John C. Palumbo and Barry Tickes
A number of selective aphicides are being developed that provide selective aphid control, with little or no toxicity or repellency to honey bees. Fulfill® (pymetrozine, Novartis) is presently labeled on leafy vegetables and has an SLN registration for Brassica seed crops in Arizona (AZ-000004). Our experiences in lettuce suggests that the product can provide 10-14 residual control of aphids when applications are initiated when aphids first begin to colonize on foliage. Other promising candidates (not labeled) Aphistar® (triazimate, Rohm&Haas) and Pirimor® (pirimicarb, Zeneca) have excellent contact and systemic aphid activity on a number of crops. Similarly, studies in lettuce have shown that these two compounds provided about 14-21 d residual aphid control. Unfortunately, both products are carbamates, and their future status is not known. Another promising product under consideration is Assail® (acetamiprid, Ceragri), which is also safe to pollinators. The compound is a neonicitinoid, similar in activity to Admire® and the product was recently granted a registration for use in broccoli and cauliflower in California. In previous field trials, it has shown good control of green peach aphid on lettuce and broccoli. Selectivity can also be achieved by applying the pesticides to the plant without exposing pollinators to the toxicant. Platinum® (thiamethoxam, Syngenta), also a neonicotinoid, has recently been labeled on melons for whitefly control with labels pending on leafy vegetables and Brassica crops for aphids. It is applied in-furrow at planting and has similar activity as Admire. The primary difference between the two products is that Platinum is very mobile in the soil and moves readily with furrow irrigation. Trials in head lettuce and melons have shown that residual aphid control is actually better when the product is applied at side dress rather than at planting. This approach extends residual control closer to harvest. It may be possible to use this approach in Brassica seed crops by side-dressing the product at layby, thus providing residual control at the time aphids begin to colonize in the spring. Given that the products will soon be labeled on cole crops, evaluating this approach may result in an effective management tool. We completed a replicated study in 2003. Note: Admire is not labeled for use on seed crops.
Because the value of these compounds for aphid control in Brassica seed crops grown in Arizona needs to be determined, we conducted studies to measure aphid control with these new experimental compounds under non-blooming (early aphid development) and blooming (heavy aphid pressure) conditions. We also studied aphid population dynamics by identifying and quantifying the aphid species complex on a broccoli seed crop and determined their distribution on plants during the pre-bloom growth period. Ultimately, our goal is to gather data to assist Arizona seed growers and PCA’s in making management decisions and to support registrations for new insecticides.
2003 Study: The study was conducted in a 2-acre broccoli ‘Marathon’ seed field at the Yuma, Arizona. Male and female transplants were established in the field on single row, 42 inch beds on 4 and 25 October, respectively. Plants were furrowed irrigated throughout the trial. Plots were established in the field by equally dividing the field into plots 8 beds wide by 80 ft long. Equal numbers of male and female plants were distributed equally on alternating beds within each plot. Each treatment was replicated three times in a randomized complete block design. For insecticide trial the following 8 treatment combination were evaluated.
Several insecticide treatments were applied in this trial. A single Platinum (8 oz/ac) and two Admire (24 oz/ac) treatments were side-dressed on the shoulder of beds, 2-3 inches below the soil in 30 gpa final dilution on Nov 30. Foliar applications were made with a Melroe sprayer (UA YAC) that delivered a directed spray at 25 gpa and 40 psi through 3 nozzles per bed. The first application was made on Feb 18th at 1800 hr. (pre-bloom). A second application was made on March 22nd . Plants were blooming and bees were actively working the field. A third application was made post-bloom on Apr 4 after the bees were removed.
Aphid populations were assessed similar to the 2001 study by visually examining young and old leaves from both male and female plants prior to the first spray application, and seed pod extensions during seed production. Beginning in mid-November, sampling was initiated to determine the abundance and location of aphid species during the pre-blooming growth period. We randomly sampled 80 male plants and 80 female plants about every 14 days from the 2-acre block. From each plant we selected an older leaf from the frame and a younger leaf from the terminal area of the plant. All aphids on each leaf were identified to species and counted. Following the spray applications, the number of seed pods (extensions) infested with aphids was recorded. The number of aphids on each pod was estimated on March 30 by randomly selecting 3 light-moderate and 3 heavy infested pods from each plot and counting the total number of aphids. Treatment means were analyzed using a 1-way ANOVA and means separated by a protected LSD (P<0.05).
Results and Discussion
2001 Study: During the pre-bloom growth period (January-March), our plant counts revealed that two distinct aphid populations were distributed within the cauliflower plants. The frame leaves were largely infested with green peach aphids (GPA >90% ) with a small proportion of cabbage aphid and turnip aphid present. Conversely, as plants began to extend and flower production began, the plant terminals and seed pods were predominately infested with cabbage aphids (CA; > 90%) and a small percentage of GPA (Table 1).
