It looks like most areas escaped a frost last night, mostly due to a breeze that continued all night that mixed up the air. There is a slight risk again tonight with calmer air, but forecast dewpoints are +1C for Delhi, which would decrease the risk of a severe frost.
There has been a lot of damage reported from last week’s freeze, mostly for gardens that were not protected with row covers. These gardens will be prone to foliar diseases, especially next week when temperatures and humidity increase. Ensure gardens are protected with fungicides for both Alternaria and Botrytis before the warm-up.
Prolonged cold temperatures appear to have stunted emergence for older gardens, and this may result in shorter canopies and slightly distorted leaves. These plants will also be more susceptible for foliar diseases in the coming weeks.
I am seeing and have reports of reduced emergence, stunted plants and severely malformed leaves (Figure 1, 2, 3). This appears to be a separate issue from the overall stunting that cold temperatures can cause, or the direct damage from freezing (e.g., kinked, swollen and split stems, and glassy leaves). Leaves tend to be more strap-like with upward cupping. Although the cause would be difficult to prove, it is most likely glyphosate damage based on the pattern and the symptoms.
Figure 1. Upward facing cupping and strap-like leaves on a ginseng plant likely due to glyphosate damage. The tallest plants in the canopy likely emerged first and have the highest chance of being damaged.
Figure 2. Highly distorted leaves likely due glyphosate damage. (Photo Courtesy Amy Shi, OGGA)
Figure 3. Severe upward facing cupping and distortion likely due to glyphosate damage. (Photo Courtesy Amy Shi, OGGA)
As indicated on the labels, glyphosate should not be applied in the fall because it can damage the emerging tops in the spring. This is thought to be due to the wet straw, cold temperatures and low sunlight at that time of year, which allows the glyphosate to soak into the straw rather than dry up on the surface and be exposed to sunlight. This prevents the glyphosate from breaking down entirely. It is possible the same thing could happen in the spring if the straw is wet at the time of application and temperatures are cool. We had a two-week stretch at the end of April in which it rained virtually every day. If glyphosate was applied during that period, it could have soaked into the straw and either contacted the emerging ginseng shoots directly or caused damage later as the tops emerged through the straw.
Leaf folder larvae have been reported beginning to roll up leaves earlier this week. Since they are still small and will still pull in more leaves over the next week or so, now is a good time to apply an insecticide. The hope is that the insect pulls treated leaves into the leaf fold and then feeds on them. Insecticides should only be needed in high-risk areas, such as those with a history of leaf folder damage or areas next to forests.