AgreeCulture Today

In every field, weeds are always present. But what exactly are weeds? Well, some people define weeds as an unwanted, undesirable and useless plant. But no plant is completely useless. We may then define weeds as plants that are unwanted at a particular time and place and whose economic use has not yet been discovered. A plant species can only be called as weed if humans have not yet found a use for it. “One man’s crop maybe another’s weed.”

Some plant species though occur 99% as weeds in some fields. Echinochloa spp. and Monochoria vaginalis in rice fields for example. R. cochinchinensis and Cyperus rotundus in corn and vegetable fields respectively are considered as weeds. 10% of the 300,000 angiosperm species behave as weeds 99% of the time.

The unique characteristics of weeds have made them difficult to control in the field. They have excellent adaptations to disturbed environment and occupy the ecological spaces left open in agroecosystems. Other characteristics of weeds include their rapid vegetative growth, reproduce rapidly and mature early, very prolific and produce plenty of seeds, can survive and adapt to adverse conditions, dormancy of propagules or can be induced to dormancy under favorable environments, and are adapted to crop competition.

Rapid Vegetative Growth and Reproduce Rapidly and Mature Early

Weeds have numerous tillers for grasses, rapid tuber and shoot formation for sedges, and faster stem elongation and branching for broad leaves. Also, weeds are able to reproduce sexual and asexually. These have allowed the weeds to be able to maintain high population densities if not managed effectively. They also mature early so they are able to reach their reproductive period at a lesser time, hence more plants capable of to reproducing.

Very Prolific and Produce Plenty of Seeds

R. cochinchinensis can produce more than 700 tillers and branches and can produce inflorescence. Perennial weeds can reproduce rapidly through vegetative means through tubers, rhizomes, and stolon. Scirpus maritimus, a perennial sedge, can produce more than 100 dormant and non-dormant tubers in one cropping season in irrigated rice paddies.

Ability to Survive and Adapt to Adverse Conditions

Weeds are capable of resisting drought and excessive moisture stress. Large crabgrass (Digitaria sanguinalis) form contractile roots and arrests its growth during extremely dry conditions and resumes their normal conditions until a favorable condition is met. The common purslane (Portulaca oleracea) incline their leaflets upward to reduce exposure to sun during dry conditions thus reducing excessive moisture loss due to transpiration.

Propagules Possess Dormancy or Can be Induced to Dormancy

Dormancy is a mechanism that enables the species to survive under unfavorable conditions. This mechanism is common to weed species and until a favorable condition for growth is observed.

Adapted to Crop Competition

Weeds have proper synchronized germination. They are able to germinate at the right time in favorable environments. Their seedlings are fast growing and can be rapidly established. Their quick response to moisture and nutrient availability make them well adapted to crop competition in the agroecosystem.

It is very important to know the characteristics of weeds so that proper and effective weed management measures can be design to solve weed issues. What even makes it difficult is that weeds are also plants, like the crop planted in the field, anything that can harm them can possibly harm the crop as well. The soil too is a seed bank of thousands of weeds so it is expected that a weed can grow in empty spaces in the agroecosystem. Weeds are also are important in disease development because some weed species are alternate hosts of some pathogens. Weeds also provide a niche for other insect pests in the field, hence, controlling them is a very important management practice in the field.

This entry was posted on Wednesday, January 14th, 2009 at 10:09 pm and is filed under Agriculture, Pests, Weeds. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.