Battling bacteria to keep a jump on Jack Frost

The recent cold snap - a headstrong heave from Mother Nature that has caused some of the South's worst agricultural damage in 20 years - underscores the need to solve a stubborn and perennially costly farm problem: frost.

While vegetable farmers and citrus growers total up the damage from the recent freeze - tallies top $250 million in Florida and $200 million in Texas - scientists are progressing in devising weapons to combat the unpredictable foe.

The good news: Researchers now understand what causes much of the frost damage.

The bad: It may be several years before an effective, low-cost elixir can be created for widespread commercial use.

Certainly there's no lack of need for one. Frost inflicts some $6 billion worth of crop damage worldwide each year. At least $3 billion of that usually occurs in the US. Florida alone lost 25 percent of its citrus crop in 1981 and 1982 to the cold.

To cope with the problem, farmers have tried many ingenious solutions over the years: round-the-clock burning of smudge pots and gas heaters, spraying water on trees (it gives off enough heat when freezing to warm an orchard several degrees), and laying a blanket of insulating foam over low-growing plants.

But these palliatives protect orchards and fields for only a short period of time when there is a slight drop in the mercury - and usually at great expense. Keeping fuel-oil burners glowing one night, for instance, can eat up a citrus grower's entire profits for a year.

Now, however, researchers are closing in on more permanent ways to take some of the pain out of this dreaded yearly ritual. The culprit that apparently causes the damage, curiously, isn't Jack Frost at all, but bacteria that live on plants and cause ice crystals to form when below freezing. Scientists have known about the irksome organisms for several years. The trick has been to control them.

Several approaches are emerging. Researchers at the University of Colorado's Cooperative Institute for Research in Environmental Sciences (CIRES), for instance, are devising specific viruses that will kill off ice-forming bacteria but not any beneficial organisms on the plant. The chemical brews would be sprayed on like herbicides.

In the lab, CIRES scientists using the technique recently ''supercooled'' a soybean plant to 14 degrees F. without damage. This is well below the temperature at which most crops would need protection. More than 90 percent of all frost damage occurs within five to ten degrees of freezing.

University researchers will field test the sprays this winter. Depending on the results - plenty of technical, not to mention some environmental hitches could arise - a brew could be on the market by year's end. ''There is no doubt we are going to control frost,'' says Russell Schnell, a CIRES researcher. ''It's a question of how and when.''

Another potentially effective, if controversial, tack is being taken by scientist Steven Lindow at the University of California, Berkeley. He is using genetic engineering to try to produce bacteria that, when sprayed on plants, would prevent frost-creating organisms from developing on leaves and stems in the first place. The aim is to take advantage of a sort of bacterial Darwinism: In the struggle for the survival of the fittest, the ''ice nucleating'' bacteria are displaced by their engineered brethren.

But concern about the safety of releasing man-tailored organisms into the environment has been raised, and field tests have been delayed until spring.

In Canada, researchers at the Alberta Research Council are hunting for strains of wheat and barley that lack frost-forming organisms to begin with. But the scientists have had limited success so far. At the University of Georgia, research is under way to create bacteria-controlling chemicals that might reduce the impact of frost on apples, peaches, and strawberries.

Dramatic results in controlling cold-weather damage have been reported by a Hungarian scientist, too. Dr. Tibor Farkas of the Hungarian Academy of Sciences research center in Szeged has been trying to build up fatty substances in plant cells. These control the cell's fluidity, which, in turn, affects the plant's ability to survive low temperatures. He has been able to improve the survival rate of some wheat, bean, and fruit varieties by more than 20 percent over untreated crops.

Puzzles remain about how the process works. Some US scientists suspect it has to do, again, with controlling ice-forming bacteria.

Frost-proof orchards anytime soon? Not likely. Some scientists still doubt bacteria are even the root cause of cold-weather damage, at least for tree-fruit crops. George Yelenosky, for one, a US Department of Agriculture scientist in Florida, says there has been plenty of damage to citrus trees there without any trace of ice-forming bacteria being found.

For now, at least, it's still smudge pots and water sprinklers.