Yuma County, Ariz. melon growers are planning a voluntary host-free period this summer to help reduce the movement of cucurbit yellow stunting disorder virus (CYSDV) from spring into fall cucurbits.

Members of a CYSDV task force consisting of growers, pest control advisors, researchers, Extension personnel, and others met in February to share the latest CYSDV information and lay the groundwork for the program. In early March, growers and others met to adopt host-free period rules that growers could live by.

The host-free period will run from July 10 through Aug. 3. However, there is no penalty for non-compliance. The host-free effort will include all commercially-grown melons including greenhouse cucurbits.

This will be the second consecutive year for a CYSDV host-free period in Yuma County where about 1,500 acres of fall melons are grown each year.

“This will be a voluntary host-free period this summer,” said Milas Russell, Yuma County melon grower and leader of the task force. “If the virus continues to be an issue in Yuma County in 2009, the host-free period could become a mandatory program.”

CYSDV infects melons, cucumbers, and gourds, plus winter and summer squash. Spring cucurbits grown in Yuma County include cantaloupes, honeydews, mixed melons, and watermelons. Fall cucurbit production includes cantaloupes and honeydews, Russell said.

The sole vector is the B biotype of the sweet potato whitefly, Memicia tabaci. CYSDV is not transmitted in seed. The plant holds the virus for seven to nine days.

CYSDV symptoms mimic water stress and occur first on the plant's outer leaves. The interveinal chlorosis, a yellowing between the leaves, streaks the leaves that later turn bright yellow. Older leaves drop as the plant's internal transport system breaks down. CYSDV typically devastates melons by reducing fruit size and sugar content — in addition to shortening the crop's shelf life.

“The fall melon growers agreed that there needs to be a host-free period,” said Russell, who grows spring and fall melons on about 800 acres in Yuma County. He owns Sandstone Marketing Inc.

“The host-free period should run a minimum of three weeks,” Russell said. “The effort should be self-policing.” Growers are expected to disk under crop residue by July 10.

There is some conflict between spring watermelon growers and fall melon growers over the host-free period, Russell acknowledged. Watermelon growers prefer extending the crop as long as financially feasible to take advantage of good markets that could exist after July 4. They prefer that the host-free period start some time after July 10.

“From the standpoint of the fall melon producer, every commercial grower should comply with the host-free period,” Russell said.

An absolute 100 percent host-free period is impossible, Russell said, citing urban garden-grown cucurbits, plus volunteer cucurbits that sprout in fields planted later in cotton and sudangrass, as well as in summer-flooded fields.

Russell said the primary source of inoculum that impacts fall melons is later-grown cucurbits or over-summered cucurbits like watermelons that can be harvested until August.

“There's a bridge between the spring and fall melons. We're trying to create a gap,” Russell said. “I think the issue with watermelon growers can be overcome.”

A mandatory program could require the Arizona Department of Agriculture's (ADA) involvement to develop rules and possible enforcement provisions. The ADA would hold a public comment period for any such proposal.

Current economic woes in Arizona have the state legislature considering substantial ADA budget cuts that would entail staff reductions, according to Ed Hermes, the department's legislative liaison and public information officer. Hermes said a mandatory host-free period including field checks and enforcement could be a problem.

“We don't have the staff to handle compliance at this point,” Hermes said.

Russell said the ADA should not be involved unless the voluntary program fails to work. Russell called last year's voluntary CYSDV host-free period in the Yuma Valley successful, with lower fall melon virus incidences compared to 2006 numbers. About 95 percent of the commercial cucurbit acreage was disked down by July 15 last year. The host-free period was not as successful in the Wellton-Mohawk and Roll areas due to the longer watermelon season.

Russell plans to contact the county agricultural commissioner in neighboring Imperial County, Calif., to pursue possible host-free participation by cucurbit growers there. He said Sonora, Mexico cucurbit growers held a voluntary host-free program in 2007.

Kurt Nolte, director, University of Arizona (UA) Yuma County Cooperative Extension, and a task force member, supports a host-free period this summer.

“The thought is to break the cycle of the virus traveling from spring host cucurbits to the fall host cucurbits,” Nolte said. “With the host-free period, I think they are shooting right down the center and hoping for the best.”

Six weeks is the best time frame for a host-free period, said Nolte, but realistically that won't occur due to the economics of producing fall melons.

Last fall task force members Nolte and John Palumbo, Yuma Agricultural Center research entomologist, monitored whitefly in the Yuma Valley during the host-free period and noticed a substantial decrease in whitefly population and movement.

In April, Nolte and Palumbo will begin evaluating current melon varieties for susceptibility.

While CYSDV-resistant germplasm doesn't exist, encouraging research is under way at the USDA-Agricultural Research Service in Salinas, Calif. and at the Texas Agricultural Experiment Station, Weslaco, Texas.

CYSDV was initially confirmed in desert-grown cucurbits in Imperial County, the Yuma Valley, and Sonora, Mexico in fall 2006.