The Tomato Magazine
August 2007
By Salvador Vitanza, Sally A. Miller, Mark Bennett, Richard Derksen and Celeste Welty
The health and productivity of peppers are affected by many factors,
including climate, fertility, cultivars, plant population density, pest
management practices, pesticide application technology and pests. The
impact of stand density on yield has been studied for bell and non-bell
peppers, but very little information exists regarding implications on
pesticide effi cacy. Although greater pepper fruit yields usually result
from higher plant stand densities, increasing crop canopies might diminish
the amounts of spray deposits reaching the surface of fruits and leaves
at middle or low plant elevations. The use of different pepper cultivars,
spray application technologies and plant stand densities may produce diverse
outcomes in fruit yield and insect pest or disease damage. The objective
of these studies was to determine the effect of plant population density
and pesticide application techniques on fruit yield and control of key
insect pests and diseases of peppers in Ohio. Plant population density
was investigated at different within-row spacing for single and twin rows.
Methods
Three trials were conducted on commercial Ohio farms in 2004 to evaluate
the effect of plant stand density on yield and pest management efficacy
in bell and jalapeno peppers. All on-farm trials were
conducted using a randomized complete block design with six replications;
crop and pest management inputs were provided according to the standard
practices at each farm. The Greene County trial was conducted in a 70-acre
fi eld of plastic-mulched, drip-irrigated bell ‘Colossal’ peppers.
Plant stand densities tested were 13,583, 12,676 and 9,004 plants per
acre, equivalent to 14, 15 and 24-inch, withinrow spacing, respectively.
The Wood County trial was conducted in a 16-acre, non-irrigated field
of jalapeño pepper (‘Ixtapa X3R’), comparing a stand
density of 8,896 plants per acre to a stand density of 11,268 plants per
acre. The Henry County experiment was conducted in a 60.8-acre, non-irrigated
bell pepper (‘North Star’) field to compare the grower’s
traditional density of 11,860 plants peer acre to an experimental density
of 9,688 plants per acre. The data from all the trials conducted in commercial
farms were analyzed with the general linear models procedures in SAS.
Two additional trials were established in 2005 on the OSUOARDC North Central
Agricultural Research Station (NCARS) in Fremont, Ohio, to test the interaction
between plant stand density and pesticide application technology in bell
and banana peppers. Treatments were factorial combinations of two-row
arrangements, three-plant population densities and three levels of pesticide
application
technology. Applications were made using half the recommended rates of
insecticides and fungicides by a conventional boom sprayer. Row arrangements
were twin and single rows. Plant population
densities were low, medium and high, corresponding to 22, 15 and 11-inch
within-row spacing in single rows and to 30, 20 and 15-inch within-row
spacing in twin rows, respectively. In all trials, fruit
were harvested from the center of each plot in two or three harvests.
All fruit were inspected for external damage (sunscald, blossom end rot,
bacterial spot and bacterial soft rot) and then cut open to inspect for
internal browning, likely due to Alternaria sp., and to determine the
presence of, or damage by, larvae of European corn borer (ECB), fall armyworm,
corn earworm (CEW) or beet armyworm (BAW). Total yield was the total weight
of all harvested fruit per plot. Marketable yield was the total weight
of all the harvested fruit per plot with a good external appearance. The
estimated clean yield was obtained by multiplying the total yield by the
percentage of clean fruit per plot. Both trials were terminated early
due to heavy damage by Phytophthora capsici. Therefore, in the fi nal
harvest, bell pepper green fruit with a diameter larger than 5 cm were
collected in addition to red fruit. Green and red fruit from this harvest
were evaluated separately.
Results
On-farm trials. Clean yields were not signifi cantly affected by plant
population densities in bell peppers at the Henry County site. However,
at the Greene County site, bell peppers planted at the
second highest stand density had the greatest marketable and clean yields,
while sustaining the least amount of sunscald damage. At the Greene County
site, sunscald damage was most prevalent at the lowest plant stand density.
At the Wood County site, total, marketable and clean yields of jalapeño
peppers were greater at 22,368 plants per acre than those obtained at
8,896 plants per acre. Average weight per fruit was not signifi cantly
affected by plant stand density in bell or jalapeño peppers.
On-stand trials. Yield was higher in single-row than in twin-row bell
pepper plots. However, peppers in twin rows were less damaged by caterpillars
than those in single rows. Bell peppers planted at low stand density produced
lower clean yield than peppers at the middle and high plant population
densities. Weight per red fruit was lower at the high plant stand density
than at middle row low plant densities. Numbers of sunscald-damaged fruit
were generally higher in single than in twin rows, except for plants at
the highest stand density. Untreated plots sustained more sunscald damage
than treated plots, except for the untreated plots at the highest stand
density. Sunlight at ground level under the crop canopy was more intense
in single than in twin rows and less intense at the highest than at the
middle and lowest plant stand densities.
The incidence of Phytophthora blight was higher in twin than in single
row plots. Although the total number of infected plants was less at the
lowest stand density than at the medium and high stand
density, no signifi cant differences in the percentage of infected plants
were found among plant stand density levels. The number of total plants
per plot (apparently healthy plus showing blight symptoms)
were generally greater in twin than in single rows at all plant stand
density levels.
For banana peppers, total, marketable and clean yields were greater at
high and medium than at low plant stand density. Weight per fruit remained
unaffected by plant stand density. Caterpillar damage or presence was
more abundant at medium than at high plant stand densities.
Conclusions
Bell pepper fruit yield increased proportionally with plant stand density
in the trial conducted at the OSU-OARDC NCARS. Weight per bell pepper
red fruit was lower at the highest than at the middle
or lowest stand densities at the research station, but remained unaffected
at tested stand densities on commercial farms. Most other workers have
reported that bell pepper fruit size or quality is not
affected by stand density. On commercial bell pepper farms, the relationship
between fruit yield and plant stand density was not clearly determined,
but on the commercial jalapeño farm, greater yield was obtained
at the higher stand density. A broader range of stand densities evaluated
on commercial farms should have resulted in more pronounced yield differences.
In banana peppers, stand density did not infl uence weight per fruit.
Sunscald damage to bell pepper fruit was greater at low stand densities,
especially in single-row plantings. This is to be expected
because a denser crop canopy should provide better protection against
direct sun exposure to fruits. It is likely that in the NCARS trial, greater
bell pepper yields obtained in single rows than in twin rows, at equivalent
plant stand densities, corresponding to Phytophthora blight damage because
Phytophthora was more prevalent in twin rows than in single rows. Additionally,
early trial termination due to Phytophthora blight might have infl uenced
results by underestimating the cumulative insect and disease damage that
might have been produced in a longer fi eld season and minimized yield
differences among treatments. Greater bell pepper fruit damage by caterpillars
in single versus twin rows might have been related to greater amounts
of fruit in single rows rather than pest levels or pesticide spray effi
cacy.
Editor’s note: Salvador Vitanza (Svitanza@ag.tamu.edu)
and Celeste Welty (welty.1@osu.edu) are with the Department of Entomology,
The Ohio State University, Columbus, Ohio; Mark Bennett (bennett.18@osu.edu),
the Department of Horticulture and Crop Science, OSU, also at Columbus;
Sally Miller, the Department of Plant Pathology, OSU, Wooster, Ohio; and
Richard Derksen (Rich. Derksen@ars.usda.gov), USDA-ARS, also at Wooster.
© 2007 Columbia Publishing
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