How much weed is in a joint

Weed control in cultivated hemp (Cannabis sativa)

With the release of the cultivation of low-THC varieties, the old hemp cultivation has found its way back into the fields. Production takes place primarily for the extraction of seeds and oil, a smaller proportion is used as a renewable raw material in fiber processing. In practice, weed control is mainly carried out mechanically with a single use of hoe. Hemp has a rapid youth development and is highly competitive against weeds. This is particularly true of stands for fiber production, which are grown with a higher stand density and larger varieties. Nevertheless, the official advice was confronted with questions about chemical weed control. Since international experience could not be implemented, also due to a lack of drug approval in Germany, investigations into the possible use of herbicides were necessary.
The selectivity of various herbicides was tested in field trials at one location over three years (1996-1998). In a randomized plot of land (plot size: approx. 10 m²) repeated three times, the crop tolerance of herbicide applications was rated according to the BBA scheme.
The majority of the examined preparations / active substances led to an almost complete destruction of the stand in the form of thinning, compression and growth deformation. Such severe damage was caused by both soil agents and typical leaf preparations. Sulcotrione, Pyridate, Carbetamid + Dimefuron, Metamitron, Ethofumesat, Pendimethalin, Phenmedipham, Ioxynil, Bentazon, Mecoprop-P, Fluoroglycophen, Fluroxypyr and Metazachlor + Quinmerac proved to be harmful. Unacceptable levels of damage (60 to 80% phytotoxicity) were caused by prosulfocarb, MCPA, tribenuron and dicamba. Pure grass products such as Fusilade ME and Focus Ultra (compressions 5-10%) showed justifiable crop compatibility. Special preparations such as Lontrel 100 (thinning: 0-5%, shortening: 4-15%) and Hoestar (thinning: 2-20%, shortening: 5-47%; enabled a crop that was still productive.
Hemp was found to be very sensitive to broadly acting preparations with dicotyledon. The use of conventional broad-spectrum herbicides is therefore not possible either pre-emergence or post-emergence. In addition to the confirmed selectivity of graminicides such as Fusilade ME (Fluazifop-P) or Focus Ultra (Cycolxydim), only the special preparations Hoestar (Amidosulfuron) and Lontrel 100 (Clopyralid) showed a justifiable influence on the culture. In cultivation practice, there are therefore strong weeds with couch grass (Agropyron repens), Burdock weed (Galium aparine), Thistle species (Cirsium ssp., Sonchus ssp.) or chamomile species (Matricaria ssp.) combative. Normally, however, a one-time mechanical weed control will be sufficient.