Some areas received yet another round of strong thunderstorms with high winds that knocked down shade on Wednesday along with heavy, wind-blown rains. Those gardens knocked around by high winds may be more prone to Botrytis over the next week or so due to the physical damage to the leaves and stems. Phytophthora may be the bigger issue with fields flooded by heavy rains.
Alternaria and Botrytis
Alternaria is beginning to show up in older gardens. It is critical to get good spray coverage with fungicides at this time of year to ensure some protection of all plant parts, especially the inner canopy and stems. If there are untreated surfaces within the canopy, Alternaria can take hold and linger all season. Even one spray with good coverage of the inner canopy can provide a long period of protection, since spray residues in these areas are protected from both degradation by sunlight and wash-off by rain/irrigation water. With the added risk of Botrytis is some fields damaged by strong winds, choose products or tank mixes that provide control of both diseases.
Leaf folders are present in tightly rolled clusters of leaves in older gardens. Once they reach this stage, it is difficult to reach them with insecticides. Products registered for control of leaf rollers in ginseng may also suppress leaf folders, but they are all best applied when larvae are small. It is unclear if it is too late to provide any control of leaf folders currently. Success/Entrust insecticides can be applied to larger larvae but would require the caterpillar to come out of the roll to feed on treated leaves and there is no evidence that leaf folders come out of the roll once it is formed. It is possible they leave the roll occasionally to fold new leaves into the roll. It is becoming evident that leaf folder larvae start to attack the leaves as they unfold in mid-May. In fields with heavy infestations, sprays may need to be applied during top emergence next spring.
Symptoms of lingering root diseases are also starting to be evident in the tops. An area of stunted tops often signals some damage to roots from previous years. When tops start to wilt or arch over, that is a good sign that the disease is continuing to progress and controls may be necessary. As most growers know, the location and pattern of damage is usually an indication of the cause of the root rot: irregular patches of missing and wilting tops in low areas are most likely due to Phytophthora, the same pattern not confined to low areas is most likely due to Cylindrocarpon, and distinct circles of missing plants that expand over time are probably due to Rhizoctonia. Irregular patches of stunted plants without obvious wilting can be due to other issues like Pythium, root-knot nematodes or severe rusty root. Examining the roots is the only way to distinguish some of these issues.
There are no reports of major issues with other insect pests like cutworms, grubs and aphids, but if present, damage should be showing up now. Aphids are often found feeding along the stem, often below the flower cluster, and the underside of the leaf along the veins. Controls are only necessary if aphids are widespread (e.g., multiple aphids on >25% of plants in an area). Cutworms and grubs are often confined to seedling gardens. Cutworms caused severed tops, while grubs lead to small circles of missing plants with tops pulled into the straw from below. There are no products registered for grub control after seeding. Products for other insects are not always necessary unless they are widespread. Sprays can sometimes kill off beneficial insects that would keep pests populations low naturally, leading to larger issues in the future. Sometimes a localized spray with a backpack sprayer is sufficient for problem areas of minor insect pests.
Storage of Dried Roots
Growers have been asking about optimal storage conditions for dried roots given the current market conditions. Click here to refer to a previous article on how to optimally store dried ginseng. The article has been updated to provide additional information.