02229naa a2200181 a 450000100080000000500110000800800410001910000190006024501060007926000090018552016140019465300160180865300270182465300240185170000170187570000170189277301380190911255952016-10-13       2016    bl uuuu     u00u1 u    #d1 aARA??JO, E. R.  aFeasibility of a weather-based decision support to control onion downy mildew.h[electronic resource]  c2016  aOnion downy mildew is one of the major production constraint. Weather-based decision support has been an important tool for the rational use of fungicides. The present study established a chemical management strategy of the disease based on temperature and relative humidity. We defined daily severity values (DSV) according to temperature range (08-13.9??C; 14-21.9??C; 22-29??C) and relative humidity ≥ 90% to carry out the spraying. The cultivar EMPASC 352 ? Bola Precoce was used. The treatments were applications of mancozeb/copper oxychloride or metalaxyl-M/chlorothalonil as a function of DSV (6-11; 12-17; ≥ 18), besides weekly sprays using these fungicides or water. The concentrations of mancozeb, copper oxychloride, metalaxyl-M, and chlorothalonil for all treatments were 1,875 ppm, 2,100 ppm, 100 ppm and 1,000 ppm, respectively. Downy mildew epidemics started by natural infection. Disease severity (area under disease progress curve-AUDPC) and yield of commercial bulbs were quantified. We have reduced by 20% the number of metalaxyl-M/chlorothalonil sprays in comparison to fixed calendar of application, maintaining the same levels of AUDPC and yield. Treatments using mancozeb/copper oxychloride not differ from the control (water weekly). Yield keeping associated with sprays reducing, as observed in this work, should be considered according to the extension acreage, average price of fungicide and onion for each region. Furthermore, this reduction implies less fungicide residue accumulation in the environment and less contamination risk of both field workers and consumers.  aAllium cepa  aPeronospora destructor  arational management1 aALVES, D. P.1 aKNOTH, J. R.  tIn: CONGRESSO BRASILEIRO DE FITOPATOLOGIA, 49., 2016, Macei??, AL. Resumos... Bras??lia: Sociedade Brasileira de Fitopatologia, 2016.