Diversity of weed flora in onion fields of Punjab, Pakistan.
Weeds are serious management threat for onion (Allium cepa) production but very little information is available on their distribution frequency in various agro ecological zones of Pakistan. A project was designed to investigate distribution frequency of weeds of onion in Lahore, Kasur and Shiekhupra districts of Punjab, Pakistan. This study was designed in order to categorize the weeds and their relationship with crop production and protection. A detailed survey was carried out on autumn crop during the months of December-March 2013-2016. The information for weed distribution and its associated factors for crop production technology and effect of weed frequency and its impact on plant stand quality and yield were observed. On an average of 163 fields from more than 50 locations representing different sowing methods and location types were visited in each year. Field survey was classified on the basis of location type (rural, suburban and urban), method of sowing ridge, border, and intercrop. A total 33 weeds belonging to 16 angiosperm families were noted in onion fields that included Amaranthus hybridus, Amaranthus retroflexus, Anagallis arvensis, Atricaria chamomilla, Avena sterilis, Capsella bursapastoris, Carduus nutans, Chenopodium album, Chenopodium murale, Convolvulus arvensis, Cyperus rotundus, Digitaria sanguinalis, Euphorbia prostarta, Fumaria indica, Galium aparine, Lactuca serriola, Lolium temulentum, Malva sylvestris, Medicago polymorpha, Polygonum aviculare, Papaver rhoeas, Parthenium hysterophorus, Poa annua, Rumex dentatus, Setaria verticillata, Silybum marianum, Sinapis arvensis, Solanum nigrum, Sonchus asper, Sonchus oleraceus, Sorghum halepense, Stelleria media, Vicia sativa and Xantium strumarium. The highest weed invasion was in suburban areas where onion was grown on commercial or house hold consumption basis while lowest weeds frequency was in urban areas where small kitchen gardening was done. In kitchen gardening intercropping is also helpful to decrease the weeds invasion. The weeds C. album L., C. rotundus L., S. nigrum L., M. polymorpha L. showed 100% prevalence, while E. prostarta L. were in least frequency of 18%. This revision highlighted the requisite to grip weeds in order to grasp higher onion yields. It was observed among other families i.e. Fabaceae and Euphorbiaceae disturb the bulb size, number of leaves and plant height. Plant health quality was affected even at 18-20% distribution frequency describing the collective performance of weeds on agronomic traits of onion crop. Poaceae and Papaveraceae family weeds proved more harmful for onion plant stand, yield quality and all of the test parameters.