Weed Resistance to Herbicides: The Challenges

Transcription

1 Weed Resistance to Herbicides: The Challenges Charlie Reinhardt Dean: Villa Academy Extraordinary Professor of Weed Science, UP AVCASA 2015 Congress 8-9 September 2015

2 The challenges can be grouped under: Chemistry factors Plant factors Environmental factors Human factors

3 Chemistry (Herbicides and Adjuvants)

4 HOW HERBICIDES WORK Herbicide application Damage to plants Uptake by plants Mode of action Mechanism of action at site of activity Translocation in plant system

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6 Herbicide Resistance Global Status Weeds have evolved resistance to 21 of the 25 known herbicide sites of action Weeds have evolved resistance to 148 different herbicides Over 400 unique cases of herbicide resistant weeds globally More than 200 species (± 60% dicots and ± 40% monocots) Herbicide resistant weeds have been reported in 65 crops in 61 countries Source: Dr Ian Heap, 2013:

7 Summary of herbicide mechanisms-of-action registered for use in SA soybean Mechanism-of-Action (plant process inhibited) Herbicides per M-o-A Weed spectrum Grass only Broadleaf only Grass + Broadleaf 1. Long Chain Fatty Acid 6 6 n/a n/a 2. Photosystem II 2 n/a n/a 2 3. Carotenoid 1 n/a n/a 1 4. Acetyl CoA Corboxylase (ACCase) 6 6 n/a n/a 5. Acetolactase synthase (ALS) 4 n/a 4 n/a 6. Cell division 2 2 n/a n/a 7. Protoporhyrinogen (PPO or PROTOX) 2 n/a 2 n/a 8. Enolpyruvyl shikimate-3-phosphate synthase (EPSPS) 1 n/a n/a 1 Total = 24

8 Herbicide a.i. Weed spectrum 1. Mechanism of action: Inhibit fatty acid synthesis Acetochlor Grasses / Sedges mainly None Alachlor Grasses mainly None Dimethenamid-P Grasses / Sedges / Broadleaf None Metazachlor Grasses mainly None Metolachlor Grasses / Sedges mainly None s-metolachlor Grasses / Sedges mainly None Weed resistance history 2. Mechanism of Action: Inhibit electron transport in Photosystem II Bendioxide (=Bentazone) Broadleaf / Sedges Yes, one weed, Amaranthus hybridus in Canada Metribuzin Broadleaf / Grasses Yes, multiple (22 cases), e.g. Chenopodium album, Eleusine indica 3. Mechanism of action: Inhibit carotenoid biosynthesis (DOXP enzyme 1-deoxy-D-xyulose5-phosphate synthase) Clomazone Broadleaf and grasses Yes, limited (2 cases), e.g. Echinochloa crusgalli in USA

9 Herbicide a.i. Weed spectrum Weed resistance history 4. Mechanism of action: Inhibit acetyl Co-enzyme A carboxylase (ACCase) Cycloxydim Grasses Yes, multiple weeds, e.g. Digitaria sanguinalis Fluazifop-p-butyl Grasses Yes, multiple weeds, e.g. Digitaria sanguinalis, Sorghum halepense, Eleusine indica Haloxyfop-R-methyl Grasses Yes, several weeds, e.g. Sorghum halepense Propaquizafop Grasses Yes, several weeds, e.g. Digitaria ciliaris, Sorghum halepense, Eleusine indica Quizalofop-P-ethyl Grasses Yes, multiple weeds, e.g. Digitaria sanguinalis, Sorghum halepense Quizalofop-P-tefuryl Grasses Yes, limited, winter grass weeds

10 Herbicide a.i. Weed spectrum Weed resistance history 5. Mechanism of action: Inhibit acetolactase synthase (ALS or AHAS) Imazethapyr Broadleaf weeds Yes, multiple weeds (>100 cases), e.g. Xanthium strumarium, Bidens pilosa, Parthenium hysterophorus, Ambrosia artimisiifolia, Euphorbia heterophylla, Sorghum halepense, Sorghum bicolor. Chenopodium album, Digitaria sanguinalis Chlorimuron ethyl Broadleaf weeds Yes, multiple weeds (53 cases), e.g. Xanthium strumarium, Bidens pilosa, Parthenium hysterophorus Diclosulam Broadleaf weeds and nutsedge Yes, few weeds (4 cases), e.g. Ambrosia artimisiifolia, Euphorbia heterophylla Flumetsulam Broadleaf weeds Yes, several weeds (14 cases), e.g. Amaranthus hybridus, Lactuca serriola, Euphorbia heterophylla

11 Herbicide a.i. Weed spectrum Weed resistance history 6. Mechanism of action: Inhibit cell division Pendimethalin Grasses mainly Yes, several (9 cases), e.g. Eleusine indica, Echinochloa crus-galli, Poa annua, Sorghum halepense Trifluralin Grasses mainly Yes, multiple (25 cases), e.g. Eleusine indica 7. Mechanism of action: Inhibit protoporphyrinogen oxidase (PPO or Protox) Flumioxazin Broadleaf Yes, single case of Ambrosia artimisiifolia Fomesafen Broadleaf Yes, several (9 cases), e.g. Ambrosia artimisiifolia, Euphorbia heterophylla, Amaranthus hybridus 8. Mechanism of action: Inhibits enolpyruvyl shikimate-3-phosphate (EPSP) synthase Glyphosate Pre-plant burn-down, and in glyphosate-tolerant soybean Yes, multiple (32 species, 242 cases), e.g. Conyza bonariensis

12 Number of species 1975 Year

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14 Conclusions on chemistry Chemical weed management has challenging times ahead. In absence of new mechanisms-of-action, reliance has to be on existing chemistry in the foreseeable future. New generation HT crops will likely slow down but not stop the evolution of more resistant weeds, and even worse, weeds with multiple herbicide resistance. New adjuvants can offer solutions. The answer: More crop and herbicide rotation and use of mixtures!!!

