it very gently to and fro - if the root system is healthy it will resist the pressure, but if it moves easily then there is very possibly a problem with the roots.

If this seems likely, the next step is to dig the whole thing out of the ground, clean off the soil from around the roots to check out what is going on down there. If there is any black, dead-looking tissue, try to clean it away until you find healthy reddish or pinkish tissue in the caudex. You may have to use a knife or saw to cut away the dead material. At the same time, cut off any yellow or brown leaves close to the trunk. If you still have a significant piece of healthy caudex left you could wash it down with a fungicide solution such as Thiram or dust the cut surfaces with Flowers of Sulphur in an attempt to prevent further rot. The next step is to place it in a warm, dry spot so the wounds you've made can start to heal. Leave it to dry off for quite some time - they can be left for weeks and still survive. Check the caudex every now and then to see if the rot has stopped. After a while, if it looks reasonably stable, you can try planting it in a pot of free-draining mix, or even plain pumice sand, in the hope that it will send out new roots - just like a giant cutting.

This process will take several months, but if you're lucky the plant will survive and eventually recover.

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.