March 29th, 2004
War of the Roses

photo: spring Cankerworm

For the last two years, after I acquired a dozen or so heirloom roses, I’ve spent the thirteenth week of the year battling a little green inchworm–spring cankerworm. As the cedar elm and oak trees leaf out, it floats down on a silken thread until it finds the tenderest new leaves, mostly those on the roses or the flower buds of the lilies. It exudes a sticky web and curls the leaves around it, munching away happily. In stage 2, it acts rather like a hornworm, munching leaves along a branch, denuding it.

This year, I was looking for them and I’ve caught them in stage 1. As soon as I notice. leaves balling up, I began spraying. Last year I sprayed with insecticidal soap. But since I have to repeat the process every day for 7 to 10 days until the cycle is over, this year I’ve use diluted apple cider vinegar instead. Vinegar smells less toxic to me, but is like an acid bath for the soft inchworms.

The three hybrid musk roses, ‘Buff Beauty’, ‘Penelope’, and ‘Prosperity’ have suffered the most so far. Their leaves are not glossy and the buds form down in the new growth and so are quickly bitten off. ‘Blush Noisette’ and ‘Madame Joseph Schwartz’ (pictured) have bunches of buds which shoot out away from the new leaves, and so are initially less vulnerable. Although, as you can see, once these loopers get big they go anywhere for a bite.

‘Souvenir de la Malmaison’ which was so ravaged last year, bloomed early this year and is holding her own.

Zanthan Gardens History

2005-03-24. First spring cankerworm spotted.
2006-03-14. First spring cankerworm spotted. Are they earlier this year, or am I more vigilant?

by M Sinclair Stevens

2 Responses to post “War of the Roses”

  1. From Anne:

    You mentioned using diluted apple cider vinegar — what is the dilution. I use plain white vinegar to kill weeds, so I would think dilution is pretty important!

    I use about a tablespoon to a quart of water. I started very weak because I didn’t want to harm the roses. They seem okay so far. Still experimenting, though. — mss

  2. From Carol Embry:

    Do you ever use BT for these pests. If so, is it effective. It is very hard to watch helplessly as my beautiful antique roses are ravaged by these worms, while I hope and wait for the BT to do its work. I tried Concern with no results. I would think the vinegar would need to actually get on the worms and that is hard to accomplish with the worms rolled up inside leaves or worse, inside the buds.

    Carol, I haven’t tried BT. But from what I can see, you are right, the vinegar has to actually get on the inchworms. It is labor-intensive, but since I’m looking over each rose anyway. BT is one of those good ideas I’ve never tried. The real solution is in the article I linked to above. Unfortunately, it is too late for that this year. — mss

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