Magazine - Professional Turf Diaries With Jerry. Pt. 3

By Jerry Spencer in Consultancy on 26th Feb 2008 6:00

In Jerry's diaries we will look at ethofumesate. Ethofumesate has been available for years but is seldom used as other ‘easier’ options are now available which are not always the best option.

Poa annua control in creeping bentgrass.


Creeping bentgrass is more sensitive to ethofumesate than perennial ryegrass. However, when using a lower herbicide rate Poa annua control may not be as good. Poa annua control with ethofumesate was erratic at the lower rates (< 0.825 kg/Ha).
Results conducted in North Carolina indicated that Poa annua was effectively controlled for 7 to 8 months in creeping bentgrass greens when ethofumesate was applied at 0.56 kg/Ha to 0.85 kg/Ha in each of three applications. They found that the highest control was obtained when the first application was made in October than when applied earlier or at a later date. Poa annua control in Rhode Island was also effective in creeping bentgrass when ethofumesate was applied at 0.56 kg/Ha to 0.85 kg/Ha in 2 or 3 applications. Dates of treatments in Rhode Island ranged from September + October + November, October + November + April, to October + November. However, there were some indicates from these dates that the November treatment resulted in better Poa annua control than did the September treatment. Poa annua was reported to be affected with ethofumesate at > 0.87 kg/Ha, but Poa annua was most susceptible when treated prior to the four-leaf growth stage. However, the optimum ethofumesate rate for Poa annua control in creeping bentgrass was 0.87 kg/Ha.
The control of Poa annua in creeping bentgrass in Australia was improved during winter and early spring from sequential ethofumesate and bensulide treatments. The control was only 56% by late spring when ethofumesate was applied at 0.18 kg/Ha in each of three applications compared to 78% from the same ethofumesate treatments plus bensulide at 18.75kg/Ha applied in the autumn and spring.

Summary.
To control Poa annua effectively with lower rates of ethofumesate (< 0.85 kg/Ha) in creeping bentgrass it will require moreapplications and the timing of application may be more important than when the herbicide is applied at rates 0.85 kg/Ha

Poa annua control in dormant couch.
Ethofumesate was applied to an infested dormant common couch with Poa annua in Georgia at the time similar treatments were made to a weed-free couch green overseeded with perennial ryegrass. Ethofumesate applied at 1.12 kg/Ha in October resulted in poor Poa annua control (28%) by mid-April. When the 1.12 kg/Ha rate was applied in October and repeated in November the control was > 80% at three sites in March. However, by mid-April the control at two sites dropped to 66 and 76% while the control at the third was excellent (98%). When rates for ethofumesate were increased to 1.68 kg/Ha and applied in two applications in October and November Poa annua maintained a high level throughout the spring. When ethofumesate treatments were delayed until November and December, the control was consistently lower than when treatments were made in October and November. Treatments delayed until after January had little or no activity on Poa annua in Georgia but was excellent for 10 weeks when ethofumesate was applied at 1.12 kg/Ha in December and again in January in Mississippi.

Summary.
There are many PRE herbicides that will provide excellent Poa annua and other winter annual weeds in dormant couch in Georgia and other southern states with a single autumn application such as oxadiazon, pendimethalin, and prodiamine.
The performance of these herbicides are consistently higher on many winter annuals than ethofumesate. The herbicide should be limited only to couch overseeded with perennial ryegrass. Ethofumesate can also suppress the growth of couch when applied while actively growing at time of overseeding with perennial ryegrass.

Effects of N with ethofumesate for Poa annua.
N positively increased the efficacy of ethofumesate on Poa annua control while increasing bentgrass safety. Ethofumesate applied at 0.85 kg/Ha in October, November, and April controlled 38% Poa annua while the control increased to 82% when N at 0.225 kg N/100 m2 was applied with the herbicide. While information in the literature on this subject is limited, results on sequential applications of N and Fe with ethofumesate has also improved the efficacy of ethofumesate.

Summary.
Sequential applications of N with ethofumesate offers a mean to improve the activity of ethofumesate on Poa annua control while improving the safety of the treated turfgrass.

