Weed management in raspberries

Good weed management increases raspberry plant growth and yield, makes harvest easier, and reduces insect and disease pressure.

Raspberry growers, especially organic growers, often have to apply a variety of preventative, cultural, and physical approaches to their weed management strategy due to the restricted use of herbicides.

Prevention (prior to planting)

Planting cover crops the year prior to bramble establishment can help reduce weed pressure and increase soil organic matter. This can be an effective way to reduce perennial thistle and quackgrass populations. Grasses and grains usually make the best cover crops for transition into berry production because of their thick canopies and fast establishment.

The use of reusable plastic tarps in tandem with cover crops has been shown to be 96% effective in suppressing weeds in organic production prior to planting. Tarps are often impermeable, depriving weeds of light and moisture needed for germination. Tarps and plastic sheeting also increase root-zone temperatures which can dry out weed seeds and hasten the breakdown of cover crop residue. Applying tarps or removable plastic sheeting after terminating cover crops, for three weeks prior to raspberry planting can provide growers the additional support needed for a successful weed prevention plan.

See Solarization and occultation.

Production years

Control weeds before they produce seeds. Research has shown that annual and perennial weed species such as foxtail (Setaria species) and bindweed (Convolvulus arvensis) can produce up to 2,500 and 300 seeds per plant, respectively. Palmer amaranth, a pigweed species on the Noxious Weed List, has been found to produce up to 1 million seeds per plant.

Weed seeds can survive for a number of years in the soil, depending on the species. Therefore, allowing just one large weed to drop seeds can cause a nuisance in following years.

Use different weed management strategies in the rows and between the rows:

• Between-row: Most growers simply maintain grass strips between the rows and keep them mowed to reduce weed growth. 
• For high tunnel raspberries: Growers can choose one or a combination of four between-row weed management methods. These methods are discussed in the High Tunnel Raspberries section.
• In-row: Hand-weeding and a small selection of herbicides are the main options in the rows. Refer to the Midwest Fruit Pest Management Guide for raspberry herbicide options.
• Once stands are established, hoeing and mulching in the rows is risky. Hoeing can damage the canes and crowns, and mulch can create a wet soil environment that encourages root rot.

It is okay to put temporary mulch, like straw, in the rows during the planting year, but once the plants are established, mulch should not be used in rows. Mulch around canes encourages phytophthora root rot due to increased moisture and decreased soil temperatures.

Once the stands become established, the canopies will compete with weeds somewhat by shading the ground.

If permanent mulch is left in the rows, manage irrigation carefully to prevent overly wet soil and moldy mulch. It is difficult to control this in an open-field setting but is easier in high tunnels.