**3. Effect of weed interference on cucumber**

Weed interference is the detrimental effects of weed on crop resulting from their interaction with each other. Weeds are considered as the most harmful pest of crops, and their interaction with crops have considerable consequences on the economy, society, and the environment [33]. They limit crop productivity and profitability, alter the ecosystem function and hamper the sustainability of the agricultural system. Yield losses and reduced profitability due to weed interference is considered one of the major problem in cucumber production [10]. Even with advanced technologies, producers record high losses due to weed interference. According to estimates, between 45–95% potential yields of cucumber is lost due to weed interference depending on the type and density of weeds growing in the crop community, duration of weed interference, stage of crop growth at which the interference takes place and the crop variety [4, 22]. Generally, losses due to weed interference in cucumber can either be direct or indirect. Direct losses due to weed interference includes damages caused by weed's allelopathic interaction with cucumber and competition for growth resources such as nutrients, water, light and space [5, 10]. Weed interference affects cucumber production indirectly by sheltering crop pest and diseases, interfering with timeliness and efficiency of harvest, increasing harvest difficulties, reducing fruit quality and consequently increasing the cost of processing [34, 35]. Weeds are potential source for diseases and pest including powdery mildew (*Podosphaera xanthii*), gummy stem blight (*Didymella bryoniae*), fungal root rot (including *Pythium, Rhizoctonia* and *Fusarium*), thrips (Thrips palmi) which may be hosted by a variety of weeds including *Portulaca spp, Amaranthus spp*, *Gomphrena celosioides* and white fly [36–39].

Weed interference in cucumber begins during the very early stages of vegetative growth [5]. Unfortunately, cucumber is not a strong competitor at the early stage, therefore weeds out grow them during the early stage of crop growth, resulting in high yield reduction [4]. Weeds that germinates at the same time as cucumber such as annual weeds like *Amaranthus spp*, *Xanthium strumarium* and *Ambrosia artemisiifolia* grows faster and maintain canopy above and below the top of cucumber. Hence, these weeds intercept photosynthetically active radiation at the expense of the crop, resulting in reduced yield [40, 41]. Furthermore, weed-inflicted shading of cucumber flowers promotes flower abortion. Although cucumber becomes less vulnerable to weed competition after the vines run out or when they become well established, the crop may take a few more weeks to close canopy. Weeds that emerge during this period may complicate harvest by concealing fruit or hampering manual picking with prickly foliage, or entangling vines, and promote fungal diseases by limiting air circulation. *Solanum carolinense* is a host for cucumber powdery mildew fungus (*Erysiphecichor acearum*), and many common weeds such as *Amaranthus spp* and *Cyperus spp* can carry cucumber mosaic virus [42].
