Influence of Planting Date and Insecticidal Control on
Seasonal Abundance of Lettuce Aphids on Head Lettuce
John C. Palumbo
Yuma Agricultural Center
Abstract
Small plot studies were conducted from 1999-2001 to examine the population
abundance and control of the lettuce aphid on winter and spring head lettuce
crops. In each year, Seven, 0.25 acre planting of head lettuce were established
beginning in Sep-Oct with final harvest occurring in April. Replicated plots
within several planting were treated with an Admire treatment at planting, a
side dress application of Platinum post-planting or allowed to remain untreated.
Lettuce aphids were first detected in our experimental area in December in PD
3 in 2001, but in 2002 first occurred in lettuce almost 2 months later (Feb 21).
Similarly, lettuce aphid abundance was much greater in 2001 than in 2002,
probably a result of temperature difference. Temperature had an important
influence upon lettuce aphid development based on our field observations.
Population appeared to increase in early March when the average daily
temperature was about 65 E F. We observed a sharp decline in population
abundance in April where daytime highs exceeded 90E F. Insecticide treatments
also influenced seasonal abundance. Under heavy aphid pressure in 2001,
lettuce treated with Admire in the early planting dates appeared to prevent
lettuce aphids from significantly infesting lettuce heads at harvest. However,
lettuce aphids in the last 3 planting dates were able to colonize plants and infest
a larger proportion of heads at levels not considered commercially acceptable.
Under lighter pressure in 2002, lettuce aphids did not significantly colonize
Admire treated lettuce. Green peach aphid, potato aphid and foxglove aphids
were also present in both years, but seldom reached economic levels, and where
completely controlled in plots treated with soil, systemic insecticides.
Introduction
A new aphid species, the currant-lettuce aphid, Nasonovia ribisnigri (Mosley), has been creating problems for
lettuce growers throughout the western United States. Commonly referred to as the lettuce aphid (LA), this pest was
first found in Salinas in 1998 causing economic losses to summer head and leaf lettuce crops. Infestations of this
species were also reported on lettuce in the Imperial Valley, central Arizona, and Baja California, Mexico in early
1999. The first reported incidence of the lettuce aphid in Yuma was on an untreated head lettuce field in midMarch 1999 in the Gila Valley, and from head lettuce plots at the Yuma Ag Center (Palumbo 1999). Specimens
were collected and sent to Tucson, where they we positively identified as N. ribisnigi. The lettuce aphid was found
again in the Yuma Valley in February of 2000 (Palumbo 2000a).
This aphid species is quite different from green peach aphid and potato aphid (GPA) commonly found on leafy
vegetables in the desert. First, the lettuce aphids deposit their young near the terminal growing points of the plant.
The aphids collected from head lettuce in Yuma were found predominantly on the cap leaf and within the head
(Palumbo 1999). Furthermore, the aphid looks distinctively different than any other aphid found locally on lettuce.
The apterous aphids we observed were orange- pink in color with dark bands across their abdomen and on their legs.
Their legs are quite spindly, giving them almost a spider-like appearance. Alate adults were similarly distinct from
either GPA or PA.
This is a part of the 2002 Vegetable Report, University of Arizona College of Agriculture and Life Sciences, index
at: http://ag.arizona.edu/pubs/crops/az1292/
There is much uncertainty surrounding this new species, and its ability to thrive within our desert growing
conditions. Preliminary efficacy studies suggest that foliar sprays, when timed properly and with proper coverage,
can control the lettuce aphid for up to 14 days (Palumbo et al. 1999). However, we don’t have enough experience
with this species in the desert to really know how effective a foliar spray program will be throughout the season,
especially if lettuce aphids migrate into fields late in the season near harvest. Perhaps a more important question is:
Will soil applications of systemic insecticides (Admire, Platinum) provide seasonal control of the lettuce aphid?
