Potassium silicate, acibenzolar-S-methyl and fungicides on the control of soybean rust/Silicato de potassio, acibenzolar-S-metil e fungicidas no controle da ferrugem da soja

Soybean production can be affected by the occurrence of several diseases. Among them, the rust, caused by the fungus Phakopsora pachyrhizi, has been outstanding. Nowadays, new strategies to control soybean rust need to be searched. Therefore, this study aimed to evaluate the efficiency of potassium silicate (KSi), acibenzolar-S-methyl and some fungicides on the control of soybean rust. An experiment was carried out under field conditions in a randomized complete block design with 10 treatments and three replications. The cultivar 'Monarca' was used because it is susceptible to rust. The treatments used were: T1 - control (plants sprayed with water); T2 - KSi (1.2kg [ha.sup.-1]); T3 - KSi (2.4kg [ha.sup.-1]); T4 - KSi (3.6kg [ha.sup.-1]); T5 - KSi (4.8kg [ha.sup.-1]); T6 - tebuconazol (125g de a.i. [ha.sup.-1]); T7 - potassium cloride (61.72g [L.sup.-1]); T8 - mancozeb (2400g de a.i. [ha.sup.-1]); T9 - mancozeb (2400g de a.i. [ha.sup.-1]) + KSi (1.2kg [ha.sup.-1]) and T10 - acibenzolar-S-methyl (125g de a.i. [ha.sup.-1]). Plants from the two lateral lines were inoculated with a suspension of 5 x [10.sup.5] uredospores/mL at the V4 growth stage to produce inoculum to infect plants at the two central lines. Plants were sprayed with the products that constituted the treatments T2, T3, T4, T5, T7, T8, and T9 at V5, R1, R4, and R5.4 growth stages; and the treatments T6 and T10 at R1, R4, and R5.4 growth stages. Plants were sprayed using a costal sprayer in a volume of 200L [ha.sup.-1]. A total of five disease severity evaluations at the low, medium and high part of the plant canopy were done using a diagrammatic scale ranging from 0.6 to 78.5%. Data were used to calculate the area under rust progress curve (AURPC). There was no effect of the KSi rates on AURPC and final disease severity ([Y.sub.max]) at the low, medium and high part of the plant canopy. Yield was also unaffected. The treatments 8, 9, and 10 had an intermediary efficiency on rust control. The treatment 6 was the most efficient on rust control giving the lowest values for AURPC and [Y.sub.max] for the low, medium and high part of the plant canopy. High values for yield were also obtained using this treatment as compared to the others.