Two field trials were conducted at the newly reclaimed sandy clay loam soil at El-Nubaria region – Alexandria Governorate, A.R.E. in the two successive growing seasons 2008/2009 and 2009/2010 to investigate the effect of three pesticides: insecticide (pirimiphos-methyl), fungicide (metalaxyl) and the herbicide (pendimethalin) combined with two sowing dates, early, mid-Nov. and late date 5th Feb. on some growth characters: i.e., plant height, number of leaves/plant, fresh weight of leaves/plant, dry weight of leaves/plant, average weight of bulb and total yield of onion plant (Allium cepa L.) c.v. Giza 20. The recommended rates of these pesticides were individually applied.
The obtained results showed that all the studied parameters were significantly increased with the three pesticides, and pendimethalin was highly effective followed by metalaxyl while pirimiphos-methyl was the least effective. Total yield mean values were 22.40 and 22.68 ton/fed for pendimethalin and 18.96 and 19.14 ton/fed for metalaxyl and 10.06 and 10.70 ton/fed for pirimiphos-methyl compared with the control 8.32 and 8.64 ton/fed in the first and second seasons respectively.
All the studied parameters were increased in early sowing date, mid-Nov. compared with the late sowing date, 5th Feb. in the two seasons.
The interactions between the three pesticides and the sowing date had a significant effect on: number of leaves/plant in the first season, fresh weight of leaves, dry weight of leaves, average weight of blub in the two seasons and total yield in the first season.
The highest values of all these parameters occurred on pendimethalin at early sowing date, mid-Nov.