The Allium Industry in California and The History and Importance of White Rot

The Allium Industry in California and The History and Importance of White Rot Ron Voss, Vegetable Crops Department, Univ. of California, Davis Robert Ehn, California Garlic and Onion Research Advisory Board General Information on the Industry California is the largest producing state in the U.S. of garlic and onions. California produces 8-9% of the commercial garlic in the U.S., with adjoining states Nevada and Oregon the major seed garlic producing states. California is the largest producer of processing onions in the U.S., one of the top fresh market onion producers, and the largest green onion producer. Most of the green onion production currently is in northern Mexico states. Garlic and onions are major vegetable crops in California with each contributing $15 3 million farm gate value annually. The importance of garlic rose dramatically from the 196 s to the late 199 s, when imports from China became an ongoing factor. Garlic production increased 6% during that period, with 9% of the production currently in the San Joaquin Valley. The three components of the garlic industry are dehydrated/processed, fresh market, and seed. Figure 1a, 1b and 1c illustrate the trends of fresh and processed garlic acreage, production and value from the late 196 s to the early 2 s. Figure 2 shows the changes in average yield during this time, which increased from six to ten tons per acre during the 198 s to mid-199 s, when virus-tested seed garlic was adopted by the industry. The low yield in 1998 reflects the first year that garlic rust (Puccinia allii) was found in California. Figure 3 illustrates the value of garlic on a per-acre basis to producers, and the relative value of hand-harvested fresh market compared to the mechanized harvest value of processed garlic. While Gilroy, north of the Salinas Valley, claims to be the Garlic Capital of the world, Fresno County has established itself as the center of garlic production in the U.S. Garlic acreage has increased from less than 7, acres in 198 to nearly 15, acres in 199 and more than 3, in 2. However, due to increased competition from China and the consolidation of garlic and onion processors, 24 acreage dropped to 23, harvested acres. Approximately 75% is processed. The farm-gate value of garlic in California is approximately $1 million for fresh market and $75 million for processed garlic. Compared to world production, California, Fresno County, North America, and the Western Hemisphere are relatively small components. Asia grows 75% of

the world s garlic acreage and produces 85% of the tonnage. China grows garlic on nearly one-half of the world garlic acreage and produces two-thirds of the tonnage. Figure 3a and 3b illustrate the area planted to garlic in the various continents. Figure 4a and 4b illustrate the production of garlic on a world wide basis. Table 1 provides the actual and relative garlic production in China, India, Korea, U.S., Others, and total for the world. While vastly different in absolute production, the relative increase of garlic production in the U.S. surpasses all other countries 6% during the 199 s. China also increased production dramatically during the 199 s, by nearly 4%. Worldwide, the increase in garlic production/consumption was more than 3% from 199 to 19999. One can speculate for the causes of these increases, but the research validation of health claims would be a leading hypothesis. Additionally, within the U.S., the widespread and increasing interest in ethnic foods, many of which include garlic as a staple component, probably also contributed. The statistical picture for onions is similar (See Table 2). Asia produces and consumes more than one-half of the world s onions, with India growing more than any other country. Like garlic, the U.S. produces approximately 3% of the world onions. Fresno County is also California s leading producer of onions, increasing from approximately 6, acres in 198 to nearly 2, acres by 199, with approximately two-thirds being dehydrated/processed. Figures 5a and 5b illustrate the California acreage and production of onion in recent years. History of White Rot in California White Rot (Sclerotium cepivorum) is a fungus capable of infecting any species of the genus Allium. The disease has been found in most of the onion and garlic producing regions of the U.S., Canada and Mexico. It has also been reported in most of the major onion and garlic production area of the world. White Rot ((Sclerotium cepivorum) was first recorded as found in California in 1939. By 195 it was widespread in the Gilroy area, soon to spread to the Salinas Valley and then to Tulelake in northern California. It was not identified in the San Joaquin Valley until the mid-198 s and for the first time in Kern County, in the southern San Joaquin Valley, in 1996 (See Table 3.) Throughout western U.S., white rot has been identified in several locations in each of the states. Table 4 indicates our records on where white rot has been identified in California, Nevada, Oregon, Idaho and Washington. We do not claim that this is a complete list, and some of the finds are still questionable. White Rot is typically spread by movement of infected soil or plant matter, on equipment, harvest bags and boxes and by humans. Allium sets and transplants may also carry the pathogen. The reproductive structures may be moved short distances by water, animals and blowing soil. As few as 2 infected plants can contaminate an entire field through disking or cultivation. Once the disease is established, yield reductions of 5% to 8% are possible. White Rot progresses through a disease cycle, initially forming on a host plant. The reproductive structures for White Rot are sclerotia, a uniformly round

