Two herbicide experiments were carried out in 1980 to evaluate Alachor and Metribuzin alone or combined for weed control in sweet potato cultivar Miguela at the Isabela and Fortuna Substations, Metribuzin at 1.12 kg ai/ha rate controlled effectively both broadleaf weeds and grasses. A minimum rate of 6.73 kg ai/ha of Alachor was needed for acceptable weed control. Metribuzin at the 1.12 kg al/ha rate in combination with Alachor at the 3.36 kg ai/ha rate provided the best weed control. There was no visible herbicide injury to sweet potato plants at the Isabela Substation. Moderate crop injury as a consequence of Metribuzin application at 2.24 kg ai/ha was apparent at the Fortuna Substation. The highest tuber yield was obtained with Metribuzin at 1.12 kg ai/ha in combination with Alachor at 3.36 kg ai/ha at both Substations. Metribuzin at 1.12 kg ai/ha rate alone or in combination with any other herbicide also produced good tuber yield. Sweet potatoes with standard herbicide treatments, Diphenamid and Chloramben, yielded poorly because of weed competition.
The uptake, distribution, and metabolism of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] by sugarcane(Saccharum officinarumL.) cultivars ‘PR980’ and ‘PR1048’ were determined 3 and 10 days after root treatment with 18.4 μM14C-ring-labeled diuron. Uptake and distribution did not account for the differential tolerance of the two cultivars to diuron. Concentration of unmetabolized diuron was higher in the shoot and root of susceptible cultivar PR1048 than in tolerant cultivar PR980 at 3 and 10 days after treatment. The predominant metabolic pathway for diuron metabolism in both susceptible and tolerant sugarcane cultivars appeared to be the formation of mono-methyl diuron and its conjugation. The metabolic process was more rapid in PR980 than PR1048, apparently accounting for the tolerance of PR980.
Four greenhouse experiments were conducted in 1981-82 to determine the effect of different irrigation regimes on the phytotoxicity of prometryn [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] in four soils. The fresh weight of pigeon pea plants treated with prometryn at rates of 2.24 and 3.36 kg/ha was greatly reduced in San Anton soil (Mollisol) as the irrigation regime increased to a maximum. This finding confirms our assumption that excessive irrigation has contributed to the aggravated prometryn injury to pigeon pea plants. However, no significant fresh weight reduction was noted in Corozal (Ultisol), Coto (Oxisol) and Fraternidad (Vertisol) clays under increased irrigation regimes. Precaution should be taken not to overirrigate the soils having a texture similar to that of San Antón. To avoid crop injury precaution should also be taken not to use prometryn for weed control in pigeon peas during the prolonged rainy months of September to November.
Field experiments were carried out during 1988-89 at the AES-UPR Lajas substation and on a private farm in its vicinity to evaluate the efficacy of imazapyr and picloram in the control of Albizia and mesquite in two selected pastures. Both herbicides were applied by the following methods: basal bark, cut stump, frill treatment and infection. Basal bark was the most effective method for albizia control when using imazapyr at 0.237L/3.8L application; infection, the least effective. Cut stump was the most effective method when using imazapyr at 0.355L/3.8L; frill treatment, the least effective. Basal application was the most effective method when using an undiluted formulation of picloram; cut stump, the least effective. For mesquite control, cut stump was the most effective method when using imazapyr at both rates of application. Cut stump was the most effective method of picloram application; basal bark, the least effective. The mortality data of both affected species were analyzed on the basis of individual herbicide, irrespective of method of application. A significantly higher percentage of mortality of both species was registered with picloram than with imazapyr.
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