Efeito do extrato aquoso de folhas de juazeiro (Ziziphus joazeiro Mart.) no controle do ácaro vermelho (Tetranychus ludeni Zacher, 1913) em algodoeiro (Gossypium hirsutum L.)

Abstract

Pests are one of the main factors affecting the operation of the cotton crop and among the species of economic importance, stands out the red spider mite Tetranychus ludeni. The use of synthetic miticides to control this pest, although effective, can cause problems for humans, the environment and resistance of these arthropods the products. Therefore, there has been growing interest in using plant extracts to control mite. In view of this, aimed to evaluate the intensity of injuries caused by T. ludeni and their feed preference in four varieties of cotton (BRS 201, BRS Safira, BRS Verde and BRS Aroeira). They were also carried out tests of toxicity, repellence, efficiency, phytotoxicity and residual effect of aqueous extract of juazeiro leaves in control of T. ludeni in var cotton. BRS 201. The first experiment was carried out in wooden cages lined with voile fabric type, which were placed on the cotton varieties, arranged in square and a central vessel containing bean-to-hog (control). 60 days after planting, the bean to hog plants were infested with 30 females of T. ludeni. To estimate the intensity of injuries, 0, 12 and 25 days after infestation, leaves were evaluated using a visual rating scale with limits of 0 to 4. After 25 days of infestation was taken for sampling the number of mites/plant. The experimental design was a randomized block design with three replications. The extracts concentrations (w/v) were 0%, 1.5%, 3.0%, 4.5%, 6.0% and 7.5%. For the assessment of toxicity leaf discs were used (Ø 3 cm) of cotton BRS 201. On each disc were placed 10 adult females of T. ludeni. They were then sprayed the extracts of concentrations with the aid of a manual spray bottle. The arenas were kept in climate chamber. After 48 hours, was performed counting living and dead individuals. The experimental design used was completely randomized, with six treatments and 10 repetitions. The repellency test was conducted in arenas containing two leaf discs (cotton variety of BRS 201), one disk treated (immersed) with the aqueous extract of juazeiro sheet (LC50) and the other with distilled water. Then they were placed in Gerbox® type plates and interconnected by a cover slip, which were released 10 adult females of the mite. After 48h, it was noted and the number of live mites on each disk. The experimental design used was completely randomized with two treatments and 10 repetitions. In the experiment III, to evaluate the control efficiency at 60 days, the cotton plants were infested with 30 adult females of T. ludeni mite. At 15 days after infestation the jujube extract at a concentration of 3.54% (w/v) (LC50) was sprayed on plants. After 48 hours was performed T. ludeni adult female count with manual loupe aid with 9 cm³ area up to 120 hours. To evaluate the residual effect after 60 days, the cotton plants were previously sprayed with the LC50 (3.54% (w/v)) of juazeiro extract. After three hours, one day, two, four, eight and sixteen days, arenas leaves were collected and made with leaf discs. In each arena are placed 10 adult females of T. ludeni. The arenas were kept in B.O.D. chamber. After 48 hours was performed counting living and dead individuals. To evaluate the plants phytotoxicity notes were assigned according to the intensity of symptoms. The experimental design used was completely randomized with two treatments and 10 repetitions. The results were submitted to analysis of variance and the means compared by Tukey test at 5% probability. In relation to feed preference, there was no significant difference in the number of T. ludeni individuals among the tested cotton varieties. However, compared to the level of injuries caused by this mite it has been observed that varieties BRS 201 and BRS Verde were the most significantly attacked. For toxicity of extracts to T. ludeni, there was a significant difference. The highest concentrations were 48-64% mortality with moderate toxicity to mite T. ludeni. The LC50 determined was 3.54% (w/v), with mortality and 76.47% repellent effect. There was control efficiency for 120 hours, with an average of 78.02%, with no significant difference between the assessment intervals. The juazeiro extract has a low residual effect for mortality and oviposition of T. ludeni over 16 days, taking better action by contact. The plants showed no toxicity symptoms. With these results, we can infer that the varieties BRS 201 and BRS Verde are more susceptible to attack T. ludeni and the jujube extract has potential as an alternative control of T. ludeni in cotton, with a promising strategy to be inserted into programs management of this pest in the semiarid region.