Citrus losses may be minimal from freezing nights

Oranges in Tulare County’s citrus belt are covered with ice. Growers turn on their sprinklers and the ice that forms protects the fruit from internal damage.
Photo/Cecilia Parsons

A worker in Tulare County works quickly to harvest mandarins last week in advance of a potentially damaging freeze.
Photo/Cecilia Parsons

After five long, freezing nights spent turning on water and wind machines to protect their crops, San Joaquin Valley citrus growers are hoping they have dodged widespread frost damage.

Sunday night recorded the lowest temperatures in the valley citrus belt to date and California Citrus Mutual is reporting the seedless mandarin crop has likely sustained moderate damage due to the low temperatures and their duration. Navel oranges, especially those on edges of groves in the coldest areas, sustained minor damage. Extent of the damage will not be known for several days. Citrus growing areas in Riverside, Ventura and Imperial counties experienced lows in the 30s.

Lows Monday morning were in the lower 20s in many areas, with Ducor recording 22 degrees.

On Monday morning, Joel Nelsen of California Citrus Mutual reported some freeze damage is expected in lemon and mandarin crops, but navel orange damage is not expected to be extensive. The extended cold spell, which began Jan. 10, has been expensive for California citrus growers who have spent $17.5 million on frost protection last week.

Seventy-five percent of the valley's navel orange harvest remains in the field. Harvest for the Murcott and Tango mandarin varieties harvest begins this month. Only 30 percent of the Valley lemons have been harvested.

"(Sunday) night, the cold began earlier and it stayed cold," said Nelsen. There was little cloud cover to provide much of an inversion layer that makes wind machines more effective.

Mandarin growers were running their wind machines at least 13 hours in the coldest areas. Navel growers started about 1:30 a.m. Many growers began running water in their groves earlier in the day to warm the ground.

On previous nights, there was enough of an inversion layer that made wind machines more effective in drawing down warmer air aloft. By Saturday night, skies were clear with little cloud cover, extending the duration of low temperatures. Low temperatures in the mid-20s were recorded throughout the citrus belt with lows reaching 25 degrees in a few areas.

Nelsen said duration of cold temperatures is the critical factor. Even though temperatures dropped lower and for longer periods of time during Saturday night, Nelsen said it was not significant enough to cause widespread fruit damage. Fruit on edges of groves farthest from wind machines are expected to incur some damage. Ice crystals forming inside the juice sacs will cause them to burst and the fruit will dry out. The mandarin crop is most likely to see frost damage due to the thinner skin of the seedless fruit, he said.

At this point in the season, navel oranges have reached a higher sugar content and are better able to withstand freezing temperatures for longer periods of time.

Cold temperatures averaging in the low 30s hit citrus production areas in Ventura, Riverside and Imperial counties where fruit has a higher sensitivity to cold due to overall higher temperatures. No damage has been reported where frost protection was provided.

While the freeze event may have shifted grower priorities last week, the Asian citrus psyllid is still a chilling factor in this year's citrus harvest.

This pest, which can carry the deadly citrus disease Huanglongbing, or citrus greening, was trapped in two San Joaquin Valley sites in October and November—the first time the pest has been found in the state's prime citrus growing area. The single adults are believed to be hitchhikers into the area and not a signal of an established breeding population of ACP.

Trapping and visual surveys around the two sites have failed to find additional ACP.

In Tulare County, 163 square miles—a five-mile radius around two sites where ACP were trapped late last year—are restricted areas. Citrus nursery stock cannot be moved outside the area unless it was grown inside an insect-proof structure. Citrus harvested inside the restricted areas must either be packed inside the area or be cleaned of stems and leaves before it is moved outside.

On Dec. 31, CDFA announced another option. Growers with citrus inside the two restricted movement areas in Tulare County can opt for chemical treatment prior to harvest to minimize spread of ACP.

This treatment option is much less expensive and favored by growers, said Tulare County Agricultural Commissioner Marilyn Kinoshita. The option had to first be approved by CDFA and updated compliance agreements are required. Growers can choose from a list of approved products, time the application prior to harvest and treat. Kinoshita said they have seven days after treatment to complete harvest. Cost of the treatment option is half of the $10- to $15-per-bin cost of running fruit through a packing line.

Porterville lemon grower John Konda, who grows citrus inside the Terra Bella restricted area, said the chemical treatment is a much better option cost-wise in spite of the extra paperwork required.

Growers outside the restricted areas have not been impacted by the ACP requirements. Leonard Massey of B&Z Nursery said the restricted zones, which are smaller than the normal 20-mile quarantine zones, do not include any large commercial nurseries.

Even with the recent freeze, University of California researcher Beth Grafton-Cardwell said she isn't convinced the ACP threat is gone in the valley. The pest doesn't move much in cold weather, but when temperatures warm up, they could still be found, she said.

Citrus growers hoping that the freeze wiped out any ACP lingering in the San Joaquin Valley should know that is not the case, said Shirley Batchman, director of governmental affairs for CCM. On a trip to Florida, Batchman said she visited an ACP research laboratory where she was shown a container with frozen ACP.

"When they began to thaw, they started moving," Batchman said. "It can't get cold enough to kill them, so don't count on that."

The ACP trapping program in Southern California counties continues to find the pest, Grafton-Cardwell noted. Researchers are also working on a better ACP trap. Grafton-Cardwell said the pest is attracted to color and volatile oils—both found on citrus leaves and the yellow sticky traps currently in use—don't specifically attract ACP.

(Cecilia Parsons is a reporter in Ducor. She may be contacted at ceciliaparsons8@gmail.com.)

Permission for use is granted, however, credit must be made to the California Farm Bureau Federation when reprinting this item.