15 Plant (Weed) factors

16 Resistance to glyphosate in Brazil Conyza bonariensis Conyza canadensis Resistant plant Susceptible plant

17 Growth stage of weeds affect their response to most herbicides Reduced tillage, e.g. orchards, vineyards Annual cropping system

18 ROLE OF GROWTH STAGE: Response of six Conyza bonariensis populations treated with glyphosate at the leaf stage Fresh mass (g) De Rust Gariep Hatfield Middelburg Oudtshoorn Wilderness Glyphosate dosage

19 .. Response to glyphosate applied at the leaf stage De Rust Gariep Hatfield Middelburg Oudtshoorn Wilderness Fresh mass (g) Glyphosate dosage

20 leaf stage leaf stage

21 Conyza bonariensis (flax-leaf fleabane) in Western Cape

22 Conyza sp (fleabane) on winter fallow in the eastern Highveld

23 Hard-to-control and late-emerging weeds will thwart attempts to prevent seeding!

24 Commelina benghalensis Wandering jew

25 Ipomoea purpurea Morning glory

26 Digitaria sanguinalis ( crab finger-grass )

27 Imaginary herbicide resistance

28 Chloris virgata

29 Chloris virgata grown from seed collected at Oudtshoorn; treated on 4 Dec with Roundup Turbo rates (left to right) of: 0; 0.25x; 0.5x; 1x (=2L/ha); 2x; 4x

30 Chloris virgata grown from seed collected at Roedtan; treated on 4 Dec with Roundup Turbo at rates of (left to right): 0; 0.25x; 0.5x; 1x (=2L/ha); 2x; 4x

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32 Be on lookout for new weeds!

33 Macrotyloma axillare an indigenous species encroaching on no-till fields on Springbok Flats

34 One year s seeding is seven years weeding! Too little is known about weed seeds in the soil seedbank!

35 Herbicide-resistant weeds start at low numbers The frequency of herbicide resistant individuals: one in a million

36 What makes Conyza bonariensis (flax-leaf fleabane) prone to development of resistance to herbicides? Annual growth habit Prolific seed producer High seed germination More than one reproductive generation per growing season High genetic diversity

37 Glyphosate mechanism of action

38 SAHRI (SA Herbicide Resistance Initiative) at University of Pretoria website address: Screening of weeds in glasshouse for sensitivity/tolerance/resistance towards glyphosate. Project is supported by Monsanto

39 Glyphosate dose-response curves of hairy fleabane biotypes from Piketberg and Malmesbury Shoot fresh weight (% of untreated control) WP35-S WP38-R Glyphosate dose (g ae/ha)

40 Greenhouse screening of weeds for herbicide resistance GR 50 values estimated using the dose-response equation: Y = d / (1 + exp [b (log x log e)]} Y - Fresh-biomass reduction expressed as a percentage of untreated control d - Upper limit e - Herbicide dose required to reduce growth by 50% (GR 50 ) b - Slope of the curve around GR 50 x - Herbicide dose Resistance level: R: S ratio (GR 50 of resistant biotype / GR 50 of most susceptible biotype)

41 No. Locality seed sourced Crop system GR 50 (g ae ha - ) estimate R/S factor 1 Modder River Lucerne George 1 Orchard: Hops George 2 Pasture De Rust 1 Lucerne Malmesbury 2 Wheat Darling Wheat Wellington Wheat Fauresmith Pasture Orania Orchard: Pecan De Rust 2 Orchard: Olive Durbanville Vineyard Rawsonville Orchard: Peach Riebeeck-Wes Vineyard Worcester Vineyard Porterville Vineyard De doorns Vineyard Bonnievale Vineyard Citrusdal Orchard: Citrus Clanwilliam Roadside Stellenbosch Vineyard Montagu Vineyard Malmesbury 1 Vineyard Piketberg Vineyard Swellendam Wheat

42 Environmental factors that can cause weeds to appear herbicide-resistant Post-emergence herbicides: Stress factors causing reduction in weed growth activity, e.g. drought, heat, cold. Pre-emergence herbicides: Enhanced inactivation / degradation due to increased organic carbon content and soil microbial activity in soil.

43 Human factors

44 Golden rules for managing herbicide resistance 1. Keep weed numbers low reduce the 1 in 1,000,000 chance that an individual weed plant in a population could, in a natural way, evolve herbicide resistance; 2. Prevent weed seed production because resistance is genetically inherited and is spread through seed; 3. Do not rely on a single herbicide, or a single mechanism-of-action; Employ more than one herbicide mechanism-of-action formulated herbicide mixtures and tank-mixtures; 4. Avoid under- and over-dosing since both promote resistance; 5. Integrate different weed control methods where applicable.

45 THANK YOU FOR YOUR KIND ATTENTION! STICK TO THE NARROW ROAD OF ACTING RESPONSIBLY TOWARDS, AMONGST OTHERS, NATURE!!