A project at the Pukekohe Research and Demonstration Farm is trialling the use of a trap crop as part of an integrated pest management (IPM) approach to controlling a significant crop pest in sweet corn.
Green vegetable bug (GVB) can cause significant damage in fresh market and processed sweet corn crops. The insect invades crops when cobs are developing, puncturing corn kernels through the wrapper leaves which results in discolouration of the kernel. The discolouration is enhanced in the processing of corn and can lead to whole crops being rejected. In fresh market corn, whole cobs may be rejected if secondary rotting occurs.
The only products registered for the control of GVB in NZ were broad-spectrum pesticides which have since been phased out of use by regulators. Finding an alternative control for GVB is a priority for the A Lighter Touch programme as it is a high priority crop protection control gap in sweet corn. Previous trials evaluated biological and synthetic options, but the results were inconclusive.
The vegetable industry is looking for new solutions for GVB management that will support an IPM approach to crop protection, and trap cropping is a practice that has the potential to be part of that solution.
In the foreground the trap crop is beginning to flower, with the sweet corn crop behind it. Credit: Olivia Prouse
The A Lighter Touch-Vegetables New Zealand project underway at Pukekohe is based on previous research conducted in New Zealand and overseas. It involves selecting one or more other species of plants that flower and set seed that the pest likes to feed on as the trap crop. The trap crop is planted around the outside of the sweet corn, with the goal of aligning the flowering time of the trap crop with the sweet corn crop.
The green vegetable bug migrates from the surrounding area into the crop, and encounters the flowering trap crop first, which provides the pest with a food source they find attractive and will feed on. A non-planted area is maintained as a barrier between the trap crop and the sweet corn, encouraging the pest to stay in the trap crop and continue feeding.
This barrier of bare ground between the trap crop and the sweet corn essentially removes the “green bridge” that the pest uses to migrate into the crop. It also gives protection in case of heavy rain or wind which causes the crop to be pushed over, ensuring that the sweet corn crop does not come into contact with the trap crop.
The barrier of bare ground between the trap crop and the sweet corn essentially removes the “green bridge” that the pest uses to migrate into the crop. Credit: Olivia Prouse.
This season, the focus for the project team at the demonstration farm has been about identifying from previous research the best trap crop species to use for GVB, and aligning the trap crop flowering with the sweet corn flowering. The aim is for the trap crop to have a staggered flowering so when the sweet corn crop flowers, the trap crop remains an attractive food source to the pest.
The sweet corn crop at the demonstration farm was planted in January, with harvest expected in April. The trap crop will be monitored through the project to determine if it is achieving the objective of controlling the GVB and keeping it out of the sweet corn crop.
