Insect Management

Imported Cabbageworm

Caterpillars in Brassicas

    All three of the key caterpillars pests of Brassica crops have been found this week – including a few cabbage loopers.  Its not surprising to see cabbage looper at this time of the year, especially when other migratory moths are also arriving on storm fronts.  Loopers, along with imported cabbageworm and diamondback moth – generally known as ‘worms in cabbage’ – are more attracted to the waxy crops such as cabbage, broccoli, cauliflower, and collard than to the ‘glossy’ leaved Brassicas such as Bok choi and Chinese cabbage – but they can be found in all of these.     Diamondback  moth and imported cabbageworm have several reproductive cycles each year, and you may see new flushes of moths or butterflies, eggs, and then caterpillars, in a single crop.

    Scout undersides of leaves to look for fresh damage and to catch the caterpillars when they are small and damage is slight.  Check heading brassicas as soon as heads start to form. Greens such as collards, kale, and Chinese cabbage should be scouted at all growth stages.

    Quick ID Cues: Diamondback moth catperillar: very wiggly when poked, pointed on both ends, not fuzzy, only grows to about ½ inch. You may find white silken cocoons, with a green full-grown catperillar or a brown pupa inside. Imported cabbageworm: gray-green, slightly fuzzy, and sluggish. Grows to > 1 inch and favors the center of the head as it gets larger. Produces wet green frass (droppings). Cabbage looper:  light green, smooth, ‘loops’ up like an inchworm as it moves, grows 1 ½ to 2 inches.  Eats big holes in leaves.

The following thresholds are based on checking 25 plants. If you find one caterpillar per plant, it’s considered “infested”.

Action thresholds for caterpillars in Brassicas:

Crop & Stage                                       % Infesed Plants

Cabbage & Broccoli, Cauliflower                      35%

  pre-cupping (before head formation begins)        

Cabbage & broccoli                                          15%

  head formation to maturity        

Cauliflower 

  After heading (before tying)                             10%

Kale, collards & other greens                            10-15% 

    See 2006-2007 New England Vegetable Management Guide for insecticides. There are many effective options! Use selective products to maintain the natural enemies that keep aphids in check!

Updated August 2006