Theoretically, Admire should provide good control of the lettuce aphid, as it does other aphid species. It has been
the standard product used for aphid control in desert lettuce for the past 9 years. A single at-planting application
usually provides season-long control of green peach and potato aphids (Palumbo et al. 1999). This is achieved by
preventing aphid colonization early-mid season when these aphids feed on leaves lower on the plant where Admire
has systemically moved to. However, we are not sure of the duration of residual control in lettuce heads treated with
Admire or Platinum on spring crops. Preliminary studies suggest that this may vary depending on planting date and
temperature (Palumbo 2000b). Therefore, this project was initiated to determine the seasonal abundance of lettuce
aphid on head lettuce throughout the lettuce growing season, and to assess the residual efficacy of Admire and
Platinum soil applications against lettuce aphid populations.
Materials and Methods
Studies to examine aphid abundance and control were conducted on head lettuce at the Yuma Agricultural Center,
Yuma, Arizona. Beginning in mid-October, 2000 and mid-September 2001, ¼ acre plots of head lettuce were
planted on 2-3 week intervals. Tables 1 and 2 provide the planting date and lettuce variety for each planting. On
each planting date (PD) lettuce was direct seeded into double row beds on 42 inch centers. Each planting was
subdivided into plots consisted of 4 beds, 75 feet long. Plots were arranged in a randomized complete block
design with four replications with a total of 10 plots established in each planting.
Within each planting date, five plots were randomly selected and imidacloprid (Admire 2F) at 20 oz / acre was
applied. The Admire was applied to plots during the bed-shaping operation by injecting the chemical 1.5" below
the seed. Plots were furrow irrigated to a stand. The remaining five plots were left untreated at planting. In planting
dates 5 and 6 in the 2000-2001 study, thiamethoxam (Platinum 2SC) was applied post-planting at a rate of 11
oz/acre as a side dress application to ½ of each untreated plots (2 beds * 80 ft) on 28 Feb. Side dress applications
were made by placing the product near the bed shoulder at approximately 3-4” below the soil. Plots were irrigated
2 days following side dress on March 1. No other insecticide applications were made during the study.
Aphid populations were assessed by estimating the number of aphids/plant by taking whole plant destructive
samples. The dates and plant stages for each sample event is shown in Tables 1and 2. On each sampling date, 10
plants were randomly selected from each plot and placed individually into large 4-gal tubs. Each plant was sampled
by visually examining all plant foliage and counting the number of alate and apterous aphids present. At harvest,
infestation levels of apterous aphids were estimated by randomly selecting 10 plants within each replicate, visually
counting the number of aphids on frame/wrapper leaves and heads, and separately recording aphid numbers for each
location. Data was analyzed using ANOVA and mean differences were estimated using a protected LSD(0.05) or a
paired t test(p< 0.05).
Results
2000-2001 Study
The early planted lettuce in PD 1 completed harvested on Jan 25 and was disked under
before lettuce aphids (LA) were found on the research center. Green peach aphids (GPA) reached >25 /plant near
harvest. LA were first detected in our experimental area on Jan 24 in PD 2 and 3 in untreated plants (Fig 1 and 2).
This initial population consisted of a single, wingless mature form and several newly deposited immatures on a
single plant. No alates (winged forms) were observed. The following week, winged and wingless lettuce aphids
were found in PD 2 which was just approaching harvest stage. Aphid abundance was very low (@5 aphids / plant) in
heads in both treated and untreated plots. Aphid population numbers were similar in PD 3 at that time. Although
not statistically significant, LA in the Admire-treated lettuce heads were virtually non-existent compared with
heads sampled in the untreated plots (Table 3). In contrast, Green peach aphids were heaviest during this season in
PD 2 and 3, where populations peaked at greater than 75 and 40 per plant respectively. Similarly head
contamination was greatest in the untreated plots during these two plantings. GPA failed to significantly colonize
Admire treated plants.
In PD 4, LA were first detected at about 90 days after planting (Mar 3) when plants were just beginning to form
heads (Fig 2). By the next sample date, population abundance had increased in both the untreated and Admiretreated lettuce, and peaked at about 10 aphids / plant. At harvest the untreated plants had significantly higher number
of LA than the untreated plants (Table 3). GPA peaked about 3 weeks before harvest in untreated plots (>20 aphids
/plant) but dramatically declined thereafter (Fig 2). This coincided with a increase in average ambient temperature
above 60° F and resulted in lower aphid numbers in heads at harvest than in the previous plantings (Table 3).
LA was much more abundant in later lettuce plantings where Platinum side dress applications were also evaluated.
