What is in this article?:
- California garlic, onion growers tackle white rot challenge
- DADS cost very high
- Biotech approaches
- White rot control continues to be the biggest challenge facing the research-driven marketing order for California garlic and onion producers.
- California produces 91 percent of U.S. garlic production. Fresno, Kings and Kern are the top garlic producing counties with 17,731 acres planted last year. Onion acreage is split between fresh market and processing with the total at nearly 49,000 acres statewide.
DADS cost very high
The dilemma with using DADS, according to advisory board technical director Bob Ehn, is that the product is extremely expensive. Applying DADS to an entire field costs $200 per acre. As a result, few growers use it.
"It is only made in limited quantities twice a year due to low demand," says Ehn. There is an effort to secure grant funding to study the use of GPS to use variable rate applications to target only infected areas of a field.
Although white rot declines year-by-year in the absence of allium crops, enough to regenerate an infestation, or strike, can persist in soil for as long as 40 years. That's the big problem in managing it.
It moves unseen at a rapid rate through roots. Damage is not observed until it reaches the base plate of a plant. Death of the plant comes soon afterward. It appears more in garlic because planting times coincide with the end of its overwintering phase. Soil temperatures of 58 to 60 degrees are ideal for it to spread. Mild winters encourage infections.
White rot is triggered by the characteristic hydrogen sulfide odor detected from onion or garlic fields after a rain. Ehn noted that if there were a way to plant with true seed (as onions are) instead of vegetatively with cloves, perhaps spread of the disease could be controlled more successfully in garlic. White rot readily attaches to garlic crop residue and cloves for seeding, whereas few diseases are spread by seed.
Farmers cannot kill white rot. They must learn to manage it.
White rot closed down garlic in the Tulelake area, where most of the California industry seed once was produced. Seed is now grown in white-rot-free fields in Shasta County, Nevada, and Oregon.
Current research Ferry is conducting includes use of mass spectrometry to see concentration and movement of the fungicide Folicur in Tulelake clay soils and sandy soils. She is also comparing fungicide levels in plant roots, bulbs and leaves. Ferry said knowing how the fungicide acts in various soil types and how it correlates to the amount of disease in the field may allow for reducing the number of applications.