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The Coastal Gardener: No need to panic over a few summer pests

July 16, 2010|By Ron Vanderhoff
  • Rose Slug is especially common on rose leaves right now.
Rose Slug is especially common on rose leaves right now. (Ron Vanderhoff )

Summer is upon us. Not only are temperatures rising, but so is the likelihood of a few garden pests. The three that seem to be getting the most attention right now, turning up in gardens from Laguna Beach and Newport Beach to Huntington Beach and Costa Mesa, are rose slugs, giant whiteflies and citrus leafminer.

If you have one or all three of these pests, don't panic. Learn a bit about them and then decide on the best strategy — which might be to do nothing at all. Where possible I always suggest organic or natural solutions, which are not only more environmentally appropriate, but build healthier gardens over time.

Rose slugs get busy every year once the weather warms up, usually about May or so. By July the damage is very noticeable on rose leaves. The leaves become riddled with hundreds of holes and irregular scratches. Heavy infestations can skeletonize the entire leaf, leaving just the veins.

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The culprit is the larva of an insect called a sawfly, more commonly referred to as a rose slug, even though it's not a slug at all. If you turn over a few chewed leaves and look very carefully at the backside you will see the little green larvae. If you have only a few roses, or a lot of patience, you can choose to pick off the larva by hand.

You can also knock off the little guys with a strong spray of water from the hose. Horticultural oils and natural plant oils can be used when rose slugs are first attacking. Oils are an environmentally safe approach, but should be used with caution in very warm weather.

Spinosad, a naturally occurring biological insecticide, seems to be the treatment of choice for most rose enthusiasts. Always spray during the evening hours, in order to minimize the negative effects Spinosad will have on honeybees and native pollinators.

Giant whitefly still gets lots of attention. Since Crossing the Mexico border in 1992, it has become a noticeable summertime pest on several subtropical plants, especially hibiscus, giant bird of paradise, citrus and canna lilies.

An exciting development in whitefly control has come to light over the past several years. Plants that are well mulched with worm castings repel a variety of pests, especially whiteflies. Apparently the worm castings raise the level of the chitinase enzyme in the plants, which whiteflies find distasteful and avoid.

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