In PD 5, LA abundance peaked at >50 aphids per plant in untreated plants prior to harvest. LA populations in the
Admire treated lettuce were significantly higher than that observed in the Platinum treated lettuce applied at 2nd side
dress (Fig 3), and were significantly lower than the check at harvest. GPA numbers peaked at about 20 aphids per
plant in the check 3 weeks prior to harvest and crashed to insignificant levels at harvest. In PD 6, LA abundance
peaked at harvest when they exceeded > 60 aphids / plant in untreated plants. In contrast to the previous planting,
Admire provided significantly better control of LA than did Platinum applied at 1st side dress (Fig 3, Table 3). GPA
peaked on Mar 3 similar to the previous planting and crashed to very low numbers in all plots prior to harvest.
Lettuce aphids reached their peak abundance of the season in April on plants in PD7. Plant sizes were small (<10
leaves/plant) at the time aphids were first detected (Fig 4). LA numbers in all plots remained low until about 26
March when the population in the untreated check began to increase. Aphid numbers in the untreated check were
significantly greater than the Admire treatments for the next two sample dates when they peaked at greater than 750
aphids / plant (Figure 4). LA in the Admire plots increased at significantly lower levels, but reached nearly 300
aphid / head at harvest (Table 3). Similar to the previous planting GPA began to increase in the untreated plots early
in March, but crashed to negligible levels during the last two weeks of the season and were almost non-detectable at
harvest (Fig 4; Table 3)
2001-2002 Study. The study was slightly modified in 2001 by planting our first plots in mid-September, and only
making one planting after mid-December. In addition, Platinum was not side dressed in any of the plantings. As
expected, the first lettuce planting (Sep 17) completed harvested on Dec 1 without any presence of apterous aphids.
Temperatures during the growing period were unusually warm. Similarly, temperatures were very warm during PD
2 until mid-December when average ambient temps dipped below 50 F. LA was not found on lettuce plants, but for
the first time, foxglove aphid (FA), Aulacorthum solani, was found at low levels (Fig 5). This aphid species infests
lettuce similar to LA. GPA numbers were quite low and did not begin to colonize unitl January following warmer
temperatures. A similar trend in aphid abundance was observed in PD 3, where LA was still not observed (Fig 5).
Both FG and GPA were found at very levels.
There was no significant colonization of marketable heads by
apterous aphids in any of the first 3 plantings (Table 4).
LA was first found in the experimental site on Feb 21 in PD 4 (Fig 6), but was of no consequence as head
contamination was negligible at harvest (Table 4). FA and GPA populations in the untreated plots peaked at harvest
on Mar 5. FA infestations were considerably higher in PD 5 (Fig 6), peaking at Harvest and causing significant
contamination of head (>10 aphids / head). LA and GPA populations remained low throughout the season in PD 4,
and occurred at insignificant levels on head at harvest (Table 4). In PD 6, LA occurred at higher levels than
previous plantings, but were still relatively low and did not cause significant head contamination (Fig 7, Table 4).
However, GPA reached their greatest abundance on untreated lettuce plants in PD 6, peaking in late March just prior
to harvest. At harvest, most of the aphids were found on the frame leaves, with only marginal head contamination.
Similar to the previous year, LA reached their peak abundance of the season in April on untreated plants in PD7.
Plant sizes were small (<15 leaves/plant) at the time aphids were first detected (Fig 7). LA numbers remained low
until about 3 April when the population in the untreated check began to increase. Aphid numbers in the untreated
check were significantly greater than the Admire treatments for the next two sample dates when they peaked at
greater than 90 aphids / plant, (Figure 7). LA in the Admire plots remained at significantly low levels compared with
the untreated plots (Table 4). Both FG and GPA populations were very low during the March and April in PD 7 and
were almost negligible at harvest (Fig 7; Table 4). Overall, aphid populations for all species never reached economic
levels in the Admire treated plots, regardless of planting date.
Discussion
In general, our objective for establishing the distinct lettuce plantings was to have plants available for aphid
colonization at any time during the growing season. In addition, the experimental design allowed us to begin
identifying planting and harvest windows that were susceptible to lettuce aphid in the desert. The Admire and
Platinum treatments were obviously included to provide an indication of how well these systemic insecticides could
prevent damage from lettuce aphid contamination.
