Tobacco split worm, Phthorimaea operculella, is a common, though sporadic insect pest of flue-cured tobacco. In the post-tobacco program era, with more and more flue-cured acreage going to burley production, the insect has the potential to decrease the quality and value of the burley crop.
On flue-cured tobacco, these one-third inch long, white to pinkish colored leaf miners can destroy the leaf, causing significant yield losses. It is most common in flue-cured tobacco producing areas in North Carolina and Virginia.
It has been much less a problem in southwestern Virginia and other more traditional burley production areas.
On burley tobacco, the splitworm, which is also known as the potato tuber worm, causes minimal damage to the leaf in the field. However, the insect continues to feed on burley leaves and stalks in the curing barn.
During its long exposure to burley leaves, the splitworm feeds between upper and lower surfaces of the plant, and especially on older leaves. It causes gray to brown splotches on the tobacco leaf. During curing these splotches deteriorate and weight is lost due to tunneling in the leaves.
The tobacco splitworm is a leafminer, which feeds inside the leaf. Its feeding habit makes it difficult to control with traditional insecticides. Control requirs timely, directed sprays with high volumes of water.
It also is a late season insect. On flue-cured tobacco, it can be controlled in the field, but this is more difficult on burley. Even burley leaves fairly far along in the curing process can contain live, feeding splitworms.
“We don’t know the extent of economic damage the splitworm causes on burley tobacco. We are looking at the impact this insect has on quality — the leaf mining causes problems, and the insects leave droppings, which can have a negative impact on quality,” notes Paul Semptner, an integrated pest management specialist at the Southern Piedmont Research and Education Center in Blackstone, Va. He points out that little yield loss is expected from splitworm damage, but quality impacts can be significant.
Semptner says his research team is looking at several insecticides and the timing of these pesticides to determine best options for controlling splitworms. He notes that it feeds primarily on the bottom of the leaves, which requires a high gallon (50 gallons or more) application that is oriented to the lower leaves.
Warrior, a pyrethroid, has been the most effective insecticide for controlling the tobacco splitworm. However, it has a 40-day pre-harvest interval. So, on flue-cured tobacco, it is already too late to use this insecticide. Burley can be harvested from Aug. 10 to late September, so Warrior may be an option. However, Semptner warns that Warrior may not break down on burley tobacco as well as flue-cured tobacco because of less heat in the curing process.
Another problem is the numerous generations of tobacco splitworms that can occur after infected leaves are harvested. “Dipel can be used late in the season, and we are looking at using that material late in the season to control late generations of tobacco splitworm that may develop in the barn,” Semptner says.
Splitworms can produce an egg to egg generaton of leafminers in as little as 18 days. In warm, late season weather, and certainly in the curing barn, the normal 25 day life cycle often shrinks to 18 days.
The hot, dry weather that has plagued much of the burley growing area is ideal for development of tobacco splitworms. In these conditions as many as seven or eight generations can develop.
Growers should be especially aware of tobacco splitworms in areas where potatoes, eggplant and peppers are grown and are susceptible. Horse nettle and ground cherries are also ideal hosts.
As more and more burley production moves into traditional flue-cured areas, the increase in economic damage is expected from tobacco splitworm. Once the 2006 crop gets into its late season phase, growers are advised to check leaves for miner damage and to contact tobacco IPM specialists in North Carolina and Virginia.