The occurrence of hardlock in Louisiana cotton is sporadic, but it can be a serious problem. Hardlock occurs when the bolls open and the lint does not fluff. The epidemiology and influence of stinkbug injury on this problem are not fully understood. Research was initiated in 2004 on the LSU AgCenter Macon Ridge Research Station near Winnsboro, LA to study the interactions between southern green stink bug injury and fungicide applications (Topsin M WSB) on hardlock incidence and yield losses in cotton. Four fungicide/stink bug treatments were evaluated: 1) non-treated (no fungicide/no infestations), 2) fungicide/no infestations, 3) no fungicide/infestations, and 4) fungicide/infestations. Topsin M fungicide was applied to selected plots (2 rows by 10 feet) weekly for 5 to 6 week beginning at first bloom. To document boll development, white flowers on individual plants in each plot were labeled using a “snap-on tag” bearing the date of anthesis. Tags were attached to the peduncle beneath the white flower. Nylon-mesh cages were placed over all plots when crop development was approximately 2 nodes above the uppermost first position white flower and southern green stink bug adults were placed within infested plots (30 per plot). Weekly infestations (10 adults per plot) in the same plots continued until crop maturity (five weeks after initial infestation). Precipitation in the form of natural rainfall or overhead irrigation was applied weekly to all plots to enhance hardlock development. To document the effects on boll development at maturity, seed cotton was hand-havested from one row and segregated into one of four categories: 1) no hardlock, no stink bug injury; 2) no hardlock, stink bug injury; 3) hardlock, no injury; and 4) hardlock, stink bug injury.

Hardlock incidence varied considerably among treatments. Topsin M did not reduce hardlock incidence in non-infested treatments. In 2004, hardlock incidence in infested plots receiving fungicide applications was 50% less than that in infested plots not receiving fungicide applications; however no differences were observed in 2005. Many hardlocked bolls contained both hardlocked and normal locules. This pattern of incomplete hardlock could have been influenced by stink bug feeding. In both years, hardlock incidence increased dramatically in infested plots not receiving fungicide applications when compared to other non-infested treatments; however, seed cotton yields did not differ among treatments (P = 0.05). Data collection for 2006 is ongoing. This research supports previous work that stink bug injury to bolls increases the incidence of hardlock.