A project focusing on the control of thrips in strawberries has identified a weed which is acting as a reservoir for the pest, allowing them to quickly repopulate in crops after control measures.
The A Lighter Touch-Strawberry Growers NZ project is focusing on the control of thrips, in particular the species Frankliniella intonsa (intonsa), which continues to be a challenging pest to control in strawberries in mid-summer in the Auckland and Waikato regions. Barker’s of Geraldine is also supporting the project, and Bioforce through provision of the biological control agents (BCAs).
The first stage involved landscape scouting for intonsa thrips to determine which plants the thrips population builds up on prior to migrating onto strawberry crops in mid-summer. The second part tests the effectiveness of three different predatory insects, or BCAs, in controlling pest thrips.
The Landcare Research team carrying out the landscape survey for thrips near strawberry fields in Auckland. Credit: Landcare Research.
Landcare Research undertook the first stage this past summer, starting the season by surveying both the strawberries and other vegetation up to 250 meters from a west Auckland strawberry field that has battled high thrips pressure for years. The focus was on flowering plants as both intonsa thrips, and another strawberry pest species Frankliniella occidentalis (western flower thrips) are flower-inhabiting thrips.
In November, intonsa thrips were found only in low numbers in the strawberry plants, but were completely absent in surrounding vegetation in November and December. However, western flower thrips were abundant during the same period in the strawberry plants and continued to be present in the strawberries and other vegetation until February, except in white clover in November.
In January and February, intonsa thrips reached high numbers in strawberry as well as in white clover but were not found in other vegetation, except in narrowleaf hawksbeard in February.
White clover was found to be the main weed host for both thrips species late in the season. Credit: Landcare Research.
The survey work showed white clover is the main weed host for both intonsa and western flower thrips late in the season. It is serving as a reservoir for both thrips species, allowing them to quickly repopulate strawberry fields after control measures have been taken. The results also found that western flower thrips were the most abundant thrips species in the field surveyed.
Identifying white clover as a reservoir for the pests opens the door to potential new control measures, including releasing BCAs which predate against thrips into surrounding clover, as well as the crop, or removing the clover, and with it a large nearby thrips population.
The next step for this project will be to evaluate the effectiveness of three different BCAs against both thrips species.
