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Scouting Watch

May 29, 2007

European pine sawfly larvae continue to be common throughout the state. These greenish larvae with dark green stripes and black heads occur in groups on the tips of scotch, mugo, and other pines. They can be removed by hand, pruned off, or sprayed with many chemical insecticides. Although they look similar to caterpillars, they are wasp larvae and not controlled with Bacillus thuringiensis kurstaki.

Alder leafminers, hawthorn leafminers, and columbine leafminers have been found as small, young, white mines in northern Illinois. As long as the mines are still small and white, removing and destroying the leaves reduce the amount of damage later in the season caused by subsequent generations. These leafminers typically do not cause enough damage to affect the health of the plant. For that reason, insecticide applications are usually not recommended.

Viburnum crown borer adult males are being caught in pheromone traps in northern Illinois. Application of permethrin (Astro) is recommended to the stems and base of the plants 1 week after peak adult male catch.

Rose slug is being found on roses. This is not a true slug but is a sawfly larva.

Both the rose slug and bristly rose slug cause window-feeding and skeletonization on rose leaflets. Damage is commonly severe enough to remove half or more of the foliage. Older larvae do not have the slime coating of the young larvae, appearing more like caterpillars than slugs. As with European pine sawfly, this is not a true caterpillar and is not controlled with Btk. Carbaryl (Sevin), permethrin (Astro), and other pyrethroid insecticides are effective against this wasplike insect. (Phil Nixon and Morton Arboretum)

Author: Phil Nixon


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