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Cabbage Caterpillar

by Nanette Londeree, Master Rosarian

Sometimes you see ‘em, sometimes you don’t. But you can sure tell they’ve been there when your rose petals, leaves and canes are punctured, chewed, shredded, skeletonized, mined or just plain missing. It’s those nasty pests with chewing mouthparts that bite, rip, rasp or tear plant tissue doing the damage. The cast of characters that go for roses includes beetles and their larvae (Fuller rose beetle, Hoplia beetle), the dreaded curculio weevil, rose slugs (larvae of sawflies) and a host of caterpillars. Other chewy eaters that inhabit the garden, though usually don’t bother roses too much, are grasshoppers, katydids and the all too ubiquitous snails and slugs. So what to do? Here are suggestions for coping with insects and mollusks that chew through your plants:

  • Cultural methods – many of the chewers aren’t terribly picky about what they consume, particularly many caterpillars and grasshoppers. If it’s green and succulent, they’re likely to eat it. The primary cultural method of control is good garden sanitation – eliminate habitats for the insect pests to hide, reproduce and over-winter. And go light on chemical fertilizers that promote lots of lush new growth – it’s a real attractant to both chewing and sucking pests.

  • Mechanical and physical methods – adult forms of unwanted pests are often visible and easy to remove by handpicking. Head out to the garden when you’re most likely to see them (might be nighttime so bring a flashlight), with a small container or bucket filled with some soapy water. Pluck the little beast from its feeding spot and drop it into the bucket. For snails and slugs, a well-placed saucer of beer (any kind will do), or other yeasty brew is a great attractant – they’ll head for the aromatic mixture, fall in and drown. If you’re growing plants in containers, add a rim of copper foil (available at most nurseries) – the slimy critters won’t cross it. Large infestations of caterpillars are best remedied by cutting off the afflicted portion of the plant and disposing of it. If you observe any egg masses you’re sure belong to the pest you’re trying to control, remove and destroy them.

  • Biological methods – encourage generalist predators (birds, beneficial insects, toads) to the garden by providing their desired habitat. Microbial based products, such as Dipel DF, contain bacteria (Bacillus thuringiensis) pathogenic for a range of caterpillars and leafrollers. There are reportedly species of beneficial nematodes that may offer control for some types of caterpillars, leafminers and rose chafers.

  • Chemical methods – start with the least toxic chemicals; consider using a broad spectrum product (they kill anything they contact) only as a last resort

  • A dormant spray with horticultural oil may help reduce pests from overwintering. Bonide All Season Horticultural Oil Spray is a parafinic-oil product that can control overwintering eggs of bud moths and leaf rollers.

    Brown Garden Snail

  • Insecticidal soaps utilize potassium salts of fatty acids as the active ingredient. A product like Safer’s Insect Killing Soap is labeled for use against grasshoppers and sawfly larvae. Note that while the ready to use formulas have low toxicity, the concentrated form (that you dilute before use) wears a Warning label.

  • Sluggo does a great job killing snails and slugs, and its active ingredient, iron phosphate, is safe to use around the garden, even food crops. (Labeled Caution)

  • Neem seed based products (with the active ingredient azadirachtin) are derived from natural sources, are approved to control a range of insects when in the larval, pupal and nymphal stages (it’s a growth regulator / inhibitor). Though it doesn’t kill adults, it may repel and in some cases reduce egg laying and hatching. Azatin XL is labeled for use on roses for managing chewers - bristly rose slug, earwigs, grasshoppers, tent and orange tortrix caterpillars, leafrollers, bud worms, rose curculios, and rose chafers. (Labeled Caution)

  • Another insecticide derived from natural materials is Conserve SC, labeled for use on roses against any lepidopterous (moth and butterfly) larvae and sawflies in addition to numerous sucking pests. It is a spinosad. (Labeled Caution)

  • Mavrik, a synthetic pyrethroid type pesticide (fluvalimate is the active ingredient) controls a HUGE range of pests; the chewy type includes curculios, rose chafer , tent caterpillars, tussock moths and grasshoppers along with sucking pests and beneficials. (Labeled Caution)

  • The label on Ortho® MAX Flower, Fruit & Vegetable Insect Killer claims that this synthetic product kills 100 different pests including most of the chewers! The label also indicates it is toxic to wildlife and bees. It is an organophosphate, the same family of pesticides as Orthene and Malathion. (Labeled Caution)

  • Mesurol 75-W is a molluscide (kills snails and slugs) that also works on sucking insects – specifically aphids, thrips and spider mites. It is labeled Danger – the most toxic level of pesticides available. It’s in the carbamate family along with Sevin.
  • While chewing pests can be a real nuisance in our gardens, they usually don’t do too much damage. We’re fortunate not to have Japanese beetles that can easily decimate the spring garden. Let’s hope they never make it west of the Rockies!

    Photos by Gary Scales - cabbage caterpillar and brown garden snail
    Author’s disclaimer: Inclusion of a product in this series of articles does not constitute endorsement either by the author or the Marin Rose Society. Products are included for informational and descriptive purposes only.

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    Last Modified: 08/06/2013