Abstract
Onion thrips (Thrips tabaci Lindeman (Thysanoptera: Thripidae)) can be a pest in organic onion production on Prince Edward Island. This study was to examine the effect of planting time and variety on infestation levels and damage by onion thrips on cabbage (Brassicae oleraceacapitala (L.)). A field site was planted with 2 main and 8 lesser varieties of cabbage over 4 planting dates. Some varieties were short season and harvested on July 31 with longer season varieties harvested on September 2. Blue sticky traps were used to capture thrips migrating into the field site from July 22–September 2. Traps were counted weekly and cabbage heads within the field site were visually surveyed for thrips. At harvest, heads were weighed and measured, thrips damage was assessed then the head was dissected and thrips counted on the first four layers of the head. Thrips exhibited a preference for Lennox over Bronco throughout the season although thrips populations were not high enough to effect economic damage in 2014. Planting date influenced cabbage head weight and size with later plantings yielding the largest heads. Use of planting date and variety to avoid thrips populations is discussed.
Highlights
Onion thrips represent a serious threat to cabbage production in cabbage growing regions of the world (Garamvölgyi et al 2004; Shelton et al 2008)
Of the varieties commonly planted in Prince Edward Island (PEI), it is unknown whether thrips show a preference, or if selecting early developing varieties and planting early in the season will serve to avoid the thrips populations
The objectives of this work were to evaluate the influence of planting date and cultivar on the incidence of T. tabaci within a commercial organic cabbage planting, and determine if monitoring with sticky traps can predict thrips damage
Summary
Onion thrips represent a serious threat to cabbage production in cabbage growing regions of the world (Garamvölgyi et al 2004; Shelton et al 2008). Damage can appear as a bronze discoloration and/or a rough texture on leaves within the head (North and Shelton 1986b) causing injury up to 20 layers deep (Trdan et al 2005; Respondek and Zvalo 2008) and reducing marketable production. For Prince Edward Island (PEI), thrips can cause significant loss to the cabbage crop in organic fields. Control is often recommended at the early head formation stage (7.5 cm leaf ball) (PEI Department of Agriculture, Fisheries and Aquaculture 2005), with pesticides available for conventional producers (Shelton et al 1998; Trdan et al 2007). Cabbage planted later in the season (July 25 vs July 3) experienced less damage for specific varieties. It is speculated that these later planted cabbage heads experienced lower thrips pressure due to reduced immigration into the field (North and Shelton 1986b; Shelton and North 1986), or increased mortality due to high rainfall during the latter part of the season. Of the varieties commonly planted in PEI, it is unknown whether thrips show a preference, or if selecting early developing varieties and planting early in the season will serve to avoid the thrips populations
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