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Where the daminozide is.

In the United States, 75 percent of all daminozide, the carcinogenic plant-growth regulator that the Environmental Protection Agency will seek to ban (SN: 9/7/85, p. 149), is used on apples. "We use it primarily on those that are heading for the fresh market," says Drl Derr, executive vice president of the International Apple Institute in McLean, Va. Though precise figures are not available, Derr estimates that 80 percent of all McIntosh and Stayman apples are routinely treated with the controversial chemical. "And on Red Delicious, which is the single largest variety that we grow, I would guess it would be at least 50 percent," he told SCIENCE NEWS.

Not all "eating" apples have been treated, however; EPA estimates that treated apples account for only 35 percent of those sold as fresh. And some treated apples -- especially the misshapen or scarred -- will end up in juice or processed food, Derr notes.

Daminozide is used primarily to hold apples on the tree longer, providing them a chance to firm up and increase their color. "There are some other 'stop drops,'" Derr says, "but they're not widely used or nearly as effective."

Peanut growers are the second-largest users of daminozide. However, not only do their crops contribute less to contamination of the food chain, but their industry also stands to suffer relatively less under a daminozide ban. In Georgia, where half of all U.S. peanuts are grown, only 10 to 25 percent in any year are treated, according to Craig Kvien, a University of Georgia peanut specialist in Tifton. Moreover, only growers able to charge a premium for their crops--like the seed producers--tend to use the costly chemical treatment, he says. Seed peanuts are planted, not eaten.

On peanuts, daminozide is used to control "rank vine growth," a condition leading to excessive moisture-trapping foliage that can incubate fungi. The chemical also sets peanuts closer to the plant's taproot, making them easier to harvest. And for these applications there are alternative chemicals, called sterol biosynthesis inhibitors, which Kvien says have been used in Europe for several years but are not yet on the U.S. market.

For several years, the Coastal Plain Experiment Station, where Kvien works, has experimented with these fungicical agents. The chemicals work by inactivating a fungal enzyme called P-450. A similar enzyme in peanuts, also inactivated by these compounds, inhibits production of the plant growth hormone, gibberellin. Depending on how they are formulated these chemicals can be fungicidal, growth regulating or both. Kvien says a number of U.S. chemical companies have been exploring their potential for peanuts, apples, pecans and peaches. Though not stopdrop chemicals, they could benefit orchard owners by limiting the need for costly pruning.
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Title Annotation:plant-growth regulator used on apples and peanuts
Publication:Science News
Date:Sep 14, 1985
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