Weed Competition in

 Transplanted Sweet Peppers

L. C. Liu J. Gonzilez-Ibaiiez Megh R. Goyal
 Agricultural Experiment Station, Mayaguez Campus
 University of Puerto Rico, Venezuela Contract Station
 Rio Piedras, Puerto Rico 00927


 Two field experiments were conducted in 1983-84 at the
Fortuna Research and Development Center, Puerto Rico, to
determine the economic threshold of pigweed (Amaranthus
dubious jungle rice (Echinochloa colonum) and horse
purslane (Trianthemaportulacastrum) and their critical period
of competition in drip irrigated peppers (Capsicum annuum
L. var. Cubanelle). Pepper seedlings were 42 days old at
transplanting. In the economic threshold study, weed popula-
tions were adjusted to 0, 2, 5, 10, 20, 40, 80or 120 plants/m2.


In the critical period study, weeds were allowed to grow for 0,
12, 24, 36, 48 or 60 days after transplanting and were kept free
until harvest. The economic threshold was found to be 2 to 5
plants/m2 for pigweed; 5 to 10 plants/m2 for jungle rice; and
20 plants/m2 for horse purslane. The critical period of weed
competition ranged from 24 to 36 days.
Keywords: Peppers; weeds; competition; economic threshold;
critical period; drip/trickle irrigation.


 Peppers are second only to tomatoes among vegetables of
 economic importance in Puerto Rico. Their commercial produc-
 tion in 1980-81 was 4,064 metric tons with a farm value of $2.1
 million (Anon., 1981). In the same year, 2,245 metric tons of
 peppers were imported into Puerto Rico from the nearby Carib-
 bean Basin and U.S. mainland to meet the local demand. One of
 the major factors limiting local pepper production has been the
 high cost of labor required to control weeds. In Puerto Rico,
 Goyal (1983) found that weeding accounted for 27.1% of the
 labor in a non-mulched pepper field. Before mulching becomes a
 standard practice in pepper fields, we need to know to what ex-
 tent pepper plants tolerate weed competition without it
 significantly affecting their yield. In the States, Mendt and
 Monaco (1979) studied prickly sida (Sida spinosa L.) and
 cocklebur (Xanthium pennsylvanicum Wallroth) competition in
 transplanted peppers. They found that cocklebur reduced pepper
 yield, but prickly sida did not. As these two weeds are not com-
 mon to pepper fields in Puerto Rico, we directed our research ef-
 forts to specific weed-pepper competition found under our condi-
 tions. Most of the published research on peppers in Puerto Rico has
 been confined to fertilization (Alers-Alers and Orego-Santiago,
 1977; Rivera and Irizarry, 1984). Weed control data are scarce.
 Two field experiments on transplanted peppers were thus con-
ducted at the Fortuna Research and Development Center, Juana
Diaz, Puerto Rico during 1983 and 1984 to determine the
economic threshold of pigweed, jungle rice and horse purslane in
peppers; and the critical period of weed competition in peppers.
Information of this nature can also be used as guidelines for an
integrated weed control program.

MATERIALS AND METHODS

Experiment 1983
 The experiment was conducted on a San Ant6n soil (30%
sand, 35% silt, 35% clay, 17% organic matter, pH 7.1) at the
Fortuna Research and Development Center, Juana Diaz near
Ponce, located in the semi-arid region of Puerto Rico. The field
was prepared by plowing and harrowing twice and partitioned in-
to 3.1 x 3.7 m plots. Each plot consisted of 20 pepper plants ar-
ranged in four rows. The plant spacing was 0.3 m down the row.
The layout of the experiment was a randomized complete block


198


design with four replications. Forty-two day old pepper seedlings
(var. Cubanelle) were transplanted on September 8, 1983 on
both sides of a biwall drip line in a zigzag pattern at a distance of
15 cm from the drip line. The drip irrigation system described by
Goyal (1983) was used in this study. The pepper plants received
the first application of fertilizer (10-10-8) at the rate of 224 kg/ha
on September 20, 1983 and a second application of the same
fertilizer at the rate of 392 kg/ha one month later. Insect and
disease control were achieved by spraying a recommended rate of
Malathion once on September 20, 1983; Lannate twice on Octo-
ber 19 and 28, 1983; and Manzate once on November 18, 1983.
 In the economic threshold study, individual weeds (pigweed,
jungle rice and horse purslane) were adjusted by hand to 5, 10,
20, 40, 80, and 120 weeds/m2, 21 days after transplanting. The
populational densities were maintained until the last harvest by
removal of excessive number of weeds. In the critical period,
mixed weeds were removed by hand or hoe at 0, 12, 24, 36, 48 to
60 days after transplanting. The plots were kept weed-free
thereafter. The gross income from different treatments was
calculated on the basis of a farm level price of $0.84/kg of pep-
pers, using the marketable pepper yield from five pickings. The
net return was obtained by deducting the cost of production as
described by Llorens et al. (1984). The experiment was ter-
minated on December 27, 1983.

Experiment 1984
 The first experiment was repeated on the same site during the
summer of 1984. The same design and planting distance were
used as in the previous experiment, with a minor modification.
The modification consisted of the elimination of the 120
weeds/m2 treatment and the addition of a 2 weeds/m2 treatment
in the economic threshold study. The 42-day old pepper seed-
lings (var. Cubanelle) were transplanted on March 1, 1984. The
same weed adjustment and removal methods were adopted as in
the winter experiment. The pepper plants received a first applica-
tion of fertilizer at the rate of 224 kg/ha on March 23, 1984 and a
second application of the same formula at 785 kg/ha on May 8,
1984. Pest control was achieved by applying recommended rates
of Lannate twice (March 14, and April 19, 1984) and Kocide
twice (April 13 and 18, 1984). Chlorotalonil, at a 0.5 kg/ha rate,
was applied on May 25, 1984. Gross income from the peppers was


 PROCEEDINGS of the CARIBBEAN FOOD CROPS SOCIETY-VOL. XX