Reflective
and wavelength-selective plastic mulches (colored mulches), such as
silver reflective and IRT-100 (infrared-transmitting; green) or SRM-red
(selective reflective mulch-red) mulches, respectively, are mulch
materials that are increasingly being used commercially. Colored mulches
have advantages similar to black or clear plastic mulches with additional
benefits related to altered quantity and quality of reflected light
into the plant canopy. The effects of colored plastic mulches on plant
growth and yield have been studied in a number of vegetable crops
such as bell pepper, cowpea, muskmelon, tomato and potato.
Previous field research with black and/or white plastic mulches indicated
higher watermelon yield compared to bare ground culture. Very limited
research has been conducted to evaluate watermelon crop response to
colored plastic mulches in the field. The effect of light quality
on the growth of young watermelon plants in controlled environments
was evaluated previously, light environment changes (high far red
to red light ratio exposure; FR/R) by partitioning more photosynthate
to vegetative parts, resulting in plants with elongated leaf petioles
and internodes. Researchers demonstrated that vegetative plant growth
can be directly affected by the quantity of radiation reflected from
certain mulches. Even though the effect of colored mulches on watermelon
is temporal, until the vines of the crop cover the mulch, there is
the hypothesis that early plant response to the light environment
can induce modifications in the plant growth that continue after the
vines cover the plastic.
The objective of this experiment was to determine the effect of different
reflective and wavelength selective plastic mulches on insect populations,
plant growth, and yield of fieldgrown watermelon.
Colored plastic mulches listed in Table 1 were
evaluated for their effect on the production of a triploid (‘Honeyheart’)
and a diploid (‘Sangria’) watermelon cultivar during the
spring growing season. Colored mulches affected cucumber beetle populations;
the SRM-Red (Selective Reflective Mulch) and yellow plastic mulch
plots had among the highest cucumber beetle populations recorded in
both cultivars while the silver-reflective and the silver-on-black
plastic mulches had among the lowest. In general, most mulched plots
had longer vines than the bare-ground treatment, with few differences
in vine length among treatments by 4 weeks. There are no differences
among mulch treatments in first and total ‘Honeyheart’
harvest while the IRT-100 (infrared transmitting; green), PST (photosynthetic
reduced transmitting), and silver-on-black plastic mulches had the
highest first ‘Sangria’ harvest and among the highest
total ‘Sangria’ harvest. Plants in plastic mulch treatments
had higher yields as a result of higher fruit number per area. Fruit
weight, length, and diameter and total soluble solids for both cultivars
were not affected by colored plastic mulch treatments. Additional
research is suggested.
| Table 1. Treatments evaluated for air
and soil temperature, plant growth, insect populations and watermelon
yield, 1997 an 1998. |
| Mulchz |
Color/type |
Company |
| Al-Or brown (aluminum organic) |
Brown/wavelength selective |
Polywest, Sandiego, CA |
| Black |
Black |
Climargo, Quebec, Canada |
| Bare ground |
- |
- |
| Blue-painted black |
Blue |
- |
| IRT-100 infrared transmitting |
Green/wavelength selective |
Ken-bar, Reading, Mass |
| PST (photosynthetic red. transmitting |
Green/wavelength selective |
Climargo, Quebec, Canada |
| Silver-reflective |
Silver-reflective |
Clark Ag Plastics, Greenwood, VA |
| Silver-on-black |
Silver-reflective |
Climargo, Quebec, Canada |
| SRM-Red (selective reflective mulch) |
Red/wavelength selective |
Ken-bar, Reading, Mass |
| White-on-black |
White/reflective |
Climargo, Quebec, Canada |
| Yellowy |
Yellow |
-/Polywest, San Diego, CA |
z
All plastic mulch treatments thickness was 1 mil, except for Al-Or
brown, 0.8 mil, silver reflective, 0.9 mil, and yellow-polywest, 1.25
mil.
y Yellow-painted black mulch in 1997 and yellow on brown mulch (Polywest)
in 1998
|
