Ginseng is showing early signs of senescence in most gardens, but senescence is more advanced in some areas. Early senescence is often due to hot conditions earlier in the year, moisture stress at times, and root diseases and disorders like Pythium root dieback, abiotic rusty root, or Cylindrocarpon. Excess nutrient concentrations in the soil could also lead to early senescence if it damages fibrous roots. The risk of foliar diseases, especially Alternaria, is higher when plants are stressed.

As fall approaches, it is important to keep monitoring soil moisture levels and irrigate when necessary. Although days are shortening, temperatures are falling, and the ginseng is beginning to senesce, the crop still needs a steady supply of moisture to prevent plants from shutting down too early. Low moisture before harvest may also increase the risk of red root/red vein after drying. In recent years, hot and dry conditions in the fall have become more common.

Potential Effects of a Super El Niño

Forecasters are predicting a potential “super El Niño” this year and potentially the strongest on record. El Niño is a warming of the surface temperatures of the equatorial Pacific and has implications for global weather patterns. Historically, it has had its largest effect on the late fall and winter weather patterns in this area. Looking back at the 4 previous super El Niño seasons (1982/83, 1997/98, 2015/16 and 2023/24), they all caused very mild late falls and winters, often beginning as early as September and continuing into the spring. There were still cool periods at some point over the winter, but mild predominated. For example, in Delhi, temperatures hit 20°C in both November and December, 1982. The high temperature in November of 2015 was 23°C. The average high temperature for December to February for all 4 super El Niños was 2.8°C compared to the long-term average of 0.2°C over the same period.

A warm fall and winter could allow ginseng diseases to be active much later in the fall than normal. Growers may need to apply fungicides for soilborne diseases like Phytophthora and Cylindrocarpon later than normal to prevent disease from progressing over the off-season. However, because this may be an unprecedented El Niño and because weather patterns are very complex, it is possible that the weather this winter could be different than previous El Niños. Fungicide decisions should be made based on soil temperatures. Once they cool to below about 8°C, soil pathogens are likely no longer active and fungicide sprays are not necessary.

Leaf Folders in Seedlings

This week, in one of our seedling research gardens, we discovered feeding damage and leaf rolling from leaf folders (Figure 1). This is the first time we have been able to confirm the presence of leaf folders in seedlings. The small caterpillars in the leaf folds (Figure 2) would be the result of eggs laid in the garden in July by adult moths that flew in from nearby gardens or forested areas. The damage occurred next to a wooded hedgerow. Older gardens with leaf folder issues are present in the area. Adults emerging from these gardens may have found alternative host plants in the hedgerows. It is also possible that the insects are common to forests and hedgerows in this area.

Figure 1. Window-like feeding and leaf rolling of seedlings on August 18 caused by the zigzag Herpetogramma leaf folder.

Figure 2. A small leaf folder caterpillar inside a leaf fold on a seedling.

At this time of year, damage appears as “windows” because the very young caterpillars cannot chew through the whole leaf. They only make small leaf folds until they are large enough to drop to the ground to overwinter. They would then continue their life cycle and cause more damage next spring. It is difficult to control the caterpillars with insecticides at this time of year because their emergence is spread over a 4- to 6-week period. It is best to control them next spring when their emergence is less staggered.

Harvest Timing and Root Conditioning

Due to the heavy rains two weeks ago in some areas, growers may consider harvesting some fields early. Other fields may not be harvested until October. It is important to remember that harvest timing affects how long the roots need to be conditioned in the cooler before drying. Conditioning increases the sugar content of the root and improves internal colour. It simulates what happens in the field in late fall as the roots prepare for winter.

Starchy roots like ginseng prepare for winter by converting starch to sugar. This lowers the freezing temperature of the root and gets the root ready for the spring when sugars need to be mobilized to the developing top. Sugar content and sweetness of the root can increase significantly. In carrots, the sugar content can double or triple in the late fall, usually after the first hard frosts. For ginseng, this process likely begins in early- to mid-October and is complete by sometime in November. If you harvest in August or early September, the roots need up to 6 weeks of conditioning. If you harvest in mid-October, the roots may only need 2 to 4 weeks of conditioning. Roots harvested in November would have gone through the entire process in the field and may not need conditioning at all, depending on fall temperatures.

New Guide to Ginseng Production Available

A new version of OMAFA Publication 848 Guide to Ginseng Production has been published and is now available as a downloadable PDF, or to order as a print copy for $20. Both copies are available at Publications Ontario.

This publication provides an overview of ginseng production from site selection through to postharvest activities, including seed handling and seeding, pest management, fertility recommendations, optimizing pest control, and root quality considerations. The new version includes significant updates based on OMAFA and OGGA research over the past decade, especially to the sections on ginseng replant disease, Ilyonectria root rot (Cylindrocarpon), nematodes, rusty root, leaf folders, and fumigation and its alternatives. This version also contains many embedded photos and new colour illustrations.

The publication does not contain pest control product options, since these are provided in the Ontario Crop Protection Hub. While the publication does go through key production considerations related to pests, more detailed pest information along with more photos is available in the ginseng module of Ontario CropIPM.