Are the Growing Tips on Your Tomatoes or Potatoes Yellow and Curling?
If you see the growing tips of your newly planted tomatoes or potatoes curling and going yellow, they may be infected with a bacterium of the genus Liberibacter. This disease is spread by psyllid sap sucking insects. The diseases caused by this bacterium are known as Psyllid Yellows in the plant and Zebra Chip in the tubers of affected potatoes. Liberibacter was first identified in Auckland in 2008 where it was infecting greenhouse crops of tomatoes and capsicums. It has since spread widely to home gardens.
There is not yet any effective treatment for the bacterium itself. Control of the disease is only possible by control of the psyllid insect that transmits it. The psyllids are sap sucking insects about the size of aphids but looking more like little cicadas. The eggs are laid on the underside of vulnerable plants. The nymphs are scale-like sedentary and wingless but will move if disturbed. The winged adults and nymphs use their hypodermic-like proboscis to feed on sap, usually on the undersides of leaves. The psyllids will feed on capsicum, chilli, egg plant, kumara and tamarillo as well as potato and tomato. Also, they may feed on bindweed and this can be a source of infestation and infection.
It is important to treat vulnerable plants early, particularly potatoes. The attack by the psyllids and the infection from Liberbacter can significantly weaken the plant and greatly reduce crop yield. Spray the underside of leaves with McGregor’s Pyrethrum and then the next day with Spraying Oil. Spray regularly in the growing season, more frequently if evidence of psyllids is found. Also remove or treat with herbicide any bindweed in the garden to prevent this being a reservoir of infestation.26 November 2020