Herbicide Longevity in Alaska Soils. Steven Seefeldt

Transcription

1 Herbicide Longevity in Alaska Soils Steven Seefeldt

2 % of herbicide General Principles Persistence is the length of time a herbicide will stay in the soil Typically it is defined as half-life Many factors will influence the halflife Herbicide fate Days

3 General Principles Persistence is generally associated with Adsorption to the soil High Medium Low Decomposition Weakly persistent <30 day half life Moderately persistent 30 to 100 days Strongly persistent >100 days

4 General Principles Adsorption is a function of Negatively charged organic matter and clay Chemistry of the herbicide molecule Paraquat and Diquat have strong positive charges so they bind easily and irreversibly to clay and organic matter

5 General Principles Decomposition is a function of Sunlight (photochemical) Chemical reactions in soil Microbial Herbicides can be food for microbes Microbe populations can respond making soil active herbicides less effecient

6 General Principles Adsorption and decomposition rates are impacted differently by soil moisture Increased moisture decreases adsorption Increased moisture increases decomposition Pursuit (imazethapyr) and a drought in the PNW

7 General Principles Adsorption and decomposition rates are impacted differently by soil moisture Increased moisture decreases adsorption Increased moisture increases decomposition Pursuit (imazethapyr) and a drought in the PNW Temperature does not alter adsorption rates but it does alter decomposition rates Generally increased temperatures increase decomposition rates

8 Advertised half lives Typically large ranges on the labels Herbicide Half life Time until gone 2,4-D 10 days 1-4 weeks Glyphosate 47 days Strongly adsorbed to soil Metribuzin A few days to >4 months Depends Triclopyr 10 to 46 days 10 hours in water at 25 C Metsulfuron 1 to 7 weeks High ph slows degradation Aminopyralid 35 day average 0.6 day half life in water

9 Alaska Studies Past From Conn and Cameron 1988 Canadian Journal of Soil Science 68: In Delta Junction Metribuzin 12% left after 115 days 3% left after 3 years Metribuzin A few days to >4 months Depends

10 Alaska Studies Past From Conn and Cameron 1988 Canadian Journal of Soil Science 68: In Delta Junction Metribuzin 12% left after 115 days 3% left after 3 years Metribuzin A few days to >4 months Depends Norway study 2007 confirms 30 day half life during summer, 983 days otherwise

11 Alaska Studies Past From Conn and Cameron 1988 Canadian Journal of Soil Science 68: In Delta Junction Triallate 61% left after 115 days 10% left after 3 years Consequence was AK taken off Triallate label

12 Alaska Studies Past Newton et al Environmental Science and Pollution Research 15: Near Fairbanks and Homer Triclopy, Hexazinone, Imazapyr, Glyphosate Summer degradation as expected Very reduced degradation in winter Could not calculate half life

13 Alaska Studies Past Ranft et al 2010 Weed Technology 24: Triclopyr During summer half life was 10 days based on chemical extraction and 22 days based on plant bioassay. Triclopyr 10 to 46 days 10 hours in water at 25 C In winter degradation ceased.

14 Results: Delta Junction CRP 0-5 cm Soil froze about 110 DAT and thawed about 276 DAT 5-15 cm cm

15 Alaska Studies Past Three graduate students 2,4-D, Triclopyr, Glyphosate During summer normal half lives No measurable degradation during winter

16 Alaska Studies Current Aminopyralid and Clopyralid Both are synthetic auxins Auxin is a plant hormone Involved in cell division Involved in cell growth Auxins move in the phloem to the growing points Both have soil and foliar activity

17 Alaska Research Current Continue work started in plots sprayed for each of 5 herbicides at Palmer, Fairbanks, and Delta Junction Aminopyralid Clopyralid Metsulfuron Chlorsulfuron Dicamba

18 Alaska Research Current Vegetation was measured in 2011 in detail Weed Control Aminopyralid Clopyralid Plants per meter square Chickweed Corn Spurry NL Hawksbeard Dragonhead Lambsquarters Pineapple Weed Shepherd s Purse Total 1,

19 Alaska Research Current Vegetation was visually estimated in 2012 for most abundant weed species Aminopyralid reduced NLHB, CQ, RO, LQ Clopyralid reduced EQ Dicamba had no impacts Metsulfuron reduced EQ 50% Chlorsulfuron reduced CW, LQ

20 Some Label Restrictions

21 Examples of Injury, raised beds Marigolds Potatoes Tomatoes

22 Injury 2 years after a spot spray

23 Unexpected Injury, potatoes

24 Visual injury Dose response Aminopyralid Clopyralid

25 Is there herbicide in the tuber? Tubers were sent to the Montana Department of Agriculture Laboratory at Montana State University to extract the herbicide Dr. Rick Boydston with ARS in Prosser, WA funded the work ($150/sample)

26 Is that herbicide herbicidal?

27 Is that herbicide herbicidal? Aminopyralid

28 Is that herbicide herbicidal? clopyralid

29 Conclusion Aminopyralid and clopyralid management Their residues are in the plant and soil They pass through ruminants unchanged They will accumulate in potato tubers Some plants are more sensitive than others There are potential bioassays Half lives are currently unknown

30 Background Clopyralid Discovered 1961 Sold in 1978 in Europe Sold in 1987 in US Curtail, Stinger, Confront

31 Background Clopyralid Discovered 1961 Sold in 1978 in Europe Sold in 1987 in US Curtail, Stinger, Confront Now off patent Post emergence in pasture, rangeland, and CRP Mostly used to control orange hawkweed

32 Background Aminopyralid Sold as Milestone Still on patent Expensive Sold about 2005

33 Background Aminopyralid Sold as Milestone Still on patent Expensive Sold about 2005 Used in rice, pastures rangeland, ROW, wheat, oil palm, and rubber plantations Not used much in AK currently

34 Alaska Research Future Dr. Tomco at UAA has put together an innovation grant that was funded to characterize Aminopyralid degradation in the soil He has several other grants submitted and obtained to determine aminopyralid impacts on soil organisms and herbicide decomposition in lakes (part of the elodea project)

35 If time tell story Salt rising Before freeze After freeze Plant release Tolerant versus susceptible Freeze and release Toxic or not

36 Questions