Four-wheel drive tractors are providing tow-truck service following heavy rainfall late last week that soaked the nation’s “winter salad bowl” region in southern Arizona and California, plus northern Mexico.

Last Friday, the day after the heaviest downpours, tractors chugged to pull vegetable harvesting machines buried in 3 feet of mud from rain-drenched vegetable fields.

The El Niño storm pummeled the region where about 90 percent of the U.S. supply of winter vegetables is grown. The first rain fell last Tuesday and was followed by a gully-washer Wednesday night and Thursday on the once hard desert soils.

The last major rain storm of this magnitude dates back to the early 1990s.

“For the three days after the storm (last Friday through Sunday) we experienced about a 30 to 40 percent reduction in harvesting as a result of the Thursday rain event,” said Kurt Nolte, director of the University of Arizona Cooperative Extension, Yuma County, Yuma, Ariz.

On Monday Nolte said harvest was about 75 percent to 80 percent of normal in most head lettuce varieties. The harvest of baby leaf lettuce acreage was still down.

Nolte says about 3.5 inches fell in the Bard-Winterhaven area of California which is adjacent to Yuma just across the Colorado River (the border between Arizona and California). About 2.8 inches fell in Yuma County; more than the annual precipitation amount in recent years.

“We exceeded our annual rainfall in about 12 hours,” Nolte said. “We had a massive rainstorm between noon and 6:00 p.m. Thursday.”

Over the weekend iceberg lettuce prices increased to about $12 per 40-pound carton, up from about $8 last Wednesday. Iceberg prices Monday were about $15, almost double since before the storm.

If El Niño-associated rains continue over the next few months, Nolte believes head lettuce prices could hit the $25/carton range, if the ground does not dry significantly.

Each iceberg lettuce carton contains about 24 heads.

While the skies have since cleared, another one-half inch is predicted this Wednesday plus the same amount this weekend. The long-term forecast is for above-normal rainfall in the area through March.

“They are still slogging around in about 12 inches of mud even though we’ve had several days of good weather and some drying has occurred,” Nolte reported Monday. “There is so much water standing on the ground. Even though we have some harvest crews in the field they are very inefficient in terms of their mobility.”

Without additional rain, Nolte believes vegetable harvesting, planting, and field work could be resumed fully in seven to 10 days.

The weather-related disruptions include a myriad of issues beyond the vegetable harvest. Muddy fields prevent growers from moving spray equipment into fields to manage pests and diseases.

“We are very concerned about powdery mildew, bottom rot, and root rot because the soil is so saturated,” Nolte reports.

Another timely issue is needed fertilization. Due to the saturated soil conditions, tractors cannot gain field access to apply needed liquid fertilizer to plants a month away from maturity.

The winter vegetable-growing season generally runs from September to early April. About 90 percent of the last head lettuce planting is now in the ground, Nolte says. About 70-80 days are required to grow a head lettuce crop at this point in the season.

About 125,000 acres are planted in winter vegetables in Yuma County, including about 95,000 to 100,000 acres of leafy greens.

Soggy fields also have limited cultivation, weeding, and thinning. Since last Thursday’s deluge the top layer of soil, about one-quarter inch, has dried. The layer has created a crust that can hamper seedling emergence.

“It almost acts like a dried frosting on a birthday cake; it crusts over and it’s very hard,” Nolte said. “The top layer could cause quite a bit of damage in subsequent days because we can’t get in the field to break up the layer.”

In Imperial County’s Bard-Winterhaven area about 4 inches of rain fell last week on Topflavor Farms, says owner-operator Steve Alameda. Three inches of rain alone fell last Thursday on the 1,000 acre vegetable operation.

“Harvest is a mess,” Alameda said. “We’re trying to make the best of it. We’re trying to make our orders. People place orders and we have to do our best to fill them.”

Alameda is harvesting about 20 percent to 25 percent less produce due to the mud and the difficulty maneuvering through the field. He is moving produce trailers from the field with one-third to one-half the normal load to reduce the chance for field damage.

“Hopefully the (yield) losses in product will be offset by increases in prices. That’s the best we can hope for right now,” Alameda said.

Heavy rains caused damage to Alameda’s spinach and baby greens.

Despite the last challenging week there is good news. Nolte says growers were aware of the impending heavy rains about seven to 10 days before arrival. Growers halted scheduled irrigations, quickly applied fungicides, and pushed additional tractors into service in advance of the storm.

“We knew this was going to be a significant storm so additional tractors were brought in to move equipment in muddy soil conditions.”

A head lettuce harvest rig is powered by an on-board diesel engine. After the rain one to two tractors were attached to each harvester to help pull it through the field.

Soil types vary in Yuma County. About 70 percent is a sandy-clay texture. Soils in the south Yuma Valley are about 100 percent clay which hold more water and drain poorly. Meanwhile soils on the Yuma Mesa area have sandy, more permeable soil.

Nolte says the baby leaf lettuce industry was affected by the rain more than the carton lettuces (head and romaine). Baby leaf beds are shallower; flooding was common on the bed tops.

“The equipment to harvest baby leaf lettuce is a rotary-mechanized cutting machine that has a heck of a time getting into wet fields,” Nolte explained. “We also cannot get into the fields to plant baby leaf lettuce. It may be several days or weeks until the ground is dry enough to plant.”

Baby leaf lettuce is a short duration crop which normally reaches maturity in about 30 days. An unknown planting schedule for baby leaf could lead to crop failure, Nolte says.

Overall, growers are now examining harvest and tractor schedules. A long-term concern is the ruts created by harvest equipment which can lead to future soil compaction issues. Some growers are hesitant to move heavy equipment onto wet ground.

Nolte says growers will likely use heavy tillage this summer to break up compacted soil. The Yuma area still struggles with compaction issues from heavy rains which fell over a two-month period in 2005.

“Last week’s wide-spread rain event was significant because it affected all (winter vegetable) growing conditions in the desert southwest,” Nolte said. “This was a significant rain event due to its duration, intensity, and proximity to local production zones.”

Weather experts predict another half inch will fall this Wednesday and another half inch this weekend. They are expecting above-average rainfall through March tied to El Niño.

About 1.6 inches of rain was detected last week at the California Irrigation Management Information System (CIMIS) site in Holtville (Imperial County).

Khaled Bali, irrigation-water management advisor and acting director, University of California Cooperative Extension, Imperial County, says about 60 percent to 70 percent of the county’s heavy clay soils have a slow water infiltration rate. He says rain water has a slower infiltration rate than irrigation water.

email: cblake@farmpress.com