showed strong herbicidal potential to control Phalaris minor Retz. [21]. Acroptilon
repens L., a commonly found weed in the western United States, showed herbicidal
potential against Echinochloa crus-galli (L.) P. Beauv., Agropyron smithii Rydb.,
and Bromus marginatus Steud. [22]. Aqueous extract of different plant parts of
Croton bonplandianum Baill. exhibited herbicidal potential against the weeds
including Melilotus alba L., Vicia sativa L., and Medicago hispida Gaertn. [23].
Two weed species, i.e., E. crus-galli and winter cherry (Withania somnifera (L.)
Dunal), were tested for their potential to control Avena fatua L., and allelopathic
extracts from both the weeds inhibited the germination and seedling growth of A.
fatua [24]. However, rare studies are available on identification and extraction of
herbicidal compounds from weed species.
D’Abrosca et al. [25] identified 24 different phytotoxic compounds in Sambucus
nigra L. belonging to various groups including lignans, cyanogenins, phenolic glycosides, and flavonoids. These phytotoxic compounds showed strong inhibitory effects
on germination and growth of lettuce (Lactuca sativa L.), onion (Allium cepa L.),
and radish (Raphanus sativus L.) [25]. Honeyweed (Leonurus sibiricus L.)
contained various phytotoxic compounds that showed an inhibitory effect on rice,
wheat, and mustard [26]. Aqueous extract of Conyza canadensis L. showed a strong
inhibitory effect on various crops due to the presence of different phenolics, including gallic acid, syringic acid, catechol, and vanillic acid [27]. Sasikumar et al. [28]
stated that the strong inhibitory effect of different plant parts of Parthenium
hysterophorus L. on the germination and growth of various crops was due to the
presence of phenolic acids identified in this weed. Similarly, Chenopodium
ambrosioides L. and E. crus-galli also contain various phytotoxic compounds that
were found to inhibit the germination and growth of different crop species [29, 97].
Zohaib et al. [30] reviewed more than 30 weed species containing phytotoxic
compounds that showed strong inhibition against various crops and weeds; the
phytotoxic potential of these weeds can be explored to manage weeds. The most
commonly found phytotoxic compounds in weeds were alkaloids, fatty acids,
phenolics, terpenoids, indoles, lignans, cyanogenins, flavonoids, and coumarins
[30]. Furthermore, allelopathic compounds released from aquatic weeds showed
more phytotoxic activity against various terrestrial weeds and crop plants [31],
because plants of a certain ecosystem might be well adapted to the allelochemicals
compared to the ones of any other ecosystem [31, 32]. Thus, phytotoxic compounds
released from aquatic weeds can be identified and used as potential bio-herbicides. In
crux, the use of weeds to make herbicides can be an environment-friendly option to
control weeds in crops for sustainable crop production.
3
Ways to Use Allelopathic Potential for Weed Management
3.1
Intercropping
Growing of crops together at the same time in the same field is an important
strategy to increase input (land, fertilizer, and water) use efficiency and to enhance
crop yield and economic returns [33]. In addition, intercropping especially with
508
N. Farooq et al.
repens L., a commonly found weed in the western United States, showed herbicidal
potential against Echinochloa crus-galli (L.) P. Beauv., Agropyron smithii Rydb.,
and Bromus marginatus Steud. [22]. Aqueous extract of different plant parts of
Croton bonplandianum Baill. exhibited herbicidal potential against the weeds
including Melilotus alba L., Vicia sativa L., and Medicago hispida Gaertn. [23].
Two weed species, i.e., E. crus-galli and winter cherry (Withania somnifera (L.)
Dunal), were tested for their potential to control Avena fatua L., and allelopathic
extracts from both the weeds inhibited the germination and seedling growth of A.
fatua [24]. However, rare studies are available on identification and extraction of
herbicidal compounds from weed species.
D’Abrosca et al. [25] identified 24 different phytotoxic compounds in Sambucus
nigra L. belonging to various groups including lignans, cyanogenins, phenolic glycosides, and flavonoids. These phytotoxic compounds showed strong inhibitory effects
on germination and growth of lettuce (Lactuca sativa L.), onion (Allium cepa L.),
and radish (Raphanus sativus L.) [25]. Honeyweed (Leonurus sibiricus L.)
contained various phytotoxic compounds that showed an inhibitory effect on rice,
wheat, and mustard [26]. Aqueous extract of Conyza canadensis L. showed a strong
inhibitory effect on various crops due to the presence of different phenolics, including gallic acid, syringic acid, catechol, and vanillic acid [27]. Sasikumar et al. [28]
stated that the strong inhibitory effect of different plant parts of Parthenium
hysterophorus L. on the germination and growth of various crops was due to the
presence of phenolic acids identified in this weed. Similarly, Chenopodium
ambrosioides L. and E. crus-galli also contain various phytotoxic compounds that
were found to inhibit the germination and growth of different crop species [29, 97].
Zohaib et al. [30] reviewed more than 30 weed species containing phytotoxic
compounds that showed strong inhibition against various crops and weeds; the
phytotoxic potential of these weeds can be explored to manage weeds. The most
commonly found phytotoxic compounds in weeds were alkaloids, fatty acids,
phenolics, terpenoids, indoles, lignans, cyanogenins, flavonoids, and coumarins
[30]. Furthermore, allelopathic compounds released from aquatic weeds showed
more phytotoxic activity against various terrestrial weeds and crop plants [31],
because plants of a certain ecosystem might be well adapted to the allelochemicals
compared to the ones of any other ecosystem [31, 32]. Thus, phytotoxic compounds
released from aquatic weeds can be identified and used as potential bio-herbicides. In
crux, the use of weeds to make herbicides can be an environment-friendly option to
control weeds in crops for sustainable crop production.
3
Ways to Use Allelopathic Potential for Weed Management
3.1
Intercropping
Growing of crops together at the same time in the same field is an important
strategy to increase input (land, fertilizer, and water) use efficiency and to enhance
crop yield and economic returns [33]. In addition, intercropping especially with
508
N. Farooq et al.