Arizona Head Lettuce Insect Losses 2001/2002
John C .Palumbo
The data presented here is an attempt to provide actual
insect loss data for head lettuce and to estimate the level of insecticidal
control needed to prevent key insect pests from reducing yields. This
information was collected from surveys of pest control advisors from the
Yuma area. Eighteen surveys were distributed to PCAs and consultants in
May, 2002. A total of 4 surveys were returned which account for 12,700
acres of fall and spring head lettuce or about 24% of the total acres
grown in 2001-2002. All data were averaged over the total number of surveys
returned. Additional input was provided by myself through informal discussions
with 2 additional PCA's who did not complete the survey and 2 lettuce
Information in Table 1 is provided to describe the acreage represented by the surveys and factors which affected head lettuce yields. In addition, costs associated with aerial and ground applications, and insect management fees for scouting were estimated. Table 2 describes the percentage of acres where key insect pests were present and required treatment to prevent yield reductions. Included with those estimates are the frequency and costs of insecticide applications directed towards those insects. These costs represent a loss to the grower associated with preventing insects from damaging plants and reducing yields. Finally, based on that information, actual percent yield reductions (heads not harvested due to insect damage or injury) were estimated for those acres.
The results of this survey represent a total of 12700 acres gown in Yuma during 2001/2002; 7200 acres of fall lettuce (acres planted in September and October) and 5500 acres of spring lettuce (planted in November and December). The estimated average yields per carton were 17 and 13% less than the estimated potential yield for fall and spring lettuce respectively. These values are also fairly consistent with the PCA and grower estimates of factors responsible for yield losses. Weather appeared to be the major factor responsible for yield reductions. Temperatures were above normal throughout the fall season and accelerated maturity in many cases and affected head size. In contrast, the spring season was drier and cooler than normal and also resulted in reduced head size. Overall, weather was blamed for a reduction in supply of and the resulting high lettuce prices in 2002.
Compared to the 2000/2001 survey, application costs and the average number of treatments were higher in 2001/2002. The greater number of applications may be a reflection of the heavy worm pressure experienced in the fall crops and the high thrips numbers in the spring. The cost of scouting (Monitoring cost $ / acre) was lower in 2002, and probably reflect difference in survey respondents.
Insects important at stand establishment (ground beetles, earwigs, crickets, flea beetles and salt marsh caterpillars) were present only on fall crops and required control to prevent damage on less than 25% of those acres. A single insecticide treatment at an average cost of $16.00 per acre was used to manage these pests. Salt marsh caterpillars and earwigs were not present in 2002. Leafminers were present on only 5% of the fall acreage, but did not require treatment. No reduction in head lettuce yield by these pests was reported.
The lepidopterous larval complex consisting of beet armyworm, cabbage looper and budworm/ bollworm accounted for the greatest number of applications in head lettuce. This complex was present on 100% of the acreage and required a total of 8 applications in both crops. The average cost of an application was estimated at $24-26 / acre. No yield reduction due to lepidopterous larvae was reported.
Silverleaf whitefly was present on 100% of the fall crop, but only 83% of the crop was treated. A single application at $60 / acre indicates that a majority of growers are applying Admire (16oz/acre) at planting for control of this pest. As usual whiteflies were not present on spring crops and required no control. Green peach and potato aphids were not reported to be present on fall or spring crops, but a single application at $60/acre shows that most growers are applying Admire to spring crops to preventatively control aphids. No yield reduction was reported for either whiteflies or aphids in 2001/2002.
Thrips are becoming a more important pest in desert lettuce as indicated by their presence in fall lettuce and the increased costs required to control them in spring crops. An average of 44% and 100% of the acreage required treatments for thrips in fall and spring lettuce respectively. Control costs averaged $23-27 / acre. Thrips were the only insect pest in the survey that were estimated to cause yield reduction. A 3% reduction in lettuce yields was reported in the spring head lettuce. Trash bugs were also present in 100% of both the fall and spring acreage surveyed. In most cases, a single application was applied preharvest to prevent contamination of marketable heads by these plant bugs and beetles. The cost of control for trash bugs was included in the cost of a pyrethroid ($8.00-12.00) commonly used in combination with other chemistries for worm control near harvest.
In general, 7-8 insecticide applications were made to fall lettuce and 5-6 applications to spring lettuce for preventing insect damage. Although the information in Table 2 suggests that 23 total applications were made to fall lettuce, many of the sprays were applied as broad spectrum treatments aimed at controlling more than one insect species. For example, insects at stand establishment (ground beetles, crickets and flea beetles) were controlled with the same insecticide application. Additionally, the lepidopterous complex (beet armyworm, cabbage looper and budworm/bollworms) were controlled with the same foliar applications. Similarly, these same treatments (Lannate + pyrethroid and Success) were often used to suppress thrips. In spring lettuce, applications of the same compounds were often primarily directed towards thrips control, with the secondary purpose of controlling lepidopterous larvae.Table 1. Background Information - Yuma, AZ
Table 2. Head Lettuce Insect Losses Summary - Yuma, AZ
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 Associate Research Scientist (Entomology)
University of Arizona, Tucson, Arizona.
Material written October 2002.
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