The female plants were in full bloom when the 1st application was made. Tables 1 and 2 show the subsequent changes in aphid populations at 3 and 7 DAT, respectively. Both the Pirimor and Aphistar provide excellent knockdown of established CA on plant terminals and seed pods and resulted in significantly fewer infested seed pods compared with the untreated control. The Fullfill spray provided good control of the GPA found on the frame leaves, but provided marginal knockdown of CA on plant terminals and seed pods. Although aphid numbers were not statistically different among the insecticide treatments, it was clear that the Fulfill treatment allowed a much higher number of aphids to remain in seed pods. Furthermore, the aphid numbers increased significantly in the Fulfill treatment from 3 to 7 days after treatment. Consequently, we applied a second application of Pirimor to the Fulfill plots.
Following the second application (Tables 3 and
4), the Aphistar and Pirimor applications significantly reduced aphid
numbers and infested pods for 28 days following the application. No damage
to the seed pods in treated plots was noted. Aphid numbers in the untreated
plots declined steadily during the 28 day period but this was due to the
large number of lady beetles that migrated into the plots. Unfortunately
most of the seed pods in the untreated plots were seriously damaged due
to excessive aphid feeding.
2003 Study: Similar to 2001, results from our pre-bloom
sampling surveys showed that the primary aphid species found were cabbage
aphids, turnip aphids, and green peach aphids. Geeen peach aphids tended
to colonize plants slightly earlier and were found to primarily on the
older frame leaves low on the plant (Table 6). In
most cases, male and female plants were colonized to the same extent.
Their numbers peaked in late January, and were found on seed pods at very
low densities. Cabbage and turnip aphids behaved similarly, and were combined
for this summary. There appeared to be no clear preference between their
colonization on older and younger leaves. Similarly, they appeared to
colonize males and females equally. During the bloom period (March-April),
the population was almost exclusively cabbage aphid feeding on seed pods
and extensions. Their numbers were higher than green peach aphid, and
rapidly colonized seed pods and extensions once pollination was completed
and bloom had dropped. Cabbage aphid was the primary species (>90%)
found feeding on developing seed pods in this test. Based on both years
results, sampling for aphids on seed crops should begin a week or so prior
to bloom. Scouting should focus on younger leaves from the terminal area.
Once blooming begins, sampling should focus almost exclusively on newly
developing seed pod extensions.
Of the bee safe products, Pirimor provided the most consistent residual aphid control similar to 2001. This was achieved with 3 applications at a 3 oz rate. Both Assail or Fulfill worked well on foliage, but did not provide comparable control on seed pods. Given Fulfill’s weakness as a contact material on seed crops, it should not be recommended for cabbage aphid control on broccoli seed crops. Although Assail performed better, it needs to be further evaluated before recommendations can be made. Both the side-dress applications of Platinum and Admire provided good aphid suppression prior to seed pod extension. A single Capture application following bloom rapidly controlled colonizing aphids in these plots. The Capture spray will likely provide some control of false chinch bugs on maturing plants (False chinch bugs were not present in the test). The Admire only treatment did not provide adequate protection from aphids during seed production.
In general, the pre-bloom application did not appear to prevent aphids from quickly colonizing seed following extension and bloom (Table 7, Fig 1). In years where aphids number are lighter (such as 2001), a pre-bloom application may significantly suppress colonization.. As noted above, aphid densities were extremely high in the untreated check, and to a lesser extent in the Fulfill plots. The aphids had a direct impact on plant mortality. We had intended to measure seed quality in the plots, but seed yields were not taken due to heavy late season losses to Sclerotinia and bird damage in all plots.
Funding for this research was provided by the Seed Trade Association of Arizona. We would like to thank Sakata Seed Co., Yuma, AZ for providing the transplants at no-cost for the 2003 study. We would also like to thank Dune Co. of Yuma for making the spray application at no-cost in the 2001 study. We also acknowledge the following personnel at the Yuma Agricultural Center, Clay Mullis, Andreas Amaya, Luis Ledesma, Leonardo Chavez, Javier Ruiz and Gerardo Villegas for their assistance in completing this project.
Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director Cooperative Extension, College of Agriculture and Life Sciences, The University of Arizona.
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Information provided by:
John C. Palumbo, firstname.lastname@example.org Research Scientist (Entomology)
Barry Tickes, email@example.com Extension Agent, Yuma County
University of Arizona, Tucson, Arizona.
Material written February 2004.
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