Essential oils (EOs) are alternatives to synthetic insecticides used to control aphids that attack brassica species. However, the effects of species such as the Brazilian pepper tree (BPEO) Schinus terebinthifolius (Raddi), lemon eucalyptus tree (LEEO) Eucalyptus citriodora (Hook), and citronella grass (CGEO) Cymbopogon winterianus (Jowitt) on these organisms, as well as on beneficial insects, has been poorly studied. This work was aimed to evaluate the activity of BPEO, LEEO, and CGEO, at concentrations of 0.5% and 1%, on aphids Brevicoryne brassicae (Linnaeus) and Myzus persicae (Sulzer) (Hemiptera: Aphididae) applied on leaf discs and/or cabbages, as well as the chemotaxic effects on its natural enemy Diaeretiella rapae (McIntosh) (Hymenoptera: Braconidae). The results showed that the essential oil of C. winterianus had a higher mortality rate for B. brassicae (100%) (0.5%, 48 h) and M. persicae (98.99%) (1%, 48 h). The average number of aphids (both species) found on cabbage leaf discs treated with 0.5% and 1% of the three essential oils (separately) was always lower than those found on leaf discs treated with water. Essential oils at 1% presented significantly higher mortality rates for B. brassicae and M. persicae than the control treatment. Females of D. rapae were attracted to plants of green cabbage with essential oil (0.5%) of S. terebinthifolius, but did not respond to E. citriodora and were significantly responsive to plants sprayed with water when contrasted with those in the presence of C. winterianus oil.

Two field experiments were established at the Agricultural Experimental Station of the National Research Centre at Nubaria, Beheira Governorate, Egypt to study the herbicidal potential of the leaf extract of Eucalyptus citriodora at 5, 10, 15, 20 and 25% compared to two hand hoeing, unweeded treatments and the chemical herbicides Bentazon + Clethodium, Bentazon + Fluazifop-P-butyl and Butralin on pea plants and associated weeds. The results indicated that two hand hoeing achieved the maximum weed depression as expressed by the dry matter of total weeds. The dry matter of total weeds decreased by 95.08 to 94.77% as compared with unweeded treatment 50 and 70 days after sowing (DAS) followed by Butraline (93.93–94.65%), Bentazon + Clethodium (93.26–94.07%), Bentazon + Fluazifop--P-butyl (91.82–92.77%) and leaf extract of Eucalyptus at 25% (91.61–91.95%). Furthermore, the reduction in weed development was accompanied by enhanced pea growth and yield. The results revealed that two hand hoeing was the best treatment to increase plant height, shoot dry weight and SPAD value at 50 and 70 DAS. Also, two hand hoeing produced the maximum values of pod length and number of seeds/pod. The results also indicated that Bentazon + Clethodium treatment gave observable values [recorded 72.96% in pod yield (ton ⋅ fed.–1) over that of unweeded control] of number of pod/plant, weight of pod/plant, seed yield/fed and protein percentage. Also, the results revealed great increases in the growth of pea as well as yield due to treatment with E. citriodora dry leaf extract at 25%. [recorded 64.8% in in pod yield (ton ⋅ fed.–1) over that of unweeded control]. So, the results indicated using Bentazon + Clethodium as well as E. citriodora dry leaf extract at 25% to control weeds associated with pea plants. The authors suggested application of E. citriodora dry leaf extract at 25% in controlling weeds associated with pea plants as a safe method that avoids environmental contamination.