Nani Gould and Douglas G. Pfeiffer
Department of Entomology
The apple maggot (AM), Rhagoletis pomonella
(Walsh), is an important
pest in the northeastern United States and has recently been introduced
into the Pacific Northwest. More insecticide is applied annually in
orchards in northeastern North America to control the AM than against
other single insect pest (Reissig et al. 1983). Populations seldom
damaging levels in Virginia, but this has become complicated due to
sanctions made on apples headed for import to Brazil. Previously apples
could be exported to Brazil after 40 days in cold storage. This
put the US at a disadvantage because once the fruit was released their
market value had dropped considerably due to competition from other
The Brazilian protocol affects growers from California to New York, despite the fact that infestation in the western states has not reached the level it has in the northeast. The Brazilian protocol calls for a very strict threshold on AM infestation. It specifies that if one AM adult is found in an export block, the fruit for that block will be held at the packing house for 14 days. If a subsequent AM is detected within this period, the fruit will be considered infested (Gutierrez, 1996). According to this report, infestation is defined as either 1 pupa or larva found or 2 or more adults found within the 14 day period within a 1/2 mile of each other. When infestation has been determined, all of the fruit within the 1/2 mile area of detection will be considered ineligible for export to Brazil for the remainder of the shipping season. At the packing house the fruit that is to be exported to Brazil will be sampled by very strict and uniform guidelines. One hundred apples from each lot will be sampled and taken from at least two cartons. Each sample will be examined for external injury and 20 apples will be cut and inspected internally. If AM injury is found, 100 apples from other lots of the orchard will be internally inspected and if any additional AM are found the shipment will be rejected. If the fruit passes certification it will be shipped directly to the packing house ready for export to Brazil.
The systems approach for monitoring for AM, outlined by the protocol, is divided into two options: High-density trapping and intensive-insecticide control programs. The high-density trapping option calls for the use of red spheres or yellow panel traps to be placed in the orchard at 1 trap per 10 acres. They will be monitored throughout the emergence periods on weekly intervals. If AM are detected an insecticide will be applied within seven days and will be followed by two other treatments every 10-14 days. The intensive insecticide control program method begins with detection of AM using trapping or a degree-day model. The pesticide treatments continue on the same spray schedule as the high density trapping option. This approach can be broken down into three different methods. First, low density trapping can occur at the known region of earliest AM emergence and will continue through the early emergence period. In this method, all growers would base their timing decisions on regional trapping data. Second, site-specific trapping can be implemented where a grower can provide data for a particular orchard. In this approach traps can be placed more frequently in the orchard, 40/640 acres vs. 5/640 acres for the low density trapping method. Finally, the degree-day model can be used as an alternative to trapping to determine early AM emergence. Sprays should begin at 900 degree-days above 50oC starting with January 1, and they should be repeated every 14 days.
The following table contains predicted emergence dates for several Virginia counties during the 1996 season. Dates of first emergence vary by more than two weeks.
|County||Date of 900 DD|
The Brazilian protocol has a strict threshold for AM, and growers need to be very careful in their methods for monitoring and spraying their orchards. Up to date degree-day data should be kept of the orchard especially the date on which 900 degree-days were reached because that is when spraying will begin. During trapping, the traps that caught the flies and the date of capture should all be recorded. This could help in later comparison with the degree-day data to see how accurate it was in predicting first adult emergence and whether more flies were caught on the edge of the orchard or in the center. Finally the spray records should be complete for reference by inspectors enfocing the protocol.
Gutierrez, N. 1996. US apple certification protocol to Brazil systems approach for apple maggot.
Reisseg, W.H., B.H. Stanley, M.E. Valla, R.C. Seem, and J.B. Bourke. 1983. Effects of surface residues on azinphosmethyl on apple maggot behavior, oviposition, and mortality. Environ. Entomol. 12: 815-821.
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