Keeping pest populations lower for longer: capturing the benefits of native vegetation

Date Issued:2012-03-27

Abstract

The relative timing of pest and beneficial arrival in the crops, and how the landscape context facilitates or hinders colonization processes is thought to be one of the key processes of lower pest populations. Early removal of pests avoids future damage, and often more importantly, it avoids future damage by the pests' offspring. Using crop scouting reports from the Border Rivers region of 4 fields with either low (<2%) or high (<20%) surrounding native vegetation, we evaluated for focal pests the: a) number of days to reach threshold, b) number of days above threshold, and c) number of above-threshold events. Our results show that pest population rarely reached threshold; only four species broke threshold for a total of 31 times in four years. We found no difference in the number of days to reach threshold between the two native vegetation treatments. However, there was a slight trend for aphids and Green Vegetable Bug (GVB) to spend more days over threshold in fields with low native vegetation (LNV) than in fields with high native vegetation (HNV). The opposite was true for plants infested with mites, which were above threshold for more days in fields with HNV. When considering all of the times that pest populations went above threshold, the LNV fields had an average 'broken-threshold' score twice as high as the HNV fields, and by comparison three organic cotton fields only broke threshold on average once a year. Further, when considering natural enemies, there was a significant but weak correlation between predatory beetles and aphids in HNV fields, but not in LNV fields.Ultimately this work was undertaken to evaluate the merit of simple measures to capture the value of native vegetation for the ecosystem services of pest control. Although additional study should be undertaken, the results have identified that there is scope to change crop scouting sheets for better capture of information to measure the value of native vegetation, and provide spray decision guidance. The new crop scouting report format could incorporate a section to track population trends of pests and beneficials over time, also allowing for easy accounting of the above measure. The results from this project suggest that these simple measures have merit when trying to link effects from native vegetation with the ecosystem services of pest control, but an investigation of more fields and regions is warranted.

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