When the serious and deadly weed called branched broomrape shows up, probably in a processing tomato grower’s field, the alarm has to be sounded and means to control it have to be put in place. All that is happening this year, accompanied by a certain amount of tension and frustration.
Reasonably widespread efforts to control the dreaded weed have been conducted previously, always with the hope and a faint promise that prevention will be lasting. But its appearance in a few isolated fields in Yolo, Solano and San Joaquin Counties this year where tomatoes were being grown for processing has shown that any promises of eradication are hollow, and that new control methods are needed.
Seemingly harmless because it can’t grow on its own and must attach to another living plant for its supply of life-giving oxygen, broomrape might appear to have serious limitations. But what it lacks in self-sufficiency it compensates for in seed production. One plant can produce more than 100,000 seeds, each only three millimeters in length, able to lie dormant for 35 years
“Broomrape is easily spread by boots, equipment and water,” said Zach Bagley, managing director of the California Tomato Research Institute. He told journalist Bob Johnson that his organization and the industry as a whole spent more than $1.5 million from 1973 to 1982 trying to eradicate the weed. Until now industry leaders considered the project successful.
Writing for the popular Ag Alert, published weekly by the California Farm Bureau, Johnson reported that once ground has been infested by broomrape the crop options for that field are extremely limited, and for a long time.
Bagley said the host range for broomrape includes quite a few important Central Valley crops such as safflower, carrots, bell peppers, a number of brassica species, lettuce, several bean varieties, melons, potatoes, olives and many common weeds. Once a field has been infested a fresh crop planted there is likely to be doomed for years and years.
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Leading the effort to find an effective control material is Brad Hanson, University of California Cooperative Extension weed specialist. He and his associates are trying to learn if applying an herbicide at a low rate – enough to stunt the weed, but spare the crop – will be an effective strategy. One of the materials they are experimenting with is registered in California for use in wheat fields but the other is not registered. Either can be applied through a grower’s irrigation system.
Timing of herbicide applications is critical, and the researchers are conducting germination studies that will help pinpoint the right time to apply a chemical control. Soil temperature and moisture are being observed closely to determine when the broomrape germinates.
Hanson emphasized that the current research is not aimed at eradication of the weed, but control enough to allow growers to live with it without huge losses in their basic crop. Israeli growers have brought control to that modest level, down from losses of 70 percent.
He urges growers to report any incidence of the dreaded weed, but understands that some might be reluctant to acknowledge it. He says that allowing it to go unreported and risking its spread could be disastrous. CTRI’s Bagley said the most effective means of controlling branched broomrape is active concern for its presence in tomato fields.
Bagley concluded his recent comments by saying: “The harvest of infested fields or blocks … is extremely ill- advised. . . because of the biology of this weed and its standing in a California Department of Food and Agriculture Class A status.