Is There a Raspberry Safe Herbicide?

Indications

• Raspberry plants growing among invasive weeds may show signs of disease or insect infestation. Weeds provide shelter for harmful pests and diseases like tomato ringspot virus. Many common weed plants choke out raspberry plants as they compete for sunlight, nutrients and water. They also increase the humidity near the ground, which creates ideal conditions for the development of fungal diseases. Raspberry plants deprived of sunlight will present yellowing leaves, and excess competition for water may lead to wilting, drooping, or papery leaves.

Integrated Pest Management

• Integrated Pest Management (IPM), outlines environmentally sound methods to control weeds and pests. Washington State University's guide to Integrated Pest Management for raspberries recommends viewing weed control as an ongoing process. Gardeners should identify areas inhabited by different types or concentrations of weeds, as these may require a different herbicide or frequency of application. The most effective management plans may combine manual methods like tilling or mowing in addition to the application of safe chemical herbicides.

Herbicide Rotation

• IPM theory recommends rotating the use of different short-residual herbicides to prevent weeds from becoming resistant to chemical activators due to repeated exposure. Short-residual herbicides break down in the soil faster.

Pre-Emergence Herbicides

• Pre-emergence herbicides cover the top layer of the soil in which weed seeds typically germinate. These herbicides only act on newly developing plants, and do not kill existing weeds. Isoxaben, a broad spectrum pre-emergence herbicide, effectively eliminates many common weeds, but gardeners should not apply this herbicide when the plant bears fruit. Gardeners should only use diuron on raspberry plants older than one year. Pre-emergence herbicides rated appropriate for use without exclusions on raspberry plants include dichlobenil, norflurazon, and terbacil.

Post-Emergence Herbicides

• Post-emergent herbicides destroy above-ground plants and may occupy a more precise functional niche than broad-spectrum pre-emergence herbicides. They often act either specifically on single plants or plant families or on all plants indiscriminately. For example, pelargonic acid acts well on sowthistle and chickweed, but only in warm conditions. Fluazifop and clethodim present gardeners with effective post-ermegence herbicides for use only after the plant bears. Safe post-emergence herbicides with fewer limitations include carfentrazone, glyphosate, and Sethoxydim.