NATURE’S TURN: Unwelcome cabbage white butterflies and dreaded cross-striped cabbage moths
July 15 – 28, 2019
Mount Washington — Have you spotted romancing white cabbage butterflies? Also known as the adult phase of the imported cabbage worm, they have recently re-appeared for the season all over our region, scouting our gardens for cabbage family plants on which to lay their eggs. White with one or two black spots on their forewings, the cabbage white has a wingspan of 1.3 to 1.9 inches. As I write beside my garden, Pieris rapae is fluttering feverishly in and around the garden: This insect is diurnal, i.e. active during the day. Earlier, a pair danced together in flight, courting. For gardeners and farmers, that dance announced that, if not accomplished already, strategies must be in place to protect a major group of food plants, the brassicas, from being eaten by several different predators.
Until last year, the imported cabbage worm – a soft, slightly fuzzy green worm – was the only cabbage-family pest most of us had experienced. Although a nuisance requiring constant attention, the worms can be picked off plants and killed before they inflict lethal damage. Everything changed when, at the end of September 2018, I found the broad leaves of one of my kale plants riddled with holes. There was nothing left to eat! Voracious, dark-appearing, smooth worms with yellow stripes down their sides were finishing off the plant. I found out that the offenders, identified as cross-striped cabbage worms, had arrived in New England from points south due to warming temperatures. The adult is a nocturnal moth with a wingspan of about one inch.
Looking forward to robust harvests ahead this season, I am anxious to protect beautiful, maturing Romanesco broccoli, Russian and lacinato kale, young red cabbage plants and just-seeded turnips. I purchased row cover designed to exclude insects and I refreshed my memory of folklore that recommends dusting moist plants with rye flour or cornmeal to kill worms that ingest it. I am also considering bacillus thuringiensis and insect netting. See Resources, below, to learn more.
To keep up with current conditions, I interviewed Susan Scheufele of the UMass Extension Vegetable Program. She confirmed the challenges ahead regarding Evergestis rimosalis, the cross-striped cabbage worm, that, based on the Vegetable Program’s useful “Pest Sighting Calendar,” is predicted to be active in New England beginning the third week of August. Susan alerted me to other cabbage family pests that may, literally, blow in with storms. The diamond-back moth Plutella xylostella would be active all season and the cabbage looper Trichoplusia ni, also a moth, is expected in late July. For descriptions of their larvae and a wealth of information about cabbage pests and beyond, see UMass educational materials, below.
UMass educational materials
Subscribe to Garden Clippings newsletter – https://ag.umass.edu/home-lawn-garden/newsletters/garden-clippings/garden-clippings-2019-vol-384
Vegetable Pest Scouting Calendar – http://ag.umass.edu/sites/ag.umass.edu/files/pdf-doc-ppt/pest_scouting_calendar_veg_notes.pdf
Caterpillars in Brassica crops – http://ag.umass.edu/vegetable/fact-sheets/caterpillars-in-brassica-crops
More cross-striped cabbage moth and worm identification and recommendations
https://bugguide.net/node/view/11183/bgimage and pupa https://bugguide.net/node/view/57 and image of moth http://v3.boldsystems.org/index.php/Taxbrowser_Taxonpage?taxid=21323 and http://masterofhort.com/tag/cabbage-worm/