The timing of lettuce aphid occurrence and subsequent seasonal abundance differed considerably between the two
seasons. In 2000-2001 lettuce aphids occurred earlier and in higher numbers than in 2001-2002. Lettuce aphids
were first found in late December, about 2 months earlier than we found them in 2001-2002. This may largely be
due to differences in temperature and annual rainfall between the two seasons. We further suspect the population
immigrated from the west near the Colorado River, and Alogdones, Mexico where we received reports of lettuce
aphid attacking organic lettuce about the same time. It is unknown exactly when they first arrived, but based on our
intensive sampling, we feel fairly confident it that it was probably within a week from the time we first detected
their presence. In 2001-2002, we suspect they moved in from a similar location but much later due to the cold
weather we experienced in December and January.
It is difficult to conclude what the influence that planting date has on the seasonal abundance of lettuce aphids.
When the aphids were first detected on the research center in 2000-2001, winged forms had the opportunity to
preferentially colonize any of the 5 distinctly different ages of lettuce ranging from newly emerged seedlings in PD
6 to nearly mature heads in PD 2. Why they initially chose PD3 is unknown. Peak seasonal population abundance
occurred in the later plantings (PD 6 & 7), but these were also the last plantings to be infested. This may suggest that
given a choice, lettuce aphids prefer older plants. Further research will be needed to determine how valid this idea is.
In 2001-2002, lettuce aphids were found on the last 4 planting at much lower densities than previous years, and only
developed economic infestations on PD 7. This was largely due to the late arrival of winged aphids moving into the
experimental area. These migrations also coincided with warmer temperatures.
We do know that temperature has a significant influence upon lettuce aphid development and population growth.
This is supported to a large degree by our field observations (Palumbo 2001). Furthermore, based on recent
laboratory studies by Bill Chaney, University of California in Salinas, the optimal temperature for lettuce aphid
biological development appears to be around an average of 66EF. This is consistent with the average temperatures
recorded during March and April in these studies. Based on AZMET data, the average daily temperature was about
65EF at YAC during this time. This may explain why the populations did not appear to really increase until early
March in 2001 and April in 2002. A similar response was seen in 1999 and 2000 in our studies in Romaine and head
lettuce (Palumbo 1999, 2000b). In those studies we saw a sharp decline in LA populations near harvest in late
plantings following extended periods of unseasonably, warm temperatures in April (averaged 73EF), where
daytime highs exceeded 90EF. In this study, LA during the late plantings peaked at high levels at harvest when
temperatures averaged between 65-70EF. We cannot completely attribute these dynamics to temperature because of
the high densities of natural enemies associated with heavy aphid colonies on lettuce plants. We feel confident
though that the combination of the two factors was responsible for the decline of the lettuce aphid populations
during April.
The application of soil, systemic insecticide also had a significant affect on lettuce aphid population growth. We
were surprised by the marginal level of lettuce aphid control provided by the systemic insecticides in 2000-2001.
Lettuce treated with Admire in the early planting dates, appeared to prevent lettuce aphids from significantly
infesting lettuce heads at harvest. In the later planting dates (PD 4-7), both Admire and Platinum contained
significantly fewer aphids and infested plants than the untreated control (Fig 2-3). However, lettuce aphids in the
last 3 planting dates were able to colonize plants and infest a larger percentage of heads than would normally be
considered commercially acceptable. It is apparent that the Admire provided some residual control, but based on the
results of this study, it is difficult to determine the length of effective residual activity Admire has against lettuce
aphid under heavy population pressure. In contrast, during the 2001-2002 season, population pressure was much
lighter and occurred later in the growing season. As a result, Admire provided almost complete control of LA. Thus,
under lower infestation levels, Admire appears to provide excellent residual control.
