**7. Chemical weed management**

Chemical weed management in cucumber is mainly through the use of herbicides of different active ingredients. Although only limited herbicides are registered and available for weed control in cucumber, herbicides are an essential component of a successful weed control program in cucumber production [78]. These herbicides either pre-emergence or post-emergence, when applied at correct dosage and appropriate timing hampers weed growth and development [6, 7]. Herbicides use in cucumber reduces drudgery and labor requirement, and makes weed control easy, efficient and economical. It also improves soil structure by boosting soil moisture and reducing soil erosion. However, effective weed control with the use of herbicides is limited by the potential for crop injury from registered herbicides [7, 28,]. Herbicides application at too high rate can damage cucumber while too low rate will not provide the expected weed control [5]. Best results from herbicides application in cucumber are obtained when the weeds are at their highest susceptible stages and the crop is at its highest tolerance stages. Selection of a suitable herbicide program for cucumber depends on the population, growth stage, biology and ecology of the infesting weed species [10, 14, 15]. Much of chemical weed control in cucumber revolves around two key herbicides: ethalfluralin and clomazone which gives a reasonable control over most weeds [20]. Both herbicides are safe to use on cucumber and are generally applied pre-emergence for grass and broadleaved weed control [34]. Pre-emergence and post-emergence herbicides are used for effective weed control in cucumber. Pre-emergence herbicides can be applied before the planting of cucumber. These herbicides remain active in soil and provide control of weeds before they emerge. However, pre-emergence herbicides should be used with extreme care as they can damage the cucumber seedlings [5, 20]. Although pre-emergence herbicides such as N-1-naphthylphthalamic acid (naptalam) provides satisfactory control of the grasses and broadleaved weeds, erratic performance of the herbicide was observed in cucumber [79, 80]. Cucumbers were tolerant to 3.4 to 4.5 kg/ha of naptalam applied immediately after seeding but were injured by applications at emergence or vining [79, 80]. Reduced yields and crop injury with pre-emergence applications of CDEC at 4.5 kg/ha was also reported in cucumber [79, 80].

**119**

*Weed Interference and Management in Cucumber (*Cucumis sativus *L.)*

Registered herbicides for broadleaf weed control in cucumber include halosulfuron, clomazone, ethalfluralin, bensulide, paraquat, carfentrazone and glyphosate. Glyphosate, paraquat, and carfentrazone are effective on *Palmer amaranth* when applied as post-emergence herbicide. However, these herbicides are only registered in cucumber for non-selective control of emerged weeds pre-plant, pre, or post along the crop rows with the use of spray guard [81–83]. These herbicides lack residual control and have limitations when applied post-directed [20], including the failure to control weeds beneath or closes to the crop canopy. Therefore, additional post herbicides that are non-toxic to the crop would be beneficial. Halosulfuron is registered for pre and post-emergence control of some *Amaranth* species [84] but does not give an effective post-emergence control of *Palmer amaranth* [85]. Clomazone has poor efficacy on *Palmer amaranth* when applied alone [85, 86]. Ethalfluralin applied as pre-emergence herbicide provides good early season control of *Palmer amaranth* [87]. Bensulide is an herbicide used as pre-emergence in cucumber and can be tank-mixed with naptalam. Bensulide primarily controls annual grasses, with suppression of only three broadleaf weeds [88]. Bensulide may persist in the soil for months, which may result in potential injury to cucumber [34]. Farmers also often use a combination of clomazone and ethalfluralin for weed management in their cucumber production. Clomazone applied alone suppresses several annual broadleaf weeds and grasses. Clomazone controls *galinsoga* species (Galinsoga spp.), common lambsquarters (Chenopodium album L.), spurred anoda (Anodacristata L.), and velvetleaf (Abutilon theophrasti Medicus.) [20]. However, the herbicide has potential to injure cucumber and adjacent vegetation as a result of volatilization and drift. Ref. [46] found that clomazone caused chlorosis in cucumber plants, though recovery was rapid. Similar to clomazone, ethalfluralin provides efficient control of many broadleaf and grass weeds and may injure cucumber. Carpetweed (*Mollugo verticillata* L.), common lambsquarters, pigweed spp. (*Amaranthus* spp.), common purslane (*Portulaca oleracea* L.), and annual grasses are controlled by ethalfluralin. Injury to cucumber from ethalfluralin differs from that of clomazone in that stunting of plants and thinning of plant stand may occur. A major factor that increases injury from ethalfluralin in cucumber is rainfall, irrigation and increased seeding depth [34, 88]. Combination of clomazone and ethalfluralin provided excellent control of annual grass and broadleaf weeds. Ref. [46] reported that applying clomazone and ethalfluralin together controlled hairy nightshade (*Solanum sarrachoides* Sendt.), redroot pigweed (*Amaranthus retroflexus* L.) and smartweed (Polygonoum persicaria L.) better than either herbicide alone. Although this herbicide combination is effective against a number of weed species, they have little to no activity on weed species such as smooth pigweed (*Amaranthus hybridus* L.), morning glory species (*Ipomoea* spp.), and yellow nut sedge (Cyperus esculentus L.) weed species which interferes with harvesting and reduce cucumber fruit quality [26].

