Weather, Frost and Disease

Some areas have experienced frost damage, mostly during last week’s frost events. Most of the damage is confined to field edges and low areas. We used to think that damage along field edges was due to colder air outside of the field where the tarps did not provide protection, but it now appears that the air is just as cold inside a garden (although coldest in low areas where the cold air pools). The plants on the edge of the garden can radiate additional heat towards the sky at night, making the plant surfaces in these areas even colder than the air.

Beyond frost damage, prolonged cool temperatures during emergence can sometimes stunt the canopy and lead to malformed leaves. It is unclear if this is due to the cool temperatures directly or due to more glyphosate damage as the plants spend more time coming through the straw, and the glyphosate residues remain active within the straw.

Row covers put out earlier this month may have caused physical damage to some of the tops as they blew in the wind. High winds on Tuesday could have led to sandblasting of plants on the windward side of gardens. Some damage to shade structures is also reported, which could have caused physical damage to some ginseng tops. The combination of frost, cold temperatures, sandblasting and physical damage could lead to high foliar disease pressures this year.

A very moist airmass is moving in for the weekend, along with warmer air next week. This will greatly increase the risk of Alternaria and Botrytis, especially in frost-damaged gardens. A soaking rain is also in the forecast, along with moderate temperatures, meaning Phytophthora will also become active. Plants are also at their most susceptible stage for foliar Phytophthora.

Leaf Folders

Leaf folders are active again and around the 3^rd instar stage (10-12 mm long) (Figure 1). The best time to start spraying is during the emergence and unfolding of older plants, when caterpillars are more exposed. Now that they are forming leaf folds, it is harder to contact the caterpillars with insecticides. Based on our observations last year, the caterpillars do leave their leaf folds occasionally to form new ones. This provides some ability to control them, but multiple applications may be necessary, spaced 7 to 10 days apart, depending on label requirements. Leaf folders are usually patchy in the field, and it is easy to scout for their presence. Always base the need for insecticides on a scouting program, or you may be wasting money. There is nothing registered for control of leaf folders directly, but products applied for cutworm or leafroller control will likely also control leaf folders, if used at the right stage.

Figure 1. A leaf fold on a ginseng leaf on May 21 (top photo: leaflet at the 11 o’clock position) and the caterpillar inside (bottom photo).

Cutworms and Grubs

This is the most active period for feeding by both cutworms and grubs. Since we lost the ability to apply Admire insecticide at seeding last year, there may be more grub issues this year. Both these pests are more common in seedlings and lead to similar damage. Cutworms sever the top entirely, and the top is often left upside-down on the straw (Figure 2). Grubs feed within the soil and pull the tops into the straw as they feed (Figure 3). Look for small, circular patches of missing plants. Often, there will be one or two wilting tops on the edge of the patch, and one or two tops pulled into the straw. The grub can often be found feeding under the wilting tops. There are no products registered to control grubs on ginseng. Even if there were, grubs will stop feeding and pupate within a week or two. There are several insecticides registered for cutworm control in ginseng. To determine what is registered, visit the Ontario Crop Protection Hub. For more information on the biology and identification of these pests, consult the ginseng module of Ontario CropIPM.

Figure 2. A ginseng top severed by a cutworm.

Figure 3. A grub patch showing both tops pulled into the straw (centre) and tops that have already been killed (top left).

IPM Scout Training – June 4

The Ginseng IPM training session will occur on Thursday, June 4 from 1:00 to 3:00. This session will provide an overview of the diseases, insects and disorders that affect ginseng and how to monitor and identify them. Here are the event and registration details:

• Workshop Leaders – Sean Westerveld / Melanie Filotas
• Location – In person (just south of 785 Byerlay Sideroad, Courtland)
• Raindate – June 5, 1:00 – 3:00 pm
• Click here to register