GPA was most prevalent during the late-October and November plantings in 2000-2001. Contamination of lettuce
heads was only significant in the untreated lettuce during PD 1-4, when aphids approached 15 aphids/head. In each
of these plantings, Admire provided economic control of GPA with negligible head contamination. In the later
plantings, GPA populations did develop early-mid season, but consistently declined near harvest resulting in no
significant contamination at harvest. Interestingly, GPA was only a problem in head lettuce when average
temperatures near harvest when temperatures averaged around 55EF. When temperatures exceeded 60EF, GPA
began to rapidly decline. In 2002, GPA was only an economic concern during that December planting, when
temperatures were well above 55EF. Thus, it is not clear what influence temperature has on the GPA aphid complex
in the desert. Perhaps the most interesting observation made in 2002 was the incidence of the foxglove aphid. This
aphid species infests lettuce similar to LA and occurred in Salinas about the same time as lettuce aphid did.
Behaviorally it is similar to lettuce aphid as it prefers to infest the heads. Our data in head lettuce though suggests
that it may be less inclined to exclusively attack heads like the LA, as it be readily found infesting the frame and
wrapper leaves on plants (Table 4).
In conclusion, lettuce aphid is probably not a serious threat to the lettuce industry in the desert under present
conditions. Based on the above studies, only the December and January planting dates sustained economic
infestation levels in lettuce. We know that temperatures have a significant influence on population growth and
seasonal abundance. Temperatures during the spring 2000 growing season were unseasonably warm and dry, and
unusually cool in spring 2002. We had previously speculated that lettuce aphid population dynamics might be quite
different under more “normal” weather patterns in the winter and spring which may in turn influence lettuce aphid
control with soil systemic treatments. The contrasting results observed between the two years within this study
verify this. Furthermore, we had previously speculated that lettuce aphids were probably reintroduced each season
via transplants and equipment moving between the coast and desert. However, lettuce aphids have consistently
appeared in similar locations on both experimental plots and commercial fields in the north Yuma Valley for the
past 4 years. We now feel that it is highly likely that this aphid is over-summering in the desert, perhaps on some
unknown secondary host near the Colorado River. Finally, the fact that lettuce aphid has not been a larger problem
in commercial head lettuce and romaine over the past 4 years is probably reflective of suppression resulting from
current management practices. Most spring lettuce acreage in Yuma is treated with Admire at planting, which when
coupled with foliar spray treatments of Lannate+pyrethroids for western flower thrips can significantly suppress
lettuce aphid colonization (Palumbo 1999). Thus, under current growing practices and pest management programs,
the threat of lettuce aphid causing economic damage to spring lettuce in the Yuma area is low. However, the threat
is much greater to organic growers and conventional producers who do not use soil, systemic insecticides.
Acknowledgments
Funding and support for this research was provided by the following sources: Arizona Iceberg Lettuce Research
Council, Bayer Corporation and Novartis Crop Protection. Special thanks to Louis Didier, Select Seed of Arizona,
for selecting the lettuce varieties and providing the seed used in this study. I gratefully acknowledge the excellent
assistance from the personnel at the Yuma Agricultural Center including Clay Mullis, Francisco Reyes, Andreas
Amaya, Luis Ledesma, Lisa Cary, Leonardo Chavez, and Javier Ruiz..
Literature Cited
Palumbo, J.C. 1999. Preliminary examination of the population dynamics and control of the lettuce aphid in
Romaine, pp.130-135. In D.N. Byrne and P. Baciewicz (eds.), 1999 Vegetable Report, University of
Arizona, College of Agriculture, Series P-117, AZ1143.
Palumbo, J.C. , C. Mullis, F. Reyes, A. Amaya, and L. Ledesma. 1999. Application and timing of insecticides for
aphid management in head lettuce, pp. 94-107. In D.N. Byrne and P. Baciewicz (eds.), 1999 Vegetable
Report, University of Arizona, College of Agriculture, Series P-117, AZ1143.
Palumbo, J. C. 2000a. Lettuce Aphid Returns to the Yuma Valley, pp. 4. University of Arizona, Cooperative
Extension. Yuma County Farm Notes, Feb 2000.
Palumbo, J.C. 2000b. Seasonal Abundance and Control of the Lettuce Aphid, Nasonovia ribis-nigri, on Head
Lettuce in Arizona, pp. 97-105. In D.N. Byrne and P. Baciewicz (eds.), 2000 Vegetable Report,
University of Arizona, College of Agriculture and Life Sciences, AZ1177.
