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Industrial Hemp Varieties Exhibit the Same Tolerance Level to PRE-Herbicides

By Ivan Cuvaca and Jon Scott
Industrial hemp is getting more attention lately as at least 46 U.S. states work on legalizing its production. However, herbicides registered for in-season weed control in industrial hemp are scarce, or nonexistent. To partially help with this issue, a greenhouse study was conducted this summer at the University of Nebraska-Lincoln to test tolerance of three industrial hemp varieties to preemergence herbicides commonly used in corn and soybean.
The study was laid in a randomized complete block design with a split-plot arrangement. The main plot consisted of 14 soil-applied herbicides (Table 2) and the subplot consisted of three industrial hemp varieties: Cherry Wine, Canda and Delores. Each treatment was replicated three times. Seeds of industrial hemp were sown in 21” by 15” by 4” trays filled with a loamy textured soil (Table 1). Each tray consisted of three rows of industrial hemp 5” apart with each variety sown per row per tray at a 30 seeds per row. The seeds were placed ½” deep and apart. Herbicide application was conducted immediately after sowing. Half an inch of irrigation water was supplied for herbicide activation, and then watered daily as needed. Industrial hemp injury was assessed visually at 7, 14 and 21 days after treatment (DAT) using a scale ranging from 0% (no injury) to 100% (plant death). Visual injury ratings were based on symptoms including chlorosis, necrosis, bleaching, stand loss, and stunting of plants compared with non-treated check. The experiment was run twice, (run-1 initiated in June and run-2 in August) and data were analyzed in R (statistical software).
Table 1. Soil description
TextureSilty clay loam (14% sand, 50% silt and 36% clay)
Organic matter (%)1.7
There was no statistical difference between the two runs, thus data were combined and summarized in Table 2. In general, injuries varied from yellowing to leaf bleaching (Figure 1) and ranged from none to 100% (dead).
All three hemp varieties were equally sensitive, or tolerant, to tested herbicides (Table 2). Sharpen, Permit, Prowl H2O and Valor EZ caused light and temporary injuries within the first 7 DAT; past that, no injury was evident in any of the three varieties tested indicating complete recovery (Table 2). Stinger, Sulfentrazone 4F and Surpass NXT caused temporary injuries (4-15%); therefore, these products could be used but with caution. Python, Dual II Magnum and Surestart II caused unacceptable injuries ranging from 25-40%, while Balance Flexx, Tricor 4F and Command caused injuries over 90% (plant death); therefore, these products should be avoided. These results are similar to the results with the same herbicides from our field study (see Industrial Hemp Tolerance to Soil-applied Herbicides).
Figure 1. Industrial hemp injury at 7-14 d after treatment with Command (A), Surestart II (B), Surprass NXT (C), Dual Magnum II (D), and Hornet (E).
Table 2. Industrial hemp injury ratings at 7, 14 and 21 d after treatment (DAT) with 14 preemergence herbicides
Herbicide (rate/acre)Variety7 DAT14 DAT21 DAT
1 Sharpen (1 oz)Canda900
Cherry Wine500
2 Dual II Magnum (1.67 pt)Canda61524
Cherry Wine51526
3 Hornet (2 oz)Canda41620
Cherry Wine61719
4 Python (0.4625 oz)Canda121823
Cherry Wine81517
5 Stinger (2.6 oz)Canda105
Cherry Wine202
6 Surpass NXT (13 oz)Canda5815
Cherry Wine4814
7 Surestart II (1.5 pt)Canda102538
Cherry Wine51937
8 Balance Flexx (6 oz)Canda3381100
Cherry Wine3377100
9 Permit (0.66 oz)Canda200
Cherry Wine000
10 Prowl H2O (3 pt)Canda530
Cherry Wine020
11 Tricor 4F (8 oz)Canda2395100
Cherry Wine2095100
12 Command (32 oz)Canda919798
Cherry Wine899798
13 Sulfentrazone 4F (8 oz)Canda1043
Cherry Wine556
14 Valor EZ (2.04 oz)Canda100
Cherry Wine110


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