Combinations of Selected Sulfonylurea Herbicides with S-Metolachlor for Nutsedge Control in Tomatoes

Abstract

In 2005 and 2006 field studies were conducted at Auburn University’s E.V. Smith Research Station, Chilton County Research and Extension Center, and Wiregrass Research and Extension Center to evaluate combinations of selected sulfonylureas and S-metolachlor in controlling yellow nutsedge. In the summer of 2005 a study was conducted to evaluate nutsedge punctures with halosulfuron and S-metolachlor alone or in combinations. In bareground and plastic mulch, both S-metolachlor and halosulfuron resulted in a rate-dependent reduction in yellow nutsedge foliage. Main effects of both herbicides were significant, but the interaction was not, so theses two herbicides were additive with respect to their ability to control nutsedge. The most effective treatment was the high rate of either halosulfuron or S-metolachlor alone. In May of 2006, two field studies were conducted to evaluate combinations of halosulfuron and S-metolachlor on tomato yields. No interactions were observed so data was pooled over both locations. Nontreated bareground plots yielded the lowest of all treatments. Complete control of all weed species except yellow nutsedge was obtained in all plastic mulch treatments. Nutsedge growth resulted in 143 g of biomass and 31 punctures per plot. Plastic mulch treatments yielded 10.8 kg/plot of tomatoes, resulting in a three-fold increase compared to bareground. S-metolachlor PRE neither improved nutsedge control or tomato yield relative to plastic mulch treatments. S-metolachlor plus halosulfuron applied PRE, produced similar results compared to S-metolachlor PRE. S-metolachlor PRE followed by halosulfuron POST was the most effective treatment. However, nutsedge biomass and punctures were reduced 50 and 29% compared to plastic mulch alone. There was no PRE-applied treatment identified that reduced nutsedge penetration. Halosulfuron POST remains the most effective treatment in controlling nutsedge. Overall efficacy with respect to preventing plastic mulch punctures was marginal; as a result plastic mulch is largely limited to a single cropping season. In the fall of 2006 another field study was conducted to evaluate herbigation utilizing selected sulfonylureas and S-metolachlor combinations. All injected treatments compared to PRE applications had lower nutsedge biomass. Injected treatments resulted in a decrease of nutsedge biomass and number of punctures along with a higher percent control for all contrasts except the S-metolachlor/trifloxysulfuron tank mixture. Results from this one-time field study appear promising for this type of application. There is a need for further studies to determine the efficacy of this cost-saving application method should be repeated.