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

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

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
Texture Silty clay loam (14% sand, 50% silt and 36% clay)
pH 6.6
CEC 21.9
Organic matter (%) 1.7

Results

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).

Industrial hemp injury
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) Variety 7 DAT 14 DAT 21 DAT
1 Sharpen (1 oz) Canda 9 0 0
Cherry Wine 5 0 0
Delores 9 0 0
2 Dual II Magnum (1.67 pt) Canda 6 15 24
Cherry Wine 5 15 26
Delores 9 17 27
3 Hornet (2 oz) Canda 4 16 20
Cherry Wine 6 17 19
Delores 8 12 23
4 Python (0.4625 oz) Canda 12 18 23
Cherry Wine 8 15 17
Delores 14 23 25
5 Stinger (2.6 oz) Canda 1 0 5
Cherry Wine 2 0 2
Delores 3 2 5
6 Surpass NXT (13 oz) Canda 5 8 15
Cherry Wine 4 8 14
Delores 6 10 17
7 Surestart II (1.5 pt) Canda 10 25 38
Cherry Wine 5 19 37
Delores 13 26 44
8 Balance Flexx (6 oz) Canda 33 81 100
Cherry Wine 33 77 100
Delores 37 83 100
9 Permit (0.66 oz) Canda 2 0 0
Cherry Wine 0 0 0
Delores 4 0 0
10 Prowl H2O (3 pt) Canda 5 3 0
Cherry Wine 0 2 0
Delores 1 2 0
11 Tricor 4F (8 oz) Canda 23 95 100
Cherry Wine 20 95 100
Delores 25 95 100
12 Command (32 oz) Canda 91 97 98
Cherry Wine 89 97 98
Delores 9 97 98
13 Sulfentrazone 4F (8 oz) Canda 10 4 3
Cherry Wine 5 5 6
Delores 9 15 14
14 Valor EZ (2.04 oz) Canda 1 0 0
Cherry Wine 1 1 0
Delores 4 1 0