Scarlet Oak Sawfly Outbreak
Each In late June and early July of 1997 and 1998, damage to oak foliage in southern Ohio was detected through the Division of Forestry’s aerial survey.
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| Aerial photo showing damage |
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| Scarlet oak sawfly larvae |
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Scarlet oak sawfly adults on skeletonized leaf
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 Additional Information |
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About mid-July, property owners began calling to report browning in the tops of oaks. The insects were not found during initial ground checks, probably because they had progressed in their life cycle and were no longer feeding.
Further ground-checking in mid August revealed the second generation larvae of the scarlet oak sawfly, Caliroa quercuscoccineae, feeding on pin oaks, scarlet oaks, black oaks, some red oaks, and some white oaks. The insect skeletonizes leaves in the upper 1/3 to 1/2 of tree crowns. Tissue between leaf veins is eaten, leaving brown leaf “skeletons” hanging in the tree.
Adults are fly-like insects which emerge in the spring to lay eggs in rows along leaf veins, which also damages leaves of host trees. The larvae are one inch long, dark green to black, and slimy. The slime coat helps them stick to leaves as they feed. Entomologists reported that the weather permitted three generations of the insect to develop this year.
They also felt that defoliation from first generation larvae was unusually heavy this year. Even so, control is not necessary, except for some cases involving small ornamental trees or severe outbreaks lasting more than two years.
Natural enemies normally control insect numbers, plus leaf damage from second and third generation larvae occurs late in the season, minimizing impact on the host. Repeated defoliation, however, may decrease growth, reduce vigor, or kill trees.
The aerial survey performed by the Division of Forestry in 1997 revealed 174,197 acres of scattered damage in Lawrence, Scioto, and Adams Counties. Lawrence, among the hardest hit, was also surveyed by the USDA Forest Service. Approximately 70,341 acres were damaged in Lawrence County, an estimated 60,054 acres in Scioto County, and about 43,802 acres in Adams County. A more intensive survey in 1998 showed that sawfly damaged 294,426 acres of forest in the same general region as the previous year
Neighboring states also reported damage caused by scarlet oak sawfly larvae this summer. The Forest Service survey showed 30,900 acres damaged in Boyd County, Kentucky and 115,600 acres damaged in Cabell and Wayne Counties in West Virginia. |