University of Connecticut Integrated Pest Management Program  

A weed is frequently defined as a plant out of place. Using this definition, a tomato plant growing in a flowerbed is as much a weed as pigweed or crabgrass. Experience shows that this is not true. Weeds that persist in cultivation are unique, highly-adapted plants. Problem weeds persist as a result of their tremendous reproductive capacity and recycling potential. Weed populations survive in their unstable habitats by having short life cycles, producing abundant small seeds, and, often, more than one seed generation in a year.

The soil maintains a reservoir of dormant, long-lived weed seeds with variable germination times and, thus, necessitates the use of control measures year after year in the same areas. For example, over 30 years would be required to deplete the soil of 10 million weed seeds per acre; assuming that 75% germinate each year, that 99.5% of emerged weeds are controlled, and that each surviving weed produces 100 seeds. If 100% of the emerging weeds were controlled, it would still require 14 years to rid the field of weed seed.

Weeds result in more crop loss than insects and plant diseases combined. Weed competition causes losses by:

1. Reducing crop growth through competition for water, mineral nutrients, light and possibly CO².
2. Necessitating the use of control measures, which may, themselves, injure the crop and reduce yield.
3. Interfering with harvesting and thereby increasing harvest costs and yield losses.
4. Lowering the quality of the crop through contamination with weed plant parts and by preventing uniform crop maturation.
5. Reducing yield and quality as a result of increased adverse effect of disease, insects and nematodes and by interfering with operations to control pests and diseases.
6. Allelopathy, which is the inhibition of plant growth caused by the release of metabolic substances from another plant.

The effects of weed interference with the growth of garden plants must be limited in order to obtain a productive and aesthetically pleasing garden. There are three strategies we can use to deal with weed problems.

Prevention is aimed at keeping weeds out of the garden and landscape. This involves using clean, weed-free, crop seed to prevent the introduction of new weed species. Flower and vegetable transplants and woody plants purchased for the garden should be inspected carefully and any weeds removed before planting.

Equipment should be cleaned after use to remove adhering soil that might carry weed seeds or other weedy plant parts into the garden. This is especially important if tools are used outside your normal garden area. Mowing informal or unmaintained areas of the landscape to prevent weeds from going to seed will reduce the chances of weed seed being introduced to your garden areas.

Eradication involves eliminating all live plants, plant parts and seed from an area. This is seldom practiced but should be considered if new potentially troublesome weeds like quackgrass appear in the garden.

Weed Control is the most common option in dealing with weed problems. Control limits the interference of weeds with a crop to levels we can tolerate. Destroy weeds as soon as they appear or prevent them from ever getting started. Allowing weeds to become established will result in their being hard to control. Proper cultivation, hand weeding, flaming, use of mulches and application of herbicides are good ways to control weeds.

ipm@canr.cag.uconn.edu

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