Damage assessment and action threshold for mirids, Creontiades spp. in Bollgard II cotton in Australia
1QDPI&F, Plant Science, Kingaroy, QLD, Australia and
2QDPI&F, Plant Science, Toowoomba, QLD, Australia
Correspondence: moazzem.khan@dpi.qld.gov.au
Two species of mirids, green mirid (GM), Creontiades dilutus (Stal) and brown mirid (BM), Creontiades pacificus (Stal), have emerged as important sucking pests in Bollgard II cotton in Australia. In conventional cotton mirids have been well studied as pests of the seedling and squaring stage, while in Bollgard II cotton they are found throughout the season and little is known about their damage in the boll stage. We conducted a series of glasshouse and field trials to understand mirid damage in Bollgard II cotton and to develop an action threshold for the pest. Trials showed that while GMs were abundant throughout the season, BM's were found mainly later in the season and GMs were the dominant species. The nature of damage for both GM and BM at boll stage was similar. At boll stage mirid damage caused black spots on the boll wall, warty growth inside the boll wall and brown colored lint. Bolls up to 20 days old incurred significantly more damage then older bolls; preferred age being 15 days or less and bolls less than 7 days old could abort. All stages of mirids caused damage to bolls and damage is cumulative. However, 4th and 5th instar nymphs and adults caused significantly more damage than younger nymphs. Trials also showed that in Bollgard II cotton at squaring stage (from emergence to 60% plants with first flower), plants recovered later in the season from the damage caused by 4 mirids per meter provided fruit loss was <40%. Early boll stage (from 60% plants with first bolls to 60% bolls at 25 days old) was the critical stage for mirid damage and 3 to 4 mirids per meter caused significant yield loss. At late boll stage (from 60% boll at 25 days old to harvest) mirids failed to cause any significant yield loss. These findings were used to recommend and action threshold for mirids in Bollgard II cotton in Australia.