California Central Coast strawberry growers Jerry Cardenas and Vividiana Gomez peered over their fields in late July with a solemn look ingrained on their faces.

A strawberry disease called pallidosis-related decline (pallidosis, for short) was killing their strawberry plants, and robbing the growers of fruit and income to pay the bills.

“I estimate my losses at about $300,000 from the disease on about 31 acres of strawberries,” said Cardenas, a second-generation grower.

Cardenas is the owner of Big J Produce near Santa Maria in Santa Barbara County, the third-largest strawberry-producing county in California.

“This is a serious financial loss for us,” Cardenas said.

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Cardenas’ farm is located in the heart of the Santa Maria Valley, about seven miles east of the Central Coast.

Cardenas is one of about 400 strawberry growers in California. Combined, these growers earned about $2 billion in farm income in 2011 from about 38,000 acres of berries.

About a dozen of Cardenas’ 90 acres of strawberries were severely infected with the disease. Of the two strawberry varieties grown, the most damage was in the San Andreas variety. The BG-1975 variety had less damage.

Cardenas removed 50, 40-inch strawberry beds with 75 percent to 100 percent of pallidosis disease. About 75 beds were 35-50 percent infected.

Cardenas is growing strawberries on a one-year land lease.

Pallidosis disease symptoms

The symptoms of pallidosis-related decline in strawberry include stunted plant growth, brittle roots, purple foliage, and the eventual death of the plant, according to Surendra Dara.

Dara is the University of California Cooperative Extension (UCCE) strawberry, vegetable, and IPM farm advisor in Santa Barbara and San Luis Obispo counties. 

The extent of infection can vary from mild disease symptoms to total plant dieback.

Once inside the plant, viruses can remain systemic in the plant tissue. The plants must be removed.

For the disease to occur, one of two viruses must be vectored to the plant by the greenhouse whitefly, Trialeurodes vaporariorum: strawberry pallidosis associated virus or beet pseudo yellows virus.

Avocados, caneberries, grapes, lettuces, peppers, tomatoes, and ornamentals are hosts for the greenhouse whitefly.

Examples of non-whitefly transmitted viruses required for pallidosis disease to occur include: strawberry necrotic shock virus, transmitted by pollen; or strawberry mild yellow edge virus, transmitted by aphids.

Aphids are not typically a problem in strawberry.

No chemical product can prevent or control the disease; not even fungicides or soil fumigation.

PCA input

For Cardenas, plant discoloration started around May 1 as the plant turned from a normal green color to a purple shade. Plants were dead by late May and into early June. Cardenas immediately contacted pest control advisor (PCA) John Gracia of AG RX in Santa Maria.

After plant examination, Gracia first thought mites could be the culprit. Yet in March, the miticides Epi-Mek and Acramite were applied to the crop. Due to a heavier than normal whitefly population this spring, Gracia had prescribed the insecticides Courier, Esteem, and Oberon which provided good whitefly control.

“The disease was most likely brought in by the whitefly,” Gracia said.

The whitefly is generally not a major concern in strawberry production in the valley. Yet an increase of strawberry acreage likely increased whitefly numbers.

“In the future, we have to be more aggressive on whitefly control,” Gracia said. “We cannot afford to take the risk anymore.”

Given the situation, Gracia says area-wide grower control of whiteflies is needed to protect the crop.

“If one strawberry grower keeps their field clean but their neighbor doesn’t then none of the fields will stay clean,” Gracia said.

He says additional research is needed on the disease and related viruses.

Gomez crop damage

A few miles north of Guadalupe in San Luis Obispo County, Viridiana Gomez stood by her pick-up parked next to a 13-acre field of San Andreas strawberries grown by the Gomez family.

Viridiana’s father, Juan Gomez, is president of Del Campo Berry Farms, based in Santa Maria.

This is the Gomez family’s first crop of strawberries. The transplants were planted last October. The Gomez’s first noticed the plants changing colors in March. Two to three weeks later some plants were dying.

“When we first saw a problem, we didn’t have a clue on the cause,” Viridiana said. “We thought it might be a soil problem or a chemical issue.”

The Gomez’s PCA took a sample which was submitted to a lab for analysis. The sample came back positive for pallidosis.

About two-thirds of the Gomez crop has been lost to pallidosis. The strawberry crop was grown for the juice market. Dead plants were removed. New transplants were planted.

“The field looks like its getting better now,” Gomez said.

Strawberries are nearly a $2 billion crop in California.

Pallidosis management

The greenhouse whitefly is a one-millimeter-long insect with four nymphal instars which are flat, oval, and transparent. Fifth instar nymphs move around as crawlers searching for a preferred feeding site on the leaf.

Laboratory analysis is critical to determine if the plant malady is present. Growers can provide samples to UCCE or county agricultural commissioner’s office for no-charge testing. Samples can also be sent to commercial labs.

Heather Scheck, plant pathologist with the Santa Maria agricultural commissioner’s office, received nearly 20 suspect samples for testing. One sample tested positive for pallidosis.

Unknown is the amount of pallidosis in California strawberry-growing regions. Pallidosis disease was first reported in California in 1975.

Dara recommends these methods to help limit the disease:

  • Utilize good agricultural practices, including regular monitoring, communication, and collaboration between growers and PCAs, to limit the spread of the vector and the pathogens.
  • Use clean transplants;
  • Rotate chemical insecticides with different modes of action for vector control;
  • Alternate with botanical or biopesticides;
  • Conserve natural enemies;
  • Timely control of pest infestations especially in upwind fields;
  • Timely diagnosis of the pest and disease; and a
  • Host-free period to break the disease transmission.

Several web pages with information on the disease can be found online, including the UC IPM pest management page at www.ipm.ucdavis.edu/PMG/r734101211.html. Dara has several online articles available at http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=10523and

http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=10824.

California strawberry growers produce almost 90 percent of the nation’s crop, according to the California Department of Food and Agriculture. Strawberries are the state’s 14thlargest exported crop with export values of about $336 million.

The leading strawberry counties include Monterey, Ventura, Santa Barbara, Santa Cruz, and San Luis Obispo, respectively.

cblake@farmpress.com

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