Farm Progress

Sweet orange scab is the latest citrus pest-disease found in Arizona;APHIS confirms 10 positive SOS finds in Yuma County and central Arizona;APHIS expected to implement a statewide SOS quarantine soon;Citrus growers, packers, and nurserymen prepare for new regulations.   

March 21, 2011

7 Min Read

Superman’s comic hero ability to stop a locomotive and leap tall buildings in a single bound are traits needed by the Arizona citrus industry to control pest and disease threats including the latest villain – sweet orange scab (SOS).

SOS is a fungal disease of citrus found in different citrus varieties and caused by Elsinoë australis. The result is scab-like lesions on the fruit rind and occasionally on leaves and twigs.

The Arizona Department of Agriculture (ADA) conducted public meetings in early March in Phoenix and Yuma on citrus pest and disease threats. State and federal plant pest regulators discussed the latest developments on SOS, the Asian citrus psyllid (ACP), and citrus greening (Huanglongbing disease or HLB).

“A (SOS) quarantine is coming to Arizona,” Jerald Levitt told the crowd at the Yuma Agricultural Center. Leavitt is the USDA Animal and Plant Health Inspection Service (APHIS) state plant health director for Arizona. APHIS planned to enact the statewide SOS quarantine in mid-March.

The good news is the APHIS quarantine comes at the end of Arizona’s 2010-2011 citrus season. The two citrus sectors likely to be effected the most by the APHIS regulations are packinghouses and plant nurseries. Packinghouse regulations will mostly take root this fall when the next harvest begins.

As of mid March, the APHIS laboratory in Beltsville, Md., had confirmed 10 positive finds of SOS in Arizona through DNA testing.

The Arizona SOS finds include two in commercial lemons in Yuma County, according to Gary Russell of APHIS in Phoenix, Ariz. Five positive SOS cases were found in Mesa in Maricopa County (central Arizona) including three in sweet orange and one each in tangelo and mixed citrus (four commercial finds).  Two of the three finds in nearby Queen Creek were in commercial citrus. All non-commercial finds were in residential citrus.

“This is another in a series of problems for the citrus industry in Arizona,” said Mark Spencer, citrus grower, packer, and partner with Associated Citrus Packers, Inc. in Yuma, Ariz.

“We must continue to be resilient. It doesn’t sound like sweet orange scab will be the one (problem) to put us away all together.”

According to APHIS, infected fruit can drop prematurely. The disease can stunt young citrus seedlings. SOS is spread slowly by microscopic fungal spores produced in the scabs. Trees are more susceptible to infection with new shoot growth and when petals begin to fall. As the growing tissue matures, it becomes less susceptible.

Spores can spread the disease to susceptible plants with sufficient moisture in the environment. The fungus can live through the winter in the tree canopy on limbs and on fruit infected during the previous season. Symptoms of the disease can be visually detected year around. The disease produces symptoms within a week.

SOS marketability

“SOS doesn’t affect the fruit itself or taste but it does affect the marketability of the fruit,” said Tess Williams, trade specialist with APHIS-PPQ in Phoenix.

Australia has banned the importation of Arizona citrus due to SOS, says Williams. APHIS is working to reopen the market for the 2011-2012 Arizona citrus shipping season.

About 80 percent of Arizona citrus is grown in Yuma County (mostly lemons), says Glenn Wright, University of Arizona citrus specialist. The balance is grown in Maricopa and Pinal counties. Statewide, citrus acreage totals about 17,300 acres. About one-third of the crop is exported; mostly to Japan, Canada, South Korea, and Hong Kong.

SOS was first confirmed in the United States in July 2010 in Springs, Texas near Houston on residential lemon and tangerine trees. APHIS enacted a federal quarantine in Texas and Louisiana after additional finds. Arizona and Florida are next in line.

“The only state left that hasn’t detected SOS in the continental U.S. is California,” Levitt said. “They are out looking for it.”

SOS is expected to be a smaller threat in Arizona compared to the ACP insect first found in Arizona in late 2009. The ACP is the primary carrier of HLB which has devastated Florida’s citrus industry. Every tree infected with HLB eventually dies. The fruit becomes sour and unmarketable. The pest-disease combo has impacted global citrus production.

SOS requires high levels of humidity and rain to thrive.

“The Arizona environment is not very conducive to a rampant spread of SOS,” said John Caravetta, ADA associate director and head of the plant services division. “That’s why it appears to be well managed through cultural practices.”

Suggested cultural practices include clean orchard floors and approved fungicides for SOS and citrus scab.

“Keeping the orchard floor clean is part of the process to keep from generating inoculum from infected fruit that will sporulate with the fungus,” Caravetta explained.

Citrus from quarantined Arizona will be allowed to move interstate to all states with a certificate if washed, brushed, and the fruit surface is disinfected with one of three APHIS-approved chemical treatments.

Brothers Mark and Bill Spencer are fourth generation citrus growers; each with 30 years experience in production and packing. Mark says existing company packinghouse procedures already meet most of the APHIS requirements. Tweaking at the wash line will include increased chlorine use to 200 parts per million and fungicide use during the entire packing season.

The company exports 25 percent of the fruit. Exports account for about 35 percent of the FOB sales. Japan is Associated Citrus Packers’ largest export destination followed by Australia. It takes about 21 days to ship lemons from Yuma to Australia.

APHIS requirements

Spencer’s concern is whether the new APHIS-required packing procedures will impact fruit quality during the overseas transit.

“When a container of fruit arrives in Japan or Australia they open it up and go through a representative number of cartons,” Spencer explained. Citrus with mold, skin breakdown, or tip injury on lemons can lower the price.

“If those arrivals suffer it could cost me a lot. Reduced quality could eventually cost me my markets and even my business.”

Citrus nurserymen Alan, Mark, and Stacey Loghry operate Sunset Nursery in Yuma. They are reeling from the financial pinch caused by the regulations of the ADA’s ACP quarantine enacted in part of Yuma County in November 2009. The ACP was found in the county one month earlier.

In neighboring California, the ACP was first trapped in San Diego County in Fall 2008. The insect was later found in Imperial, Los Angeles, and Orange counties. Quarantines were enacted in the counties. HLB has not been found in California or Arizona.

The dual-state ACP quarantines currently limit the Loghry’s sales to within the quarantine areas in Yuma and southern California. Prior to the ACP quarantine, Sunset’s citrus tree sales in Phoenix and Tucson comprised the majority of the company’s sales. The Loghrys can no longer ship nursery stock to those areas.

The APHIS SOS quarantine will prohibit Sunset Nursery sales in California since the state does not have the disease.

“We’re frustrated,” the Loghrys said. “We can’t ship in Arizona (outside of the Yuma quarantine) due to ACP. With the SOS quarantine we can no longer sell in California. Here we sit.”

Texas likely had SOS years before detection since the disease is so similar to other citrus maladies. Arizona is likely in the same boat; the fungus has probably for a long time.

For Yuma citrus grower Jerry Driedger, SOS is another problem that growers have to deal with.

“There’s not much we can do in the field,” said Driedger, general manager of Marlin Ranching. “SOS is extremely difficult to find since it looks like thrips scars and other damage on fruit. This will likely be a problem impacting the packinghouse, marketing, and exports, but not a significant impact on the growing side.”

Caravetta and Levitt discussed limited state and federal funds available to deal with SOS in Arizona. Caravetta says ADA will allocate more dollars to the ACP-HLB efforts than SOS since ACP-HLB is the larger threat to the state’s citrus industry.

“It’s a triage – it’s simply an assignment of priorities,” Caravetta said. “The greatest threat to the Arizona citrus industry is citrus greening.”

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