Palumbo, J.C., C.H. Mullis, F.J. Reyes, A. Amaya, L. Ledesma, and L Carey. 2000. Population Dynamics and
Distribution of Aphid Species on Head Lettuce In the Yuma Valley, pp. 69-83. In D.N. Byrne and P.
Baciewicz (eds.), 2000 Vegetable Report, University of Arizona, College of Agriculture and Life Sciences,
AZ1177.
Palumbo, J.C. 2001. Influence of Admire® and Platinum® on the Population Growth of the Lettuce Aphid Under
Field Conditions, pp. 14-19. In D.N. Byrne and P. Baciewicz (eds.), 2001 Vegetable Report, University of
Arizona, College of Agriculture and Life Sciences, AZ 1252.
Table 1. Lettuce varieties, sample dates, and plant growth stages for seven plantings of head lettuce, Yuma
Agricultural Center, 2000-2001.
Planting
Date
(Variety)
Event
1
2
3
4
5
6
1-Oct 11
Sample date
Nov 9
Dec 1
Dec 21
Jan 4
Jan 16
Jan 25
(Grizzley)
Plant stagea
3-4
9-10
16-17
20-22
4”
Harvest
2- Nov 1
Sample date
Dec 6
Dec 21
Jan 4
Jan 16
Jan 24
(Wolverine)
Plant stagea
3-4
6-7
10-11
16-18
3- Nov 15
Sample date
Dec 21
Jan 4
Jan 16
(Del Rio)
Plant stagea
3-4
6-7
4 - Dec 1
Sample date
Jan 16
(Jackel)
a
Plant stage
5 - Dec 15
7
8
Feb 5
Feb 15
Mar 3
18-20
20-21
3.5”
Harvest
Jan 24
Feb 5
Feb 15
Mar 3
10-11
12-14
16-18
4”
Harvest
Jan 24
Feb 5
Feb 15
Mar 3
Mar 14
Mar 26
2-3
3-4
7-9
10-12
18-20
3”
Harvest
Sample date
Jan 16
Jan 24
Feb 5
Feb 15
Mar 3
Mar 14
Mar 26
(Diamond)
Plant stagea
1
2-3
6-7
9
13-15
2.5”
Harvest
6 - Jan 15
Sample date
Feb 5
Feb 15
Mar 3
Mar 14
Mar 26
Apr 9
(Diamond)
Plant stagea
2
4-5
7-8
10-12
18-20
Harvest
7 - Feb 1
Sample date
Feb 15
Mar 3
Mar 14
Mar 26
Apr 9
Apr 20
3”
Harvest
Plant stagea
2-3
7-8
12-13
16-18
Estimated average number of frame leaves per plant or head diameter (in).
(Beacon)
a
Table 2. Lettuce varieties, sample dates, and plant growth stages for seven plantings of head lettuce, Yuma
Agricultural Center, 2001-2002.
Planting
Date
(Variety)
Event
1
2
3
4
5
6
1-Sep 17
Sample date
Oct 10
Oct 23
Nov 1
Nov 9
Nov 19
Dec 1
(Mohawk)
Plant stagea
4
8
12
15
18
Harvest
2- Oct 10
Sample date
Nov 7
Nov 15
Nov 28
Dec 8
Dec 19
Jan 3
Jan 14
(Wolverine)
Plant stagea
5
10
12-13
17
20
3”
Harvest
3- Oct 28
Sample date
Nov 27
Dec 7
Dec 18
Jan 4
Jan 16
Jan 25
Feb 4
(Grizzly)
Plant stagea
5
9
12
16
20
4”
Harvest
4 – Nov 15
Sample date
Dec 31
Jan 10
Jan 23
Feb 1
Feb 12
Feb 21
Mar 5
a
7
(Wolverine)
Plant stage
5
9
13
16
18
3”
Harvest
5 - Dec 3
Sample date
Jan 19
Jan 28
Feb 7
Feb 17
Feb 26
Mar 11
Mar 22
(Diamond)
Plant stagea
5
8
10
12
16
4.5”
Harvest
6 – Dec 12
Sample date
Feb 2
Feb 12
Feb 23
Mar 5
Mar 16
Mar 27
Apr 6
(Diamond)
Plant stagea
4
7
11
14
18
4”
Harvest
7 – Jan 14
Sample date
Feb 17
Feb 26
Mar 11
Mar 22
Apr 3
Apr 15
Apr 25
20
4.5”
Harvest
Plant stagea
4
6
9
13
Estimated average number of frame leaves per plant or head diameter (in).
