Johnson Grass, Alas

Nature struck back again--this time at weed-killing 2,4-D. Last week the Department of Agriculture glumly admitted that Johnson grass is showing signs of making itself immune to 2,4-D.

Johnson grass, originally and recklessly introduced as a forage crop, is a pest in much of the South, especially in cane fields. Its perennial rootstocks can be clawed up through cultivation, but the pesky seeds keep blowing into cultivated fields from a distance.

In theory, 2,4-D is supposed to kill only broad-leaved plants, not grasses, but Department of Agriculture men at Houma, La. found that when the potent chemical was applied directly to the soil surface, it prevented the sprouting of nearly all Johnson grass seedlings.

There might have been more rejoicing if the experts had not remembered the sad case of DDT, whose use has developed in many places new breeds of resistant insects. Forewarned by this disturbing experience, they gathered seed from some of the hardy Johnson grass survivors and tried the effect of 2,4-D on the second generation. It was just as they feared. Twice as many grass seedlings poked through the soil and twice as many grew to full, pestiferous maturity.

Agriculture is now investigating reports that ragweed, the terror of hayfever victims, is also developing a taste for 2,4-D. "Chemical weed control," a spokesman concluded wearily, "is another field in which agricultural science must always look for something new."

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