Growers feared that brown stink bug, an invasive insect that moved into California’s southern desert several years ago from Arizona, would damage cotton in California as in the southern U.S. In the south, primarily Georgia, boll rot and cotton staining created by brown stink bug feeding causes serious economic losses.

Brown stink bugs feed on cotton bolls causing smaller bolls to fall off of the plant. Damaged bolls that remain on the plant have smaller seeds. In the southern U.S., brown stink bugs vector pathogens such as boll rotting bacteria that stain cotton and cause cotton boll rot. Brown stink bug often migrates into cotton from nearby host plants such as broadleaf weeds, corn, sorghum, millet, and snap beans. The presence of host plants in close proximity to susceptible crops, like cotton, increases the difficulty of managing brown stink bug.

The fear of similar losses in California from brown stink bug prompted many growers to apply more insecticides than in the past on their cotton fields to prevent brown stink bug feeding and resulting cotton boll losses. To learn more about brown stink bug, affiliated Entomology Advisor Vonny Barlow monitored commercial cotton fields to determine the extent of damage brown stink bug was causing. He compared two sampling methods: using a sweep net and pheromone traps.

Barlow observed that both sampling methods yielded brown stink bugs. More bugs were found in pheromone traps over the same time period when compared to sweep sampling, but pheromone traps were more labor intensive than sweep net sampling. He did not observe a relationship between internal boll warts from feeding bugs and cotton boll rot. Barlow concluded that in Southern California, boll rot from brown stink bug feeding may not be an issue for cotton. These findings suggest that insecticide applications for brown stink bug may not be needed in cotton, saving growers the cost of unnecessary insecticide applications. And by not applying an insecticide for brown stink bugs, secondary pest outbreaks of spider mites and aphids are prevented.

A survey of growers following Barlow’s research determined that growers in the Palo Verde Valley were not applying pesticides and damage from boll rot was extremely low. "Once we figured out brown stink bug was not doing serious damage, we stopped spraying," says a local pest control adviser.