Effects of seed treatment and foliar fungicides on Helminthosporium leaf blight and on performance of wheat in warmer growing conditions.
As the wheat (Triticum aestivum L.) cultivars of south Asia are susceptible to Helminthosporium leaf blight (HLB) caused by Cochliobolus sativus and Pyrenophora tritici-repentis, chemical control through seed treatment and foliar fungicides could increase yields. A field study was conducted in 2002 and 2003 to determine the effect of seed treatment and foliar fungicides on disease and performance of wheat. Presown seed infection by the pathogen was determined in a laboratory test. Seed was treated with Vitavax® 200B, Bavistin® and Simonis carbendazim in 2002, and Areestin® instead of Simonis carbendazim in 2003. One and two foliar sprays with Opus®, Allegro®, Horizon® and Tilt® were tested, along with a control treatment. Cochliobolus sativus was isolated from 8 and 34% presown seeds in 2002 and 2003, respectively, and no P. tritici-repentis was found. Seed treatments were not equally effective: Vitavax® 200B increased germination by up to 43% in both years and reduced seedling infection by C. sativus in 2003. The foliar fungicides reduced HLB severity and increased grain yield. Compared with the control, the highest reduction in area under disease progress curve (AUDPC) was 53% in 2002 and 63% in 2003. The highest increase in grain yield over the control due to fungicide spray was 38% in 2002 and 83% in 2003. Grain infection in 2002 (39%) and 2003 (70%) in the control plot was reduced to 16 and 24%, respectively, thanks to the application of foliar fungicides. Two fungicide sprays in most cases did not reduce the AUDPC and grain infection and increased grain yield any more than did one spray. The results show that seed treatment was not effective in reducing HLB severity and increasing grain yield, but foliar fungicide spray was. The cost-benefit analysis shows that one spray could be cost-effective for all four fungicides when a susceptible cultivar is planted under high HLB severity.