Leafrollers and Leaf Folders
This appears to be a bad year for leafrollers/leaf folders in ginseng. Based on previous research we conducted to identify the species, the primary insect growers are dealing with now are leaf folders, although other species have also been found. Leaf folders are caterpillars just like leafrollers but tend to fold leaves into a bundle rather than roll the leaves (Figure 1). The specific species affecting ginseng is the zigzag Herpetogramma moth (Herpetogramma thestealis) (Figure 2). Other reported hosts include basswood and hazel trees and spikenard, a close relative of ginseng.
Figure 1. Bundles of folded leaves probably due to the zigzag Herpetogramma leaf folder.
Figure 2. The adult zigzag Herpetogramma moth.
Unlike most leafroller species, which appear to come out of the roll at night to feed, this species of leaf folder appears to feed only within the bundle. There are reports that some Herpetogramma species may come out and form a new bundle when they are done feeding within the original bundle, but this hasn’t been confirmed for the zigzag species. This may be the only opportunity to control them. It is nearly impossible to target the caterpillars within the roll with insecticides. However, if the leaves are treated before the caterpillars leave to form a new bundle or fold in new leaves, it may be possible to control them.
There are no insecticides registered for control of leaf folders in ginseng. Insecticides applied for the control of leafrollers or cutworms may also control leaf folders. The insects are likely to only leave the bundle at night, if ever, so timing insecticides in the evening as is done for cutworm control has the best chance of reducing populations. It is important to confirm that the caterpillars are still actively feeding within the roll if there is to be any chance of success, since once they pupate there is no chance to control them.
There is little information on the life cycle of the zigzag Herpetogramma. In North Carolina, adults were seen flying in mid-summer in higher elevations with a similar climate to southern Ontario. This suggests there is only one generation per year. In lower elevations with a longer growing season, two generations were seen. So far, we have only seen one generation per year in Ontario. There are leafroller species known to attack ginseng, so scouting for issues should continue even if this particular species is done for the year.
This is also a bad year for aphids in many crops. There are high populations of green peach aphid and black bean aphid on many crops. Aphids are not usually a major issue in ginseng, so growers may not be accustomed to watching out for them. Look closely on the flower stock and along the vein on the bottom of the leaves. Green peach aphids are the primary aphid identified to date in ginseng (Figure 3), but other species may also affect ginseng. Control is only required if populations are high. It may not be economical to apply an insecticide if the damage is not noticeable. Several effective fungicides are available for control of aphids in ginseng. Consult OMAFRA Publication 847 Crop Protection Guide for Ginseng or the Ginseng Manager App for control options.
Figure 3. Green peach aphids on a ginseng flower stalk.
Another mild frost has occurred in some areas of Norfolk County. It is too early to determine if there is any damage from this latest event. It is also not known how susceptible plants are to frost once they are fully emerged, since frost this late in the season has not been seen in at least a few decades.
Alternaria remains the biggest disease issue right now. As always, lack of control of Alternaria comes down to poor choice or rotation of fungicides and/or poor coverage. The disease can also be enhanced when plants are stressed due to low soil moisture, hot temperatures and lack of air flow through the garden, or improper fertility.