Split apps of pre-emergent herbicides.
- First, less chance of turf injury; as you applying lower rates you are less likely to damage turf;
- Second, split applications work really well on freely draining rootzones i.e. sand; they reduce the chance of waste from leaching and
- Third, using pre emergents this way gives longer weed control later into the season especially if you use them with a post emergent sulfonylurea herbicide application at the same time..
Things to think about when using split applications.
Always remember, that to work these chemicals need weed seeds to be germinating in the soil. This means that the water volume you use is important to wash the chemical off the turf surface and into the soil. Most pre-emergents are rapidly absorbed into the cuticle, so if you don’t apply the correct water volume they give poor weed contol.
Soil moisture also affects the length of weed control. Moisture moves the chemical through the upper soil layer to create a protective layer and is also needed for weeds to germinate. Therefore to get the best results you need to make sure that there is good soil moisture before and after you apply a pre emergent herbicide.
Granular pre emergents are also worth looking at due to their ease of use. Bear in mind though, that they can be vulnerable to heavy downpours that will wash product away so water these in as soon as you can.
Pre-emergent herbicide half life dependant upon soil moisture content
Approximate half-life in moist soil
Approximate half-life in saturated soil
Trials using split apps of pre-emergent herbicides.
- In a trial using Freehand® and Specticle®, split applications of a half rate followed by a half rate three weeks later, gives longer weed control than the full rate.
- You get season-long summergrass control with split applications of prodiamine, pendimethalin, and dithiopyr, and it doesn’t matter which you use for the first and/or second application. The aim is to apply the same amount of active ingredient, as because split applications are more effective they give more consistent summergrass control than single applications.
- Research at CAFS into the effects of mowing height on single and split applications of preemergence herbicides for summergrass control.
- When mowed at 14mm, split applications give better control than single applications;
- When the height of cut is increased to 50mm, there are differences between single and split applications.
- When you mix Dispatch® with pre-emergents, it gives better summergrass control than only using pre-emergents. Recent trial work with abamectin plus Hydroforce® Ultra also gives better results and shows that soil wetting agents work as carriers for some turf chemicals.
- If you water in pre emergence herbicides straight after applying with 2.5 to 5mm of water, it gives up to a 50% increase in summergrass control in fairway-height Kentucky bluegrass.
- Pre-emergent herbicides don’t affect divot recovery.