*DOI: http://dx.doi.org/10.5772/intechopen.99564*

**8. Integrated weed management in cucumber**

Integrated weed management is the major component of a sustainable cucumber farming. Considering the diversity of weed problem, no single method, whether physical, mechanical or chemical can provide the desired level of efficiency under all situation [19]. Hence, cucumber growers should focus on adopting integrated weed management system to widen weed control spectrum and efficiency in a sustainable, economical, and environmental manner. Integrated weed management involves coordinated use of multiple tactics for optimizing the control of all classes of weed in an ecological and economical sound manner [43]. These tactics can be direct weed control through physical (manual and mechanical tillage/land

#### *Weed Interference and Management in Cucumber (*Cucumis sativus *L.) DOI: http://dx.doi.org/10.5772/intechopen.99564*

*Cucumber Economic Values and Its Cultivation and Breeding*

context of integrated weed management.

**7. Chemical weed management**

management, weeds in fallow fields are killed and the weed seeds buried in deep soil layers where they cannot emerge. Mechanical weed control in cucumber also involves plowing or disking to destroy weeds by exposing them to variations in light, moisture and temperature [77]. Secondary tillage practices such as harrowing is also used to dislodge and shred weeds in cucumber field. Although these practices destroys weed quickly, they do not provide season-long effect because some weed seeds are still present close to the soil surface [77]. It is therefore imperative to use mechanical weed management before or during early flowering to prevent the production of large quantity of weed seed, and engage follow-up weed control practices to achieve effective weed control. The best practice is usually to cultivate cucumber at the preliminary stage of weed growth when the weeds are still physiologically immature to exert significant competition with the crop [65]. Mechanical weed control cannot be used as the singular method of weed management because it may provide favorable conditions for emergence and dispersal of dormant weed seeds. It also impact the soil structure negatively resulting in soil dryness and compaction [65]. Hence, mechanical weed control must be used only as a supplement to other weed control practices within the

Chemical weed management in cucumber is mainly through the use of herbicides of different active ingredients. Although only limited herbicides are registered and available for weed control in cucumber, herbicides are an essential component of a successful weed control program in cucumber production [78]. These herbicides either pre-emergence or post-emergence, when applied at correct dosage and appropriate timing hampers weed growth and development [6, 7]. Herbicides use in cucumber reduces drudgery and labor requirement, and makes weed control easy, efficient and economical. It also improves soil structure by boosting soil moisture and reducing soil erosion. However, effective weed control with the use of herbicides is limited by the potential for crop injury from registered herbicides [7, 28,]. Herbicides application at too high rate can damage cucumber while too low rate will not provide the expected weed control [5]. Best results from herbicides application in cucumber are obtained when the weeds are at their highest susceptible stages and the crop is at its highest tolerance stages. Selection of a suitable herbicide program for cucumber depends on the population, growth stage, biology and ecology of the infesting weed species [10, 14, 15]. Much of chemical weed control in cucumber revolves around two key herbicides: ethalfluralin and clomazone which gives a reasonable control over most weeds [20]. Both herbicides are safe to use on cucumber and are generally applied pre-emergence for grass and broadleaved weed control [34]. Pre-emergence and post-emergence herbicides are used for effective weed control in cucumber. Pre-emergence herbicides can be applied before the planting of cucumber. These herbicides remain active in soil and provide control of weeds before they emerge. However, pre-emergence herbicides should be used with extreme care as they can damage the cucumber seedlings [5, 20]. Although pre-emergence herbicides such as N-1-naphthylphthalamic acid (naptalam) provides satisfactory control of the grasses and broadleaved weeds, erratic performance of the herbicide was observed in cucumber [79, 80]. Cucumbers were tolerant to 3.4 to 4.5 kg/ha of naptalam applied immediately after seeding but were injured by applications at emergence or vining [79, 80]. Reduced yields and crop injury with pre-emergence applications of CDEC at 4.5 kg/ha was

