ISSUE 16 August 22, 2002
TIMING OF HERBICIDE APPLICATION FOR LEAFY SPURGE CONTROL IN THE FALL
Several herbicide options are available for leafy spurge control in the fall. Each has advantages and as a group allow leafy spurge control in a variety of environments.
Tordon plus 2,4-D will has a wide window for control of leafy spurge in the fall. This treatment should be applied at 1qt Tordon plus 1 qt 2,4-D/A from late August until a killing frost in mid-October. Tordon plus 2,4-D will also control Canada thistle in the fall as well as many other broadleaf weeds. Most people are familiar with this treatment as it has been used for many years in North Dakota.
Plateau is a new herbicide that is labeled for use in pasture and rangeland as well as non-crop for leafy spurge control. Plateau generally provides better long-term control of leafy spurge than any other treatment available but has a relatively narrow window of application in the fall. Research at North Dakota State University has shown that Plateau should be applied at 8 oz product/A with 1 quart of methylated seed (MSO) oil in mid-September. Application in mid-August or early October resulted in a 20 to 30% decrease in leafy spurge
control (Figure). The addition of 28 percent UAN liquid fertilizer to Plateau plus MSO has occasionally increased long-term leafy spurge control.
(Data are 12 months after treatment. From Markle and Lym, Weed Technology, 2001, 15:474-480).
Plateau can reduce grass production the following season, especially the cool-season species. The label allows Plateau to be applied up to 12 oz product/A, but NDSU research has shown little increase in long-term control and much higher grass injury when Plateau is applied at the maximum rate.
Plateau is safe to use near and around a variety of trees. Check the label for the specific species you are concerned about. Research has found that conifer species can show temporary yellowing of stem tips, especially young growth candles. However, these injury symptoms generally dissipate without any long-term injury to the tree. Plateau will kill lilacs if applied directly to the foliage.
Paramount is an auxin-type herbicide with moderate soil residual that will control both annual grasses and some broadleaf weeds, especially field bindweed and leafy spurge. Paramount has a wide window for leafy spurge control in the fall and can be used from early September to mid-October. The current labeled use rate is only 0.5 pounds DF which will suppress leafy spurge but not provide long-term control. The manufacturer is working to increase the maximum labeled use rate. In the interim, to increase long-term control, Paramount can be applied with Distinct, a combination of Banvel plus diflufenzopyr. Diflufenzopyr is an anti-auxin compound that when added to Paramount can double long-term leafy spurge control. Currently, diflufenzopyr is only available in combination with Banvel. The current maximum use rate of this mixture is Paramount at 8 oz/A with Distinct at 6 oz/A plus 1 qt MSO/A. Paramount alone or combined with Distinct should be applied during either the true-flower or fall regrowth stages prior to a killing frost. Paramount is labeled for leafy spurge control only in non-cropland, industrial sites, and roadsides that are not hayed or grazed.
Glyphosate + 2,4-D (Campaign or Landmaster BW) will provide season-long leafy spurge control, but there is a risk of grass injury, especially when fall-applied. Glyphosate + 2,4-D at 3.38 pints of Campaign or Landmaster BW applied once during the early seed-set growth stage in July will provide 75 percent or better leafy spurge control with 0 to 10 percent grass injury. However, when fall applied control drops to 60 to 70 percent control and grass injury increases to 30 percent or more. This is the least expensive herbicide treatment available for leafy spurge control and costs about $8/A. Glyphosate plus 2,4-D can be used in areas with a high water table, next to streams and lakes, and is safe for use under trees.
PERENNIAL WEEDS: 10 THINGS NOT TO DO
1. Ignore small patches - The infestation may have started in a corner of a field and would have been much less trouble to control then but do not delay - control before the patch spreads.
2. Misidentification - The first commandment in successful control is knowing the real identity of the enemy.
3. Let plants go to seed - Perennials can expand by seed and vegetatively.
4. Manage in conventional crops - The advent of glyphosate resistant crops allows effective and economic control of perennial weeds.
5. Let them have the fence rows - Thatís where many bad infestations start so monitor them close.
6. Use tillage before planting - This is not an effective control strategy in a glyphosate resistant crop. Tillage resets the development clock (plants will reach the bud to flower stage later) and may result in erratic emergence than when left undisturbed (except burndown). If perennials are present - think no-till.
7. Apply to young perennials - With in-crop applications, apply when perennials are larger and more shoots have emerged. The Hunter-method of Canada thistle control should be used if at all possible - see page 102 paragraph T2 in the ND Weed Guide.
8. Disregard cultivation - Perennial are set back considerably by tillage. Cultivation used in combination with herbicides results in better control.
9. Spread propagules with tillage equipment - Root segments, tubers, and rhizomes can be carried from field to field without proper cleaning and prevention. The rush to get across the fields may cause people to overlook the sanitization of equipment.
10. Map - Fall is an excellent time to map the weed patches and areas in fields where perennials are established. This is better than guessing next spring after you have been out of the field for a while.
SHIFT FOR BIOTECH WHEAT
Monsanto announced it will shift its strategy for introducing the world's first biotech wheat to include an emphasis on developing enhanced health, taste and texture traits to appeal to food companies and consumers and hopefully open up world markets to the controversial grain.
Genetically modified Roundup Ready wheat could create several efficiencies in crop production but staunch opposition to biotech wheat in many key international markets has made U.S. farmers fearful about adopting the technology and virtually the entire organized U.S. wheat industry has demanded that Monsanto move cautiously in any introduction.
As a result, the shift by Monsanto came about in the last few months after input from different players in the wheat industry which caused Monsanto to backed off of its previously-stated timeline for introducing Roundup Ready wheat by 2005. Delaying the timeline will allow time for Monsanto to increase market acceptance before the introduction of the new biotech wheat seed.
NDSU Extension Weed Specialist