Potato growers on guard from diseases

Managing Editor

PAINTER, Va. (June 14, 2016) — The recent confirmation of late blight in a potato field in Accomack County has last week been accompanied by the confirmed presence of a bacterial disease, Dickeya dianthacola, that caused losses for some Delaware farmers last year.
According to Dr. Steve Rideout, Virginia Tech Extension plant pathologist and director of the Eastern Shore Agriculture Research and Education Center, some of the tissue samples sent to Maine for diagnostic testing were positive for dickeya, which exhibits symptoms similar to black leg; darkened stems, wilted plants and tuber rot.
In the University of Delaware’s June 3 Weekly Crop Update newsletter, Dr. Kate Everts, Extension vegetable pathologist said samples with black leg symptoms from Delaware and Maryland potato fields have also been sent for testing.
“At this point in the growing season, there is little that can be done to prevent or manage the disease,” Everts wrote. “However, growers should avoid excess irrigation and have a balanced fertility program.”
Last year, an outbreak of Dickeya caused significant crop losses for some growers.
Plant pathologists say the bacteria has probably been in the region for a few years but on a smaller scale and weather conditions and other factors led to an increased presence last year.
It’s unclear how long the bacteria has been present in the region and economic thresholds of it are undetermined.
The bacteria is often spread from the potato seed piece and though it doesn’t appear to overwinter in Mid-Atlantic soil, there’s evidence that it can last longer in corn stubble and in brassica crops like broccoli, making it tough to pinpoint the initial source of the bacteria. Once present in a field, there is no effective chemical control to address it.
With harvest on the Virginia’s Eastern Shore a few weeks away, plant pathologists urge growers to leave fields suspected of or confirmed with dickeya to dig last and disinfest equipment with quaternary ammonium as typical sanitation products such as bleach are not effective on dickeya.
Late blight, however, has some options for prevention and control and Rideout said with frequent favorable weather conditions this year, “growers have been pretty diligent about putting on protectants” and since the confirmation he’s “imploring and begging growers to take this seriously. It can wipe out a crop if we don’t handle it properly.”
The strain confirmed on June 3, US23, can also infect tomato plants, another of the major vegetable crops on Virginia’s Eastern Shore, and was the same strain detected on tomato transplants in a Garrett County, Md. greenhouse on May 17.
Treatment options aside, Rideout said less rain would go a long way in keeping late blight under control.
“I think what we really need is drier weather,” Rideout said. “May’s been wet. It can sure get worse if it’s a wet June.”