Magazine: Sulfonyl Ureas and Tracking
By Jerry Spencer in Consultancy on 4th Nov 2007 9:00
With all of the registered sulfonyl urea herbicides that are used to control perennial ryegrass or Poa annua in warm-season turf there is a danger of lateral movement or “tracking” occuring and the subsequent injury of neighboring cool-season grasses.
Work both there and in the USA has shown that:
· Some Sulfonylureas require watering after application.
· Some Sulfonylureas recommend the use of surfactants.
· Sulfonylureas should never be applied within seven days of organophosphate insecticides to avoid excessive herbicide injury.
· Turfgrass tolerance can vary widely between seemingly similar herbicides. Halosulfuron can be safely applied for sedge (Cyperus spp.) control in both cool- and warm-season turfgrasses. In contrast, trifloxysulfuron (Monument) adequately controls sedges, but will cause significant injury to, or loss of, some cool-season turfgrasses. Therefore, the simple mistake of confusing two SU herbicides can have severe consequences.
· Do not mix sulfonylureas with other chemicals that control grass weeds i.e graminicides. Amongst these can be included diclofop-methyl. If this occurs the activity of the graminicides can be severely impaired.
Although turfgrass managers have several new Sulfonylurea herbicides for weed control, the speed at which these herbicides are coming to
market can make it difficult to recall which herbicide is most useful for a given situation. The intention of this article is to produce a quick reference to detail turfgrass tolerance and weed control for all sulfonylurea herbicides that are currently used, or being developed, for use in turfgrass weed control. Much of this information comes from the USA and consequently this article is not endorsing the use on unregistered pesticides but instead is a summary in many cases on overseas research.
Because of the importance of herbicide absorption by the plant from the soil for complete control, it stands to reason that application methods that maximize both root and foliar absorption could increase efficacy. Irrigating after application or applying the herbicide at higher spray
volume could potentially put greater amounts of the herbicide in contact with the soil to be absorbed by roots and rhizomes.
However, caution should be taken to minimize the lateral movement of sulfonylurea herbicides in surface water. Heavy irrigation or rainfall soon after herbicide application could move the herbicide laterally and injure sensitive species. Application in the proximity of sensitive species, such as on green surrounds and approaches should be done with caution.
If you must apply a sulfonylurea herbicide in the proximity of a sensitive non target plant species, here are some general suggestions:
· Plan your herbicide application as best you can around the weather. Apply when you know rain will not occur for at least two days.
· Apply the herbicide and allow it to absorb into the foliage for four to six hours. Maximum foliar absorption of sulfonylurea herbicides occurs within four hours (Askew and Wilcut, 2002; McElroy et al., 2004). Thus, the remaining herbicide does not need to stay on the foliage.
· After four hours, use two or three light, frequent irrigations to move the herbicide into the soil profile. Make sure irrigations are light enough to wash the remaining herbicide from the leaf, but not enough to create mass water flow over the surface. Irrigation rates are especially important on heavy clay soils with low infiltration rates.
These steps can also aid with another potential problem with sulfonylurea herbicides which is relocation by equipment and human
traffic. Tracking of sulfonylurea herbicides can occur when sufficient quantities of the herbicide remains on wet foliage and, before the herbicide can dry; traffic moves the herbicide on to nontarget species. Sometimes herbicide is slow to dry because conditions are not optimal for drying on the foliage. Weather conditions such as overcast skies with high humidity could potentially reduce herbicide drying.
In other cases, herbicide may dry properly but the chemical remains on the leaf surface and is later re-dissolved with dew. Thus, precautions should be taken to insure that herbicide is washed from treated leaves after maximum absorption has occurred.
· SU herbicides adsorb on the soil more under acidic soil conditions and de-sorb to the soil solution under basic soil (high pH) conditions. Hence, basic soils are prone to cause phytotoxicity or injury to plants more than acidic soils.
· Herbicide resistance to SU herbicides has been observed in field crops so golf course superintendents should rotate SU's with other herbicides with a different mode of action.
· SU herbicides should be applied at least 10 days to 14 days before overseeding to reduce injury to ryegrass.
· Optimum control of weeds is observed when SU herbicides are applied to actively growing weeds.
· Since most of the SU herbicides are very toxic to cool-season turf, care should be taken to reduce spray drift.
· Tank-mixing with other herbicides or insecticides may lead to turf injury.
For more contact or view:
e-mail: jerry.spencer@etpturf.com.au
web: www.etpturf.com.au
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With all of the registered sulfonyl urea herbicides that are used to control perennial ryegrass or Poa annua in warm-season turf there is a danger of lateral movement or “tracking” occuring and the subsequent injury of neighboring cool-season grasses.
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