Pearl Millet Tolerance to Selected Herbicides

Tolerance of pearl millet to selected herbicides applied and incorporated before planting was evaluated in the field at Manhattan, Kansas, in 1978 and 1979. Atrazine, terbutryn and bifenox only slightly injured pearl millet seedlings. Seedling injury due to propazine was greater in 1978 than in 1979, while injury due to cyanazine was greater in 1979 than in 1978. Plant height and yields were not significantly reduced by triazine herbicides or bifenox either year. Propachlor prevented emergence. Pearl millet exhibited no tolerance to EPTC plus R-25788 and only limited tolerance to butylate plus R25788. Growth of pearl millet [Pennisetum americanum (L.) Leeke], an important cereal crop in droughty areas of the world, is currently being investigated under Kansas conditions. Large scale production of pearl millet will be possible only if selective herbicides are applied at planting time to control weeds. Panchal et al. (1974) reported that keeping pearl millet weed-free for six weeks after planting prevented yield losses. Atrazine applied before weeds or millet emerged increased yields 28 (Tomer and Singh, 1973), 100 (Panchal et al., 1974), and 150 percent (Jain et al., 1971). Yadav et al. (1978) reported that yields of pearl millet treated with atrazine at 0.8 kg/ha at planting time were equivalent to yields from plots kept weed-free by hand weeding. Ashrof et al. (1977), however, observed that atrazine at 0.8 kg/ha (the same rate) reduced shoot and root growth and chlorophyll content of pearl millet. Research pertaining to chemical weed control in pearl millet has focused on herbicides used in grain sorghum [Sorghum bicolor (L.) Moench] production. I Contribution no. 81-53-j, Department of Agronomy, Kansas Agricultural Experiment Station. 2 Present address: Institute for Agricultural Research, Ahmadu Bello University, Zaria, Nigeria. This content downloaded from 157.55.39.112 on Wed, 07 Sep 2016 05:24:23 UTC All use subject to http://about.jstor.org/terms 106 TRANSACTIONS OF THE KANSAS ACADEMY OF SCIENCES Objectives of the research reported here were to determine 1) if pearl millet grown under Kansas's conditions tolerates herbicides used in sorghum production and 2) if herbicides phytotoxic to sorghum also are phytotoxic to pearl millet. METHODS AND MATERIALS Tolerance of pearl millet to selected herbicides was evaluated at the same site at Manhattan, Kansas in 1978 and in 1979. Conventional methods for seedbed preparation were used on a Reading silt loam soil (fine, mixed, mesic, typic Argiudolls) with 2.6 percent organic matter content and a pH of 6.3. Herbicides were applied June 5, 1978, and June 12, 1979, with a tractor-mounted sprayer equipped with tapered flat-fan nozzles with water as a carrier at a volume of 1.87 L/ha and pressure of 1.2 kg/cm2. Treatments included triazine herbicides (atrazine, propazine, cyanazine, or terbutryn), a diphenylether herbicide (bifenox), and an acetanilide herbicide (propachlor) alone and in combination with atrazine, bifenox, or a substituted urea herbicide (linuron). Herbicides were applied at rates recommended for grain sorghum. Thiocarbamate herbicides (EPTC or butylate) in combination with protectant (R-25788) also were applied to determine their efficacy in controlling volunteer millet. Herbicides were immediately incorporated 7.6 cm deep with a power-driven rotary tiller. Simultaneous planting of 'RMP l' pearl millet 2.5-cm deep and furrow application of the insecticide carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate) were within eight hours after herbicide application. The plots consisted of four rows each 9 meters long and 76 cm wide kept weed free by occasional hand hoeing. Data were collected from the center two rows of each plot and consisted of visual injury ratings and plant height. Grain yields were obtained after millet heads were harvested by hand in early October, dried, and threshed. Data reported represent means of three replications in a randomized complete block design. RESULTS AND DISCUSSION Atrazine, terbutryn, and bifenox applications caused only slight injury in pearl millet seedlings either year (Table i). Seedling injury was greater when cyanazine or propazine was applied in 1978 or cyanazine in 1979. Propachlor applied alone or in combination with other herbicides prevented pearl millet from emerging both years. EPTC plus protectant R-25788 applied as a tank mix combination also prevented millet emergence, while butylate plus R25788 severely reduced but did not completely prevent emergence. Atrazine, propazine, terbutryn, or bifenox did not significantly reduce plant height or yields either year. Cyanazine also did not significantly reduce yields even though it severely injured seedlings in 1979. Some of the pearl This content downloaded from 157.55.39.112 on Wed, 07 Sep 2016 05:24:23 UTC All use subject to http://about.jstor.org/terms VOLUME 84, NUMBER 2 107 Table 1. Seedling injury and growth of pearl millet treated with indicated herbicides at Manhattan, KS in 1978 and 1979. Injury ratingab Heighta Yielda Herbicide Rate 1978 1979 1978 1979 1978 1979 (kg/ha) -----(cm) ---------(kg/ha) Atrazine 2.4 0.10 d 0.10 c 113 ab 160 a 857 a 3218 a Propazine 2.7 0.27 c 0.03 c 117 ab 163 a 920 a 2984 a Cyanazine 1.7 0.20 cd 0.50 b 125 a 135 a 1185 a 2863 a Terbutryn 2.7 0.13 d 0.10 c 130 a 157 a 1011 a 2836 a Bifenox 1.4 0.10 d 0.03 c 135 a 166 a 1662 a 3138 a Propachlor 3.4 1.00 a 0.98 a 0 c 0 c 0 c 0 c Propachlor + atrazine 3.4 + 1.4 1.00 a 1.00 a 0 c 0 c 0 c 0 c Propachlor + bifenox 3.4 + 1.4 1.00 a 1.00 a 0 c 0 c 0 c 0 c Propachlor + linuron 3.4 + 1.1 1.00 a 1.00 a 0 c 0 c 0 c 0 c EPTC + R-25788 6.7 + 0.6 1.00 a 1.00 a 0 c 0 c 0 c 0 c Butylate + R-25788 6.7 + 0.3 0.63 b 0.83 a 7 bc 30 b 372 b 280 b None 0.00 d 0.00 c 113 ab 170 a 1440 a 2997 a a Means within columns followed by common letters do not differ significantly according to Duncan's Multiple Range Test. b Injury ratings taken 10 days after treatment. Rating scale: 0 = no injury, 1.0 = complete death. millet seedlings that survived butylate applications produced seed. Yields in 1979 exceeded those in 1978 because more rain fell during the 1979 growing season (15.9 cm compared with 9.0 cm in 1978). Our studies indicate that pearl millet is tolerant of herbicides such as atrazine, propazine, or bifenox that are used to control broadleaf weeds. Tolerance to herbicides like cyanazine, terbutryn, or propachlor used mainly to control grass weeds, was acceptable only for terbutryn. Further studies are necessary to determine if susceptibility to propachlor can be prevented by planting millet several weeks after the herbicide is applied or by herbicide antidotes. Safe use of propachlor would offer options to growers to control grass weeds in pearl millet alone or in pearl millet grown with a leguminous