Leaf Folders

We are getting reports of significant amounts of leaf folders in ginseng gardens this year (Figures 1 and 2). Most of what we are seeing are leaf folders, but there could be some leafrollers in the mix as well. The difference is that they are in two separate families of moths and would require different control strategies. Leaf folders are probably very difficult to kill once they form their rolls because they do not come out at night to feed and are not exposed to the insecticide. At this time the caterpillars are mostly either pupated or getting close to pupating. It is probably too late to get any control or to prevent further damage at this stage.

Figure 1. A probable leaf folder caterpillar (Herpetogramma thestealis) that is nearing pupation and too late to control with insecticides.

Figure 2. A small patch of significant damage from leaf folders.

We know almost nothing about the life cycle of leaf folders in Ontario because this species is not a pest of any other commercial crop. We have not observed a second generation, but it is possible they will emerge again later in the summer and they are just not noticed because tops are already senescing at that time. It is best to scout for the tiny caterpillars for the rest of the summer, because that is the only stage they could be effectively controlled.

While the caterpillars do cause obvious damage, it is rare for them to cause enough damage to warrant an insecticide spray. In older gardens, even one leaf folder per square metre in the entire garden is probably not enough to cause economic damage. This leaf folder species is native to Ontario and that means it also has all its natural enemies around. Just today we found several pupae of what could be parasitic wasps inside the leaf rolls along with shrivelled up caterpillars, meaning that natural enemies may be providing control. These natural enemies could be what prevents populations from getting out of control. This may just be a boom year for the caterpillar. Randomly applying insecticides to get control of the leaf folders could kill some of the natural enemies as well, so only apply insecticides for any insect pest when needed to prevent economic damage.  

We are rearing out some of the insects to identify the species and are trying to determine the life cycle in ginseng. This may help growers time sprays better in the future.

Diseases

A bigger concern with the feeding damage from leaf folders is the botrytis blight that is developing on the damaged tissues. Ensure Botrytis is kept under control in fields with higher leaf folder populations, especially with hot and humid weather coming next week.

Alternaria leaf blight (Figure 3) is increasing, and the weather next week will be ideal for further spread. It may be too hot most times next week to safely apply fungicides so ensure the crop is protected before the heat begins on Monday.

Figure 3. An active Alternaria leaf blight lesion.

Phytophthora root rot is also active due to all of the recent rains but the hot and dry weather over the next week is much less conducive for its spread.