Two field experiments, both with Cubanelle and Yollow Wonder peppers (Capsicum annuum L.), were conducted at the Juana Díaz Research and Development Center in 1981-82. Weeds were induced to grow through periodic irrigations for 16 days before peppers were transplanted. Either glyphosate or paraquat at 1.12 kg ai/ha were then applied to control emerging weeds in two separate experimental areas 5 days before setting out transplants. Oxyfluorfen at 1.12 kg ai/ha applied 2 days before transplanting peppers caused the highest phytotoxicity (significant at P=0.05) as recorded during 14, 28 and 42 days after treatment in both experiments. Neither alachlor (1.68 kg ai/ha), oxadiazon, trifluralin nor pendimethalin applied 2 days before transplanting at 1.12 kg ai/ha was phytotoxic to peppers. There were no significant differences in Cubanelle or Yollow Wonder pepper yields among herbicide treatments and handweeded check. The highest pepper yields (47,771 and 44,964 kg/ha) were obtained in plots treated initially with glyphosate and later by either paraquat directed postemergence spray or oxadiazon pre-transplant at 1.12 kg ai/ha each, respectively. In the other experiment, hand-weeded check and preplant application of paraquat at 1.12 followed by oxyfluorfen at 1.12 kg ai/ha were the highest yielders with 47,771 and 44, 964 kg/ha, respectively.

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.

EGGPLANT (SOLANUM MELONGENA L.) TRANSPLANTS AND EXUDATES FROM ROOTS OF SEVEN WEEDS

Herbicides Metribuzin [4-amino-6-tert-butyl-3-(methylthio )-as-triazin-5-(4H)one] at 0.8 and 1.6 kg/ha active ingredient, Prometryn [2,4-bis (isopropylamino)- 6-(methylthio)-s-triazine] at 3.3 and 6.6 kg, and Chloramben [3- amino-2,5-dichlorobenzoic acid] at 3.3 and 6.6 kg/ ha were evaluated for preemergence weed control on pigeon peas during 1976 at Lajas, Puerto Rico, in a Vertisol soil. The yield with Metribuzin at 0.8 kg/ha a.i. was similar (P=0.01) to that of the hand-weeded treatment. No statistical differences in yields were observed among the hand-weeded plots, Metribuzin 1.6 kg/ha a.i., and the two Prometryn rates. The least effective herbicide was Chloramben at 3.3 kg/ha, which at the rate of 6.6 kg was toxic to the crop. Good preemergence weed control was obtained from the other herbicide treatments with no toxicity to the legume. The higher herbicide rate of each compound controlled the weeds better than the lower rate. Metribuzin and Prometryn are in the process of evaluation for registration according to the Environmental Protection Agency regulations.

Greenhouse experiments were conducted during 1969 to evaluate the enhancement of Atrazine activity by the addition of mineral and vegetable oils. Two grassy weeds, crabgrass and yellow foxtail, were used as test species. The results showed that grassy weeds may be controlled with lower rates of Atrazine by using non-phytotoxic oils as adjuvants. Differences in Atrazine enhancement were observed among the oils tested and the rates of application. Early postemergence applications (weeds at the one- to two-leaf stage of growth) resulted in better control than applications delayed 1 week.