Don Curlee: Fresno salad crops soured by malady
A savage soil-borne plant disease is threatening the window of lettuce production that Fresno County has enjoyed for decades.
Researchers are hot on the heels of the age-old wilt; but until they find a remedy, acreage on Fresno County's storied west side will diminish.
Planting lettuce back into a field where the Fusarium wilt disease has prevailed before is a gamble. Some growers have just about run out of "clean" acreage and may have to forgo growing lettuce during the fall season when high soil temperatures favor disease development.
Planting both iceberg and leaf lettuce for production in March and October has been the steady pattern for several west-side growers. Fresno County's October crop supplies nearly all the lettuce marketed in the country. Its claim to salad superiority fits between the legendary production each year in Salinas and the Yuma Valley.
The summer season for lettuce ends in Salinas in September. Producers move personnel and equipment for planting, thinning, harvesting, hauling and packaging to "the desert," as they term the Yuma Valley area.
Fresno's west side is a convenient stopover along the way to and from, providing a month of production and sales in the fall and again in spring. The area's production is about evenly divided between head lettuce, also called iceberg, and leaf lettuce led by romaine and several of its cousins.
Tom Turini, the Fresno County farm adviser assigned to aid growers in the production of vegetable crops, has diagnosed many lettuce fields affected by Fusarium wilt. Several forms of the fungus attack a range of crops, but the pathogen that attacks lettuce targets only lettuce. Plants that fall victim to it initially wilt and, later, portions of leaves will die and the center of the root turns orange to brown.
In a well-designed, sterile and professionally stocked laboratory at the Fresno County headquarters of the University of California Cooperative Extension, Turini confirms the cause of the wilt by isolating the fungus.
In studies conducted in naturally infected fields, he compared the response of lettuce varieties to the pathogen. There were definite differences among varieties, and the later the plant date the less severe the disease. That is because of the decreasing temperatures during August, and affinity of the fungus for heat.
At this point, particularly at the early plant date, no iceberg varieties were acceptable, but a few romaine varieties looked promising. If Turini can learn more about what triggers attacks by the disease, he can concentrate on finding materials that will control or prevent it.
For now, Turini and his cadre of cooperative growers do all they can to avoid planting the valuable lettuces in contaminated soil where the crop has grown previously, or where testing shows a presence of the wilt inoculum.
Incidentally the situation indicates how certain foods might disappear from our plates altogether. None of the stable farm families on Fresno County's vast west side think of themselves as lettuce growers. Instead, each fills the role of diversified grower. Most can shift the acreage currently in lettuce to crops that are not susceptible, and that sounds a death knell for the salad crop.
Thousands of west-side acres have been converted to permanent crops such as almonds, pistachios, grapes and pomegranates. Annual crops such as cotton, melons and processing tomatoes continue to dominate the scene.
But lettuce is definitely a high-value crop, at least in the good years, and that has been most years in the immediate past. Turini, growers he works with and bankers and others who are aware of its impact on the economy are eager for the puzzle of lingering Fusarium wilt to be solved.
CONTACT Don Curlee at firstname.lastname@example.org