Proper adjuvant selection to enhance the activity of triclopyr combined with metsulfuron on the control of Hedyotis verticillata

A study was conducted to evaluate the combined activity of a tank mixture of triclopyr plus metsulfuron with non-ionic surfactant (NIS), crop oil concentrate (COC), and organosilicon (OS) adjuvants on the control of Hedyotis verticillata under glasshouse and field conditions. The results of both the glasshouse and field experiments showed that 160 g ai ha⁻¹ triclopyr plus 0.2 g ai ha⁻¹ metsulfuron and 320 g ai ha⁻¹ triclopyr plus 0.4 g ai ha⁻¹ metsulfuron, with the addition of 0.25% NIS, 0.05% COC, or 0.05% OS, were effective in controlling H. verticillata . A comparison of the cost revealed that the most cost-effective combination for controlling H. verticillata is 160 g ai ha⁻¹ triclopyr plus 0.2 g ai ha⁻¹ metsulfuron combined with 0.25% NIS.     

Initial report of glufosinate and paraquat multiple resistance that evolved in a biotype of goosegrass (Eleusine indica) in Malaysia

Field and glasshouse studies have confirmed the presence of a glufosinate‐ and paraquat‐resistant goosegrass biotype that has infested a bitter gourd field in Air Kuning, Perak, Malaysia. Glufosinate and paraquat had been applied at least six times per year to the affected fields (originally a rubber plantation) for more than four consecutive years. Paraquat had been used since 1970 for weed control in the rubber plantation. An on‐site field trial revealed that the control of the goosegrass plants, measuring 20–35 cm in height, ranged from 20 to 35% 3 weeks after being treated with each herbicide at twice the recommended rate. Dose–response tests were conducted in the glasshouse, using seedlings at the three‐to‐four‐leaf stage that had been obtained from the plants that had received repeated exposure to these herbicides and a biotype with no history of any herbicide resistance. The comparison of the GR₅₀ (the herbicide rate that is required to reduce the shoot fresh weight by 50%) of the seedlings indicated that the resistant biotype of goosegrass is 3.4‐fold and 3.6‐fold more resistant than the susceptible biotype following treatment with glufosinate and paraquat, respectively. This study has demonstrated the world's first field‐evolved instance of multiple resistance in goosegrass to two non‐selective herbicides, glufosinate and paraquat.     

Resistance mechanism of Leptochloa chinensis Nees to propanil

The resistance mechanism of Leptochloa chinensis Nees to propanil was investigated, based on propanil metabolism, aryl acylamidase activity, and chlorophyll fluorescence at the 8 week growth stage of L. chinensis. The concentration of propanil in the leaf and culm extracts of the resistant (R) and susceptible (S) biotypes, as measured by gas chromatography (GC), was found to increase after propanil treatment. The concentration of propanil in the leaf and culm extracts of the S biotype at 72 h was 1.55 and 0.49 µg mL^?1, respectively. However, a lower concentration of propanil was observed in the R biotype, as compared to that in the S biotype. The residue of 3,4‐dichloroaniline, as measured by GC, was detected only in the leaf extracts of the R biotype. In contrast, no residue of 3,4‐dichloroaniline was observed in the S biotype. The level of aryl acylamidase in the leaf tissue extracts of the R biotype was ～140% higher than that in the S biotype. The fluorescence studies showed that propanil inhibited the quantum efficiency of the photosystem II in both the R and S biotypes after 2 h of incubation time. However, when the leaf disks were transferred and incubated in deionized water for 48 h, the quantum efficiency increased in the R biotype but decreased in the S biotype. These results suggest that propanil metabolism, enhanced by aryl acylamidase activity, is the most likely factor contributing towards the mechanism of propanil resistance in L. chinensis plants at the 8 week growth stage.     

Germination and seedling emergence of glyphosate‐resistant and susceptible biotypes of goosegrass (Eleusine indica[L.] Gaertn.)

Effects of environmental factors on the germination and seedling emergence of glyphosate‐resistant (R) and ‐susceptible (S) biotypes of Eleusine indica (L.) Gaertn. were examined under laboratory and greenhouse conditions. The R biotype exhibited a higher germination percentage compared with the S biotype at constant temperatures of 20 and 35°C under dark conditions, and alternating temperatures of 30/25°C, and 35/25°C during a 12 h photo period. For both biotypes, germination was optimal at alternating temperatures of 30/20°C and 35/20°C. However, there was no significant difference (P > 0.05) in the germination between the R and S biotypes at these temperature regimes. The germination of both biotypes was inhibited by osmotic stress imposed by a water potential of ?0.80 MPa. When the moisture stress was released and the seeds were subsequently transferred to distilled water, the germination was enhanced to approximately 90% and 16% for the R and S biotype seeds, respectively. Higher emergence rates were obtained in shallow seed depths (0 or 2 cm) compared to deep depths. Emergence percentage of the R biotype was higher than that of the S biotype at 0 cm and 2 cm depths. The maximum emergence percentage of the R biotype was higher than that of S biotype when seeds were sown on the surface of either loamy or clay loam soil taken from three different sites.     

Reduced rates of tank mixtures for red sprangletop (Leptochloa chinensis [L.] Nees) and greater club-rush (Scirpus grossus [L.] f.) control in rice

A study on the efficacy of tank-mix combinations on the growth of Leptochloa chinensis (L.) Nees and Scirpus grossus (L.) f. at the 3–4-leaf stage was conducted under glasshouse conditions. Sethoxydim plus cyhalofop-butyl at 8 + 25, 16 + 25, 32 + 25, 32 + 12.5, and 32 + 6.25 g ai ha⁻¹ provided good control of L. chinensis , ranging from 89–95%. However, a comparison of the costs of herbicide mixtures revealed that sethoxydim at 32 g ai ha⁻¹ plus cyhalofop-butyl at 6.25 g ai ha⁻¹ were the most cost-effective among the combinations. For Scirpus grossus , bensulfuron plus 2,4-D dimethylamine at 2.5 + 18, 5.0 + 18, 1.25 + 36, 2.5 + 36, and 5.0 + 36 g ai ha⁻¹ gave good control that ranged from 88–93%. Tank-mixing bensulfuron with 2,4-D at 1.25 + 36 g ai ha⁻¹ was, however, the most cost-effective mixture compared to the other mixtures. None of the tank mixtures tested in this study caused injury to the rice seedlings. However, further field studies need to be undertaken to verify these findings.     

Changes in seed bank size and dormancy characteristics of the glyphosate-resistant biotype of goosegrass (Eleusine indica[L.] Gaertn.)

A study on changes in the seed bank size of a glyphosate ( N -(phosphonomethyl)glycine)-resistant (R) Eleusine indica biotype was carried out on a naturally occurring infestation of a young oil palm plantation. The total number of shed seeds collected was 53% of the predicted potential total number of seeds produced by the plants. Ametryn ( N -ethyl- N' -(methylethyl)-6-(methylthio)-1,3,5-triazine-2, 4-diamine) was found to be able to control the R seed population in the soil. The periodicity of seedling emergence was influenced by rainfall subsequent to the 1 month period of seed shedding. Seed burial at 2, 10 and 20 cm depths showed that 39, 33 and 79%, respectively, of viable seed persisted in the soil after 2 years. Seeds in the state of enforced dormancy played an important role in maintaining the seed population throughout the 2 year period of burial in the soil.