Damage and benefit caused by weeds
Various studies on weeds show very large differences between their competitive abilities. In the United Kingdom, the most competitive species in cereals have been determined to be, by order of importance: Avena fatua (Poaceae), Galium aparine (Rubiaceae), Tripleurospermum maritimum subsp. inodorum (Asteraceae), Alopecurus myosuroides (Poaceae), Papaver rhoeas (Papaveraceae), Lamium purpureum (Lamiaceae) and Veronica hederifolia (Plantaginaceae). In studies performed near Madrid in Spain, the competitivity of several weeds was ordered as follows: Avena sterilis (Poaceae), Bromus diandrus (Poaceae), Galium tricornutum (Rubiaceae) and Veronica hederifolia (Plantaginaceae). During a three year study, yield losses near Madrid were estimated to be 12, 37 and 75% for densities of Avena fatua of respectively 170, 220 and 1200 plants/m².
The impacts of weeds have been the object of various studies, and with the growing interest in biodiversity there are nowadays attempts to consider the benefits of these species. The majority of data on these aspects has been assembled in the United Kingdom, looking at the advantages of the presence of weeds for insects and birds. The value of some weeds for insects and birds as well as their competitivity with cereal crops is summarized in the table below:
|
Weed species
|
Value for insects 1
|
Value for birds 1
|
Competition with wheat 2
|
|
Avena fatua (Poaceae)
|
0
|
0
|
5
|
|
Fallopia convolvulus (Polygonaceae)
|
?
|
3
|
17
|
|
Fumaria officinalis (Papaveraceae)
|
0
|
1
|
63
|
|
Galium aparine (Rubiaceae)
|
3
|
0
|
2
|
|
Lamium purpureum (Lamiaceae)
|
2
|
0
|
63
|
|
Papaver rhoeas (Papaveraceae)
|
1
|
?
|
13
|
|
Polygonum aviculare (Polygonaceae)
|
3
|
3
|
50
|
|
Sinapis arvensis (Brassicaceae)
|
3
|
2
|
13
|
1 0: no importance; 1: important for a few species; 2: important for some species; 3: important for many species
2 Density of weeds (plants/m²) that cause a 5% yield loss in wheat.
Sources
Fernández-Quintanilla C ; Dorado J (2007) [Damages and benefits caused by weeds]. Malherbologia 193, 12-16 (in Spanish).