The cooler and drier weather over the past two weeks has reduced disease issues in ginseng. Conditions have been ideal for root and berry development and may help to recover some yield potential lost in the heat wave in July. Controls for foliar diseases of ginseng should continue while the leaves are still green, but the interval between sprays can be reduced in drier weather. However, dew periods are becoming longer and this can lead to increased Alternaria activity.
Growers who experimented with different fumigants last year should assess seedling roots over the next few weeks for damage from nematodes and soil-borne diseases. This will provide an indication of the efficacy of those fumigants and help in fumigation planning for next season. Most of the damage showing up in seedlings this year was caused by root lesion nematodes. As a result, the main conclusion that can be drawn based on seedling assessments is the efficacy of the fumigants on nematodes. Root diseases take longer to develop and differences between fumigants in efficacy against diseases cannot be fully assessed until harvest. It should be noted that fumigants that control nematodes well will not necessarily control a soil-borne pathogen as well because it depends on the survival structures of the pathogen and how well the fumigant can penetrate those structures. Also, fumigation has no impact on foliar diseases or most insect pests. Damage from these pests should be ignored when comparing fumigants.
In 2010, a fumigation trial was established in a ginseng field to compare telone, chloropicrin and metam-sodium fumigants and three cover crops for control of nematodes and diseases. The final harvest assessment of this trial will occur over the next two weeks along with an assessment of berry production. Results will be reported this fall on this blog. This trial did not assess the use of tarping to seal the soil.
Fumigation trials have been established this summer at both a new and replanted ginseng site. The trials are comparing tarped chloropicrin and tarped and untarped metam-sodium fumigants to two biofumigants (Dazitol and MustGrow) and to both tarped and untarped controls. Treatments were applied in June and July. Nematode samples have been collected, but are still being analyzed. This project also includes a field trial on strawberries to compare preplant and in-season nematode controls. Preliminary results will be reported on this blog in the fall.