There have been three reports of heavy infestations of tobacco splitworms in the last 10 days, from Wilson, Lenoir, and Wake Counties. These reports showed multiple active young and advanced larvae mining tobacco leaves in the lower 2/3 of tobacco plants. Tobacco splitworm, also known as potato tuber moth (Phthorimaea operculella), is an occasional tobacco pest that may become more problematic during hot, dry periods. The latest records of high splitworm infestation levels in NC tobacco date from 2008-2010.
The cream-colored or tan splitworm larvae feed between the upper and lower surfaces of the leaf, producing yellow-to-brown galleries that can expand, darken, and tear. Damage usually begins on the lower leaves and progresses upward as priming removes infested leaves. Because old mines remain visible after larvae emerge as adults, suspected mines should be opened to confirm that they contain live larvae before management decisions are made. No research-based economic threshold has been established, although treatment may be justified when at least 10% of plants have 10 or more active mines.
At this advanced point in the season, when most growers have already started harvest, there are only a few viable management options for zero-residue tobacco producers:
Low infestation (<10% threshold):
Timely harvest is generally the only practical management option. Accelerate harvest of ready-to-harvest fields whenever possible. Removing primings and cutters reduces resources for larvae to mine into higher-value leaves.
Moderate infestation (at 10% threshold or slightly higher):
Insecticide applications are justified. Contact insecticides are unlikely to provide satisfactory control because larvae are protected inside the leaf. Only insecticides with systemic or translaminar activity will be effective against splitworms. When applied as foliar sprays, these products penetrate the leaf through systemic or translaminar movement to reach the larvae when good coverage is provided. At least 50 GPA is recommended when spraying for splitworms and most insect pests in post-topping tobacco. Coragen (chlorantraniliprole; 1-day PHI) has systemic and translaminar activity, and Steward EC (indoxacarb; 14-day PHI) has translaminar activity. These two products are specifically labeled for tobacco splitworm, but long 14 PHI makes Steward impractical once harvest is underway. Although Coragen has a shorter PHI, late-season applications may still produce detectable residues in cured leaves. Growers should consult their tobacco purchaser before applying it during harvest and must follow the current label.
Spinosad is the active ingredient in Blackhawk and also has translaminar activity. However, efficacy data against splitworms in tobacco are limited. Because this is an occasional pest of tobacco, overall data on management options are limited, especially during late tobacco season.
