story to find out more.
Scientists Collar Mystery Sunflower
Pest By Jan
February 1, 2002
Service scientists in Fargo, N.D., may have found the mystery culprit
behind unsightly blemishes that began turning up on confection sunflower seeds
At first, the prime suspect was a species of disease-causing
Alternaria fungus, a common pathogen of sunflower crops. But studies by
ARS scientists Thomas Gulya and Laurence Charlet with the agencys
Northern Crop Science
Laboratory in Fargo exonerated the fungus. When they sprayed sunflower
plants with fungicide and then examined the seeds later in the season, many
still harbored spots, otherwise known as kernel brown spot. When the plants
were sprayed with insecticide, however, the incidence of blemishes dropped
Acting on a tip from commercial growers who reported an insect
damaging nearby canola crops, Gulya and Charlet focused their attention on the
Lygus bug. Its main claim to fame is pestering cotton, even though dozens of
crops can serve as hosts. In the Northern Great Plains, where sunflowers are
king, the bugs mischief has primarily been confined to alfalfa and canola
crops--or so it was thought.
To find out, Gulya and Charlet conducted greenhouse experiments
in which Lygus bugs were placed on sunflower seedheads. They then sealed cloth
bags around the seedheads to confine the insects. Checks of the seeds at
maturity revealed tell tale brown spots identical to those seen in field-grown
seeds. The spots caused by Lygus bug feeding are most likely the result of
digestive enzymes the pest injects to extract nutrients.
For growers who produce sunflowers for the confectionary snack
market, such damage can doom seed harvests to a less profitable outlet:
birdseed. A longer story about the scientists detective work appears in
issue of Agricultural Research magazine on the World Wide Web.
ARS is the U.S. Department of
Agricultures chief scientific research agency.