Magazine - Professional Turf Diaries With Jerry. Pt. 5

By Jerry Spencer in Consultancy on 25th Mar 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.

Summary of perennial ryegrass growing alone.
Ethofumesate can be effectively used for Poa annua control in perennial ryegrass in seed production fields and on golf course fairways and other similar managed turf sites. A single herbicide application controlled Poa annua in seed fields, while two applications were needed in areas where the grass was maintained as a turf.

Kentucky bluegrass tolerance.
When ethofumesate is used for Poa annua in Kentucky bluegrass, extra caution is needed in selecting an ethofumesate rate. Kentucky bluegrass is more susceptible to ethofumesate than perennial ryegrass and creeping bentgrass. Rates > 1.4 kg/Ha caused unacceptable Kentucky bluegrass injury. Researchers in Rhode Island and Maryland also reported that severe injury occurred at rates > 2.24 kg/Ha. 0.85 kg/Ha was the maximum safe rate of ethofumesate for Kentucky bluegrass.

Summary Kentucky bluegrass.
Ethofumesate can be used for Poa annua control in Kentucky bluegrass turf. However, rates should never be higher than 0.85 kg/Ha. Some of the Kentucky bluegrass cultivars may be severely injured with ethofumesate rates less than 0.85 kg/Ha.
Therefore, it is important to know the cultivars readily susceptible to ethofumesate. Do not treat until this is known.

Creeping bentgrass tolerance.
Ethofumesate use in creeping bentgrass for Poa annua is primarily used on golf course fairways. In recent years, the herbicide has been evaluated under green conditions in the Southeast. Creeping bentgrass has more sensitively to ethofumesate than perennial ryegrass and tall fescue, but not as much as Kentucky bluegrass.

Fairways conditions.
rates > 1.4 kg/Ha caused unacceptable injury to creeping bentgrass maintain under fairway conditions. Caution should be made when selecting a rate of ethofumesate to be applied to creeping bentgrass. 0.85 kg/Ha is the maximum rate for creeping bentgrass.

Greens conditions.
It should be emphases that when creeping bentgrass is growing in compacted soils, has shallow roots, and growing in stress conditions, the turfgrass will be more susceptible to ethofumesate and other herbicide treatments. When the turf has any of these conditions, do not treat with ethofumesate.

Creeping bentgrass green had an acceptable tolerance when ethofumesate was applied at 0.85 kg/Ha to 1.12 kg/Ha. Although slight discoloration may occur following each herbicide application, creeping bentgrass tolerated ethofumesate applied at 0.85 kg/Ha in each of three applications. The > 2.24 kg/Ha rate of the herbicide did not have acceptable turfgrass tolerance. Similar response was observed in Georgia as maximum creeping bentgrass injury was only 18% when treated at 1.12 kg/Ha in September and repeated at the same rate in October. However, the timing of the second application was an important factor as related to turfgrass tolerance. Severe injury occurred to creeping bentgrass in Georgia when ethofumesate was applied at rates higher than 1.12 kg/Ha in October or at any rate in November. It was observed in Georgia and North Carolina that creeping bentgrass injury was higher in January when ethofumesate was applied during the coldest part of the year. The mean air temperature for 6 weeks after the November 30 treatment in Georgia was -120C colder during the year with the highest turfgrass injury.

Summary creeping bentgrass.
Ethofumesate can be applied in the autumn to a healthily creeping bentgrass green for Poa annua control providing the rates used are < 1.12 kg/Ha and applications not made later than October.

Sequential ethofumesate with other herbicides on tolerance of creeping bentgrass.
There are times when a turf manager must make a decision whether to apply two different chemicals together as sequential treatments. However, the turfgrass tolerance from these treatments may not be as good as from each chemical alone. The quality of creeping bentgrass in Australia was similar from ethofumesate alone or when applied with bensulide. However, when oxadiazon was used, creeping bentgrass was injured 36% from sequential ethofumesate and oxadiazon treatments. Since oxadiazon can cause moderate to severe injury to creeping bentgrass, the injury from this sequential applications was probable due to oxadiazon and not from ethofumesate in the ethofumesate plus oxadiazon combination.

Summary.
Care should be taken when more than one chemical is applied to various turfgrasses. Selected chemicals can safely be used on turf, but additional information is needed when ethofumesate is applied with other chemicals.

Effects of fertilizer applied with ethofumesate on creeping bentgrass.
When nitrogen (N) was applied with ethofumesate, the discoloration of creeping bentgrass during November, December, and March was reduced by 50%. Turf cover was slightly higher (8%) in April and turf colour was better in May from the additional of N. In Georgia when a fertility by ethofumesate interaction occurred on creeping bentgrass green, the quality of turf at the medium and high fertility levels was consistently higher than at the low fertility level.

Summary.
 Fertility applied in sequence with ethofumesate to creeping bentgrass either reduced discoloration or improved recovery compared to ethofumesate applied alone

Effects of iron (Fe) applied with ethofumesate on creeping bentgrass.
Sequential applications of ethofumesate plus flurprimidol has suppressed couch growing in creeping bentgrass in Georgia, but the treatments can cause moderate injury to the creeping bentgrass. When Fe was applied in Georgia at 1.9 kg/Ha with the ethofumesate plus flurprimidol treatments, the quality of creeping bentgrass was 17 to 31% higher at 2 to 3 weeks than with ethofumesate plus flurprimidol alone in 2 of 3 years. The results of Fe and N with ethofumesate indicate that both elements are beneficial to creeping bentgrass when ethofumesate is included as a chemical treatment.

Summary.
Some creeping bentgrass discoloration caused by ethofumesate can be masked with Fe treatments.

Tall fescue tolerance.
Tall fescue was not as tolerant to ethofumesate treatment as perennial ryegrass, but higher than creeping bentgrass and Kentucky bluegrass.

Couch cultivars.
The green-up of couch cultivars in the spring varies with dates of ethofumesate during the previous autumn and winter. In Georgia the green-up early April from ethofumesate at 1.12 kg/Ha in October and November was delayed only 7% for Tifdwarf, 16% for Tifway, 20% for Tifgreen, and 25% for Ormand couch cultivars. When the same rates were applied early February and March, the delay in green-up was > 82% for all cultivars.
The delay in green-up of Tifgreen couch in Mississippi ranged from 11% when ethofumesate at 1.12 kg/Ha was applied in December to 93% when the 1.12kg/Ha rate was applied in December and January. Plots treated with ethofumesate in December and January reduced Tifgreen couch green-up for 6 weeks. Higher rates resulted in longer delays in spring growth.

In North Carolina ethofumesate caused a premature onset of dormancy to all couch cultivars that was not dormant at time of ethofumesate treatment. He also reported that when ethofumesate was applied to couch after February 1, early spring growth may be temporarily delayed.

Summary.
The growth of couch can be expected to be delayed 6 to 7 weeks in the spring when ethofumesate was applied prior to dormancy in the autumn or when applied after January or February.

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