(Beacon)
a
Table 3. Lettuce Aphid and Green Peach/Potato Aphid Contamination on Head Lettuce at Harvest, Yuma
Agricultural Center, 1999-2000.
Mean Aphids per Plant at Harvest
Lettuce Aphid
Planting Date
Treatments
1 (Oct 18)
Green Peach/Potato Aphid
Head
Frame Leaves
Head
Frame Leaves
Admire
Untreated
0
0
0
0
0
1.9
0*
14.4
2 (Nov 3)
Admire
Untreated
0
5.1
0
0
0.6*
15.2
2.0*
38.5
3 (Nov 15)
Admire
Untreated
0.9*
6.5
0.1
0.9
0*
8.5
0.7*
42.6
4 (Dec 1)
Admire
Untreated
1.6*
9.6*
0.3
0.4
0*
2.6
0*
12.9
5 (Dec 15)
Admire
Platinum
Untreated
5.8
1.1*
8.2
0.4
0.1
0.6
0.1
0
0.3
0
0
2.5
6 (Jan 8)
Admire
Platinum
Untreated
8.8*
19.2
58.2
0.6
0.7
2.1
0
0
1.6
0
0
2.5
7 (Feb 1)
Admire
Untreated
284.5*
672.4
73.3
161.9
0.3
0.2
0.3
1.9
* Indicates that treatment was significantly different from untreated check by a paired t-test; (p<0.05)
Table 4. Lettuce Aphid, Foxglove Aphid and Green Peach/Potato Aphid Contamination on Head Lettuce at
Harvest, Yuma Agricultural Center, 2001-2002.
Mean Aphids / Plant at Harvest
Lettuce Aphid
Foxglove Aphid
Green Peach/Potato Aphid
Head
Frame
Leaves
Head
Frame
Leaves
Head
Frame
Leaves
Admire
Untreated
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
2 (Oct 10)
Admire
Untreated
0.0
0.0
0.0
0.0
0.0
0.3
0.0
0.0
0.0
0.6
0.1
2.3
3 (Oct 28)
Admire
Untreated
0.0
0.0
0.0
0.0
0.0
0.0
0.3
0.1
0.0
0.5
0.0*
7.1
4 (Nov 15)
Admire
Untreated
0.0
1.1
0.0
0.1
0.0
1.4
1.3
6.3
0.0*
3.6
0.1*
7.9
5 (Dec 3)
Admire
Untreated
0.1
1.1
0.3
0.1
0.3*
11.7
0.7
2.9
0.3
1.0
0.1
1.5
6 (Dec 12)
Admire
Untreated
0.0*
6.3
0.1
0.4
0.6
1.5
0.1*
6.3
0.1*
6.6
0.1*
42.7
7 (Jan 14)
Admire
Untreated
1.8*
91.4
0.3*
3.3
0.1
1.3
0.1
0.7
0.2
1.5
0.6*
4.0
Planting Date
Treatments
1 (Sep 17)
* Indicates that treatment was significantly different from untreated check by a paired t-test; (p<0.05)
o
Temp ( F)
2.5
1.5
1.0
1.0
Nov
15
Nov Dec
28
8
Dec Jan
19
3
Nov
7
Jan
14
Planting Date 3
Lettuce Aphid
60
55
50
Admire
Untreated
2.0
1.5
1.0
Fig 5.
