Cecil Tharp, MSU Pesticide Education Specialist

Do you know what mode of action means? 1. Yes 2. No 3. Maybe 0 of 50

Do you know the mode of action of all pesticides you use? 1. Yes 2. No 0 of 50

What is the mode of action?

Mode of Action Sequence of events from absorption into the plant until the plant dies Systemic herbicides – translocated from site of entry to area in plant where they are active. Glyphosate Contact herbicides - kill only the area where they are applied. Paraquat

Further Break Down into Groups  Weed Science Society of America has classified all modes of action into groups.  These groups are usually on the pesticide product label. This is for Milestone.

What does a group 4 mode of action mean?  Use the handouts available.  This would be a growth regulator herbicide; or a synthetic auxin herbicide. Causes abnormal growth, extended leaf terminals, curled leaves and eventual death These target broadleaf weeds Many products including 2,4-D, dicamba, picloram, clopyralid, aminopyralid, aminocyclopyraclor, milestone etc.

Common Leaf Symptoms from PGR Exposure normal cupped and blistered from PGR exposure

We have many modes of action  ACCase inhibitors (Group 1) Inhibit ACCase enzyme in grasses. Stunting, browning of grasses, Used primarily in broadleaf crops Some may be used to selectively control grasses in grass crops. Poast, Puma, Select Sethoxydim, clethodim, fenoxaprop

Aromatic Amino – Acid Synthesis Inhibitors  Group 9.  Glyphosate  Inhibits amino acid synthesis. Slow process that may take weeks. Broadspectrum, yellowing of plants, stunting

Plateau or Escort Injury Symptoms Stunting Chlorosis of youngest tissue

ALS Inhibitors  Inhibit amino acid synthesis  Sulfonylurea herbicides Vulnerable to low pH conditions  Also imazapic, imazamox, imazethapyr  Resistance and cross-resistance is common.  Targets a wide variety of grasses and broadleafs while protecting crops (selective; read label)

Do you mix your modes of action? 1. Consistently 2. Occasionally 3. Never 0 of 50

Who Cares?  Why do we need to group our modes of action?

Plants, Diseases and Insects often develop resistance to modes of action.

History of Weed Resistance  The first reported case of herbicide resistance in the United States was reported in the 1950’s. Field bindweed resistant to 2,4-D was reported in Kansas in  The greatest number has been observed with the ALS inhibitors (imidazolinones, pyrimidinylthiobenzoates, sulfonylureas, triazolopyrimidines).  25 herbicide families have confirmed resistance to various weeds.

Glyphosate No Longer Effective in Managing Kochia  From 1984 – 2013  Resistant to: Photo-System II – 5 (atrazine) ALS Inhibitors – 2 (chlorsulfuron, etc.) Sythentic Auxin – 1 (dicamba, fluroxypyr) EPSP Synthase Inhibitor – 9 (glyphosate)

Wild Oat Resistance  Cell elongation inhibitors (8)  Lipid inibitors (8) Thiocarbanates Difenzoquat  ALS Inhibitors (2) Imazamethabenz methyl  ACCASE inhibitors (1) Clodinafop Diclopop-methyl Tralkoxydim

Resistance to Persian Darnel, Green Foxtail and  Persian Darnel ACCASE inhibitors (1) ○ Diclofop-methyl  Green Foxtail ACCase inhibitors (1) ○ Diclofop-methyl ○ Sethoxydim  Horseweed EPSP synthase inhibitors (9) ○ Glyphosate

How does the plant develop resistance?

How can you combat resistance?  Mix modes of action from application to application Don’t stay with only one mode of action  Or use multiple modes of action in a tank mix Some pesticide products already deliver multiple modes of action  Use highest rates  Use multiple control tactics or integrated pest management.

Are there other reasons to combine modes of action?

Tank Mixing Multiple Products  Can cause unexpected outcomes Enhancement ○ Increases efficacy by adding adjuvants Synergism ○ By combining chemicals increased efficacy of either product is achieved Antagonism ○ Efficacy is lowered by combining the chemicals Incompatabilities ○ 2,4-D and glyphosate in hard water situations

Common Mixing Issues  WPs and ECs: they can form a putty or paste with an oily layer that floats on the top of the tank. Many physical incompatibility problems  Combinations of pesticides (ECs, for  example) are mixed with liquid fertilizers. A few pesticides are available in special fertilizer-grade formulations that reduce incompatibility problems.  Some poor mixtures result in lower efficacy from water issues.

Alkaline hydrolysis: High pH Water  Dissociation is the breaking down of a complex molecule into simpler units.  Efficacy often goes down when molecules are dissociated. Plants often won’t absorb the chemical as well. At times this may totally inactivate the pesticide. pH 6 – 7 is ideal for most pesticides but it can vary.  Weak Acid Herbicides are the most susceptible to alkaline (high ph) dissociation Roundup® (glyphosate) Pursuit® (ammonium salt of imazethapyr) Liberty® (glufosinate ammonium). 2-4D salt

Hardness of Solution Can Cause Problems in Tank Mixes  Hardness is the concentration of multi- valent cations (positively charged ions from minerals)  Cations bind with negatively charged pesticide molecules pH and hardness work together to reduce efficacy Forms insoluble salts

When is it a problem?  If the sum of the concentration (ppm) for the cations exceeds 150 ppm action should be considered:  2,4-D amine (> 150 ppm)  totally deactivated at 500 ppm)  Dicamba (> 150 ppm)  Glyphosate (> 150 ppm)  Clopyralid (>150 ppm)  sethoxydim ‘Poast’ (>150 ppm)  Imazethapyr ‘Pursuit’ (>150 ppm)  Reduces efficacy of many surfactants  Scale may plug sprayer

If you have a problem  Add an adjuvant containing sulfate or organic acids as they bind with hard minerals non-ionic surfactants increase efficacy Add ammonium sulfate (8.5 – 17 lb / 100 gallons)

Prior to tank mixing  Read the pesticide product label on compatibility issues or recommended tank mixes.  Call your product manufacturer for more information prior to mixing.  Last Resort: Can perform a jar test Check for heat, gumming, foam and scum

Order of Mixing  Always consult the label of each product for product-specific mixing instructions 1. Fill the tank ¼ to ½ with carrier and begin agitation 2. Add compatability or defoaming agents if needed 3. Pesticides, in the order of WP, DF, WDG, F, FL, ME, EC, S, SP 4. Crop oils or surfactants

Do you know what mode of action means? 1. Yes 2. No 3. Maybe 0 of 50

Do you know the mode of action of pesticides you use? 1. Yes 2. No 0 of 50

Do you mix your modes of action? 1. Consistently 2. Occasionally 3. Never 0 of 50

Thanks Cecil Tharp Montana State University Bozeman, Montana (406)