|Culpepper, A - UNIV. OF GEORGIA|
|Flanders, J - UNIV. OF GEORGIA|
|York, A - NC STATE UNIVERSITY|
Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 31, 2003
Publication Date: April 1, 2004
Citation: Culpepper, A.S., Flanders, J.T., York, A.C., Webster, T.M. 2004. Tropical spiderwort (Commelina benghalensis L.) control in glyphosate-resistant cotton (Gossypium hirsutum L.). Weed Technology. 18(2):432-436. Interpretive Summary: Tropical spiderwort (Commelina benghalensis) is a federally noxious exotic invasive weed that has recently become the most troublesome weed in Georgia cotton. Tropical spiderwort has become more prevalent in Georgia due to its relative tolerance to glyphosate (based on plant size) coupled with the widespread planting of glyphosate-resistant cotton varieties (nearly 90% of Georgia's cotton acreage). An experiment was conducted at four locations to determine tropical spiderwort control in glyphosate-resistant cotton by 27 herbicide systems. Results indicated that tropical spiderwort has a season-long pattern of emergence. As a result, management systems will need to account for both control of emerged plants at the time of application as well as provide some type of residual control. Tropical spiderwort control from glyphosate was only 53% for early postemergence over-the-top treatments. The addition of pyrithiobac to this mixture improved control to 60%, however the lack of residual control contributed to this relatively poor rating. The combination of glyphosate with S-metolachlor controlled tropical spiderwort 80% at 21 days after planting (DAT) due to the addition of residual control. Glyphosate applied late-postemergence-directed (LPD) controlled tropical spiderwort 70 and 44% at 21 and 130 DAT, respectively. At cotton harvest, systems without residual herbicides at LPD controlled tropical spiderwort 42 to 45% compared with 64 to 76% with LPD treatments that included diuron or flumioxazin.
Technical Abstract: Tropical spiderwort (Commelina benghalensis) has recently become the most troublesome weed in Georgia cotton. Most of Georgia's cotton acreage is planted with glyphosate-resistant (GR) varieties, and glyphosate is only marginally effective on tropical spiderwort. An experiment was conducted at four locations to determine tropical spiderwort control in GR cotton by 27 herbicide systems. Treatments consisted of three early postemergence over-the-top (POT) herbicide options and nine late postemergence-directed (LPD) options arranged factorially. Glyphosate POT controlled tropical spiderwort only 53% at 21 days after treatments (DAT). Glyphosate plus pyrithiobac or S-metolachlor controlled tropical spiderwort 60 and 80%, respectively. Pyrithiobac improved control of emerged spiderwort while S-metolachlor provided residual control. Pooled over POT treatments, glyphosate LPD controlled tropical spiderwort 70% at 21 DAT. Dimethipin mixed with glyphosate did not improve control. Carfentrazone, diuron, or flumioxazin mixed with glyphosate LPD improved control 9 to 15%. MSMA and MSMA plus flumioxazin were 8 and 19% more effective than glyphosate LPD. At time of cotton harvest, systems without residual herbicides at LPD controlled tropical spiderwort 42 to 45% compared with 64 to 76% with LPD treatments that included diuron or flumioxazin.