Temperatures have continued to be above normal despite the cool down earlier this week. As of April 23, we have accumulated 156 GDD (base 5), which is normally reached on May 6. Based on the current forecast, crop progress may slow relative to normal, but it looks like ginseng emergence will continue to be ahead of normal. This is all based on air temperatures. Soil temperatures are more important for determining early emergence.

Crop emergence is a critical time for managing several insects and diseases:

Cutworms

Cutworms are the caterpillars of several moth species. They act like slugs in that they are active at night, and hide in the soil or under debris during the day to avoid predators and desiccation from the sun. In ginseng, the straw layer provides this protection. There have been no studies on the cutworm species affecting ginseng, but the most common species affecting agriculture in Ontario are the black cutworm, variegated cutworm, and dingy cutworm. Based on studies in the 1970s, tobacco is also affected by dark-sided cutworm, striped cutworm and a few other minor species, and these may also affect ginseng if still present.

Black cutworm is the most common and damaging species in most crops. This species does not survive the winter in Ontario. The adults fly in from the south, usually arriving in Ontario in mid-April. Based on field crop monitoring, they are arriving now. These adults will lay eggs, and then it will take 50 Growing Degree Days (base 10) for the eggs to hatch. That would normally take a few weeks at this time of year. As a result, controls for black cutworm are not needed until the beginning or middle of May, depending on the weather.

Dark-sided cutworm overwinters as eggs. The eggs hatch in late-March or early-April. In tobacco, this species was sometimes controlled in the rye cover crop in April to prevent damage from larger caterpillars during tobacco transplanting. For ginseng, the caterpillars would be very small now and likely feeding on rye plants in the straw. They are unlikely to cause economic damage to ginseng until they become larger caterpillars over the next few weeks, and the ginseng emerges. Controls may be effective now if this species is present, but efficacy would require scouting to confirm the species and the population.

Some other cutworm species, such as striped and dingy cutworm, can survive the winter as larger caterpillars, which can cause localized damage in April. The remaining species normally appear later in the spring.

Without knowing the species of cutworms that affect ginseng in a given field, it is difficult to know when controls should be applied for optimal control. Some fields may be affected by different species than other fields. Based on the potential species and experience in other crops, controls are probably not economical yet. Scouting is important to identify if economic damage is occurring and to identify which species are affecting the crop. This should be done at night to look for active feeding or early in the morning, looking for freshly severed plants or leaves and digging around the plants to find the caterpillars. If you find caterpillars, please collect some and bring them to me for identification so we can refine the cutworm control program for ginseng.

There are three main insecticide options for control of cutworms in ginseng:

Permethrin (Pounce 384EC, Perm-Up, Ambush 500EC): these products provide control through both contact (if the caterpillar is directly hit by the spray or walks over treated surfaces) and ingestion (if the caterpillar eats foliage treated with the product). These products should be applied in the evening to moist straw to ensure they are still active when the insects come out to feed at night.

Diamides – cyantraniliprole (Exirel) and chlorantraniliprole (Coragen MaX/Shenzi 400SC): these products work best through ingestion. They need to be sprayed on ginseng tops, and then the insects need to feed on the treated plant material to be killed. These products will not be effective until more of the ginseng has emerged and can be contacted by the spray. Since these products can be absorbed to a limited extent into plant material (e.g., translaminar), they can be applied during the day and will still be active at night.

Spinosad (Scorpio Ant and Insect Bait): Spinosad is effective against cutworms, but we have no experience with this product in a bait form for cutworms. If you have experience using this product for cutworm control in ginseng, please let me know.

Leaf Folders

Based on our research last year, leaf folders begin emerging when the first ginseng tops emerge through the straw, and then emergence continues for a few weeks. This two to three-week period is the best time to control the larvae since they can still be contacted by insecticides at this time before they are protected by the leaf rolls/folds. Insecticides should only be applied if scouting indicates there is a significant population in an area of the field. Look for the caterpillars hiding between the folded leaves in emerging ginseng tops or rolling up the tip of unfolded leaves (Figure 1).

Figure 1. A leaf folder caterpillar hiding between the leaves of a ginseng tops. Caterpillars are around 7 mm long at this stage and may be accompanied by some silk webbing.

Slugs

Mature slugs are becoming active and are likely laying eggs. Some species lay eggs in the fall, and these may have hatched already. The young that hatch from the eggs are the most damaging stage. The worst damage usually begins in mid-May. Slug controls should be applied to protect ginseng throughout the spring.

Foliar Diseases

Alternaria: Alternaria requires periods of high humidity or leaf wetness under mild temperatures, and outbreaks usually begin when the canopy begins to close later in May. The canopy is usually too open with good airflow at this time of year for any significant Alternaria outbreaks. Spores may be present now on last year’s stems, and an earlier fungicide spray may reduce this inoculum. It is possible that some early infections can occur under the “tenting” that can occur when larger tops try to break through a thick straw layer, or in the middle of a large cluster of older plants.

Botrytis: In addition to high humidity and warm temperatures, Botrytis also usually requires some existing plant damage to infect ginseng. This can include damage from frost, sandblasting or insect/slug feeding. Botrytis controls are most critical after any frost events, especially if warm and humid weather occurs shortly afterwards.

Phytophthora: Phytophthora is a risk earlier than the other diseases because it is often already active in the soil from the previous season, can be active at lower temperatures, and the canopy is most susceptible as it is unfolding. This disease requires a day or more of continued leaf wetness for foliar infection, which is also most common early in the growing season. Rainy days in May that can last a day or longer, with temperatures in the 15-20°C range, are ideal for foliar infections. Ginseng plants need to be protected throughout emergence. Ensure protection of both the roots and tops through high-water-volume applications of xylem-mobile (upwardly mobile) products, or separate foliar- and root-focused applications. A good resource for summarizing fungicide mobility by product and FRAC group is available here: Fungicide Mobility for Nursery, Greenhouse, and Landscape Professionals. This is a US publication, so focus on the active ingredients, since trade names can differ in the US. Mobility of fungicides is also included in the Ginseng Pest Control Product Summary Tables 2026, which were distributed at the Ginseng Industry Day.