Ginseng emergence continues to be slow compared to last year, which probably protected the plants from significant freezes the last two nights. Looking at Growing Degree Days (GDD) Base 5°C for the spring up to April 30 at Delhi (including the forecast for tomorrow), we will likely have accumulated around 100 GDD this year. Last year, we had accumulated 170 GDD by April 30. At this time of year, it is normal to accumulate around 5 GDD per day, which means crop growth is likely around 14 days behind last year.
I also examined March and April GDD accumulation each year going back to 2002 at Delhi. The average for the past 20 years is 107 GDD, showing that we are only slightly behind normal for this time of year. Last year was clearly an anomaly. The highest GDD in March and April in that 20-year period was 186 GDD in 2012, which was mostly caused by an incredible warm period in March of 2012. The lowest GDD was in March and April of 2018 with only 28 GDD. That year, April was very cold with snowflakes falling almost every day in a two-week period in mid-April.
Air temperatures do not tell the whole story for a perennial root crop, since the soil can still be warmed by the sun on a sunny day even if air temperatures are cold, but it has not been a particularly sunny spring either. Based on the weather data, we are on track for a relatively normal emergence this year. Older plants are likely to emerge through the straw rapidly in the next mild period. Seedlings will likely emerge around the 10th of May. Emergence will be more rapid in areas with thin straw.
As mentioned in my previous blog post, there are concerning signs that root disease pressures may be high in older gardens due to the heavy rains in October and the inability for growers to get into fields to apply fungicides at that time. Growers have reported root disease issues in storage in the fall and in roots in the field this spring. These are not advanced rots, but small infection points at the junction between the fibrous roots and the taproot. It may be possible to stop the infections before they spread into the taproot, but it will be necessary to apply fungicides before soil temperatures warm. Fungicides for both Cylindrocarpon and Phytophthora root rots should be applied over the next week or so, ideally immediately before a rain to wash them into the root zone before they dry onto the straw. During crop emergence, applying a xylem-mobile fungicide for Phytophthora root rot control (e.g. Orondis, Presidio) will also lead to protection of the tops to foliar Phytophthora infection.
There have been increasing populations of leaf folders (the zigzag herpetogramma moth/caterpillar) in ginseng the past two years. These are similar to leafrollers in the damage they cause but actually only distantly related. By the time growers report having issues with significant rolling of leaves, it is often too late to provide control because the caterpillars are protected within the roll. Crop scouts and growers should be looking closely at random plants throughout the garden for the very first signs of damage. Although not entirely known, initial signs will likely include minor feeding on the leaf edges, folded leaf edges, and presence of fine webbing. A small version of the caterpillar shown in Figure 1 may also be visible. The adult zigzag herpetogramma moth may also be seen flying in a zigzag pattern within the fields or sitting on plants or posts within the garden, but it is most likely present at night (Figure 2). The moth is about 2 cm (3/4”) wide from wing tip to wing tip. It is unknown how the moth overwinters, but if it overwinters as a pupa or an adult, then eggs are likely laid at some point in May on leaves or stems. If it overwinters as eggs, then adults will not be present until after the caterpillars pupate later this spring.
Figure 1. A zigzag herpetogramma leaf folder caterpillar. After egg hatch, the caterpillar would likely be only a few millimetres in length and a dull green.
Figure 2. The adult zigzag herpetogramma moth is brown with distinct markings and around 2 cm in diameter. It flies in a zigzag pattern, hence the common name of the species.
Leaf rollers and leaf folders are often most concentrated on field edges, particularly near fence rows, hedgerows, or forested areas. It is likely damage will not occur until mid- to late-May at the earliest, but it is best to start monitoring as soon as leaves begin to unfold. Please report the first sightings of the pest to OMAFRA so we can get a better idea of optimal timing for control. The zigzag herpetogramma moth is not a common pest in agriculture, and its biology and life cycle are poorly understood. Contact me at firstname.lastname@example.org or Melanie Filotas at email@example.com to report any sightings of the moth, the caterpillar or suspected damage.
Finally, if you were not able to attend the OGGA Industry Day, I wanted to call your attention to a new OMAFRA resource that has replaced OMAFRA’s printed crop protection guides, including the Crop Protection Guide for Ginseng. It is called the Ontario Crop Protection Hub (Ontario.ca/cropprotection) and includes rates, efficacy ratings, and precautions for all of the pest control products registered for use on ginseng as well as most other crops grown in Ontario. For more information on this resource refer to this previous post: https://onspecialtycrops.ca/2022/04/04/new-ontario-crop-protection-hub-now-available-for-accessing-crop-protection-information-online/.