The label provides two rate ranges depending on the size of yellow nutsedge.
Nutsedge that is 8-15 cm (3-6?) tall: 35 - 47 g/ha (14-19 g/ac)
Nutsedge that is 8-31 cm (3-12?) tall: 70 - 93 g/ha (28 - 37.7 g/ac)
When control of yellow nutsedge was evaluated at the Elora Research Station, the 47 g/ha (19 g/ac) rate provided very effective control More recently, Dr. Peter Sikkema has evaluated yellow nutsedge control at different rates and more consistent control was achieved at the highest labeled rate. I believe that different field populations of yellow nutsedge vary in their susceptibility to herbicides and therefore you will see a range in their level of control. Ultimately, you may choose to experiment with Permit rates on your farm to come up with a rate that works best. Ideally, you start with the highest rate and scale back the rate depending on the level of control achieved. Lastly, visual control of nutsedge top growth will occur slowly, so don't be surprised if the control is not impressive two or three weeks after application.
Example: Visual control of yellow nutsedge at 2 weeks after an application of Permit (19 g/ac) + Agral 90 (0.25% v/v) (right) compared with the untreated control (left).
Is an adjuvant required?
The manufacturer (Gowan) is recommending that a non-ionic surfactant (i.e. Agral 90) be added at 0.25% v/v (2.5 L/1,000 L of water) even when tank-mixing with a glyphosate product.
Does Permit provide residual weed control?
Yes, according to the label it will provide control of the following un-emerged species. (I have condensed the list to focus on species that are typically found in corn):
- pigweed species (not group 2 resistant biotypes)
- chickweed
- cocklebur
- hairy galinsoga
- Canada fleabane (not group 2 resistant biotypes)
- jimsonweed
- lady's-thumb
- lamb's-quarters
- flower-of-an-hour
- wild mustard
- yellow nutsedge (supression of un-emerged shoots)
Do I need to worry about crop safety?
2013 University of Guelph trials (Ridgetown campus) demonstrated acceptable levels of crop safety with a glyphosate + Permit + 0.25% v/v tank-mix. However, since Permit is a sulfonylurea herbicide (in the same family as Accent, Option, Peak, Ultim etc.) the potential for crop injury may be increased when applications are made:
- during periods of large swings in air temperatures (i.e. going from a low of 7° C to a high of 30° C).
- to sensitive hybrids (historically, certain seed corn companies published this information, but I have been unsuccessful in finding any specific guidelines, so ask your seed supplier).
- during very hot and humid conditions (above 28° C)
- if a soil or foliar applied organophosphate insecticide has been used (an unlikely scenario).
Source: OMAFRA