TABLE 1. The net return for peppers derived from different populational densities of three weeds.


Net return per hectare (dollar)


Population densities


Horse purslane

1983 1984


 Jungle rice

1983 1984


 Pigweed

1983 1984


 0 plants/m2 (control) 6,033 al 5,452 a 2,011 a 6,466 a 1,146 a 7,830 a

 2 -- 4,087 ab -- 4,948 ab -- -3,245 b

 5 2,353 a 3,647 ab -3,673 b 4,460 ab .-5,826 b -2,741 b

 10 2,366 a 3,445 ab -5,086 bc 1,119 b -6,111 b -6,075 c

 20 -381 b 1,660 bc -5,416 bc -2,048 c -6,330 bc -6,342 cd

 40 -904 b 1,768 bc -6,635 ed -4,061 c -8,204 c -7,692 d

 80 -859 b -140 c -7,421 d -5,045 c -8,332 c -7,586 d
 120 -1,201 b -- -7,911 d -- -8,318 c --


1Means followed by the same letter or letters do not differ significantly at the 0.05 level.


calculated on the basis of a farm level price of $0.75 /kg, using the
marketable yield from five pickings. The net return was
calculated as in the winter experiment. The experiment was ter-
minated on June 25, 1984.


RESULTS AND DISCUSSION

Economic Threshold Study
 Table 1 shows the net return for the peppers derived from dif-
ferent populational densities of three weeds. Statistical com-
parisons were made among the net returns derived from different
weed densities and the control (0 plant/m2). The economic
threshold of horse purslane was 20 plants/m2 for both 1983 and
1984; that of jungle rice was 5 plants/m2 in 1983 and 10
plants/m2 in 1984; that of pigweed was 5 plants/m2 in 1983 and
2 plants/m2 in 1984. The cost of producing Cubanelle peppers in
Puerto Rico amounted to an average of $8, 959 per hectare (con-
trol plots). The results of the present study indicate that a horse



TABLE 2. Effect of time of weed removal on yield of peppers grown in a San
Ant6n soil.


 Yield of pepper5(kg/ha)
 Duration of weed competition 1983 1984

 0 day 15,380 a 17,801 a

 12 days 15,271 a 19,347 a

 24 13,467 ab 14,342 b

 36 10,524 b 11,250 c

 48 4,706 c 6,042 d

 60 895 d 4,689 d

 All the time infested 81 d 743 e

 1eans followed by the same letter or letters do not differ
 significantly at 0.05 level.



 VOL. XX-PROCEEDINGS of the CARIBBEAN FOOD CROPS SOCIETY


purslane density of 20 plants/m2 would leave a farmer with no
net earnings from a pepper crop. Similarly, a jungle rice popula-
tion of 5 plants/m2 would incur economic losses to growers. A
pigweed population as low as 2 plants/m2 would be sufficient to
cause financial predicament to local farmers.

Critical Period of Weed Competition Study
 The predominant weed species in plots, listed in their decreas-
 ing order of abundance, were: pigweed (Amaranthus dubius),
 jungle rice (Echinochloa colonum), horse purslane (Trianthema
 portulacastrum), spiierflower (Cleome gynandra), crabgrass
 (Digitaria sanguinalis), goose grass (Eleusine indica), purslane
 (Portulaca oleracea), and sprangletop (Leptochloa filiformis).
 Table 2 shows that pepper yield was significantly reduced after 36
 days of weed competition in 1983. The weed competition was
 even more severe in 1984 than in 1983 and yield was significantly
 reduced after only 24 days of weed competition. These results
 suggest that in pepper production weeds should be removed
 within 24 days, but no later than 36 days after transplanting.





 Acknowledgements
 This research was funded through P.L. 89-808 Section 406 CSRS-USDA. The
 authors are thankful to Mr. Luis E. Rivera and Mr. Luis Torres-Correa for their
 assistance at different stages of this study.

 References
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