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Use Roundup with Care

If you use this powerful herbicide, be sure you use it right

Roundup has its uses, but before you consider spraying the herbicide, you should know what it’s good for — how damaging it can be and where it does no good, even ill.
    Roundup kills plants by degrading the mitochondria in the roots. I began studying Roundup in 1976, when it was called glyphosate. Our research established rates of application, best time of application, plant response and phytotoxicity on desirable plants. Since then, we have learned a great deal more about Roundup and the care you should exercise when using it.
    • Never spray when the target weeds are under drought stress. To achieve effective control of weeds, the foliage should be mature. Leaves give a good indication of maturity. If 50 percent or more of the leaves on the weeds are fully grown, the Roundup will be absorbed and migrate down toward the roots. If fewer than half the leaves are mature, the Roundup will only burn the top growth. The weeds will generate new top growth from the crown or roots.
    • Never spray on smooth-barked tree trunks. Smooth bark can absorb the glyphosate, resulting in severe yellowing of the foliage, even death to the young tree
    • Avoid using Roundup to spray around raspberries, figs and other desirable plants that generate rhizomes. Roundup will travel through rhizomes to plants that have not been sprayed. This is why Roundup is so effective in controlling Bermuda grass or wiregrass.
    • Roundup should never come in contact with the roots of plants, including roots extending from the bottom of plant containers. Aggressively growing plants often send roots out through the drainage holes. The spray may affect and kill visible roots.
    • Roundup is not effective in controlling waxy foliage plants such as English ivy and vinca — unless fortified with either ammonium sulfate or household ammonia. The wax covering the leaves keeps the spray from penetrating into the leaf tissues. A teaspoon of ammonium sulfate or one tablespoon of household ammonia per gallon of spray enables the Roundup to penetrate into the leaf tissues and migrate down the vines to the roots. For best results, spray both English ivy and vinca in September.
    • Kudzu and bamboo are best controlled by spraying Roundup amended with ammonia or ammonium sulfate in mid- to late October before the first frost.
    • Brambles, honeysuckle and other weeds can be killed by using half to one-quarter the package-recommended concentration of Roundup in late September and early October. When sprayed late in the growing season, all the Roundup migrates down to the roots.


Share Your Harvest
    Vegetable gardens are feast or famine. Don’t let those zucchinis grow to baseball bat size or green or yellow beans form seeds in the pods, only to be discarded. Your local food pantry will gladly accept fresh fruit and vegetables. Food pantries as well as food banks are an excellent point of distribution that will benefit many. Many local churches operate food pantries. I give my surplus to the South County Assistant Network (SCAN), which operates a food bank every Thursday and Saturday from 8am to noon at St. James Episcopal Church on Rt. 2 near the intersection with Rt. 258 in Lothian.


Ask The Bay Gardener your questions at DR.FRGouin@gmail.com. Please include your name and address.