Pomegranate growers face threat of black heart disease

Pomegranate growers face threat of black heart disease

Heart rot diseases may go undetected initially and are a major challenge to pomegranate growers.

From advice on ways to clear pomegranates for the most lucrative export markets for the United States to pointers on how to combat the worst insect pests, growers in the central San Joaquin Valley recently were provided with a trove of advice.

They were told of precautions they can take for export of the fruit, along with tips on how to combat diseases that could sour their markets in the United States and abroad.

The advice came during a pomegranate workshop at the Kearney Agricultural Research and Extension Center in Parlier, Calif.

The session opened with a talk from Jim Adaskaveg, a professor of plant pathology with the University of California at Riverside, who talked of the importance of complying with import protocols set by lucrative markets that include the Republic of Korea.

He said gray mold posed the greatest threat to sales in that market, and in 2000-2001 there were crop losses of up to 50 percent because of it. That percentage has been cut considerably due to actions taken by the industry since then.

Today, the biggest challenges come from “heart rot,” diseases that may go undetected initially. Because of those challenges, Paramount Farming Co. has stepped up to fund research.

Adaskaveg said gray mold remains a major problem for Korean importers. It results from flower parts being infected at bloom time. When it comes to pomegranates going into South Korea, two postharvest decays are regulated under quarantine: Alternaria “black heart disease” and dry fruit rot.
For exports to Korea, Adaskaveg said, growers must register orchards and packinghouses with the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service. Field requirements include removal of old branches and fruit; training of pickers, graders and others in identification of Alternaria decay; and inspection of 2 percent of each consignment before shipment.

The bottom line, Adaskaveg said, is that “black heart” cannot be managed by postharvest treatments for the fungi that cause the decay, Aspergillus niger and Alternaria. He said black heart infestation is often not visible from simply looking at the fruit, but infested fruit often weighs less than healthy fruit.

Chlorine washes help lessen the risk of damage from gray mold and penicillium decays, he said. along with removal of contaminated fruit  and treatment with a postharvest fungicide like Scholar.


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Other speakers at the workshop included:

• Maxwell Norton, UC farm advisor in Merced County, who talked of the biology of pomegranate trees.

He noted they are native to Iran and India, like hot and dry summers and can be damaged by very cold temperatures. Norton said the trees are tolerant of saline soils and, although drought tolerant, they benefit from irrigation to produce better yields and larger fruit.

Applying “even moisture” may reduce splitting, Norton said, and researchers are looking at applying boron to counter splitting as well. But Norton cautioned that some soils, notably on the West Side of the San Joaquin Valley, may already be high in boron.

Norton said there is some experimentation with mechanical harvesting for juice. Among challenges is the fact that fruit ripens at various times, he said, meaning “it’s rare to get away with just one picking.”

Pomegranates are self-pollinating.

More details are available at http://ucanr.edu/sites/pomegranates.

Weed control

• Richard Molinar, UC farm advisor for Fresno County, who talked of weed control in pomegranate orchards.

Molinar cautioned that annual weeds can produce thousands of seeds and said the best way of avoiding the spread of weeds is to prevent them from going to seed, “keep weed seeds out of the soil profile.”

Two weeds, both of which are Roundup resistant, are major seed producers, he said. A single horseweed or marestail plant can produce as many as 800,000 seeds, and a fleabane plant 120,000.

Prowl, Goal and Surflan are among effective pre-emergents for controlling some weeds, Molinar said, and Prowl is most commonly used. Shark and Roundup are commonly used post-emergents, and it’s best to use them “at the youngest stage; if weeds are 6 inches tall, they’re difficult to control,” Molinar said.

He cautioned growers to beware of spreading some weeds with cultivation, citing the example of Johnson grass and nut sedge. “Be sure to kill them, not spread them,” Molinar said.

More details are available at http://ucanr.edu/sites/weed_management/.

• Themes Michailides, plant pathologist with UC Kearney, talked of research he and others have conducted on black heart disease with the help of funding from Paramount Farming Co.

Michailides said infections from the disease occur during bloom and the most vulnerable stage is when flowers are fully open. Fungicide sprays are effective in reducing the threat, but because flowers open in various stages, a single spray is not sufficient.

Michailides said holes in the fruit can be pathways for infection as well. Those can be made by insects that include the leaf footed bug, cracking of the fruit and thorns.

Tree decline, which devastated a Firebaugh orchard in 2008, is likely linked to very low temperatures, Michailides said. He said the orchard lost half its trees.

A sudden drop in temperatures in late fall and early winter in milder areas where the trees are not fully dormant is the main contributing factor to tree decline, Michailides said.

Root wreckers and mites

• Mike Konda, with the Fresno County Department of Agriculture, discussed management of gophers, terming them “root wreckers.”

Aside from damage the critters do to trees and plants, he said, they also can cause water loss as it pours into old gopher tunnels.

Owls are natural predators, Konda said, advising that it’s best to choose “old barn wood” over new plywood when building an owl box.

Macabee traps can be used to kill gophers, he said, along with strychnine. The poison can be dispensed with a machine pulled behind a tractor intersecting the burrow runs. Or it can be placed by hand using probes.

• David Haviland, UC farm advisor in Kern County, talked of insects and mites that pose problems for growers of pomegranates.

Among them is the cotton aphid, which was also discussed by Larry Godfrey, UC Cooperative Extension specialist with UC Davis.

Godfrey and Haviland talked of how the cotton aphid over-winters in pomegranates, and then migrates to other crops where it can cause significant damage. For example, it may carry the tristeza virus into citrus.

The damage it causes in pomegranates includes reduced shoot growth, damage to leaves, honeydew on fruit, rotten spots where fruit touch and sooty mold on the outside of fruit.

There are biological controls, Haviland said, along with chemical controls that include Lannate.

For pheromone management, Godfrey said, it’s best to combine two compounds, nepetalactone and nepetalactol. Use of neonicotinoid pesticides is being challenged because of the effects on bees.

Another pest is the tiny citrus flat mite, which causes scabbing of the fruit starting at the stem end. Sulfur dust or wettable sulfur can be used to control the pest, and Haviland said the wettable sulfur is less harmful to beneficial insects.

Katydids can cause damage by biting fruit, resulting in a “corky patch.” Delegate and Lannate are among pesticides that can be applied, Haviland said, cautioning growers to be sure to check the labels.

The leaf footed plant bug can open the way to secondary infection and it also can be controlled with Lannate.

The grape mealybug can leave honeydew deposits that lead to sooty mold, Haviland said. Material for control includes Applaud.

Other pests include the omnivorous leaf roller, which Haviland said can be controlled by using degree days to time treatments.

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