Hemp planting continues across the state. Most grain and fiber growers have gotten their seed in the ground, but cannabinoid (CBD, CBG, etc.) growers continue to transplant. The drier weather has helped growers get in the field earlier than the 2019 season. New hemp applications continue to come through the state chemist office, but largely consist of small CBD grows.
Growers should expect to manage weeds early in the season to keep pressure low. The two herbicides available for use in hemp are for between row applications only. CBD growers may like these products but they will not work for grain or fiber growers because of the tight row spacing. You can find more information on the pesticides available for hemp here https://www.oisc.purdue.edu/pesticide/pdf/pest_hemp_product_list.pdf.
We continue to find flea beetles in feral hemp populations, with over ten beetles per plant. We do not have a flea beetle threshold for hemp at this point. An artificial defoliation project in Virginia demonstrated that hemp grain yield was not affected by even high levels (75% leaf tissue removed) of defoliation, even as early as 20 days after planting (Britt and Kuhar 2019). They did conclude, the possibility that feeding injury could elicit different plant responses, like changes in chemistry. Hemp does appear to be a durable plant, able to handle large amounts of tissue removal. Defoliators like flea beetles are not the biggest concern at this point.
A more destructive pest for growers is the Eurasian hemp borer (EHB). As promised, I will continue to give updates on the progress of this pest. An adult moth was found in Jasper County on May 27th. EHB larvae were found on June 9th in the same patch as the adult moth. They are incredibly tiny larvae and while some evidence of infestation is detectable through bulges in the stem, I found quite a few larvae at the terminal ends of plants. Minor dieback can be observed with a keen eye, but a hand lens may be helpful, especially for observing young larvae.
Select Reference
Britt K and Kuhar T (2019) Effects of Defoliation in Grain Hemp. Science of Hemp Proceedings.
Eurasian hemp borer larva at the terminal end of a feral hemp plant. Jasper County, 6/9/20.
Bulge in the hemp stem caused by Eurasian hemp borer larvae.
