Economic Impact of Lygus in Arizona Cotton: A Comparative Approach
AffiliationUniversity of Arizona, Arizona Pest Management Center, Maricopa, AZ
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AbstractIn the Western U.S., Lygus spp. (Hemiptera: Miridae) can cause major losses to cotton, vegetables, seed crops, and a variety of other crops. However, the economic impact of this pest remains largely undocumented in most crops. Two major data sources were used to quantify the economic impact of Lygus in lowdesert upland cotton production in Arizona: a statewide Pesticide Use Reporting (“1080”) database and an annual “Cotton Insect Losses” (CIL) survey of cotton Pest Control Advisors (PCAs). Both data sources include information on the target pest for insecticide applications, making it possible to single out Lygus control efforts. PUR data, based on information submitted by applicators to the Arizona Department of Agriculture, provides quantitative information on a high proportion of Lygus applications in cotton, but is incomplete, since not all types of applications require reporting. These data are complemented by information from the CIL survey to provide a more complete picture, based on direct responses from PCAs about their pest management practices. While the 1080 database is very useful in documenting a high proportion of Lygus insecticide use in cotton, by definition, these data on their own cannot provide good estimates of statewide behaviors with respect to Lygus management. In contrast, this is exactly what the Cotton Insect Losses survey is designed to do. As indicated by 1080 data and CIL data from 2001 to 2005, Lygus is the most important pest in Arizona cotton most years, based on application*acres of all foliar insecticides. Other key pests by this measure are sweetpotato whitefly, Bemisia tabaci Genn., and to a lesser extent pink bollworm, Pectinophora gossypiella (Saunders). Whitefly is the most important Lygus co-target, when applications are aimed at controlling more than one pest. The most commonly used foliar materials against Lygus in Arizona cotton are acephate, endosulfan and oxamyl, and they are typically used at about 90% of maximum label rates. About 80% of Lygus applications occur between mid-July and late-August. Average spray intensity (based on average sprays per acre) was calculated independently using the CIL and 1080 data sets and compared. For every year except for 2004, the CIL data estimates a somewhat higher insecticide use against Lygus . Several reasons for this discrepancy were identified, including less than 100% pesticide use reporting on 1080s; differences in the insecticides included in the estimates (top three active ingredients only for 1080 estimate, all insecticides for CIL estimate); and differences between how the two datasets apportion a single spray event among multiple pest targets. The intensity of Lygus management varies by county, based on 1080 data and county-level information on cotton acreages. Pinal county, which has the most cotton acres, shows the highest sprays / acre of the top three active ingredients to control Lygus . Analysis of 2005 1080 data at the section level indicates a relationship between the proportion of sections where cotton is grown in a Township - Range and spray intensity for Lygus control. Growers in Township - Ranges with a low proportion of cotton sections (10–15%) tend to make more sprays per field to control Lygus . However, Township – Ranges with the lowest and highest proportions of cotton sections (<10% and >90%) tend to show trends of lower spray requirements for Lygus control. These data suggest the possibility that landscape factors can influence Lygus populations at the local level, although more research in this area is needed. Lygus is perhaps the most significant economic pest of Arizona cotton. Cotton Insect Losses survey data indicate that a high proportion of cotton insect pest management efforts are directed toward Lygus control. Up to 40% of foliar insecticide sprays target Lygus , for about one third of the foliar insecticide budget for growers most years. Despite these control efforts and associated costs, Lygus are consistently listed in the CIL by survey respondents as the most damaging insect pest of cotton, accounting for more than 50% of insect-related yield loss most years. These two different and complementary data sets provide important baseline information on the current status and economic impact of Lygus in Arizona cotton, which will be useful for measuring changes in Lygus impact and control practices over time. A number of factors could potentially impact these practices in the future including (1) the introduction of new selective chemistry for Lygus control; (2) the introduction of transgenic control options for Lygus ; and (3) landscape-level changes that can have area-wide impact on Lygus management in cotton and other crops. These data underscore the need for continued research to develop effective, selective tools for improved Lygus management in cotton, and to integrate these into effective IPM programs. Data documenting a pest’s economic impact provides a rationale for funding to support critical IPM research and education. There is a need to similarly document the economics of Lygus management in other crops including vegetables, seed crops, and alfalfa, and the impact of landscape-level factors on Lygus management in a variety of crops.