Integrated Weed Management

Integrated weed management (IWM), is a strategy to sustainably control weeds by utilizing cultural, biological, mechanical, and chemical methods. It is economically and ecologically beneficial to approach weed management with a multi-faceted plan as it reduces reliance on short-term chemical applications and makes landscapes more resilient to invasion long-term.

What is a Weed?

Plants that are considered weeds can be native or non-native species that cause economic or ecological damage. The economic impacts can include reduced forage, reduced crop yields, interference with irrigation systems or harvesting, and damage equipment or infrastructure. Ecologically, weeds can increase the risk of frost damage early in the season, harbor pests and pathogens, compete with native species for water and nutrients, alter water flows, and cause cascading effects in food chains. A large part of what may make a plant weedy is a lack of natural predators to keep populations in check. When biological controls are implemented, long-term control of weedy species can be achieved. To successfully implement an IWM strategy, consistent monitoring and management are key. As Peter Drucker said,” You can’t manage what you don’t measure.”

Control Methods

As with most problems, prevention is the best strategy. Regularly cleaning farm equipment between fields, scouting fields for emerging issues, and inspecting hay for contaminants are all good preventative techniques.

Cultural

Cultural controls take advantage of the natural growth cycles of weeds to give a competitive edge to desirable species. 

  • Cover crops that reduce light, nutrients, and water availability in off-seasons
  • Altered crop spacing allows desirable plants to reach the canopy quicker and shade out slower growing weeds
  • Crop rotation prevents weeds from adapting to a single cropping system
  • Increased biodiversity in row breaks or pastures provide a more robust and invasion-resistant landscape

Biological

Biological controls utilize the long-established relationships between weeds and their natural enemies to provide an ecological balance that keeps weeds at an acceptable level. It is ecologically and economically beneficial.

  • Classical Biocontrol is the introduction of specific insect enemies of weeds. These insect agents are carefully selected and studied to prevent non-target effects and when established provide long-term suppression of introduced weed species. There are four types of classical biological control agents: predators and pathogens that will directly attack the plant, parasitoids that exploit the life cycle of insects, and competitors that can outcompete pest species. The Insectary’s main focus and area of study is classical biocontrol.
  • Augmentative biocontrol is the large release of beneficial organisms at crucial times during the growing cycle. This typically comprises large predator releases during crucial periods of the crop cycle like releasing ladybird beetles or predatory mites in greenhouses.
  • Conservation biocontrol is a focus on preserving and integrating native beneficial insects into cropping systems. Strategies include providing habitat for insects and minimizing life cycle disturbance and increasing biodiversity.

Mechanical

Mechanical controls are usually the most labor-intensive control strategy. It includes hand pulling, tillage, burning, mowing, or any other physical removal of weed species. Control of weeds can be achieved with proper timing but improper timing, such as mowing when seeding is already occurring, can spread weed infestations.

Chemical

Chemical controls are important facets of a well-integrated weed management strategy but their use should be carefully implemented and weighed against the ecological impacts. Improper use of chemical controls can have many unintended negative consequences such as herbicide-resistant weeds, reduction of native and desirable species, or soil and water contamination. Good approaches to chemical weed control include:

  • Proper weed identification and a good knowledge of herbicide-resistant weed species in the area
  • Appropriate timing and application including proper application rates, PPE, and minimizing overspray or non-target effects
  • Diverse tank mixes that utilize multiple sites of action to prevent herbicide resistance

Resources

Integrated Weed Management

Creating an Integrated Weed Management Plan

Range, Pasture, and Natural Area Weed Management

Xerces Society Ecological Pest Management

Integrated Pest Management for Orchards

Biological Control

Cornell University Biological Control

University of California W3185

U.S. Forest Service Research & Development

CABI

USDA APHIS PPQ