Lingering wet and cool conditions in California garbanzo fields this spring ignited outbreaks of white mold and challenged plant breeders to find new varieties resistant to the lethal disease.
Garbanzo industry members caught up on strategies for managing diseases and weeds in the crop at a recent field day at the University of California West Side Research and Education Center near Five Points.
Carol Frate, Tulare County farm advisor, told the group Sclerotinia sclerotiorum or S. trifoliorum, or perhaps both, are believed to cause white mold. The mold, plus Ascochyta blight and a complex of viruses, are the major diseases of garbanzos.
“We got a tremendous amount of white mold in garbanzos this year, and we are still learning about it,” Frate said.
Sclerotinia survive in the soil for several years. When its irregular, black sclerotia are within 2 inches of the soil surface during several weeks of moisture and temperatures around 39 degrees F., they can generate spores that infect legumes.
Spores live in decaying crop residue and can move by direct contact above ground, aerially, or via roots. The disease often collapses garbanzo plants at the soil line and favors heavy canopies. It also occurs in alfalfa.
Although it is a problem at bloom time for many common beans in other areas, in San Joaquin Valley garbanzos it hits both seedlings and large plants.
This year many infections were seen high in garbanzo plants in fields with no history of the crop, and Frate said one route of infection could be aerial forms from nearby fields of garbanzos or other hosts, including alfalfa, sunflower, and rapeseed.
She said she saw the disease in the early 1990s in Tulare County on seedling garbanzos under sprinklers. It was not widely noticed in garbanzos on the west side of Fresno County until the past four to five years.
White mold management is mainly by rotation with non-host crops such as small grains or corn, Frate said. Deep plowing to bury the fruiting bodies at least 4 inches is another step. Biocontrols exist, but they require high rates and are expensive. Seed treatments are available, although they may not protect from aerial infections.
Frate and Shannon Mueller, Fresno County farm advisor, did trials with foliar fungicides for white mold at the center this year. Although Bravo, used as a protectant, was less effective in the trials, Frate said treatments with Pristine and Headline “seemed to be doing something for us.”
Certain experimental materials from USDA garbanzo breeders at Pullman, Wash., appear to have some resistance to white mold in trials at the WSREC done this year by Steve Temple, UC, Davis agronomist. He evaluated 151 USDA introductions at WSREC and UC, Davis.
His trials also showed varieties Sierra, Dylan and AWF-3 having less white mold.
He said the heavy white mold pressure during March and April indicated that several current varieties have too little resistance, even though they fared better earlier in the season.
Temple is also evaluating the USDA introductions for resistance to Ascochyta blight. He said a succession of public and proprietary varieties has appeared with varying resistance to the blight and some of the new ones are promising.
The problem now, he said, is an individual variety's resistance does not hold for both mating types of Ascochyta. Some areas of the Central Valley have the asexual type, others have the sexual type, and some have both.
He said breeders are watching very closely for the emergence of both types throughout the state because sexual recombinations of the pathogen would be stronger and need new, more complex breeding.
“Breeders around the world,” Temple said, “agree that Ascochyta is like stem rust of wheat and is able to adapt genetically very fast, compared to the time it takes for breeding for resistance. Fortunately, it is specific to legumes and doesn't have a lot of alternative hosts.”
Temple underscored the importance of management of volunteer garbanzos to prevent the disease from bridging between crops.
Kurt Hembree, Fresno County farm advisor, is continuing herbicide trials on garbanzos and searching for methods to control multiple flushes of weed pests such as sunflower and sowthistle.
The comparative trials include Sencor, Prowl and Goal, which are registered for the crop, and Chateau, Raptor and Sandea, which are not.
Among his findings, Hembree said, he learned Sandea was successful when used as a directed application but not as a broadcast treatment.
Chateau at rates of 2 ounces to 3 ounces appears to provide residual weed control for at least 30 to 60 days, although a longer period is needed.
“I really like Chateau,” he said. “It has good preemergence activity, particularly for summer weeds and winter mustards, without some of the initial injury we see with Goal.” At more than 3 ounces, the Chateau treatment showed damage similar to Goal.
He noted that germinating garbanzos have the ability to push secondary sprouts for good recovery when the original sprout is temporarily stunted by preplant Goal.
Raptor was a good performer on other weeds, but combinations with other products will be needed for sunflowers.
Goal with Sandea performed well as a preemergence treatment for nutsedge and volunteer cereals.
In a brief statement at the gathering, Ken Kirsten of Rhodes-Stockton Bean Cooperative, Tracy, said California garbanzos are superior, particularly because of their light color preferred by canners, to those grown in the Pacific Northwest.
He said despite the wet spring and some losses, his member growers are happy with their garbanzos this year in comparison with their rust-stricken wheat fields.
“They are saying if you can grow them this year, you can grow them any year,” he said. “And they are not the gamble that a lot of other bean crops are.”
Kirsten added, however, that a rapid rise in temperatures during after the cool spring could be detrimental to the crop.