Skip to main content
ARS Home » Plains Area » Fargo, North Dakota » Edward T. Schafer Agricultural Research Center » Sunflower and Plant Biology Research » Research » Publications at this Location » Publication #121415
Title: KERNEL BROWN SPOT ON CONFECTION SUNFLOWERS: DISEASE OR INSECT INDUCED PROBLEM?

Author
item Charlet, Laurence
item Gulya Jr, Thomas
item BILLER, C - NDSU PLANT DIAGNOSTIC LAB

Submitted to: Proceedings Sunflower Research Workshop
Publication Type: Proceedings
Publication Acceptance Date: 2/1/2001
Publication Date: N/A
Citation: N/A

Interpretive Summary: A new "problem" has been observed on the sunflower nutmeat used in the cereal and snack food industry. "Kernel brown spot" is the name applied to sunflower kernels which have a single, brown to black spot on the blunt end, and there is no visible damage on the exterior of the seed (hull). Since the cause of this brown spot is unknown, studies were conducted in commercial fields, and in the laboratory and greenhouse. Sprays with insecticide considerably reduced "brown spot" while fungicides had little or no effect. The same fungi were found on both healthy and "spotted" kernels, which also helps to rule out the involvement of fungi. Since many individuals have reported seeing the tarnished plant bug (Lygus species) on sunflower, canola and other crops in the Dakotas, some trials were done in the greenhouse. When Lygus bugs were put onto sunflower heads in bloom, and covered with cloth bags for several weeks, the resultant seeds had brown spots. This strongly implicates the Lygus bug as the prime cause of kernel brown spot.

Technical Abstract: Kernel brown spot, observed for the first time in 1998 on dehulled confection sunflowers grown in north central United States and adjacent Canada, is unlike any previously documented insect or fungal damage. While brown spot' does not directly affect yield, confection users in the food industry have set very low tolerance levels, thus elevating the consequences for what might otherwise be considered a cosmetic problem. Field, laboratory and greenhouse studies in the last two years have ruled out fungi as a primary causal agent, focusing attention on insects. Greenhouse trials with Lygus, the tarnished plant bug, along with numerous observations of increased numbers of Lygus in blooming sunflower fields, point to feeding by Lygus on developing seeds as the probable cause of kernel brown spot. Multiple sprays with registered synthetic pyrethroids during bloom significantly reduced the incidence of brown spot, but did not eliminate the problem completely.