Jan Feb
4
25
1.0
Nov
7
Foxglove Aphid
65
Nov
15
Nov Dec
28
8
Dec Jan
19
3
Jan
14
Green Peach/Potato Aphid
60
55
50
7
2.0
1.5
1.0
0.0
Jan
16
1.5
0.0
Jan
14
50
0.0
Jan
4
Dec Jan
19
3
55
0.5
Dec Dec
7
18
Nov Dec
28
8
60
0.5
Nov
27
Nov
15
2.5
Aphids /plant
2.5
2.0
(Oct 28)
65
o
Temp ( F)
65
Green Peach/Potato Aphid
0.5
o
Temp ( F)
Nov
7
o
Temp ( F)
1.5
0.0
0.0
Aphids /plant
2.0
0.5
0.5
75
70
65
60
55
2.5
Aphids /plant
Admire
Untreated
2.0
Foxglove Aphid
75
70
65
60
55
Aphids /plant
Aphids /plant
2.5
(Oct 10)
o
Temp ( F)
Lettuce Aphid
75
70
65
60
55
Aphids /plant
o
Temp ( F)
Planting Date 2
6
5
4
3
2
1
Nov
27
Dec Dec
7
18
Jan
4
Jan
16
Jan Feb
4
25
0
Nov
27
Dec Dec
7
18
Jan
4
Currant-Lettuce Aphid Seasonal Abundance on Treated and Untreated Head Lettuce, Yuma Agricultural Center, 2001-2002
Jan
16
Jan Feb
4
25
Planting Date 4
(Nov 15)
Foxglove Aphid
55
Admire
Untreated
8
60
55
10
6
4
8
6
4
2
2
Dec Jan
31
10
Jan
23
Feb
1
Feb Feb
12
21
Mar
5
60
55
8
6
4
2
0
0
65
10
Aphids /plant
Aphids /plant
10
Green Peach/Potato Aphid
65
o
Temp ( F)
o
Temp ( F)
60
Aphids /plant
o
Temp ( F)
Lettuce Aphid
65
0
Dec
31
Jan
10
Jan
23
Feb
1
Feb Feb
12
21
Dec Jan
31
10
Mar
5
Jan
23
Feb
1
Feb Feb
12
21
Mar
5
Planting Date 5 (Dec 3)
Lettuce Aphid
16
Aphids /plant
12
Aphids /plant
Admire
Untreated
10
8
6
4
60
55
16
14
12
12
8
6
4
2
0
0
Jan
28
Feb
7
Fig 6.
Feb
17
Feb Mar
26
11
Mar
22
55
14
10
Green Peach/Potato Aphid
60
16
2
Jan
19
o
Temp ( F)
55
65
Aphids /plant
60
14
Foxglove Aphid
65
o
Temp ( F)
o
Temp ( F)
65
10
8
6
4
2
Jan
19
Jan
28
Feb
7
Feb
17
Feb Mar
26
11
Mar
22
0
Jan
19
Jan
28
Feb
7
Feb
17
Currant-Lettuce Aphid Seasonal Abundance on Treated and Untreated Head Lettuce, Yuma Agricultural Center, 2001-2002
Feb Mar
26
11
Mar
22
Planting Date 6
Lettuce Aphid
60
55
70
o
Temp ( F)
65
65
60
55
12
12
Admire
Untreated
6
4
8
6
4
60
55
0
0
Mar Mar
16
5
Mar
27
Apr
6
40
30
20
10
2
2
Feb Feb
12
23
65
50
Aphids /plant
8
Feb
2
Green Peach/Potato Aphid
10
Aphids /plant
10
Aphids /plant
Foxglove Aphid
70
o
Temp ( F)
o
Temp ( F)
70
(Dec 12)
Feb
2
Feb Feb
12
23
Mar Mar
5
16
Mar
27
0
Apr
6
Feb
2
Feb Feb
12
23
Mar Mar
5
16
Mar
27
Apr
6
Planting Date 7 (Jan 14)
Foxglove Aphid
60
Admire
Untreated
Aphids /plant
90
75
60
45
30
70
65
60
14
12
12
10
8
6
4
0
Fig 7.
Apr Apr
15
3
Apr
25
60
14
0
Mar
22
65
16
2
Feb Mar
26
11
70
16
15
Feb
17
o
Temp ( F)
65
Green Peach/Potato Aphid
Aphids /plant
o
Temp ( F)
70
Aphids /plant
o
Temp ( F)
Lettuce Aphid
10
8
6
4
2
Feb
17
Feb Mar
26
11
Mar
22
Apr Apr
15
3
Apr
25
0
Feb
17
Feb Mar
26
11
Mar
22
Currant-Lettuce Aphid Seasonal Abundance on Treated and Untreated Head Lettuce, Yuma Agricultural Center, 2001-2002
Apr Apr
15
3
Apr
25