**118**

also reported in cucumber [79, 80].

Registered herbicides for broadleaf weed control in cucumber include halosulfuron, clomazone, ethalfluralin, bensulide, paraquat, carfentrazone and glyphosate. Glyphosate, paraquat, and carfentrazone are effective on *Palmer amaranth* when applied as post-emergence herbicide. However, these herbicides are only registered in cucumber for non-selective control of emerged weeds pre-plant, pre, or post along the crop rows with the use of spray guard [81–83]. These herbicides lack residual control and have limitations when applied post-directed [20], including the failure to control weeds beneath or closes to the crop canopy. Therefore, additional post herbicides that are non-toxic to the crop would be beneficial. Halosulfuron is registered for pre and post-emergence control of some *Amaranth* species [84] but does not give an effective post-emergence control of *Palmer amaranth* [85]. Clomazone has poor efficacy on *Palmer amaranth* when applied alone [85, 86]. Ethalfluralin applied as pre-emergence herbicide provides good early season control of *Palmer amaranth* [87]. Bensulide is an herbicide used as pre-emergence in cucumber and can be tank-mixed with naptalam. Bensulide primarily controls annual grasses, with suppression of only three broadleaf weeds [88]. Bensulide may persist in the soil for months, which may result in potential injury to cucumber [34].

Farmers also often use a combination of clomazone and ethalfluralin for weed management in their cucumber production. Clomazone applied alone suppresses several annual broadleaf weeds and grasses. Clomazone controls *galinsoga* species (Galinsoga spp.), common lambsquarters (Chenopodium album L.), spurred anoda (Anodacristata L.), and velvetleaf (Abutilon theophrasti Medicus.) [20]. However, the herbicide has potential to injure cucumber and adjacent vegetation as a result of volatilization and drift. Ref. [46] found that clomazone caused chlorosis in cucumber plants, though recovery was rapid. Similar to clomazone, ethalfluralin provides efficient control of many broadleaf and grass weeds and may injure cucumber. Carpetweed (*Mollugo verticillata* L.), common lambsquarters, pigweed spp. (*Amaranthus* spp.), common purslane (*Portulaca oleracea* L.), and annual grasses are controlled by ethalfluralin. Injury to cucumber from ethalfluralin differs from that of clomazone in that stunting of plants and thinning of plant stand may occur. A major factor that increases injury from ethalfluralin in cucumber is rainfall, irrigation and increased seeding depth [34, 88]. Combination of clomazone and ethalfluralin provided excellent control of annual grass and broadleaf weeds. Ref. [46] reported that applying clomazone and ethalfluralin together controlled hairy nightshade (*Solanum sarrachoides* Sendt.), redroot pigweed (*Amaranthus retroflexus* L.) and smartweed (Polygonoum persicaria L.) better than either herbicide alone. Although this herbicide combination is effective against a number of weed species, they have little to no activity on weed species such as smooth pigweed (*Amaranthus hybridus* L.), morning glory species (*Ipomoea* spp.), and yellow nut sedge (Cyperus esculentus L.) weed species which interferes with harvesting and reduce cucumber fruit quality [26].
