Flax yellow leaf virus

About 6 years ago, some of our phormium tenax (large flax) started to go yellow and over a period the mature plants died. At that time, Jack Craw, Biosecurity Manager in the ARC, told me it was caused by flax yellow leaf virus. This spread to neigbouring plants so that whole areas of flax yellowed off and died. The plant in the photo is nearby so that all these years later, the disease is still on the spread near the original affected plants.

Looking around Piha, I fear that the disease causing this yellowing and death has spread. It is called Phormium Yellow Leaf Phytoplasma. The disease was first described in 1908 and was responsible for the failure of the New Zealand flax industry in the 20th century. It is spread by the native flax plant hopper, oliarus atkinsoni. Symptoms are abnormal yellowing, stunted growth and premature flowering. The disease causes plants to die over a period of months to years and there is no known method of halting this decline. If you have a flax showing these symptoms you would be best to dig up and burn it in the hope of halting the spread.