With a temperature of -0.8C recorded at Delhi on Thursday morning, there is some frost damage in some areas. With a lighter freeze occurring, damage is mostly restricted to edges of gardens and low pockets where cold air pooled. For those growers who haven’t seen this damage before, frost damage to seedlings causes stems to shrivel and the top to collapse onto the straw (Figure 1). Seedlings will not recover from this damage. Damage to older plants often weakens the stem causing the top to kink over (Figure 2). These plants often curl back up towards the light, but yield will be impacted. Symptoms do not always show up immediately. It can take a day or two for the damage to be evident.

Figure 1. Seedlings killed by frost.

Figure 2. Older plants kinked over as a result of frost.

Warm and humid weather is in the forecast for the next few days. These conditions can favour the development of foliar diseases. If frost damage has occurred in a garden, the risk of Botrytis blight is especially high. Botrytis often needs damage to cause an initial infection and can then spread to healthy plants nearby (Figure 3). Products should be applied as soon as possible to protect plants from Botrytis in these gardens. Foliar phytophthora can also show up under these conditions in any areas that receive heavy rainfall.

Figure 3. Botrytis developing a stem weakened by frost.

With ginseng starting to emerge in our replant fumigation research plot, we are starting to see the progress of replant disease. Figure 4 shows a bed that was fumigated on the left and not fumigated on the right. Replant disease has completely destroyed the unfumigated plots, while the fumigated plots appear normal to this point (Figure 5). Replant disease will likely begin to spread in fumigated plots this summer.

Figure 4. 2-year old ginseng emerging in our replant research garden with fumigation on the left and unfumigated on the right.

Figure 5. Replant disease has completely destroyed the ginseng in the unfumigated plot in the background but fumigated plots in the foreground appear healthy.