It should be no surprise that temperatures this winter have been significantly warmer than normal. Crop emergence is on pace to be well ahead of normal, although cooler temperatures over the next couple weeks will hopefully slow that progress.
Based on Environmental Canada weather data at Delhi, 44 Growing Degree Days (GDD: Base 5°C) have accumulated so far this year (March 14). I have calculated spring GDD for every year since 2002 at Delhi, and this is the earliest we have ever reached this level. The next earliest was 2012 when we reached that level on March 18. That was the year of the incredible warmth in March that shattered all records for a week. On average, we don’t reach 44 GDD at Delhi until April 14, which means we are a full month ahead of normal. The latest date this was reached was May 2 of 2018.
The coming cold period will significantly slow crop development for a while. Based on the two-week forecast, we may not accumulate a single GDD again until the end of March. This will hopefully get crop emergence a bit closer to normal by early April.
It should be noted that crop emergence is dictated by soil temperatures rather than air temperatures. In addition to air temperatures, soil temperatures are affected by sunshine, wind, snow cover and the amount of frost in the ground from the winter. Since there was no frost in the ground at the start of this warm period and no snow cover for most of the winter, soil temperatures are likely even more advanced than air temperatures at this time. Even if air temperatures are cool, soil temperatures could still warm in the next two weeks if there is plenty of sunshine and nighttime temperatures are not too cold.
Glyphosate Application Cautions
Crop emergence was earlier than normal last spring. Combined with wet conditions, this resulted in significant glyphosate damage in some fields (Figure 1). Similar issues could occur this spring if growers are not careful.
Figure 1. Symptoms of glyphosate injury to newly emerged ginseng include leaf puckering, curled edges and malformation. Direct glyphosate exposure would result in the more typical yellowing or bleaching of leaves.
Spring glyphosate applications should be made while weeds are actively growing but before the ginseng tops emerge out of the soil into the straw layer. Glyphosate should only be applied in dry conditions when the surface of the straw is dry. Application to wet straw can allow the glyphosate to soak into the straw where is it may remain active for a while, rather than drying on to the straw surface and becoming inactive. The emerging ginseng shoot can contact the glyphosate in the straw, resulting in malformation of leaves and stunted tops. Similarly, application of glyphosate before a rain can wash the product into the straw or down into the emerging shoots causing more significant damage. Considering that the ginseng this year is likely at the same stage it normally is in mid-April, monitor crop emergence carefully and finish glyphosate applications before tops emerge out of the soil. The cooler weather in the forecast may provide a longer window to apply glyphosate, but plants may begin to emerge during the next warm period. Older gardens and those with thin straw cover will be more likely to be negatively affected.
