With the prolonged cold weather during emergence this year, ginseng plants will be stressed, and this will make plants much more susceptible to Alternaria leaf blight. Now that canopies have closed and hot and humid weather is forecast for the next week, it is essential to provide plants with full protection from the disease before outbreaks get out of hand. Protection and control of the disease now will prevent issues later in the season. Here are some basic principles for planning your Alternaria control program:
- Apply a rotation of effective products from different fungicide groups. Ginseng growers now have access to effective products from 7 fungicide groups. Sticking with the same group over and over will lead to resistance development and poor control.
- Ensure good coverage on all plant surfaces, especially stems. This is best achieved by calibrating sprayers and ensuring all nozzles are in worker order and delivering equal volumes of spray, using drop arms down every alley, altering your direction of travel (if possible, e.g. for canopies small enough to permit this without causing foliar damage), and using appropriate spray volume and pressure. For more information consult OMAFRA Publication 838 Guide to Ginseng Production or the following article on Sprayers101: https://sprayers101.com/spraying-ginseng/
- Choose products with the appropriate mode of action/mobility. For example, contact/protectant fungicides will not kill Alternaria that has already infected plant material. If there is active Alternaria in the garden, choose a product with at least locally systemic/translaminar activity.
- Scout known hot spots several days after spraying to determine if lesions were killed (i.e. the yellow halo around foliar lesions has disappeared). A backpack sprayer may be helpful to control hotspots if they are in areas such as post rows that are difficult to reach with the boom.
Botrytis may also be an issue in some fields with frost damage. Choose products with control of both Botrytis and Alternaria control if frost damage is present in gardens.
Now is the time to be scouting for leafrollers and leaf folders in ginseng. Both are known to occur in ginseng gardens. Look for leaves tied up into a bundle or rolled inwards (Figure 1). Leaf-folders tend to stay within the folded tissues and feed within, whereas leafrollers may leave the roll at night to feed, depending on the species. Control of these insects must occur when they are small. Once they are protected within the rolled-up leaves, which is usually when they are first noticed in the garden, it is often too late to effectively control them. Apply controls for leafrollers in areas of gardens where they occurred last year. Read product labels carefully to determine the optimal spray time. Some products should be applied in the evening or even after dark for best control. You may only need to apply a control product in sections of a garden. Some damage can be tolerated, so sprays may not be required if populations are low.
Figure 1. Folded/rolled leaves as a result of leaf-folders in ginseng. Inside the rolled-up leaves, you will find a caterpillar, webbing and/or insect frass.
Populations of several aphid species are high this spring. Ensure scouts are looking at the underside of leaves and on the flower stem. Aphids are small soft-bodied sucking insects that have two distinctive tail pipes (cornicles) on their posterior (Figure 2). Damage from aphids, which usually includes twisted and stunted leaves, could be mistaken for cold temperature injury.
Figure 2. Aphids on the underside of a ginseng leaf.
Now is also the time that grub damage becomes visible in seedlings, but you have to be looking closely to notice the damage. Look for tops sucked into the straw from below (Figure 3), eventually leading to circles of missing plants. On the edge of missing circles there will usually be a plant with wilted leaves or where the top has been recently sucked into the straw. Digging this plant up will usually reveal the grub. There are no products to control grubs once they occur in the field. However, the existence of damage is important to report, since we are losing our only product to control this pest, imidacloprid (Admire/Alias), which must be applied at seeding. Please fill out the following survey to help us plan alternative control strategies:
Figure 3. A ginseng top pulled into the straw from below as a result of grub feeding. Notice the recently wilted plant at the top of the photo, which is likely where the grub can be found.
For more information on ginseng pests along with photos and control options, consult the Ginseng Manager App which is available for download free in both iOS from the App Store or Android through Google Play.