Fall Buttercup Control in Grass Pastures and Hay Fields

Tired of looking out across your pastures and hay fields and seeing that “sea of yellow” every spring?  Unfortunately,  many producers in Tennessee are all too familiar with buttercups. According to Neil Rhodes, Professor and Extension Weed Management Specialist with The University of Tennessee, most of these members of the genus Ranunculus are winter annuals that are easily controlled with a timely application of 2,4-D, and  interest in fall applications has increased in Tennessee over the past few years.

Why spray in the fall?

Historically, the vast majority of applications for control of buttercups have been in March to early-April. However, University of Tennessee research and producer experience has continued to show that fall (late October to mid-December) is actually a better time to spray for them.  Why is that?  Buttercups emerge in the fall and they are small and actively growing then.  As we have discussed numerous times, one of the most important keys to getting good results is to spray buttercups before they bloom.  This is an automatic with fall applications, given that buttercups generally do not bloom until spring.  Also, oftentimes in the late-winter to spring it is very wet and windy, making it difficult to spray before they are in bloom.  Another  reason for fall spraying is that many producers may have more available time then, compared to the spring.  Time consuming late-winter to early-spring activities such as calving, spreading fertilizer  and getting ground ready for row crop planting often make it difficult to get pastures and hay fields sprayed on a timely basis.  Last, but certainly not least, fewer vegetable crops, gardens and active greenhouses are present then; this means the risk of off-target damage to sensitive plants is lower.

 

In most cases, 2,4-D ester at 1 qt./acre provides excellent control of annual buttercups in the fall. The same rules apply as with spring applications.  Favorable weather (3 days of day time highs of 60 F); plenty of water (at least 20 gallons per acre spray volume); and the addition of a good, nonionic surfactant (1 qt./100 gallons of spray mix)  are all important ingredients in success.  An added bonus for the fall spray program is that it is also a very good time of the year to control musk thistle, buckhorn plantain and wild turnip.  These are controlled by 2,4-D and are often present in the same fields alongside buttercups.  If buckhorn plantain is severe, consider increasing the rate of 2,4-D.   Keep in mind that 2,4-D, unlike some of our newer pasture herbicides (ForeFront HL, GrazonNext HL, etc.),  breaks down relatively quickly in soil.  A benefit of this is that with fall applications of 2,4-D, clovers can be planted the following February. 

Are buttercups becoming resistant to 2,4-D?

This is a startling question we have received from a number of producers over the past couple of years.  Our answer for now is “We don’t thinks so, and we sure hope not!”.  What has prompted this question is that a number of 2,4-D failures on buttercup have occurred in our area over the past few years.  These were not cases of late sprays, low rates, not enough water volume, or bad weather.  These were timely applications where everything was apparently done correctly.  We are keeping a close watch on this situation and are conducting research to address it.  Late this winter we scouted a number of pastures in Blount County where 2,4-D had failed the previous year.  Upon close inspection, we found that the predominant species present was not hairy buttercup (a winter annual and our most common species), but rather bulbous buttercup, a perennial that is not effectively controlled by 2,4-D.  While the leaf and flower structures of these two species are somewhat different, the most reliable way to identify bulbous buttercup is to dig up some plants and look for the swollen corm at the base of the stem.  We conducted a replicated research trial at one of the locations this past spring.  Ratings taken at 2 months after application revealed that 2,4-D ester (1 qt. /A)  gave only 42 percent control.  However, GrazonNext HL (1.6 pt./A) gave 90% control.  What we believe is happening in a number of area fields is not the development of resistance, but rather a species shift from the more easily controlled hairy buttercup to a predominance of the more difficult-to-control bulbous buttercup.  We will keep you posted on this issue.

Always remember to thoroughly read the herbicide label before application and follow all directions and precautions.

 Jeff Via

 

Knotroot Foxtail: A Major Issue in Bermudagrass Hay Production

Much of Tennessee, particularly West Tennessee, is well-suited for production of bermudagrass hay.  An increasing number of producers across our state have been successful producing high-quality bermudagrass hay in small bales for sale at a premium to horse owners, municipal zoos, and other buyers.  Weed management has always been a challenge in bermudagrass production.  However, that challenge has greatly increased in recent years for many producers in West Tennessee due to the spread of knotroot foxtail, a fast-growing, perennial weedy grass.  The grass not only reproduces by seed, as is the case with the annual foxtails, but it also produces rhizomes, or underground stems.  The key problem with this weed and the other foxtails is that the bristly seed heads in hay cause serious problems with mouth ulcers in horses.

 

Becky Muller (Shelby County Extension Agent),  Jeff Via (Fayette County Extension Director)  Trevor Israel ( Extension Assistant – Weed Management) , and Neil Rhodes (Professor and Extension Weed Management Specialist) have teamed-up to work toward solutions for producers affected by this costly weed.  During the winter of 2012, problem hay fields in several West Tennessee locations were sampled.  Dormant foxtail clumps were exhumed and inspected for the presence of the tell-tale rhizomes.  As expected, knotroot foxtail was confirmed in numerous locations.  The team visited with researchers and Extension Specialists  in other southern states where knotroot foxtail has been present for much longer than in Tennessee, and learned that although a number of investigators have conducted research on this weed over the past 2 to 3 years, the best herbicide options have only given suppression.

 

In spring, 2012, the team worked closely with a number of producers and encouraged them to implement a sequential program of Pastora + glyphosate, followed by a second application of Pastora, with the goal of seed head suppression.  Where properly implemented, the program did suppress seed heads and allow for cleaner hay for the first 2 to 3 cuttings.  However, the program is expensive and quite injurious to bermudagrass.  And, the weed rebounded in late summer. 

 

Efforts in 2013 have included numerous farm visits to work with affected producers, educational  meetings, on-farm, replicated research trials in the spring and fall, and a fact sheet that is currently in development.   It is hoped that these and other future efforts will lead toward effective, affordable solutions to this problem, thereby increasing the viability of this high value agricultural enterprise in Tennessee.

                                   

 

Jeffery D. Via