Growers reported problems affecting production, so the HDC commissioned a study. HNS 171 is designed to provide information on the scale of problems and consider what further investigations and production strategies are needed.
The study involved a review of information from literature, growers and consultants relating to the pests, diseases and disorders affecting production. A survey of 44 growers provided an overview of the difficulties faced. Case studies then provided in-depth information on current practice in producing these crops and combating the problems experienced.
The most problematic pests, diseases and disorders for Cordyline were two-spotted mite, yellow-leaf spot syndrome, tip-burn and "wobble" or "rock". For Phormium they were Phormium mealybug and two-spotted mite. A number of the conditions reported require further investigation; however, there were some suggestions that may help improve quality.
Avoid over-watering in late winter/early spring to control yellow-leaf spot syndrome and increase ventilation and spacing. For leaf-spot control, avoid wetting leaves and apply irrigation early to enable leaves to dry off before temperatures drop. Key to controlling Phormium mealybug is to quarantine stock on arrival and check each plant for infestation. Predators to control two-spotted mites can be difficult to establish; there are acaricides available, but the waxy leaves of Phormium make an adjuvant necessary. Control tip-burn by water management and calcium supplements.