Leafrollers are showing up in large numbers in some areas. The damage begins as rolled up tips or sides of leaves (Figure 1) with no other signs of feeding damage. The caterpillar will be in the centre of the roll. When they are at this stage they are still relatively small and feed within the leaf roll. As they grow they will need to come out of the roll to feed, which usually occurs at night. This is when they can cause more extensive damage as they feed directly on the leaves or on the leaf stems (petioles). When they feed on the petioles they can cause whole leaflets to droop and die.
Adult leafrollers start to fly in May and then lay eggs on the underside of the leaf (Figure 2). There may be several different species affecting ginseng, so eggs may be variable in appearance. The egg hatch stage is the best time to control the larvae, because they will not be protected by a leaf roll when the larvae are very small. Identifying these eggs requires very careful scouting of the field. In other crops, growers trap the adults to know when the eggs will be laid and they time their insecticide applications accordingly.
At the point that the leafrollers are in the roll, they are more difficult to control. However, a couple of successive sprays of different products 5-10 days apart could provide reasonable control. Spraying should be done in the evening, so the product is still on the leaf at night when the larvae come out to feed. The products either work by ingestion of sprayed leaf material or by direct contact of the caterpillar with spray on the surface of the leaf. Once the caterpillars are causing extensive damage, it is often too late to control the insect because the products are less effective at this stage and the caterpillars will stop feeding and pupate shortly after.
Before making any insecticide applications, it is important to scout the field to determine how many leafrollers there are and where they are in the garden. Leafrollers can be localized in a field. They are often found on garden edges, especially near hedge rows and forests. Some fields may not need any controls at all, and other fields may only require a spray in one section of the field. There are no thresholds established for leafrollers on ginseng, so growers will have to make a judgement call on whether the number of leafrollers warrants a spray. Generally if it is difficult to find them and they only occur as one in a hundred leaves, then it is probably not economical to spray.
There are three insecticides registered for control of leafrollers on ginseng: Dipel, Success/Entrust, and Delegate. Consult the labels for application procedures.
Other than leafrollers, Alternaria and slugs continue to be issues in ginseng gardens. Plants affected by the 2-year old wilt that I discussed last week continue to die off, but damage does not appear to be spreading to new plants. Gardens should also be scouted for Botrytis, especially after the humid weather in the forecast over the weekend. Leaf edges on many plants have had some damage from the frost cloth blowing in the wind several weeks ago, and these edges could be entry points for Botrytis if the plants are not protected.