ISSUE 5 June 2, 2005
WEED CONTROL IN ALFALFA
A number of phone calls are coming about absinth wormwood control and control of other weeds, including dandelion in alfalfa. The rains across the state and large acreage of dryland alfalfa in ND, especially new planting, have brought on ideal conditions for wormwood and dandelion growth.
Unfortunately, Pursuit and Raptor do not control wormwood and dandelion. These herbicides control a long list of annual grass and broadleaf weeds but have no activity on perennial weeds. Velpar applied to dormant alfalfa controls some perennials like dandelion and quackgrass. Perhaps Velpar has activity on absinth wormwood but NDSU does not have any data to support this. Velpar is quite expensive so a grower must decide if the cost outweighs prolonging the life of the alfalfa stand.
Some have asked how much alfalfa injury would result if 2,4-D were used to control these weeds - not a good idea. It is illegal and serious injury and alfalfa stand loss will result. The ND Weed Guide shows 2,4-DB (Butyrac 200 or other brands) (NOT 2,4-D) as a POST option to control some broadleaf weeds. 2,4-DB is converted to 2,4-D in some plants but alfalfa does not metabolize it which gives it some immunity to the herbicide. The 2,4-DB label shows control of only a few annual broadleaf weeds, application must be made to very small weeds (1 to 3 inches), and shows no control of any perennial weeds like wormwood or dandelion. Growers have indicated wormwood is at least 6 inches tall at this time of the year so being a perennial and larger than 3 inch would give 2,4-DB poor control. There are no registered products that can effectively control perennial broadleaf weeds after alfalfa has broke dormancy. 2,4-DB has a 60 day PHI and grazing restriction for establishing alfalfa and a 30 day PHI and grazing restriction for established alfalfa. Growers can refer to page 45 of the ND Weed Guide for herbicide choices for early season application to dormant alfalfa.
Roundup Ready alfalfa will be available this fall which will provide a very effective solution to weed control in alfalfa. RUR alfalfa has a very level of tolerance so higher rates can be used to control annual and perennial weeds. Multiple applications can be made during one growing season to control multiple flushes of annual and perennial weeds also.
RAPTOR AND REZULT IN FIELD PEA
Apply Raptor postemergence in field pea. NDSU research has shown control of many small weeds when applied at 2 fl oz/A with an MSO adjuvant. The recommended rate is 4 fl oz/acre for small weeds and susceptible weeds like mustard spp., redroot pigweed, ALS susceptible kochia, lanceleaf sage, marshelder, nightshades, smartweed, sunflower, and Russian thistle. Raptor may not control large grasses and wild buckwheat, common lambsquarters, and ragweed. MSO oil adjuvant enhances the activity of Raptor more than petroleum oil or nonionic surfactants. A rate less than 4 fl oz/A can legally be used but if a rate less than 4 fl oz/A is used or label directions are not strictly followed then the grower assumes all liability and the manufacturer is removed from any responsibility for weed control or crop injury that might occur. Do not apply the 4 fl oz/A Raptor rate under cold weather conditions.
Rezult: What’s in the Co-pak?
Rezult is a co-pack of Basagran 5SL and Poast 1EC. The Rezult rate of 1.6 pt/A Rezult B + 1.6 pt/A Rezult G is equal to 1 pint of Poast 1.5EC and 2 pints of Basagran 4SL per acre. Always add MSO or oil adjuvant at 1.5 pt/A + AMS at 17 lbs or 5 gallons/100 gallons of water. Rezult is very safe to spray on peas and can be applied prior to the onset of bloom.
For optimum broadleaf control, apply Rezult when the weeds are less than two inches high and when pea are 3 to 5 inches high.
Basagran is very effective on mustards, cocklebur, marshelder, and sunflower but is weak on buckwheat, kochia, lambsquarters, pigweed, nightshade, ragweed, and Russian thistle. Split applications, each at a reduced rate and applied at 7 to 10 days intervals, will give greater weed control than one application at the full rate. Research has shown that two split application, each at 1 pt/A, or 3 applications, each at 0.75 pt/A improves wild buckwheat, redroot pigweed, common lambsquarters, and kochia control.
Why add Rezult/Basagran to Raptor?
The label directs to always add Basagran to the spray mixture to safen Raptor on field pea. The mechanism of safening (antagonism) comes from the Na salt in the Basagran formulation. Sodium antagonizes weak acid herbicides (See section A6, page 71-72 in the 2005 ND Weed Guide). The label also states that adding Basagran at 1 pt/A will increase control of common lambsquarters and ALS susceptible kochia. Basagran must be added at 6 to 16 fl oz/acre to decrease the potential of crop injury. If using the 4 fl oz/A rate with Rezult or Basagran, apply NIS at 0.25% v/v and AMS at 17 lbs/100 gallons of water.
The question being addressed is why add Basagran to Raptor? Will Basagran improve weed control from Raptor? A flat rate response has been observed with many ALS herbicides, meaning that similar control can occur with reduced rates as compared to a full herbicide rate. Raptor will control all weeds that Basagran will control. So why add $10/A of Basagran to antagonize $15/A of Rapor when the rate of Raptor could be reduced to achieve similar weed control and crop safety. Unfortunately, the label is written requiring Basagran to be applied with Raptor.
Why add Raptor to Rezult/Basagran?
Raptor added to Rezult or Basagran can improved control of large wild mustard and volunteer canola. Basagran alone will give good to excellent control of 3-leaf volunteer canola or smaller. Basagran is weak on larger volunteer canola (6-leaf or larger) and control is rated as only fair. Raptor at 2 fl oz gives good to excellent control of volunteer canola from the cotyledon to 6-leaf stage. Raptor will also improve nightshade and redroot pigweed control
What Rezult/Raptor rate should I use?
If no preemergent or preplant herbicides (Spartan, Sonalan, Prowl, etc) have been applied, then 3.2 pints/acre of Rezult and Raptor at 2 fl to 4 fl oz/acre should be used. If preplant or preemergent herbicides have been used, then 1.6 pints of Rezult/acre (which equals ½ pint of Poast/A and 1 pint of Basagran/A) and Raptor at 2 fl to 4 oz/A could be suggested. Always add MSO and AMS or liquid N at the suggested rates for the Rezult. If the 4 fl oz/A Raptor rate is used, then use NIS and AMS at the suggested rates.
NDSU Extension Weed Specialist