C A L I F O R N I A
Vegetables A SPECIAL GROWERS’ REPORT OF AG ALERT ®
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Nematodes that attack carrot fields and feed on the cell contents of the roots can result in disfigured carrots, inset. Cavity spot disease, another threat, can leave carrots with lesions and blemishes. Despite some available fungicides, cavity spot is very difficult for growers to manage.
Photo/Courtesy Joe Nunez
Remedies sought for root galls that disfigure carrots
By Kathy Coatney There are two main diseases in carrots for California growers—cavity spot and nematodes. Nematodes feed on the cell contents of the roots, explained Jaspreet Sidhu, University of California Cooperative Extension vegetable crops advisor for Kern County. They cause root galls—infections that can result in disfigured, forked, hairy, or undeveloped roots. That, in turn, results in lower yields, she said. “Sometimes they’re just minor galls that could be washed away while processing,” Sidhu said. But other times, she said, they’re too big and numer- ous, and that makes the carrots unmarketable. When the growing root tip is attacked anddamagedby root knot nematodes, the rootswill bemisshapen, forked or stunted. If the carrots are too disfigured, they aren’t aesthetically pleasing to the consumers.
borne pathogens. But due to fumigant use restric- tions such as expanded buffer zones and limits on the amount of spraying allowed, it is more challenging to manage these pests. There are some fungicides available, such as Ridomil, Ranman and Reason that could be used to control cav- ity spot. But it remains a very difficult disease to man- age, Sidhu said. The crop infection may be in a field one year, then may not show up the following year. Just when growers think their crop is disease free and faces no threat, the infectionmay show up again, Sidhu said. Cavity spot is widespread in carrot production, and the pathogen expresses itself in the soil. “It’s especially challenging for the organic production because they don’t have any fungicides or biocontrol products for effective management,” Sidhu said. Researchhas been conductedondifferent organic op- tions. Sidhu said biofungicides have been hit and miss.
“And then sometimes, if you have the forked or de- formed roots, the roots pick up excessive soil from the field,” Sidhu said. That excessive soil on roots is transported to the pro- cessing facility and increases cleaning and processing costs, adding to the fallout of lower crop yields and re- ducedmarket demand. Another threat, cavity spot disease, produces small le- sions on the carrot surface. The lesions aremostly toward theupper thirdof the carrots, and there canbenumerous lesions on the carrot. Thatmeans blemishes, ugly carrots andmore unmarketable produce, Sidhu said. “Cavi ty spot is caused by di f ferent species of Pythium,” Sidhu explained, adding there is no surefire management remedy. In the past, growers have relied on broad spectrum soil fumigation to control cavity spot and other soil-
See CARROTS, Page 10
February 2, 2022 Ag Alert 9
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