the Symposium on Wheats for More Tropical Environments - cimmyt

48However, in field experiments withwheat, certain lines and cultivars haveshown a better response to normalfertUization than o<strong>the</strong>rs, probably dueto better adaptability to low-fertility andlow-pH soil conditions. It is importantto select <strong>the</strong>se cultivars, as well as o<strong>the</strong>rcrops such as barley and triticale, forbetter adaptability to Fraijanes soils.Weed controlWeed incidence is high in <strong>the</strong> threeareas where wheat research work hasbeen conducted, Cartago and centraland nor<strong>the</strong>rn Alajuela. In centralAlajuela, gramineous, cyperaceous andbroadleaf weeds prevail and, in Cartagoand nor<strong>the</strong>rn Alajuela, <strong>the</strong> broadleaf .weeds are dominant.Allelopathy and o<strong>the</strong>r factors due toweed competition have been consideredreasons for crop yield reduction, as aresult of Rottboellta exaltata andCyperus rotundus in central Alajuela.Considering solely weed competition.<strong>the</strong> gramineous weeds Eleusine indica.Digitaria spp.• Cynodon dactylon,Ixophorus unisetus and Paspalumpaniculatum have been shown to be<strong>the</strong> most important. Pennisetumclandestinum. Taraxacum offlcinale.Bidens pilosa, Amaranthus hybridus,Melampodium divaricatum andSpergula arvensis are considered to beimportant weeds in Cartago andnor<strong>the</strong>rn Alajuela.At present, <strong>the</strong> alternatives for chemicalcontrol of weeds seem to be Oic1ofopmethyland herbicides that inhibit <strong>the</strong>development of some hormone-inducedhydrolytic enzymes (hormonals).Oic1ofop-methyl is used to control somegramineous species, and <strong>the</strong>hormonals, broadleafand cyperaceousweeds. 2,4-0 or MCPA is used forpostemergence. and Perfluidone, forpre-emergence treatments. Linuron hasalso been used for broadleaf preemergencecontrol.8683l1---~~r------::!~"'~~~--r---1~---r----AtlanticOceanFraixines (1.650m)• I ,.•Fabio Baudrit Moreno r840m)10-----+-4lC'----~iiliI!=l~----=:....:....:~::...-=.==:::.:.;:....:.;.:~~....:...:.~::.:.:..-• Santiago Duran(2.337m) ~~~~~9-----.j-------+------.j--H.----+-....IIIIiI~----PacificOceanFigure 1. Wheat research centers In Costa Rica, 1984