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The performance of 19 herbicides in 50 treatments was evaluated in terms of their selectivity to soybean, pigeon pea, cowpea and field beans, and of their effect upon the weed populations of three localities in Puerto Rico represented by three of the substations of the Agricultural Experiment Station. Although the majority of the products tested were selective to the four crops at the three sites, some were more toxic to certain crops or in given localities. Fluchloralin was more toxic to soybeans and field beans at Lajas and to pigeon pea in lsabela and Fortuna. Cowpeas and field beans were very sensitive to metribuzin, while soybeans and pigeon peas were more tolerant. Toxicity of metribuzin to soybeans and pigeon peas was more pronounced at higher rates and in the lightest soil. Oryzalin was more toxic to pigeon pea in lsabela and to cowpea in Fortuna. Profluralin was more toxic in Lajas and prometryn in Fortuna than in the other sites. U 27267 was more toxic when incorporated than when applied to the surface. There were differences in the degree of weed control among products, rates and localities. The differences among localities were related to variations in soil characteristics and weed populations. The results strongly support the importance of simultaneously considering the crop, the weed population and soil characteristics before recommending herbicides.
Kaki and 28-Bushy pigeon peas were grown in the southern plains of Puerto Rico, in four spatial arrangements with six intervals of weed competition during two growing seasons to determine the influence of weed competition on crop growth, development and yield. In both growing seasons, Cleome gynandra, Amaranthus dubius, Echinochloa colona, Leptochloa filiformis, and Digitaria sanguinalis were the dominant weeds. C. gynandra and E. colona dominated the early weed flora until approximately 40 days after pigeon pea emergence. Later, weed flora was dominated by L. filiformis, D. sanguinalis, and A. dubius. The presence of weeds during early growth stages reduced initial crop growth and delayed differentiation including flowering of the two pigeon pea cultivars. Elimination of weeds at or before 21 to 28 days after pigeon pea emergence and thereafter, generally resulted in the recovery of pigeon pea plants and prevented measurable losses in final yield. The critical period for removing weeds in pigeon peas appeared to vary between the pigeon pea cultivars and between the two growing seasons. In the May 6 planting, pigeon pea yields were reduced after 28 and 21 days of early competition for Kaki and 28-Bushy, respectively. In the July 1 planting, however, losses occurred at 21 and 14 days of weed competition for the two respective cultivars. No differences were found in weed numbers or yield between the two cultivars or among spatial arrangements in either planting season. However, weed number and yield were greater during the first planting season compared with those of the second. Planting pigeon peas under short photoperiods accelerated vegetative growth, shortened the total cropping cycle, and resulted in reduced yield and total growth for both cultivars. Losses from early weed competition occurred earlier under the short-day planting than those under the long-day planting.
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