structure with a black rind surrounding a thick walled mycelium. The sclerotia structure, roughly the size of a poppy seed, can lie dormant on a decayed host plant for weeks to months after its formation. Germination occurs as a plug of mycelium which is stimulated by organic sulfur compounds formed on roots of a growing garlic or onion plant. The mycelium subsequently invades the roots then stem plate or bulb, destroying tissue of the garlic or onion plant. Within days to weeks, the bulb rots and dies. An infestation can affect from several plants to large areas of a field. Controlling White Rot in garlic and onion fields has the best potential for success when following a comprehensive approach to manage the disease. To date, no single practice has shown to effectively control White Rot, particularly after a disease outbreak has occurred in a field. This presentation provides direction for an integrated pest management approach for management of white rot. The number of infested fields in the San Joaquin Valley was only a few, with sporadic new finds, until the last 4-5 years. Table 5 shows a summary of documented white rot strikes in the San Joaquin Valley from 1994 through 25. The summary includes strikes in both garlic and processed onions. Since that time, the number of infested fields has increased markedly. The current number of fields is now approaching 1 with over 13, acres infected. The primary strategy of the California Allium industry in white rot control has been avoidance. When a field was identified as having white rot, it was placed on a centralized map, and the industry avoided planting onions or garlic in that field. Much of the world has not had the luxury of this strategy. Mexico and Egypt, for example, have such widespread infestation of the pathogen, that garlic and onions are knowingly planted into infested fields. Thus, they have moved from the strategy of avoidance to the strategy of living-with-it. The California industry may be fast approaching the time when avoidance will no longer be the strategy of choice. Hopefully, a broad system, multi-faceted approach to disease prevention and control will be available when that choice is made. A combination of biological and chemical control, plant disease resistance, scelortia stimulants, and others will probably be needed. White rot has moved from plant to plant, field to field, county to county, area to area, and state to state by several primary methods onion transplants, equipment movement, seed garlic, air/wind, and water. To minimize disease occurrence and spread, each of these primary infestation methods must be continually addressed. Economic losses to White Rot are also manifested in varied and extensive methods. Accurate statistics on actual monetary losses due to White Rot are not commonly available because the individual loss components are either difficult to quantify or difficult to separate from other costs. The components of economic loss include removal of fields from cultivation of Alliums, direct crops losses when white rot occurs, the cost of seed increase and propagation programs, seed certification programs, and the salaries of hundreds of plant pathologists using public and private funds to conduct research and education programs. Notably absent, until recently, has been the cost of chemicals, or other direct control or prevention methods. No effective chemical or biological control measures have

been available. Research reports indicate that this is not necessarily the situation now, and should improve in the near future. As California changes from avoidance to a live-with-it approach, the costs of these compounds will increase. Hopefully, components such as removal of fields from cultivation of Alliums and direct crop losses will decrease by equal or greater amounts. Specific Research Needs: The following areas of research offer the most promise in managing the white rot disease: Biostimulants o Garlic Powder o DADS (diallyl disulfide) Disease Etiology o Model development to predict ideal temperature/time to treat Chemical Control o Seed Treatment o In-furrow applications o M bromide spot treatment o Metam sodium spot treatment Soil Solarization Flooding Biotechnology o Development of Allium germplasm resistant to white rot Authors Addresses: Ronald E. Voss, Department of Vegetable Crops, University of California, One Shields Avenue, Davis. CA 95616. 53-752-1249. revoss@ucdavis.edu. http://vric.ucdavis.edu Robert Ehn, California Onion & Garlic,1629 Pollasky, St. 111, Clovis, CA 93612. 559-297-9322. robertcehn@sbcglobal.net.

Acres (1,) Acres (1,) Value ($1,) Yield (Tons/A) Production (1, Tons) Figure 1a. Garlic Production in California Acreage Figure 1b. Garlic Production in California Production 4 35 3 Acres 2 1 3 25 2 15 1 63-64 76-78 83 87 91 98 ' 5 67-69 76-78 82 85 88 91 98 99 ' '1 Figure 1c. Garlic Production in California Value of Production 2 Figure 2. Garlic Production in California Yield Per Acre 12 15 1 5 1 8 6 4 Average 67-69 76-78 82 85 88 91 98 99 ' '1 2 67-69 76-78 82 85 88 91 98 99 ' '1 Figure 3a. World Garlic Production Acres Harvested Figure 3b. World Garlic Production Acres Harvested 2 175 15 125 1 75 5 25 Africa N. America Europe S. America Asia China World 2 175 15 125 1 75 5 25 Mexico USA Africa N. America Europe S. America

Produstion (1, Tons) Production (1, Tons) Figure 4a. World Garlic Production Tons Harvested Figure 4b. World Garlic Production Tons Harvested 1 6 8 5 6 4 4 2 Africa N. America Europe S. America Asia China World 3 2 1 Mexico USA Africa N. America Europe S. America Table 1. Country China India Korea Garlic Production Production 1 MT 598 52 39 % of World 64% 5.6% 4.2% Table 1 Count. Country USA Others Count. Garlic Production Production 1 MT % of World 22 3.2% 189 2% 929 1% Table 2. Onion Production Table 2 Count. Count. Onion Production Country India China USSR* Area Cultivated Hectares, 1 s 4 3 2 % of World 2% 15 % 1% Country USA No. America So. America Area Cultivated Hectares, 1 s 6 85 13 % of World 3% 4% 6.5%

Acres Value ($1,) Figure 5a. Onion Production in California Acreage Figure 5b. Onion Production in California Value of Production 5 35 4 3 2 3 25 2 1 15 97 98 99 ' '1 1 98 99 ' '1 Table 3. History of White Rot in California 1939 First Recognized 195 Gilroy Area 1955 Salinas Valley 1959 Tulelake 1985 Central San Joaquin Valley 1996 Kern County Table 4. White Rot Infestations Western United States California Fresno, Kern, Monterey, San Benito, Santa Clara, Kings, Shasta, Lassen, Siskyou, Modoc Nevada Douglas, Lyon, Washoe Oregon Benton, Deshutes, Jefferson Idaho - Ada, Payette, Canyon Washington - Benton, Franklin, Walla Walla Figure 6 Summary of White Rot Strikes 1994-26 3 25 2 15 1 5 No. Fields 1994 1998 22 25-3 2-25 15-2 1-15 5-1 -5

SUMMARY OF WHITE ROT STRIKES SAN JOAQUIN VALLEY 1996-25 YEAR NO. FIELDS WR ACRES 1994 4 64 1995 5 96 1996 3 52 1997 1998 1999 12 1,775 2 5 8 21 8 1,462 22 14 2,47 23 19 2,825 24 11 1,669 25 8 1,5 26 1 3 TOTALS 89 14,3