Pests and Diseases: Caterpillars!

They come in various colours and sizes, but the ones most gardeners are familiar with, are the cabbage white/white butterfly caterpillars, which are green and get reasonably large -  up to 2.5 cm long! They feed exclusively on brassicas (cabbage family). 

  • Then are there are the tiny but annoying diamond back moth caterpillars which hang by fine threads from the leaves they have munched on, and lightly scrape the surface of the leaves - quite common on lettuce and brassicas. The moths are small and sneaky!

  • Green semilooper caterpillars move like inchworms as they bring their back legs up to meet the front ones. They love brassicas plus beans, potatoes and tomato plants. 

  • Tomato fruit/ corn ear worm caterpillars tunnel into unripe and ripe tomatoes, make a horrible black mess inside the tomato and then leave by an exit hole larger than where they entered, or crawl up the silk of a corn cob and munch on all the developing kernels at the tip of the cob.  

  • And then the awful army worm caterpillars…uggh

What to do?

Protect: 

If you can, covering your caterpillar-prone veggies with fine insect mesh (aka bug net) will stop the moths getting to your plants and laying their eggs. This can be a good option in summer as bug net can also provide a small degree of extra shade. However when it is cool, it can keep the leaves of the plants too humid and foliar diseases can develop.

Attract some helpers:

Plant flowers that will attract parasitic and predatory wasps into your garden. Some wasps lay their eggs inside the caterpillars and their larvae develop and kill the caterpillar in the process. Others will actually feed on the caterpillars/bring caterpillar morsels to their nest. Wasps need nectar for energy, just like bees, but can only sip from shallow flowers, as they don’t have the long proboscis of a bee. Anything in the daisy (eg calendula),  and carrot (coriander, carrots, parsley, dill etc) family is great and will also feed the bees and lots of other beneficial insects. Remember we need these plants to be flowering to attract the insects.  So plan ahead to have some flowering all the time. And remember, they take space!!

Having a section of the garden as an insectary will feed your soul with its colour and beauty as well as help create a healthier, more diverse ecosystem in your garden!

Neem oil is said to be effective against the tropical armyworm. Mix 1-2 teaspoons neem oil with about 4 litres of water and a teaspoon of  liquid soap and spray weekly on affected areas.

Lastly, there is a bacteria called Bacillus thurungiensis (Bt) which will kill caterpillars when eaten by them, but does not affect any other insects. Bt is available as dormant spores  powder form and is diluted with water and sprayed onto the crops you want to protect. And as long as you spray it only on your veggies, you won’t kill monarch butterfly caterpillars or other desirables.




Other resources:

Stuff article: Green Looper Caterpillars

Land Care Research: What is this bug? Green Looper Caterpillar

Weed and pest control: Pest Control Hub

Caity Endt

Caity has always been a keen gardener and nature lover, spending endless hours in the garden with her father as a child and eventually studying botany and ecology.

After marrying Gerald, the seeds fell on the fertile soil of Great Barrier Island, and Okiwi Passion was born.

Caity now has part time role as Food Resilience Co-Ordinator on Aotea encouraging, teaching and supporting individuals to grow more local food!

https://www.okiwipassion.co.nz/about-us/
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