This has been a rough week weather-wise for ginseng in certain areas. First a minor frost occurred the morning of May 17 and there are reports of minor damage in older gardens in some areas. This was followed by heavy downpours from thunderstorms over the last few days followed by wind and hail damage to the shade last night in some areas.
These conditions are highly conducive to the development of foliar Phytophthora and Botrytis. Ginseng should be protected from both pathogens. More targeted Phytophthora and Botrytis fungicides may be necessary to keep outbreaks of disease from spreading. Alternaria issues can also begin to flare up at this time of year. Standing water is present in some gardens, and driving through this can splash water infested with Phytophthora spores onto leaves and cause a foliar outbreak. It can also spread the spores down the row. Avoiding driving through the field can be difficult when the crop needs to be sprayed with protectant fungicides, but every effort should be made to either prevent water from standing in the field or to wait until it has drained.
Over the next month, ginseng should be monitored closely for insect pest development, especially leafrollers. Every June or July there are reports of leafrollers causing considerable damage in localized areas of a garden. Often the damage is confused with foliar Phytophthora from a distance, since leaflets can hang from the plant when the petioles are chewed off. Once the damage reaches that stage, it is often too late to control the larvae. Gardens should be closely monitored over the next few weeks for the initial signs of leaf rolling and the very small caterpillars. Dipel 2X DF is the only product registered for control of leafrollers in ginseng and must be applied when the larvae are small.
We are still looking for growers to be involved in both a replant field survey and a fumigation field survey. If you are attempting replant, or have any gardens fumigated in 2012 with chloropicrin, metam-sodium (Busan or Vapam), other fumigants or unfumigated, we would like to monitor for disease in your field. The cost is a small amount of root, but growers will gain a much higher value of diagnostic tests that can help in disease management. If interested, please contact Rachel Riddle at email@example.com.