Tom's Blog

Saturday, April 24, 2010

Controlling red raspberries

Among the various bramble species we have to deal with, red raspberry (Rubus idaeus) is by far the worst. It forms large, very dense clones, with stems close together. It can spread rapidly by rhizomes. Its seeds can remain alive for decades in forest soils, then starting to grow when sunlight becomes available. Oak savanna restoration, which involves opening up the forest and letting the sunlight in, is almost guaranteed to foster red raspberry growth.

The photo above shows a typical red raspberry patch about a month after a burn. The stem density is evident. All the stems were top-killed by the burn. I pulled one of these up by the roots to see what it looked like. As the graphic below shows, the plant had several dormant buds, two of which have resprouted.

After almost ten years working on bramble control, we have found that the best way to deal with red raspberry is to spray (with 3.5% Garlon 3A) all the resprouts that arise after burns. Fortunately, these patches burn very well, and all of the living stems are top-killed.

Yesterday I spent most of the day spraying the large patch shown in the top photo. I have been monitoring burned areas for the past week, to see when the resprouts are big enough to spray. The idea is to spray them when they fairly small, to avoid damaging adjacent "good" plants, but with enough leaf area to take in the herbicide. With an appropriate nozzle on the backpack sprayer, and a lot of caution, it is possible to spray the resprouts selectively. We add a blue dye to the spray mix to permit control, and to make sure we don't miss any resprouts.

Unfortunately, not all the resprouts come up at the same time. There will be a new "crop" ready to spray in about two weeks. Since eradication is the goal, one must return and spray these new plants. In fact, three separate "passes" through a clone during the month of May is best.

Although this approach is time-consuming, it is the best way to get rid of red raspberries in oak savanna areas. (Prairies are easier to deal with.) Fortunately, once they are eradicated it is fairly easy to keep new infestations from getting started.

Of course, this approach requires that the area can be burned. You need good fuel to carry a fire. Fortunately, brambles are quite sensitive to fire, and if the fire carries through them, they are usually killed. In fact, the dried raspberry leaves themselves help carry the fire.

Bramble control is one of the reasons why we insist on burning our oak savannas "every" year!


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