RECOVERY OF SQUASH FRUIT COLOR AFTER
CONTROL OF SILVERLEAF WHITEFLY
Alton N. Sparks, Jr and David G. Riley
Dept. of Entomology
University of Georgia
P O Box 1209
Tifton, GA 31793
Introduction
The silverleaf whitefly (SLWF), Bemisia argentifolii, also known as the B strain of the
sweetpotato whitefly, B. tabaci, is a key pest of numerous vegetable crops grown in
Georgia. In squash, this pest causes a plant disorder known as silverleaf, from which it
obtains the common name. This disorder results in a distinct ‘silvering’ or whitish
coloring of the foliage. Severe silverleaf also results in a ‘bleaching’ or loss of color in
the fruit of affected plants. Recent trials with foliar insecticides indicated a possibility of
‘rescuing’ plants with silverleaf symptoms, but did not determine if fruit color would also
respond with SLWF control. A small plot trial was conducted at the University of
Georgia’s Lang Farm in Tifton, Georgia, to evaluate the potential of squash with
silverleaf related ‘bleaching’ of fruit to recover after control of silverleaf whitefly.
Materials and Methods
Plots were established in a planting of yellow squash exhibiting severe silverleaf. Plot
size was two rows (on a 6 ft bed) by 20 feet, with treatments arranged in a randomized
complete block design with four replications. The treatments consisted of a non-treated
check and insecticidal control of SLWF. Whitefly control was obtained with a tank mix
combination treatment of Actara 25WDG (0.0468 lb AI/ac) plus Danitol 2.4EC (0.2 lb
AI/ac) plus Orthene 97 (0.5 lb AI/ac). Plots were treated on August 11, 13 and 19.
Insecticide applications were made with a CO2 pressurized (50 PSI) backpack sprayer
calibrated to deliver 30 GPA. Insecticides were broadcast with three hollow-cone nozzles
per row (one over-the-top, one on drops on each side of the row).
All fruit of harvestable size were collected on each harvest date. Numerous fruit could
not be used for color determination because of green coloration associated with virus
infection. Fruit without virus were categorized according to a color scale developed using
PowerPoint color graphics. Fruit were rated on a 1 (white) to 11 (dark orange) scale, with
most fruit falling in the 2 to 6 range. A two on this scale was near white, a three was
cream colored, a five was a ‘normal’ yellow associated with yellow squash. Average fruit
color was determined for each plot on each sample date. Number of fruit per plot used for
determination of color and average fruit color were analyzed with PROC TTEST of PCSAS. Differences were determined significant at P<0.05.
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Results and Discussion
Because of high virus incidence, number of fruit available for color determination was
relatively small, but generally exceeded 4 per plot (16 per treatment on each date). Fruit
color did improve over time in the plots where whitefly were controlled (Table 2 and 3).
The first significant increase in average fruit color was detected at 7 days after the first
insecticide application (8/18, Table 1). However, distribution of fruit by color category
showed an obvious shift toward darker fruit as early as 4 days after the first application
(8/15, Table 2).
Table 1. Average harvested fruit color, silverleaf recovery trial, Tifton, Ga., 2003.
Average fruit color rating
Treatment
8/13
8/15
8/18
8/20
8/22
Check
3.35
3.19
3.19
3.06
3.70
Whitefly
controlled
2.94
3.66
4.61
4.76
4.89
P=
0.23
0.30
0.02
<0.01
0.03
Table 2. Fruit color distribution for first three harvests, silverleaf recovery trial,
Tifton, Ga., 2003.
Number of fruit in color category
Treatment
2 (near white)
3 (cream)
4
5 (yellow)
6+
8/13
Check
4
9
10
1
0
Treated
5
11
5
0
0
Check
4
11
3
0
0
Treated
1
3
9
3
0
Check
1
12
4
0
0
Treated
0
1
6
10
5
8/15
8/18
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