California strawberry growers are joining an army of federal and state researchers in the race against time to find alternative methods of growing fruit without methyl bromide and other pre-plant fumigants.

Neil Nagata, vice chair of the California Strawberry Commission (CSC) and a 45-acre strawberry producer in Oceanside, Calif., is one of the producers involved in the effort. “California's strawberry industry would not be viable today without fumigants. If fumigants were totally banned on my farm today, I wouldn't be able to survive,” he says.

Two separate issues are currently at stake — first is the eventual ban of methyl bromide from use in many crops nationwide, including California strawberries.

The Montreal Protocol international treaty was passed in 1987 to protect the earth's ozone layer. The most popular fumigant, methyl bromide,was identified in 1992 as an ozone-depleting substance. A provision called for the phaseout of this fumigant by 2005 in developed countries and 2015 in developing countries.

However, approval of a critical use exemption allowed methyl bromide's continued use in California strawberries due to the lack of suitable alternatives. The CSC is currently seeking one-year methyl bromide renewals through the 2010 crop year.

Prior to the Montreal Protocol-methyl bromide issue, the fumigant cost about $1,000 per acre in 1990, Nagata said. Today it is about $2,500 per acre. There is not enough methyl bromide to meet the California strawberry industry's needs.

The second issue is California air quality regulations designed to reduce the amount of volatile organic compounds (VOCs) released by products into the air, including alternative fumigants to methyl bromide. The VOC issue is making strawberry production a steep, uphill battle for California growers already facing the loss of methyl bromide.

Nagata is experimenting with growing strawberries without soil. Fumigants are not needed in his experimental system.

On-farm research

“It is a substrate production (hydroponic) system,” Nagata said. “The research looks promising, but it's not there yet.”

He is experimenting with the hydroponics in producing conventional and organic strawberries above ground on table-tops where a special media (substrate) replaces traditional soil.

The trials include two strawberry varieties — 1975, a proprietary variety from Berry Genetics Inc., and Albion, from the University of California. Nagata expects his production system to use less water and produce higher yields. Trials are grown under sun and shade.

“It's a learning curve that takes a long time to learn how to produce strawberries in this manner,” Nagata said. “The bottom line is making the process economically feasible.”

UC research

Kirk Larson, University of California pomologist, has years of experience with the table-top design. With the exception of one year, Larson's table-top efforts didn't pay off.

“I can't put the economics together so it's worthwhile,” Larson said. “My experience suggests the fruit quality is more inconsistent in out-of-soil cultures. The fruit size and flavor varies due to the temperature peaks.”

Temperature peaks occur when growing berries out of the ground. In soil-based strawberry beds, nighttime temperatures can drop to the mid-50s range, Larson said. Temperatures in the table-top design can dip into the 40s at night - about 10 degrees colder.

Larson said the Dutch and the Belgians led the way with substrate technology. In the Netherlands, 10 percent of strawberry production is based on a greenhouse-type system but interest has declined over the last decade.

“It's a fun system to play with — perhaps it's a marketing angle — growing strawberries without soil fumigation,” Larson said. He is interested in Nagata's trials and the end results down the road.

“It's somewhat ironic — California has the best climate and the best soils for strawberry production in the world. Now we're seeing the move out of soil culture as a result of politics. It's crazy,” Larson said.

The best hydroponic production system Larson has seen are strawberries growing in gutters in a hanging system in greenhouses in Australia, Egypt and Jordan. The gutters hang from rafters, eight inches apart.

“From underneath it looks like a fruiting wall, but it looks like a drop ceiling with gutters with the fruit hanging down,” Larson explained. “A berry picker sits on a motorized cart and reaches up to pick the fruit. Spreading the plants down the gutter produces larger plants and fruit.”

Larson is presently based at the South Coast Research and Extension Center in Irvine, Calif.

Fumigant alternatives

The California Strawberry Commission (CSC) is investing $500,000 in alternative fumigant research targeted at emission reductions through more efficient fumigation and utilizing less material.

From 1996 to 2006, methyl bromide use in California strawberries declined about 40 percent — from about 16.1 million pounds in 1996 to about 6.5 million pounds in 2006, according to the California Department of Pesticide Regulation (DPR). Methyl bromide-applied acreage decreased 52 percent.

“Alternative fumigants cost about $900 per acre,” Nagata said. “The alternative fumigants function, but not the same as methyl bromide. The best we can do currently is try to reduce the emissions by using plastics and thio-sulfate salts.”

According to the CSC, the major alternative fumigants to methyl bromide for strawberries include:

  • Chloropicrin - for soil-borne disease control to protect the root system and crown — applied by drip or shank/broadcast;

  • Telone - for soil-borne disease and nematode control — applied by shank/broadcast;

  • Inline - a Telone-Chloropicrin mixture applied by drip providing more efficiency than methyl bromide; and

  • Metam sodium - for weed control with Inline or Chloropicrin — drip or broadcast/shank application.

According to Arysta LifeScience, the U.S. Environmental Protection Agency (EPA) in fall 2007 granted a one-year commercial registration for the new fumigant Midas in 36 states including Arizona but not in California. Jamie Sears, Arysta spokesperson, said the California Department of Pesticide Regulation has not granted Midas full registration.

