Weeds present a multifaceted problem in agriculture. Weeds are responsible for reducing crop yields by competing for space, sunlight, nutrients, and water. Weeds may also function as alternate hosts for pest insects and plant diseases that impact crop growth, yields, and quality.
Cost effective weed control is a major consideration for conventional growers and is consistently cited as the most difficult issue facing organic producers. Prior to the advent of chemical herbicides, weeds were controlled by cultural, physical and mechanical means. The introduction of chemical herbicides reduced the need for some low value rotations and mechanical cultivation, thereby saving growers time and money. At the same time, the widespread use of herbicides also led to new problems, including instances of groundwater contamination resistant weed populations.
The use of biopesticides for weed control presents a difficult challenge due to the physiological similarities between crop plants and weed species. In recent years, however, scientists have identified several disease causing organisms that specifically and effectively attack key weed species including Canada thistle and northern jointvetch. And, some plant extracts have also been identified that have broad spectrum herbicidal activity against numerous weed species. Biopesticides based on such active ingredients can be used to reduce our dependency on chemical herbicides.
As additional weed species develop resistance to chemical herbicides, there will be additional motivation to investigate biological sources for weed control.