EFFECT OF NITROGEN LEVELS, SOWING DATES AND SPACINGS ON INFESTATION WITH THE THE LEAFMINER AGROMYZA NIGRIPES (MEIGEN) (DIPTERA: AGROMYZIDAE).

The effect of 4 nitrogenous fertilization levels, 3 sowing dates and row spacing on infestation with the leafminer Agromyza nigripes (Diptera : Argomyzidae) on wheat grain yield was investigated at El­Gemmeiza Agric. Gharbia Governorate, during the wheat growing seasons 1993-1994 and 1994-1995. Results indicated that percentage infested leaves and number of mines and alive larvae significantly in­creased by increasing nitrogen levels, except up to a rate of 80 kg/fed. Further increase of N fertilization insignificantly affected insect infesta­tion or population. All considered parameters and grain yield were signifi­cantly decreased by delaying sowing dates.Row spacing had no discerna­ble effect although grain yield was significantly increased at 20 cm spacing. Interactions between N level x sowing date, N level x row spac­ing and sowing date x row spacing expressed a significant effect on per­centage infestation number of mines and alive larvae as well as grain yield. Interactions of N level x sowing date x row spacing on numbers of mines and alive larvae were significant in 1993-94 and 1994-95 seasons and on infestation and grain yield in 1994-95 seasons only. With the ap­plication of nitrogen rates of 40,50, 60, 70, 80 and 90 kg/fed. to wheat plants sown on Dec.10 at 20 cm row spacing emphasized that, all con­sidered parameters were significantly reduced. Also, plants gave grain yields at a rate of 60 kg N/fed. compared to those receiving up to 80 and 90 kg N/fed. in 1995-96 and 1996-97 seasons. It is, thus, recom­mended that application of N at a rate of 60 kg/fed. to wheat plants sown by early December at 20 cm row spacing significantly reduced in­festation and produced the highest grain yield.