EPA has granted Arysta an experimental use permit for Midas on 30 acres in California on several crops, including strawberries, Sears said. A five-acre trial was conducted last fall; the remaining 25-acre trial will occur this year. The trials are conducted on fields operated by a commercial grower and the University of California.

Midas' active ingredient is Iodomethane, also known as methyl iodide. The broad spectrum soil fumigant is designed to control soil-borne diseases, nematodes, weed seeds, and insects in crops including strawberries.

According to the CSC, the USDA spent about $200 million from 1993-2004 in the search for methyl bromide alternatives.

California production

In 2006, California grew about 88 percent of the U.S. strawberry crop, or 21 million tons, valued at almost $1.2 billion, according to DPR.

California strawberry acreage totaled 36,000 acres last year with the Salinas/Watsonville area (12,827 acres), Santa Maria (7,800 acres), Oxnard (11,903 acres), Orange County/San Diego (1,753 acres), and the San Joaquin Valley (273 acres) being the primary production areas.

Planting, mulches

Nagata earned an entomology degree from the University of California, Davis in 1988. He is a third-generation strawberry farmer whose grandfather emigrated from Japan to the U.S. prior to World War II.

Nagata plants summer and winter strawberry crops annually. Bed preparation includes lifting up the rows, building the beds, and applying fertilizer. Drip irrigation tape is buried 2 inches beneath the soil. Each bed has four rows, a 64-inch center (from furrow center to the next furrow center), and the bed top is 46 inches wide.

Plastic mulch covers the strawberry beds acting in part as a second line of defense after fumigation.

According to Larson, the typical mulch keeps some fumigation emissions in the soil. Another advantage to mulch is forming a barrier between the fruit and dirt to help maintain fruit quality.

Different colors or compositions of mulch are available that influence soil temperatures — which affects plant growth and the production cycle.

Clear plastic mulch heats the soil the most by creating a greenhouse effect, Larson said. Black mulch absorbs the heat, but only transmits the heat by conductivity to the soil. Only the soil particles that touch the mulch receive the heat transfer. With clear mulch, there's no heat transfer — the heat enters the soil. Clear mulch is about 3-5 degrees warmer than black mulch.

White mulch is actually white on top and black on the bottom. The white side reflects radiant energy back into the air and the bottom black layer is a barrier against light that helps reduce weeds. White mulch is used in the summer.

Mulch also saves from one-half to one-third of the water used versus a bare strawberry bed, Larson said.

Mulches slow the rate of VOC emissions. Some fumigant breaks down in the soil, Larson said.

The different mulches allow for the efficacy, efficiency, and practicality for each operation, Nagata noted - from warming the beds, shading from weeds, keeping dirt at bay from strawberries, and minimizing released emissions.

Nagata has experimented with different colored mulches over the years. In March, Nagata's beds were covered with black, 1.5-mil thick mulch.

Nagata switched from methyl bromide to Inline three years ago. The Inline is drip-applied 30 to 45 days ahead of planting.

The fumigant issue is just one of Nagata's chief concerns about the future of California strawberry production. Farm labor is his No. 1 production cost and Nagata supports a steady, reliable, and legal supply of workers.

Water is the second largest debit from Nagata's checkbook — he pays $900 per acre-foot for Oceanside water. The infamous court ruling on Delta smelt last fall has in part inflated Nagata's water costs while also jeopardizing his future water supplies.

“Due to the smelt ruling, the Oceanside Water Department is prepared to reduce available water by 30 percent,” Nagata said. “The department will fine any user who exceeds the 70 percent cap on use by charging additional fees above the costs for the water. If the meter continues to show excess usage, the city may place physical restrictors on the meter.”

While San Diego County (where Oceanside is located) receives most of its water from the Colorado River, the area has a contract with the Metropolitan Water District (MWD) of Los Angeles, which gets some of its water from Northern California, pumped through the Delta where the smelt is precluding full water shipments south.

Strawberry pests

The major pests in California strawberries include: the fungi botrytis fruit rot, colletotrichum, phytophthora, and verticillium; and insects and mites including the two-spotted spider mite, various worms, whitefly, aphids, and lygus.

Nagata has those pests on his farm except lygus. While soil diseases and weeds are handled by fumigation, he also utilizes beneficial insects to control insect pests. For worm control, Nagata uses Success, and Agri-Mek for mite control.

Other crops

Nagata also grows 8-10 acres of blueberries each year, and 20 acres of cherimoyas, a tropical fruit with a combined taste resembling the strawberry, mango, and pineapple. Nagata's strawberry yields average about 3,000-trays per season (trays of eight, 1-pound clamshells or 12 pints) during the six-month growing season. Fields are handpicked every two to three days.

All of Nagata's strawberries are sold through Naturipe Farms. Nagata grew organic strawberries in the past for the fresh and frozen markets. However, he could not compete against lower price frozen berries from Poland.

Strawberry varieties

Three-quarters of Nagata's strawberries are the Albion variety.

“Albion has a better flavor, longer shelf life, and grows very well in the field,” Nagata said. “Albion is more resistant to powdery mildew than the Ventana variety. Albion is the shining star of the California strawberry industry.”

About half of California's strawberry acreage is planted in the Albion variety, he said.