Multiple year ethofumesate treatments for Poa annua control.
Although ethofumesate treatments were needed in sequential years to maintain Poa annua control. Effective control was obtained during the second year using lower ethofumesate rates than used the first year. Ethofumesate applied at 0.85 kg/Ha in each of two applications in the autumn reduced Poa annua population the first year, but when repeated at the same rates the second year, the control was near complete.

Factors that influence the performance of ethofumesate on Poa annua control.
For a herbicide to be successful, it must be used at optimum rates, dates of applications, and correct timing between applications in order to obtain optimum and consistent performance. Most persons have experience excellent results from a herbicide, only to obtain unacceptable results at a different time or location. This variation may be in part due to environment, but management of the herbicide is important for successful control.

Dates of application.
Sod growers in New England has been frustrated with the inconsistency of ethofumesate performance. The lack of Poa annua control may be due to improper timing of applications. A number of persons have indicated a variation in Poa annua control with ethofumesate from different application dates. In North Carolina ethofumesate applied in October controlled a higher percentage of Poa annua than when the same rate was applied in August, September, or December. The hotter temperatures in August and September probable dissipated ethofumesate before Poa annua seed germinated while the POST ethofumesate applied in December did not control the larger Poa annua plants. Similar results were noted in Georgia as the October and November ethofumesate treatments controlled a higher amount of Poa annua than when treatments were delayed until November and December. Ethofumesate applied in spring and summer in Michigan had poor activity on Poa annua.

Rates and number of applications.
The variation in Poa annua with ethofumesate can be caused by improper rates and timing of repeated applications. Although a single ethofumesate may control Poa annua effective at some locations, repeated applications are usually needed for consistent control. In general, the number of applications with ethofumesate at > 1.12 kg/Ha will be fewer than when the herbicide is applied at < 0.85 kg/Ha. Reports showed that the first ethofumesate application was less important in controlling Poa annua than the second or third applications. For example, the first application at 0.56 kg/Ha followed by the second application at 1.12 kg/Ha will give better Poa annua control than if the first application is 1.12 kg/Ha and the second application is 0.56 kg/Ha. Poa annua control in North Carolina was higher with three ethofumesate applications than with two applications. They reported no advantage in Poa annua control when ethofumesate was applied more than three applications.


Improve inconsistent control.
Inconsistent Poa annua control may be improved from sequential PRE herbicide with ethofumesate as reported in Australia or with addition of N as reported by Spak. The inconsistent control may also be related to resistant genotypes. Further reports stated that the control of several biotypes of Poa annua collected from Georgia, Iowa, Michigan, and Rhode Island treated with ethofumesate varied in control from 13 to 100%, which indicates that resistant genotype were present.

Digitaria Control
Ethofumesate applied as PRE has good to excellent activity on Digitaria sp. The control with ethofumesate applied once at 1.12 kg/Ha in Tennessee and 1.8 kg/Ha in Rhode Island ranged from 73 to 89%. > 90% control when ethofumesate was applied at 1.12 kg/Ha in each of two applications, but two applications at 1.8 kg/Ha in Maryland controlled only 77% of the weed. These results show that the performance of ethofumesate on Digitaria sp will vary.
The performance of ethofumesate on Digitaria sp in the same plots over a 4-year period was evaluated and the control was > 80% for 10 weeks each year when the herbicide was applied at 1.12 kg/Ha in each of two years the first year and at 0.56 kg per ha in each of two applications the other years. Since Digitaria sp control in the south and other areas require up to 6 months or more. It is questionable whether ethofumesate can be economically used for Digitaria sp, when several PRE herbicides such as oxadiazon, bensulide, and pendimethalin will provide effective Digitaria sp control (> 90%) throughout a long season.
Timing of ethofumesate treatments will also influence Digitaria sp control. Digitaria sp control was not as effective when ethofumesate was applied as early POST compared with the same rate applied as PRE in Rhode Island.

Summary
Ethofumesate has PRE activity on Digitaria sp, but the response was not consistent. Multiple applications during the same year did not always improve the consistency. In most instances, ethofumesate did not perform as effectively as did regular recommended Digitaria sp herbicides. For instance two applications of ethofumesate controlled Digitaria sp 77% in Maryland while > 90% control was obtained with dithiopyr, prodiamine, and oxadiazon at the same location.

Read more articles in Consultancy, by Jerry Spencer or from February 2008.