Late season and overwintering management of the large raspberry aphid

Late season and overwintering management of the large raspberry aphid

Summary

In the Pacific Northwest, an emerging complex of viruses in raspberry has caused symptoms of crumbly fruit, resulting in lowered fruit quality and shortened life of the field. One of the important viruses is raspberry leaf mottle virus (RLMV), transmitted by the large raspberry aphid, Amphorophora agathonica. Infection rates of 100% are commonly seen in fields only four years old. Control of RLMV depends on effective management of the aphid by targeting life stages that are responsible for virus spread to new fields, such as the winged morph of the aphid, or exposed life stages, such as the overwintering egg.

Objectives/Performance Targets

1. Determine the late-season interval when control of aphids is important for reducing raspberry leaf mottle virus (RLMV) in raspberry, and if there is a date after which aphid control is unnecessary. Evaluate the effectiveness of lime sulfur, lime sulfur with dormant oil, and neem oil for suppressing aphid egg hatch.

Accomplishments/Milestones

Objective 1: From September through November 2011, 100 raspberry canes (‘Meeker’) were inoculated with RLMV by the aphid vector Amphorophora agathonica. In 2012, leaves from the floricanes and new primocanes of the plants were tested in the laboratory for RLMV. None of the plants experimentally inoculated in the fall tested positive for the virus in the spring. These results indicate either a) late season is a poor time for successful inoculation of the virus, or b) that the aphids were unsuccessful at inoculating with RLMV for some other reason.

The study was repeated in 2012 with some modifications. Ten ‘Meeker’ raspberry canes were inoculated weekly with aphids carrying RLMV from August to November 2012. Additionally, a set of 10 control plants were inoculated in the greenhouse each week with viruliferous aphids.

Work remaining: In spring 2013, the plants in the field and in the greenhouse will be tested for the successful inoculation of RLMV. If there is no effect of the late season on the rate of infection with RLMV, there will be no difference in infection rates between the field inoculated and greenhouse inoculated plants; however, if late season conditions have an impact on how successfully RLMV infects the plants, there will be differences in the infection rate between the field and greenhouse plants.

Objective 2: Amphorophora agathonica eggs were obtained during fall and winter 2011 by caging adult aphids with potted ‘Meeker’ raspberry plants. Eggs laid on raspberry leaves were removed and surface sterilized. The eggs were treated in February 2012 with lime sulfur, stylet oil, lime sulfur + stylet oil, Neem oil or water control in a Potter spray tower. Eggs sprayed with lime sulfur and lime sulfur + stylet oil had approximately 99% egg hatch suppression over eggs that were sprayed with water only.

Work remaining: Aphids were again caged with potted ‘Meeker’ plants in fall 2012 with plans to replicate the study in February 2013.

Impacts and Contributions/Outcomes

This research benefits producers in the Pacific Northwest region by informing aphid management at two points in the growing season – in the fall and in the early spring. Aphid flight between fields in the fall could be an important contribution to virus spread if plants are still susceptible to virus inoculation late in the year. Objective 1 addresses this question by looking at how susceptible plants are to acquiring RLMV, an aphid transmitted virus, at the end of the growing season under field conditions. At the beginning of the season, aphids which survive the winter will be the beginning of the next generations. One way to lower early establishment of aphid populations is to prevent eggs from hatching. Objective 2 examines the effect of lime sulfur, an agent already applied in raspberry fields for disease control in early spring, as well as other organic products on the suppression of aphid egg hatch.

Work remaining: Fact sheet on Raspberry aphid by Oregon State University Extension is in the process of getting approved. Final results will be included in a publication.

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