BACKGROUND:  Glyphosate is a widely used broad-spectrum herbicide.  Recent studies in glyphosate-resistant (GR) crops have shown that, in addition to its herbicidal activity, glyphosate exhibits activity against fungi, thereby providing disease control benefits.  In GR wheat, glyphosate has shown both preventive and curative activities against Puccinia striiformis f. sp. tritici (Erikss) CO Johnston and Puccinia triticina Erikss, which cause stripe and leaf rusts respectively. RESULTS:  Laboratory studies confirmed earlier observations that glyphosate has activity against Phakopsora pachyrhizi Syd & P Syd which causes Asian soybean rust (ASR) in GR soybeans.  The results showed that glyphosate at rates between 0.84 and 1.68 kg ha-1 delayed the onset of ASR in GR soybeans.  However, field trials conducted in Argentina and Brazil under natural infestations showed variable ASR control from application of glyphosate in GR soybeans.  Further field studies are ongoing to define the activity of glyphosate against ASR. CONCLUSIONS:  These results demonstrate the disease control activities of glyphosate against rust diseases in GR wheat and GR soybeans.