Now that ginseng canopies will soon be closing, the risk of foliar disease will only continue to increase. Alternaria, Botrytis and Phytophthora blights are all potential issues currently. Continue to protect the foliage from all three diseases, paying particular attention to ensuring good coverage of all above-ground surfaces.
With the warm weather this week insects are emerging rapidly. Cutworms and slugs are now actively feeding. Leafrollers are also likely to be present in some gardens but are usually much patchier.
Ginseng growers are usually diligent about slug management, since their damage is obvious on ginseng and they are usually widespread in a garden. They are the only pest that causes holes in ginseng leaves. Although they will chew the stem similar to a cutworm, this damage will be accompanied by holes on nearby plants, whereas cutworms will not cause holes in the leaves. The current weather is ideal for slug feeding and both adults and juvenile slugs are currently active.
Cutworm damage is not subtle either but could be confused with damping-off or grub damage if you are not looking too closely, since all three pests mostly occur on seedlings and can cause the top to collapse. Cutworms chew the lower stem resulting in the top of seedlings falling over, often face-down on top of the straw (Figure 1). Grubs will also be active now and feed on the roots and stem within the soil. As they feed, they pull the top down into the straw (Figure 2), which may be preceded by the top wilting and arching over. If grubs are a problem, there may also be patches where the straw has been dug up by skunks feeding on the grubs.
Figure 1. A seedling top severed by a cutworm.
Figure 2. Several ginseng tops pulled into the straw by a grub.
Cutworm management is more difficult than control of slugs because timing is critical, and they tend to be patchier. Slugs are controlled with baits spread over the field (e.g. Sluggo or Deadline), which provides some flexibility in control, since the baits will remain in place as long as rain doesn’t degrade them. While there are baits registered for management of cutworms too (i.e. Scorpio Ant and Insect Bait), they have not been tested for cutworm control on ginseng, although they have shown efficacy against cutworms on other crops. The other products registered for cutworm control in ginseng are permethrin (Pounce/Perm Up), Coragen, and Exirel. Permethrins will only control the cutworms if they contact the insect. As a result, they are effective if applied in the evening or at night under moist conditions when the cutworms are feeding.
Exirel and Coragen are effective when the insects feed on a treated surface. Since cutworms mostly feed on the lower stem above or within the straw, coverage of the lower stem with the insecticide will be important for good control. Application should not be followed by a rainfall or the residue will be washed off the foliage. Both products do not have a long history of use on ginseng since they were registered as part of the root vegetable crop group. Their compatibility with other products is unknown. As a result, read the labels thoroughly and contact the company before mixing with any other products or applying soon after other products to ensure they are compatible and there is no potential for phytotoxicity.
Once you see the damage from grubs, it is usually too late to control them. The only insecticide registered for grub control in ginseng (Admire/Alias) can only be applied at seeding.
Leafrollers will also be active now but can be very difficult to identify until they form their rolled-up homes in the canopy (Figure 3). By the time they form those rolls, it is usually too late to control them. Look for the small green caterpillars beginning to pull together leaves with fine silk threads. Spinosad (Success/Entrust), Delegate and Dipel 2X DF are registered for control of leafrollers in ginseng. All three products work best when the caterpillars are small.
Figure 3. Leafrollers form rolled-up homes out of leaves and then feed from within. Once they are in a roll, they are very difficult to control.