The Department of Conservation (DOC) is asking Nelson gardeners to consider planting cover crops that don’t attract the great white butterfly to their garden.
Mustard, a brassica and great white butterfly host plant, is often planted in autumn as a cover crop to clean up harmful soil fungi. DOC suggests planting cereal cover crops such as rye, oats and barley instead. These increase beneficial mycorrhizal fungi in the soil which in turn will compete with harmful soil fungi.
Other alternatives are plants from the pea family such as lupin, lucerne and broad beans. These produce organic nitrogen and will improve soil nitrogen content.
All these alternative cover crops will reduce the chances of great white butterflies laying eggs in gardens.
Great white butterfly eggs on a nasturtium leaf
DOC is attempting to eradicate the great white butterfly in Nelson Tasman to prevent it becoming a permanent, widespread pest in New Zealand. The pest butterfly poses a serious threat to endangered native cresses and home and commercial brassica crops, including crops for cattle and sheep feed. Its caterpillars feed in groups, rapidly reducing plants to a skeleton.
DOC spokesperson Bruce Vander Lee said the great white butterfly eradication programme was progressing well.
“With the public’s help reporting finds of the pest we have been able to contain and suppress the butterfly population within the Nelson city area. We’ve been getting great public support and we very much appreciate it".
“This is a crucial time though for the eradication programme when we need the public’s help to knock back an autumn butterfly breeding surge".
“We are asking people to keep checking for the great white butterfly’s caterpillars and eggs in their gardens and report any found to the Ministry for Primary Industries hotline 0800 80 99 66".
Great white butterfly caterpillars on honesty plant
“We are asking householders not only in Nelson but also those in Richmond and surrounding areas to look for infestations as the butterfly may fly further out.”
The tiny, yellow eggs and the caterpillars are clustered on the butterfly’s favoured plants, particularly nasturtium, honesty and brassica vegetables such as broccoli, cabbages and mustard. They are often on the underside of plants.
Caterpillars are very small at first and in later stages are speckled black and greyish-green with three yellow lines along their bodies.