So far this year, 130 growing degree days (GDD) have accumulated at Delhi, which is 7 days ahead of normal. The warm weather over the weekend will accelerate growth and by Tuesday, we will be back to 10-11 days ahead of normal if the forecast is accurate.

Older plants are emerging into the straw. The frosts the last two nights may have affected emerging older plants in areas with thin straw cover. Temperatures at Delhi and Walsingham were around -2.0 to -2.8°C the last two nights, with dew points in the -5 to -6°C range. That means if frost was present on the ground, temperatures at the ground were around -5 to -6°C.

Root Lesion Nematodes

The combined research of OMAFRA, OGGA, and the University of Guelph over the past 14 years has now conclusively shown that ginseng is not a suitable host of root-lesion nematodes. However, if populations survived fumigation and developed on the rye cover, they will damage the ginseng during germination. This is the time of year that nematodes that overwintered lower in the soil profile move back up to the root zone. When the rye cover is killed by a herbicide application they will have no choice but to feed on the germinating roots. Within a few weeks they begin to die off because they cannot multiply on ginseng roots. While fall application of in-season nematicides appears to be best (if needed), spring application is your last opportunity to prevent damage. However, nematicide application is probably not necessary in all fields. Ideally, soil samples collected in the fall and submitted for nematode analysis should be used to determine whether a spring application is necessary. Soil samples collected now are probably not useful because they may not capture nematodes that are still low in the soil profile and the results will probably not come back in time.

Other Considerations

Here are a couple additional considerations for the upcoming growing season:

1. Phytophthora. Phytophthora pressures will be very high in most existing fields due to last years wet weather. April has also been relatively wet, although soil temperatures are still too cold for significant Phytophthora development. If soils remain wet once the warm weather arrives, be sure to target fungicides for both the root rot and leaf blight phases of the disease.
2. Grubs. This is the last year that Admire 240 Flowable insecticide can be used for grub control in ginseng. After May of 2025, there will be no products registered for grub control on ginseng. This is the final year you can determine what potential impact this could have. Some growers never apply the product and rarely have an issue, while others apply the product every year. European chafer adults lay their eggs in late June or July. Since the grubs feed on the roots of grasses and other hosts with fibrous root systems, the adults are probably looking for grassy fields or fields covered in vegetation in which to lay their eggs. It is likely that empty fields are not a preferred egg-laying site. As a result, it is important to keep fields weed-free between fumigation and seeding. Late fumigation after the eggs are deposited, if practical, could also be a strategy to reduce grub populations without the need for an insecticide.

The updated “Ginseng Pest Control Product Summary Tables 2024” were just distributed through OGGA, listing all of the products registered for use on ginseng. If you would like a copy and have not received it through OGGA, contact me at sean.westerveld@ontario.ca. Please note the following correction for the tables: For Rootshield WP, the maximum applications is listed as “0”. This should be “NS” for not specified, meaning that the number of applications per season is unlimited. You can also look up all of this information on the Ontario Crop Protection Hub at https://cropprotectionhub.omafra.gov.on.ca/.

Finally, a reminder that Ginseng Scout Training will be held on Thursday, June 8 from 1 to 3 pm (rain date June 9). For details and to register, refer to the full IPM Workshop listing here: https://onspecialtycrops.ca/2024/04/17/2024-ipm-workshops-incl-ginseng/