Wild raspberries (Rubus ideaus and Rubus occidentalis) can quickly get out of hand in scrubby areas that are infrequently mowed. Although controlled raspberries are a great source of fruit and provide cover for small animals in U.S. Department of Agriculture plant hardiness zones 4 through 9, raspberry brambles become a nightmare when they devolve into a gnarled briar patch. Controlling these noxious weeds isn't easy, but small patches of raspberries can be destroyed using RoundUp, a glyphosate-based herbicide. For best results don't spray in the plant's dormant period.
How RoundUp Works
Glyphosate, the active ingredient in RoundUp, is a amino acid synthesis inhibitor that works specifically on the Shikimic acid pathway. Because plants manufacture their own food, they can't simply get amino acids from their diet, they have to build them from scratch. When glyphosate is working in a raspberry plant, it interferes with the production of important aromatic amino acids such as phenylalanine, tryosine and tryptophan. Without these amino acids, the raspberry slowly dies from starvation and the toxic build-up of various chemicals within its system. Fortunately, the Skikimic acid pathway is only found in plants, bacteria and fungi.
Because of the way RoundUp works, timing is important to effective raspberry control. Although you certainly can spray dormant raspberries and hope there is enough residual activity to carry the chemical into the plants' systems, without a significant amount of leaf surface area and metabolic activity, your efforts may be wasted -- woody parts of the plant simply can't absorb RoundUp well. Spraying raspberries in the fall, before dormancy begins and the leaves drop completely, however, is an excellent time for treatment, as is springtime, when the plant puts out vigorous new growth.
How to Apply RoundUp to Raspberries
When mixing RoundUp for raspberry control, add 1 1/3 to 2 ounces of concentrate to each gallon of water in your portable sprayer and mix well immediately before spraying. If your water is particularly high in salts, you may want to use distilled water for best effect, since the salts in hard water can bind with glyphosate. When glyphosate binds with calcium or magnesium, plants absorb significantly less of the product.
Choose a day when the temperature is above 60 degrees Fahrenheit, with little or no breeze, and when plants are under little environmental stress to ensure that you get the best effect from your RoundUp treatment. As with any garden chemical, make sure you read the entire label before attacking your problem raspberries with RoundUp.
Protecting Desirable Plants During Spraying
Raspberry brambles taking over parts of your yard may be enough to drive you mad, but make sure to consider your other plants before you spray. Now that you understand how RoundUp works, you'll realize that whatever plants it touches are likely to be injured or killed, depending on how much chemical is absorbed. RoundUp is safe once it has dried, but until then, run-off is extremely dangerous to other plants -- this is why it's never a good idea to spray when rain is expected or winds are high. You can further protect beloved plants and grasses by covering them in heavy plastic before applying RoundUp to nearby raspberries.
- University of Illinois Extension: Raspberry
- Michigan State University Extension: Killing Weeds in the Garden with Glyphosate
- Indiana University-Purdue University Indianapolis Department of Biology: Controlling Weeds: RoundUp
- Plant Physiology Online: The Shikimic Acid Pathway
- Iowa State University: Glyphosate
- Cornell University Pesticide Management Education Program: Glyphosate Chemical Profile
- Purdue University Extension: Understanding Glyphosate to Increase Performance
- Crop Data Management Systems: RoundUp ProMax Label
- Crop Data Management Systems: RoundUp Ultra Label
- Crop Data Management Systems: RoundUp Power Max
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