EFFECT OF SOWING DATES ON THE INSECT PESTS OF FENUGREEK PLANTS IN RELATION TO ACCUMULATED HEAT UNITS AT QALUBYIA GOVERNORATE, EGYPT

Abstract

The present work was conducted for two seasons (2010/2011-2011/2012) in the Plant Protection Research Station at Qaha, QalubiyaGovernorate to study the effect of different sowing dates (Oct.30th ;Nov.15thand Nov.30th) on the infestation of fenugreek plants(Trigonella foenum graecum) with insect pests and find models for therelationship between the accumulated heat units and seasonalpopulations of fenugreek pests. The obtained results revealed seveninsect pests infesting fenugreek plants, two species on the leaves(Liriomyza spp. and Bemisia tabaci) and five species on the terminalbuds (Acyrthosiphon pisum ; Aphis gossypii ; Aphis craccivora ;Thrips tabaci and Phytonomus brunneipennis) in different sowingdates and seasons. The seasonal populations of insect pests onfenugreek plants had varied in the three sowing dates and seasons. Inaddition, results showed that sowing fenugreek by mid-Novemberreceived lower infestation with insect pests than early and latelysowing dates (Oct.30th & Nov.30th) and the proper date for sowingfenugreek must be in the second half of November. On the other hand,results showed varied relations for accumulated heat units (DegreeDays Units) and the mean numbers of seasonal populations offenugreek pests. Calculation the accumulated heat units for thefenugreek insect pests confirmed the variability of seasonalpopulations in different sowing dates and seasons. The 1st season hashighly accumulated heat units for most insect pests than the 2nd onesand differences in the accumulated heat units ranged 7.5 -19.9% in thetwo seasons. The larvae of leaf miner, Liriomyza spp. have variedaccumulated heat units mostly increased with 13.8% in 1st season thanthe second ones. The accumulated heat units for B. tabaci were varied(435- 542.7 D°) in the two seasons and the difference reached 19.9%.There for, the insect don’t occur during the season if the accumulatedheat units below than 435 D°. The aphid species have highlyaccumulated heat units in the three sowing dates ranged 1003.3-1188.7D° in the 1st season and 901.0 - 1099.3 D° in the 2nd one withdifferences ranged 7.5 - 10.2%. Cotton thrips, T. tabaci has variedaccumulated heat units (782.7 - 891.7 D°) in the two seasons; the 1stseason has highly Degree-Days Units (DDD) than the 2nd one withdifference 12.2%. The clover leaf weevil P. brunneipennis has variedaccumulated heat units (603 - 715 D°) in the two seasons with difference 15.7%. The obtained results created beneficialmethodological developments for designing ecological zones maps fordistribution the insect pests over the country and designing dynamicprogram for integrated pest management (IPM) under differentecological conditions in Egypt.