Growers are reporting considerable plant stress from the heat wave a few weeks ago. Symptoms include heat burn to the leaves, where sections of the leaf and leaf edges turn brown and papery, and signs of early senescence, where leaves begin to turn red. Damage is worst on hills under the shade and where air flow was restricted. The worst of the damage probably occurred on the days with stagnant air, which allowed the heat to build up in the centre of gardens. The recent cooler weather should slow down senescence and increase root growth. It is too early to determine what impact this will have on final yield.
With the recent rains, damaged plant tissues will be more prone to infection by Botrytis and Alternaria. While berry production still appears to be good, berries on stressed plants are also at risk of Botrytis or Alternaria infection. In addition, there is evidence that Fusarium can infect berries and the developing seed at this stage, leading to seed issues in the future. Ensuring protection of berries from Alternaria and Botrytis may also reduce Fusarium infection. However, minimal research has been conducted on Fusarium and berry infection.
The Rhizopus or related rots of scattered 2-year plants that have been appearing over the past few weeks are drying down, and there are no reports of spread from root to root. Growers should continue to monitor for spread, but previous experience with this disease suggests spread is unlikely. Phytophthora root rot remains the biggest root rot issue at this time and activity may increase again with the recent rains. Now is a good time to thoroughly survey mature ginseng fields or sections of fields with significant disease pressures to determine if an early harvest is warranted.