Weed Control in Winter Oilseed Rape
J. Agric. Food Chem., Vol. 54, No. 16, 2006 5955
Table 1. Pre- and Post-emergence Herbicidal Activities of Compound
A in the Greenhousea
pre-emergence
postemergence
rate (g/ha) EC DS EI AR PO BJ EC DS EI AR PO BJ
300
150
50
50
50 50 90
50 50 80
90 30 100 90 98 100 90 90
80 20 100 80 95 100 85 70
a EC, Echinochloa crus-galli L.; DS, Digitaria sanguinalis (L.) Scop.; EI, Eleusine
indica (L.) Gaertn.; AR, Amaranthus retroflexus L.; PO, Portulaca oleracea L.; BJ,
Brassica juncea L. Final evaluation was made 25 days after treatment by visual
rating scales of 0−100.
germinated and grown to the 1-2-leaf stage, compound A was sprayed
at a dosage of 15, 30, or 45 g of ai/ha. The weed control was visually
determined on a 0-100 scale, where 0 indicates no visible effect and
100 indicates complete death of plants in 15 and 30 days post-
treatments, respectively.
Figure 1. Chemical structures and synthesis scheme.
Field Trial. The field test results in Table 5 were conducted in year
2005 at Shao Xin Academe of Agriculture Science, Zhejiang, People’s
Republic of China. The sandy loam soil at pH 6.8 contains 2.9% of
organic matter content. The field was rotavated. Each individual plot
was 2 m wide × 10 m long. The experimental design was a randomized
complete block with four replicates. The product was formulated as
20% suspension concentrate and applied by postemergence application
at dosages ranging from 15 to 90 g of ai/ha with a knapsack sprayer in
675 L of water/ha, when weed species had grown to the 2-3-leaf stage
and oilseed rape had grown to the 3-4-leaf stage. Evaluation was made
90 days after treatment. Oilseed rape injury was evaluated visually on
a 0-100 scale, where 0 indicates no visible effect and 100 indicates
complete death of plants.
extracted with ethyl acetate (2 × 30 mL). The combined organic layer
was dried by anhydride sodium sulfate and evaporated to give
compound 2 (30.6 g, 100%).
N-(2-Bromophenyl)-2-(4,6-dimethoxypyrimidin-2-yloxy)benzy-
lamine (A). 2-Methanesulfonyl-4,6-dimethoxypyrimidine (26.5 g, 121.6
mmol) in tetrahydrofuran (THF) (280 mL) was added to the mixture
of 2-bromo-N-(2-hydroxybenzyl)aniline (30.6 g, 110.1 mmol) and
potassium carbonate (45.7 g, 330.5 mmol) in THF (204 mL). After
the mixture had been stirred for 7 h with refluxing, the solid was filtered
off, and the filtrate was evaporated to give compound A (34.5 g, 75%)
as a white solid: mp 95-96 °C; 1H NMR (CDCl3) δ 3.79 (s, 6H, 2 ×
OCH3), 4.41(s, 2H, CH2), 4.66 (brs, 1H, NH), 5.77(s, 1H, CH), 6.50-
6.56 (m, 2H, Ar), 7.04-7.42 (m, 6H, Ar); MS, m/z (abundance) 417/
415 (M+ + 2, 7), 334 (6), 245 (100), 180 (30), 157 (48); IR(KBr)
3410 (m), 1597(s),1571(s). Anal. Calcd for C19H18BrN3O3: C, 54.82;
H, 4.36; N, 10.09. Found: C, 54.73; H, 4.42; N, 10.14.
RESULTS AND DISCUSSION
Synthesis and Spectroscopic Properties. A new herbicide,
compound A, is prepared as outlined in Figure 1. Salicylalde-
hyde reacts with 2-bromoaniline to produce Schiff base 1 in
good yield. Then Schiff base 1 is reduced by potassium
borohydride to give 2-bromo-N-(2-hydroxybenzyl)aniline 2,
which in turn reacts with 2-methylsulfonyl-4,6-dimethoxypy-
rimidine in the presence of potassium carbonate to generate
compound A.
Elemental analysis indicates that compound A is has the
molecular formula C19H18BrN3O3. In its IR spectral data, the
band at 3410 cm-1 is originated from the stretching vibration
of N-H, and the band at 1597 cm-1 is assigned to the CdN
stretching vibration in the pyrimidine ring. 1H data for compound
A are described under Materials and Methods. The crystal
structure of compound A is determined. There are three different
planes in the molecule, each of which is conjugated. The
dihedral angles between the pyrimidine plane and the planes of
the two phenyl rings are 107.85 (4) and 77.38 (2)°, and the
dihedral angle between the planes of the two phenyl rings is
103.15 (3)° (7).
Herbicidal Activity under Greenhouse Conditions. Com-
pound A was evaluated in the greenhouse after pre- and
postemergence application on several weed species. The pre-
liminary screening results in Table 1 indicate that compound
A has strong postemergence herbicidal activity in the green-
house. In a similar experiment, weak pre-emergence activity
occurs. Weeds are controlled by compound A at 150 and 300
g of ai/ha.
The herbicidal activity of compound A on weeds was further
elucidated by postemergence application at low rates (<90 g
of ai/ha) in the greenhouse. Weed sensitivities are given in Table
2. Many important weeds including Echinochloa crus-galli L.,
Alopecurus aequalis Sobol., Poa annua L., Beckmannia eru-
Herbicidal Activity in the Greenhouse. Compound A was formu-
lated as 50 g/L emulsified concentrates by using acetone as solvent
and TW-80 as emulsification reagent. The concentrates were diluted
with water to the required concentration and applied to pot-grown plants
in a greenhouse. The rate of application [grams of active ingredient
(ai) per hectare] was calculated by the total amount of active ingredient
in the formulation divided by the surface area of the pot. Fifteen seeds
of a testing plant were sown in a plastic pot (diameter ) 9.5 cm) filled
with soil with a composition of 1/1/1 m/m/m sand/silt/clay, an organic
matter content of 2.5%, and a pH of 6.7. The pots were maintained at
20-25 °C in a greenhouse. The diluted formulation solutions of
compound A were applied for pre-emergence treatment 24 h after weeds
were sown. Dicotyledon weeds at the 2-leaf stage and monocotyledon
weeds at the 2-2.5-leaf stage were treated for postemergence treatment.
Compound A was sprayed at application rates up to 300 g of ai/ha.
The herbicidal activity was evaluated visually on a scale of 0-100,
where 0 indicates no visible effect and 100 indicates complete death
of plants. Final evaluation was made 25 days after treatment.
Crop Selectivity. The conventional rice, soybean, and oilseed rape
seeds were respectively planted in pots (diameter ) 12 cm) containing
test soil and grown in a greenhouse at 20-25 °C. After the plants had
reached the 4-leaf stage, the spraying treatment was conducted at
different dosages by diluting the formulation of compound A with water.
The visual injury and growth state of the individual plant were observed
at regular intervals. The final evaluation for crop safety of compound
A was conducted by visual observation in 30 days after treatment on
the 0-100 scale.
Application Windows for A. aequalis Sobol. A. aequalis Sobol.
seeds were the sown staggered to allow application to all six growth
stages on the same day. Compound A was sprayed at rates up to 45 g
of ai/ha at each stage, and the treatments were replicated three times.
After 30 days, the response of A. aequalis Sobol. was visually evaluated
on a 0-100 scale, where 0 indicates no visible effect and 100 indicates
complete death of plants.
Time Course for Effects on A. aequalis Sobol. A. aequalis Sobol.
seeds were sown in pots as described above. After the weeds had