by Lindsay Bond Totten
Scripps Howard News Service
Broccoli is a vegetable that stirs strong passions. It's one of the most nutritious green vegetables we can eat, while reportedly possessing significant cancer-preventing compounds. Vegetarians rely heavily on broccoli because it's high in calcium and combines well with so many other foods.
Of course, broccoli has its detractors, former President Bush being perhaps the most outspoken of that bunch. Yet even he would have to agree that broccoli deserves more respect following recent revelations from the University of California:
About 10 years ago, cauliflower growers in the Salinas Valley noticed their crop suffering from a new disease. Plant pathologists identified it as Verticillium wilt, caused by the widespread soil borne fungus Verticillium dahliae.
The news was discouraging for several reasons: Not only was it the first time this devastating fungus had attacked cauliflower, but treatment is very expensive. In addition, the chemicals used for diseases of this type, called fumigants, are so toxic that most are currently under review. Farmers anticipate that some, if not all of them, will soon be taken off the market or phased out of production.
It hardly mattered, since cauliflower is not a valuable enough crop to warrant fumigation.
Crop rotation, a cultural technique routinely used by vegetable growers to disrupt disease cycles, wouldn't work in Verticillium's case because the spores of V. dahliae could lie dormant in the soil for many years.
Observant researchers then noticed that broccoli plants in adjacent fields never contracted the disease. This seemed odd, considering how closely broccoli and cauliflower are related. Pests, which attack one usually, affect the other. Yet, they couldn't even infect broccoli in a greenhouse when plants were inoculated with the fungus.
It became apparent that something within broccoli leaves rendered them immune.
Controlled studies ensued, with fresh broccoli residues being tilled back into the soil following harvest of the broccoli heads. Fields were allowed to sit fallow for three weeks, the typical "down" time between cold crops in the Salinas Valley, while broccoli residues decayed.
Cauliflower was then transplanted into the broccoli-treated soil. At maturity, the heads were firm and white and showed practically no signs of Verticillium wilt. The fungus had been virtually eliminated. Plants in control plots--no broccoli residues--were ruined.
In the battery of experiments that followed, only one soil fumigant--metham sodium--provided protection as good as or better than broccoli residues. Eureka!
One last test: Would tarping--covering the soil with plastic following treatment--improve the broccoli results? Tarping is necessary following fumigation to trap the volatile gases in the soil long enough to kill the fungus spores. The cost of huge rolls of plastic is one reason fumigation's price tag is so high, not to mention disposal costs.
In the end, uncovered fields performed just as well as those that were covered, an indication to scientists that the compounds they were dealing with in broccoli were not gaseous, so might last longer in the soil.
Farmers and researchers were pleased. The broccoli solution is safe, easy and cost effective. Since the broccoli heads aren't needed for treating the soil, just the leaves and stems, growers can realize a profit from the crop while putting the waste to good use. No other cover crop offered as many benefits; no other "pesticide" worked better.
Home gardeners probably don't have to worry about Verticillium wilt on their cauliflower just yet, but since scientists aren't sure what caused cauliflower to be attacked in the first place, there's no guarantee the disease won't spread.
Watch developing cauliflower plants carefully for signs of decline. Plants are initially infected through their roots. Lower leaves are the first to show symptoms, turning yellow, then brown.
As the disease proceeds up the stem, more leaves die, and the remaining foliage wilts during the day. The heads, if they form at all, are likely to be small. When the stalks are cut open, then inner tissue appears discolored or streaked with brown, a sure sign the fungus is at work.
If symptoms do occur, it's reassuring to know that there's a safe, effective cure readily available. Imagine that--a vegetable that fights disease on several fronts!
(Lindsay Bond Totten, a horticulturist, writes about gardening for Scripps Howard News Service.)
)
