There have been continued reports of insect damage to ginseng including four-lined plant bugs and leaf rollers. The current generations of both leaf rollers and four-lined plant bugs should be nearing an end in the next few weeks. There are no further generations of four-lined plant bug expected, but there could be more generations or new species of leaf rollers emerging later in the season.
With warm and dry conditions forecast for the next few days, the risk of foliar Phytophthora will decrease. Alternaria will be the primary concern during this period. Foliar symptoms of root diseases such as Phytophthora and Cylindrocarpon will also begin to show up over the next few weeks, particularly if conditions become dry once again. Watch for leaf discolouration or wilting, particularly in the heat of the day.
Occasionally a vascular wilt disease of ginseng is reported, and there have been reports again this year. Plants often turn red, usually in older gardens, and collapse onto neighbouring plants (Figure 1). This usually occurs on individual plants throughout the garden, and not in patches like many other ginseng diseases. When the root is dug up and sliced cross-wise, the vascular system is usually discoloured in a ring in the centre of the root (Figure 2). The disease is usually reported on former potato fields. Based on the symptoms of the disease and the cropping history, the disease is most likely verticillium wilt. We hope to get conclusive identification over the next few weeks.
Figure 1. Verticillium wilt often results in wilting and red discolouration of individual plants.
Figure 2. The most distinctive symptom of verticillium wilt in ginseng is a brown discolouration of the vascular system in the roots.
Verticillium is a disease that can be found on many different hosts including all members of the potato family (potato, tomato, pepper, eggplant), strawberries, raspberries, and cucurbits. It is a soil-borne fungus that spreads from root to root or through standing water, but could also be spread of sucking insects such as aphids. It infects roots through wounds or natural openings and colonizes the vascular system, eventually causing limited water flow to the top of the plant. Initial above-ground symptoms consist of wilting during the heat of the day followed by discolouration of the leaves and eventually permanent wilting. The best method to prevent the disease is site selection. Avoid growing ginseng on fields recently planted to one of the susceptible crops, especially potatoes. There are no products registered for control of verticillium in ginseng, and verticillium diseases cannot be effectively controlled with fungicides once symptoms show up.