Experts tackle readers’ garden questions.
“What’s wrong with my roses?”
Master consulting rosarian Baldo Villegas, who grows thousands of bushes at his Orangevale home, has heard that plea for help over and over this spring.
The major problem is not weather or pest related. It’s exposure to one specific herbicide: Roundup.
“It’s the most common of all problems I get,” Villegas said. “I get photos or phone calls on almost a daily basis. It may look like something else, but it’s Roundup phytotoxicity.”
Phytotoxicity is the toxic effect on a plant due to such compounds as pesticides, herbicides, metals and salts. Roundup is one of America’s most widely used weed killers. Its active ingredient is glyphosate, which can kill most plants including roses. But it’s not just Roundup; glyphosate is found in more than 750 garden products.
“Roses are extremely sensitive to Roundup,” Villegas explained. “It can effect them for years (after exposure).”
A sure sign of this phytotoxocity is deformed growth on new foliage and stunted weirdly shaped flower buds. New leaves tend to be tiny and yellowed. Such exposure can be fatal to older bushes or bushes weakened by stress such as drought.
There’s no quick cure. With tender loving care and patience, the rose bush may eventually regain its health. But often, it remains compromised.
Roundup is so effective on weeds because of how it works. Sprayed on green leaves and stems, it penetrates a plant’s system and moves to roots and shoots where it prevents the plant from making certain proteins necessary for growth. It eventually kills the whole plant.
Most rose cases come from accidental Roundup exposure, Villegas noted. Drift of the herbicide spray settles on the bush’s leaves. Rose bushes several feet away may be effected.
Or a bush may be exposed via its roots after an application of granular herbicides (such as in weed-and-feed lawn treatments). Glyphosate binds closely to soil particles and can persist in the soil for six months, according to university research.
“We used to recommend using a sponge or paint brush to apply Roundup directly to weed leaves to avoid exposing other plants,” said Villegas, a retired state entomologist. “But I’ve found in my own garden, that doesn’t work. The (rose) bushes above those weeds are effected.”
The best solution: Avoid using Roundup in gardens with roses, Villegas said. “If you must spray, wrap your roses in plastic to protect them as mush as possible, then apply the herbicide only on cool and calm days with no breeze very early in the morning.”
The Bee’s Debbie Arrington is a consulting rosarian and lifelong gardener.
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