How Herbicides Work. Greg MacDonald Agronomy Dept. / IFAS University of Florida, Gainesville

Transcription

1 How Herbicides Work Greg MacDonald Agronomy Dept. / IFAS University of Florida, Gainesville

2 How Do Plants Grow? Its all about carbon dioxide- CO2 Water flow Sugar movement Nutrient uptake Gas exchange - oxygen

3 Terrestrial vs. Aquatic Water movement is critical for many herbicides Dramatically changed when herbicides are placed in the aquatic environment

4 What Do Herbicides Do? Controlled/selective plant poisoning applied to soil (root uptake), water, and/or leaves (foliar uptake) contact or systemic selective vs. non-selective

5 How Do Herbicides Work? Mode and/or mechanism of action specific plant process is targeted photosynthesis enzymes growth, hormonal balance unknown?

6 Mechanisms of Tolerance X Herbicide X not absorbed Sequestered in vacuole X does not binds to enzyme Y Y1 X metabolized to Z

7 Aquatic Terrestrial 2,4-D 2,4-D* Diquat (Reward) Triclopyr (Garlon)* Fluridone (Sonar) Imazapyr (Arsenal, etc.)* Triclopyr (Renovate) Glyphosate* Endothall (Aquathol, Hydrothol) Metsulfuron, Chlorsulfuron Copper (chelates, copper sulfate) Imazapic, Imazamox* Glyphosate (Rodeo) Aminopyralid* Imazapyr (Habitat) Aminocyclopyrachlor Carfentrazone (Stingray) Chlorpyralid Penoxulam (Galleon) Fluazifop Bispyribac (Tradewind) Diuron Flumioxazin (Clipper) Hexazinone Imazamox (Clearcast) Tebuthiuron

8 2,4-D, triclopyr, aminopyralid, chlorpyralid, aminocyclopyrachlor Absorbed by foliage or underwater tissues Moves to areas of new growth Causes a disruption in hormone levels Acts like a growth stimulant in some plant tissues and a growth retardant in others Vascular tissue becomes crushed, stops movement of essential nutrients and sugars Plant essentially grows itself to death Growth regulators

9 Growth Regulator Symptoms Twisting Discoloration in terminal bud Leaves may show strapping or puckering effect

10 2,4-D & Triclopyr

11 Diquat Absorbed by foliage or underwater tissues Does not move within the plant contact Disrupts photosynthesis by stealing electrons These electrons are then passed on to oxygen, creating toxic radicals Radicals cause the cell membrane to leak

12 DQ DQH 2 O 2 -

13 Diquat Symptoms Browning of leaf tissues Rapid, within 1-2 days

14 Diquat

15 Endothall Absorbed by foliage or underwater tissues Does not move within the plant contact Appears to act directly on the cell membrane but how is unknown The cell membranes become leaky, cell contents spill out Without membranes the cells cannot make energy

16 Endothall

17 Fluridone Absorbed only by underwater tissues Does not move within the plant, but not contact takes weeks for control Prevents the formation of carotenoids which are chlorophyll protecting pigments Unprotected chlorophyll photo-oxidizes (self-destructs), leading to plant starvation

18 Fluridone Symptoms Bleached, white tissue Sometimes pinkish Symptoms can persist for weeks

19 Fluridone

20 Glyphosate Absorbed by foliar tissues only Moves to areas of new growth Prevents the formation of essential aromatic amino acids in plants Without these essential amino acids, the plant cannot make proteins, enzymes, etc. Plant cannot continue growing and eventually starves and dies

21 Glyphosate Injury yellowing massive budding

22 Glyphosate

23 Imazapyr, Imazamox, Imazapic, Penoxulam, Bispryribac, Metsulfuron, Chlorsulfuron Absorbed by foliar tissues only Moves to areas of new growth Prevents the formation of essential branched chain amino acids in plants - ALS Without these essential amino acids, the plant cannot make proteins, enzymes, etc. Plant cannot continue growing and eventually starves and dies ALS

24 ALS Injury Symptoms Stunted, yellow to purple discoloration New growth most affected

25 ALS herbicides in Water

26 Copper Absorbed by foliage or underwater tissues Does not move within the plant contact Appears to act on cell membranes or photosynthesis but how is unknown The cell membranes become leaky, cell contents spill out Without membranes the cells cannot make energy Synergy with other herbicides diquat

27 Copper

28 Carfentrazone & Flumioxazin Absorbed by foliar tissues only Does not move within the plant contact Causes the formation of a light absorbing chlorophyll precursor outside the chloroplast This compound absorbs energy from sunlight, but cannot pass through the Z-scheme The energy is passed on to oxygen, creating radical oxygen and eventual cell membrane disruption

29 Carfentrazone & Flumioxazin Injury Symptoms Speckling or bronzing of leaf tissue Tolerant plants generally outgrow injury within 2-3 weeks

30 Carfentrazone & Flumioxazin

31 Hexazinone, Diuron & Tebuthiuron Absorbed by foliage or roots Contact from foliar, systemic from root uptake Blocks photosynthesis No electron flow, buildup of exceesive energy, creates toxic radicals Radicals cause the cell membrane to leak Yellowing and browning of leaf tissue

32 X

33 How Herbicides Work Mode/mechanism of action, where a specific plant process is targeted photosynthesis pigments enzymes growth, hormonal balance

34 Hardin 1985 every good pesticide selects for its own failure

35 Resistance Terminology Susceptible - controlled using normal userates Tolerant - species never susceptible to herbicide at label use rates Resistant - originally susceptible to herbicide; over time control lost through the selection of resistant plants Cross resistance - resistant to 2 or more herbicides with similar modes of action Multiple resistance - resistant to herbicides with different modes of action

36 Mechanisms of Tolerance X Herbicide X not absorbed Sequestered in vacuole X does not binds to enzyme Y Y1 X metabolized to Z

37 Herbicide Resistance A shift in the population of a once susceptible biotype to a biotype that is resistant to normal application rates

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42 2000 No resistant weeds to glyphosate Glyphosate resistance conferred to corn, soybeans, cotton 60+ million acres of RoundUp Ready crops 2014: over 22 terrestrial weeds resistant to glyphosate

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44 Chance of selecting One herbicide-resistant plant: Ranges depending on herbicide and mechanism of action/tolerance % or 1 in 3 million to % or 1 in a billion

45 What do farmers do? Switch to different herbicides, specifically different modes of action Rotate crops corn:soybean:cotton:peanuts, etc., etc. Fallow? Change tillage, implement other weed control strategies mechanical primarily Aquatics and Natural Areas???

46 Resistance in Aquatics? Hydrilla resistance to fluridone

47 Resistance in Aquatics? Landoltia resistance to diquat

48 Herbicide Resistance 1. Shift in the amount (rate) required to achieve a similar level of control 2. Complete lack of control

49 Superweeds? No. the repeated use has selected for an alternative biotype the herbicide did not cause the mutation, it was pre-existing in the population

50 Consequences of Resistance 1. Increase the Rate increase costs/acre decrease in selectivity postponing the inevitable 2. Change control tactics, herbicides 3. May show cross resistance to other herbicides

51 What Enhances the Chances? single site of action multiple applications per season, persistence of herbicide in environment repeated use of same material stand alone treatments low, sublethal rates????

52 Resistance Management rotate herbicides with different mechanisms (altered target site) tank mix multiple mechanisms of action integrate other management methods

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