(D14)
ORANGE: Citrus sinensis (L.) Osbeck, ‘Fisher’ navel
EFFICACY OF INSECTICIDES AGAINST COMBINED POPULATIONS OF CALIFORNIA RED SCALE
AND CITRICOLA SCALE, 2004
Elizabeth E. Grafton-Cardwell
Department of Entomology
University of California
Riverside, CA 92521
Phone: (559) 646-6591
Fax: (559) 646-6593
E-mail: [email protected]
Christopher A. Reagan
California red scale (CRS): Aonidiella aurantii (Maskell)
Citricola scale: Coccus pseudomagnoliarum (Kuwana)
CRS and citricola scale are primary pests of San Joaquin Valley, California orchards. A field trial was conducted at
the Lindcove Research and Extension Center, Exeter, CA in a block of 22-yr-old ‘Fisher’ navel orange trees. The
efficacy of high label rates of an organophosphate insecticide (Lorsban) and an insect growth regulator (Applaud)
were compared to a combination of half rates of each insecticide and an untreated check. An RCB design was used
with the treatments assigned based on the densities of CRS found on twigs on 12 Jul 2004. An FMC 1093 air blast
sprayer was used to apply the insecticides diluted in 1200 gal of water per acre to three 6 row × 9 tree plots (0.40
acres) per treatment on 27 Jul. CRS densities were measured by collecting samples from 5 trees per plot. Samples
consisted of five randomly selected 1-yr-old 23-cm-long twigs per tree and five fruit (when available). Live first and
second instar scale as well as third instar and mature female scale were evaluated before treatment and at monthly
intervals following treatment. Harvest of all fruit was conducted on 2 Feb 2005, and the percentages of fruit with
CRS and with >10 CRS per fruit, the percentages of fruit graded as ‘Fancy’ and ‘Juice’, the average weight of the
fruit, and the average number of fruit per tree were determined. Citricola scales were sampled by counting live first
instar citricola nymphs on 10 leaves collected from the NE quadrant of each sample tree (50 leaves/plot) during JunNov 2004. On 30 Mar 2005, adult female citricola were counted on 10 twigs evenly distributed around each sample
tree. First instar citricola scale nymphs were counted again, on 30 Aug 2005 by collecting 75 leaves per treatment
plot collected from the NE quadrant of sample trees. Data were analyzed using ANOVA after log10 (x+1) of
numbers or arcsine square root (x) transformation of percentages and the means were separated according to LSD (P
≤ 0.05).
Examination of twigs and fruit from Aug through Oct (Table 1) demonstrated that all treatments significantly
reduced the CRS on twigs and fruit compared to the check. At harvest, all treatments significantly lowered the %
fruit in the ‘Juice’ grade and increased the percentage of fruit in the ‘Fancy’ grade. Lorsban applied alone
significantly reduced the % fruit infested with CRS and the heavily infested fruit. Half rates of Lorsban and Applaud
in combination reduced the % of heavily infested fruit. Applaud applied alone did not reduce the % CRS infestation
of the fruit. None of the treatments affected fruit weight or number of fruit per tree. Each of the treatments
significantly reduced the population of citricola scale during Aug-Nov 2004 (Table 2) compared to the untreated
check. Counts of citricola scale collected from twigs in Mar 2005 and from leaves in Aug 2005 showed that Lorsban
applied at 12 pts per acre suppressed the citricola population for a longer period of time than Applaud alone or in
combination with a lower rate of Lorsban. However, the mean number of scale found in Aug 2005 in all treatments
exceeded the treatment threshold (0.5 immature per leaf). Combining half rates of Lorsban and Applaud provided
control of CRS nearly equal to the 12 pts/acre rate of Lorsban alone, but were less effective for long term
suppression of citricola scale.
Table 1.
Harvest parameters 2 Feb 2005
Mean no. CRS per twig
Treatment/
formulation
Rate amt
product/acre
Untreated check
--Lorsban 4E
12.0 pt
Lorsban 4E
6.0 pt
+ Applaud 70WP 1.43 lb
Applaud 70WP
2.86 lb
+ NR 415 oil
0.5% (v/v)
Mean no. CRS per fruit
12 Jul
17 Aug
16 Sep
23 Aug
12 Oct
% Fruit
w CRS
% Fruit
>10 CRS
% Juice
grade
% Fancy
grade
Wt/
fruit (lb)
Fruit/
tree
2.63a
2.65a
1.27a
0.11b
1.76a
0.15b
1.33a
0.11b
2.30a
0.04b
9.9a
4.9b
3.2a
0.7b
15.7a
6.7b
46.8b
72.9a
0.63ab
0.64b
353a
372a
2.71a
0.07b
0.09b
0.00b
0.01b
6.8ab
1.4b
9.5b
67.1a
0.67ab
351a
2.64a
0.23b
0.09b
0.29b
0.12b
9.0a
2.2ab
8.4b
69.4a
0.70a
310a
Means within a column followed by the same letter are not significantly different (LSD, P > 0.05) after log10 (x+1) transformation. Untransformed means
are listed.
Table 2.
Mean no. live citricola per leaf or twig
Treatment/
formulation
Untreated check
Lorsban 4E
Lorsban 4E +
Applaud 70WP
Applaud 70WP +
NR 415 oil
Rate amt
product/acre
--12.0 pt
6.0 pt +
1.43 lb
2.86 lb +
0.5% (v/v)
12 Jul 04
a
10 Aug 04
a
a
15 Nov 04
30 Mar 05
b
30 Aug 05
17.0a
14.3a
8.0a
0.1c
2.8a
0.0b
23.6a
0.0c
52.0a
1.6c
9.4a
2.2bc
0.0b
0.2c
11.3b
14.7a
1.4b
0.0b
0.8b
10.5b
Means within a column followed by the same letter are not significantly different (LSD, P > 0.05).
a
Citricola nymphs per leaf.
b
Citricola females per twig.
a