How many times can you kill a weed? A. 1 B. 2 C. 3 if it is perennial D.Many times

Transcription

1 How many times can you kill a weed? A. 1 B. 2 C. 3 if it is perennial D.Many times 1

2 How many ways can you kill a weed? A. 1 B. 2 C. 3 if it is perennial D.Many ways 700 farmers from Indiana, Illinois and Iowa completed a survey. What % of these farmers agreed with the statement that farmers have much of the responsibility for glyphosate resistant weed populations? A.95% B.89% C.57% D.25% 2

3 What percentage of 700 farmers agreed with the statement that industry has much of the responsibility for glyphosate resistant weed populations? A.95% B.89% C.57% D.25% What choice below do these 700 farmers agree with THE MOST? A. Industry will come out with new herbicides and crops resistant to those herbicides before I need to change my weed management. B. I need to practice more complex weed management now because new options will not be developed fast enough by industry. 3

4 Sensitive Resistant Highly resistant selection pressure diploid weeds more selection pressure? Frequency in the populations AA Aa aa Site of action Single site vs multi-site Active ingredients Solo active ingredient vs mixture Application timing Preventative vs curative Application frequency Within season and history throughout the region 4

5 Genetic diversity Sexual vs asexual reproduction Short generation times Polycyclic diseases vs monocyclic disease Abundant sporulation sterol biosynthesis in membranes SBIs: DMIs: Triazoles/ Imidazoles, Amines: Morpholines/Piperidines cell division / tubulin Benzimidazoles (MBCs) mitochondrial respiration QoIs (strobilurins) RNA biosynthesis Phenylamides (PAs) Multisites e.g. chlorothalonil amino acid biosynthesis Anilinopyrimidines (APs) 5

6 Single-step mutation Substitution of one amino acid Sudden loss of sensitivity to the fungicide No observed vigor cost 6

7 QoI Binding Site and Cross Resistance all QoIs bind in a similar pattern to enzyme; therefore, there is cross resistance for ALL QoIs haploid microbe Monogenic Resistance Frequency in the populations Sensitive Resistant A a 7

8 Frequency, % Benzimidazoles, Phenylamides, Qo-inhibitors, Dicarboximides rate is not essential for selection Fungicide Sensitivity, EC Multi-step mutations Involved in ergosterol production Slow reduction of sensitivity to the fungicide No observed vigor cost 8

9 0.1 Frequency, % Polygenic Resistance Frequency in the populations shifting 30 DMIs, Amines, Anilinopyrimidines, Phenylpyrroles reduced rates promote selection stabilization Fungicide Sensitivity, EC

10 Sensitive Resistant Highly resistant selection pressure more selection pressure? diploid weeds Frequency in the populations Us Use multiple modes of action to reduce selection pressure AA Aa aa Resistance risk for QoIs, DMIs, and Multi-Sites in rusts benzimidazoles benzimidazoles dicarboximides phenylamides QoIs dicarboximides carboxanilides carboxamides SBI's phosphorothiolates DMIs anilinopyrimidines anilinopyrimi- phenylpyrroles dines strobilurins phenylpyrroles coppers dithiocarbamates copper, sulfur melanin dithiocarba- inhibitors phthalimides mates sulphur chloronitriles SAR-inducers h i g h (3) m e d i u m (2) l o w (1) intrinsic resistance risk intrinsic disease risk low (1) medium (2) high (3) seed-borne Rhyncho- (eg. Ustilago) sporium soil-borne (eg. Septoria tritici Phytophthora), Alternaria cereal eyespot solani cereal rust Monilinia apple scab Sigatoka cereal powdery mildew grape Botrytis potato blight

11 Strobilurin plus triazole: Twin biochemical modes of action Strobilurin Inhibits electron transfer in cytochrome bc1 complex of mitochondria. Therefore, disrupts energy production by the fungus. Powerful preventative action Fungal cell Triazole Inhibits sterol biosynthesis. Sterols are important components of the cell membrane. Good curative activity... also of benefit for resistance management Fungicide Resistance Action Committee (FRAC) FRAC is an international industry-based and financed organization formed in 1981 with key objectives of: Providing advice on how best to use fungicides in order to avoid, delay, manage fungicide resistance in crops Providing educational material to train more people in the science of fungicide resistance and the art of its control 11

12 FRAC Code One of the more recent contributions by FRAC was the development and implementation of the FRAC code now used on fungicide labels A fungus that becomes resistant to one fungicide in a FRAC Code may be resistant to many or all fungicides within that FRAC Code 12

13 FRAC Code Fungicide Group Risk of Resistance Developing 1 Methyl benzimidazole carbamates (MBC) High Demethylation inhibitors (DMI) (includes triazoles ) Succinate dehydrogenase inhibitors (SDHI) Quinone outside inhibitors (QOI) (includes strobilurins ) Medium Medium to High High M5 Chloronitriles Low Fungicide-resistant isolates already in the population Natural mutations responsible for most fungicideresistant isolates Fungicides applied do not cause mutations Natural mutations occur in fungi at an approximate rate of 1/0,000,000 13

14 Cercospora sojina Sexual and asexual reproduction High genetic diversity No separation based on geography Virulence to host resistance emerging Resistance to fungicides emerging Cercospora zea-maydis Asexual reproduction Low genetic diversity Two types that are geographically separated Host resistance still largely effective Application of fungicides sill effective C. sojina causes frogeye leaf spot on soybeans Frogeye may be severe under favorable conditions on a susceptible variety ~0 lesions/leaflet ~0 conidia/lesion 14

15 ~30 leaflets/plant ~6,000,000 plants/40 acre field 1.8 trillion conidia/40 acre field ~1/0,000,000 natural mutation rate 18,000 mutant isolates/40 acre field Fungicide resistance can be difficult to prevent, but proper management practices can help fungicides retain efficacy for long periods of time 15

16 Utilize non-chemical disease management when possible Apply mixes of different fungicide groups or rotate fungicide groups if multiple applications made in a season Follow label recommendations Only apply fungicides when warranted based on scouting or disease risk 16

17 Causes frogeye leaf spot of soybeans Internationally distributed Prefers hot, humid conditions Symptoms can occur anytime, but often occur after flowering 17

18 Causes gray leaf spot of corn Distributed internationally Prefers prolonged warm, humid conditions Symptoms often occur following 18