Background: Cotton is one of the most important industrial crops in Egypt and worldwide. During its growth stages, cotton is threatened by several pests including aphids (Aphis gossypii Glover) and whiteflies (Bemisia tabaci) which lead to deleterious effects on cotton growth, yield, and quality. Due to health and environmental hazards of pesticides, it is important to reduce them by using eco-friendly alternatives. Two field experiments were carried out to investigate the effect of some insecticides including profenofos (Prf), cyhalothrin (Cyh), and imidacloprid (Imd) individually or in combination with salicylic acid (SA) against cotton aphids and whiteflies. Results: All spray treatments had potent and moderated effects against aphids and whiteflies, respectively. The Prf insecticide at 100% of the recommended dose was the most effective one against both pests followed by the Cyh. The insecticidal effect of SA against the tested pests was concentration dependent. The most effective combination treatments were Prf at 75% of recommended dose + SA at a concentration of 1 mM for aphids (reduction % 95.68), and Cyh at 75% of recommended dose + SA (0.5 mM) for whiteflies (reduction of 88.00%). All tested insecticides, individually or in combination with SA, significantly increased total phenolic (TP) content in treated plants compared with control. The maximum increase in TP content was recorded in cotton plants treated with Prf in combination with SA. Conclusions: Salicylic acid enhanced the effectiveness of the used insecticides, and thus, SA could be used to lower the amount of insecticides with increasing insecticidal efficacy.

Cotton is one of the most important fiber crops worldwide. Where it is cultivated in more than seventy countries. It is the raw material for several industries such as textile, ginning, food oil, soap, and many further industries. Cotton is one of the basic sources of national income from foreign currencies (Gillham et al., 1996).