While residual herbicides work well on weeds they can restrict the next crop you can plant. T.L. Grey & A.S. Culpepper

Transcription

1 While residual herbicides work well on weeds they can restrict the next crop you can plant T.L. Grey & A.S. Culpepper

2 Often asked questions 1. Why do we have rotational restrictions on herbicides? 2. What are the most common problems? 3. What factors influence carryover? 4. What methods can growers use to reduce carryover potential?

3 Often asked questions 1. Why do we have rotational restrictions on herbicides? 2. What are the most common problems? 3. What factors influence carryover? 4. What methods can growers use to reduce carryover potential?

4 History herbicides (residual) First residuals developed early 1950 s Triazine herbicides multiple crops Corn atrazine, simazine cotton prometryn Registered in the late 1950 s Other residual herbicide families 1960 s Dinitroanilines, Uracils, Sub - ureas 1970 s Diphenylethers (oxyfluofen, fomesafen) Sulfonylureas (a lot of these!) Chloroacetamides (s-metolachlor) 1980 s Imidazolinone (imazapic) Isoxazolidinone (clomazone) 1990 s Sulfonamides (diclosulam) Triazinones (sulfentrazone) Triketones (mesotrione)

5 Chemistry Benzene CADRE imazapic 2-[(RS)-4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl]-5-methylnicotinic acid N-(phosphonomethyl)glycine Roundup glyphosate

6 Chemistry IONS What are they? an atom or group of atoms that carries a positive or negative electric charge as a result of having lost or gained one or more electrons or protons What is the importance? Think in terms of N fertilizer Ammonium nitrate NH 4 NO 3 NO can leach NH can adsorb to soil colloids

7 CARRYOVER DEFINED Potential for pesticide to cause unintended injury to succeeding crop(s). Generally think herbicide dissipation in half-life Rule of thumb: 8 half-lives before no longer an issue (but no guarantees ) SO: 1x standard herbicide rate (how much applied) Over time: -> ½ x, ¼ x, 1/256 X But how long is that????? Half-life (can be minutes, days, months, years) Varies greatly by environment & herbicide Company info and the label are the keys..

8 Often asked questions 1. Why do we have rotational restrictions on herbicides? 2. What are the most common problems? 3. What methods can growers use to reduce carryover potential? 4. What factors influence carryover?

9 Palmer amaranth changed everything ALS resistant MOA 2 Cross resistant IMI & SU families of herbicides Began to limits herbicide options Glyphosate resistant MOA 9 Multiple resistant - ALS & glyphosate Increased weed seed bank

10 Weed control options To improve and fight current weeds PREs (look to PPOs and other residuals) POST (glufosinate, auxins coming ) Led to the need for multiple modes of action for weed control Soil residuals management options

11 Southeastern US residual herbicides (non-als) peanut, cotton, vegetables Fomesafen MoA 14 - PPO Flumioxazin MoA 14 - PPO Oxyfluorfen MoA 14 PPO Reflex Valor SX Goal 2XL

12 Fomesafen use Mg year National Georgia NASS/USDA statistics Tom Potter USDA/ARS, Tifton GA

13 Rotational restrictions Rotational restrictions for common row crop and vegetable herbicides Rotational restriction Herbicide Months after application (see label!!) Use pattern Flumioxazin (Valor) Oxyfluorfen (GoalXL) Fomesafen (Reflex) Rate dependent!! (1-12 oz/ac) Can vary up to 12 months (18 for 6-12 oz rates) 1 - transplants other than labeled 2 - seeded other than those that are labeled 10 - small grains 4 - lima bean, succulent pea 8/10 - corn, pepper, pumpkin watermelon, tomato 10/12 - cantaloupe, cucumber, eggplant, squash 18 - Anything not listed above (veges) Yearly (avoid high rates) Yearly Avoid in year prior to going into veges

14 Southeastern US residual herbicides (non-als) S-metolachlor Dual II Mag MoA 15 VLCFA Acetochlor MoA 15 - VLCFA Warrant 3ME Clomazone Command MoA 13 - pigment Flumeturon Cotoran 4F MoA 7 PSII Diuron Direx MoA 7 PSII

15 Rotational restrictions Rotational restrictions for common row crop and vegetable herbicides Rotational restriction (half life associated) Herbicide Months after application (see label) Use pattern S-metholachlor (Dual) Acetochlor (Warrant) Clomazone (Command) Flumeturon (Cotoran) Diuron (Direx) Rate dependent!! (1.33 to 2.0 pt/ac) Can vary up to 60 days 4 - wheat Next season vague on specifics Rate and crop dependent!! (1.33 to 3.3 pt/ac) Can vary from 9 to 12 months Yearly (avoid repeat application) Caution due to limited info Avoid year prior for specific veges 9 months for other crops not listed (veges) Must follow 12 months Avoid year prior for specific veges

16 Southeastern US ALS residual herbicides peanut, cotton, vegetables Pyrithiobac Halosulfuron Imazapic Diclosulam Staple Sandea Cadre Strongarm and many, many more.

17 Rotational restrictions Rotational restrictions for common row crop and vegetable herbicides Rotational restriction (half life associated) Herbicide Months after application (see label) Use pattern Pyrithiobac (Staple) Halosulfuron (Sandea) Imazapic (Cadre) Diclosulam (Strongarm) 8 - tomato All other crops require field bioassy See label, varies from 0 to 36 months 9 to 40 months (some veges, months) 30 months for other crops not listed (veges) Caution Caution due to tolerance Avoid in years prior for specific veges Avoid in years prior for specific veges

18 Often asked questions 1. Why do we have rotational restrictions on herbicides? 2. What are the most common problems? 3. What factors influence carryover? 4. What methods can growers use to reduce carryover potential?

19 Soils vary greatly! Tift loamy sand 88% sand 8% silt 4% clay 1.3% OM ph 6.0 Faceville sandy loam 71% sand 13% silt 16% clay 1% OM ph

20 Soil Adsorption Soil Texture Plains GA Reidsville GA Clays > silts > sands Soil organic matter Cationic herbicide sorption with OM CEC moderate = moderate adsorption Sandy loams, sandy clay loams, clay loams Moderate pesticide adsorption But does not take much clay to adsorb a lot of herbicide. Faceville sandy loam (clayey, kaolinitic, thermic, Typic Kandiudults) Tifton loamy sand (fineloamy, kaolinitic, thermic Plinthic Kandiudults)

21 Total rainfall amounts for Reidsville, GA. Soil September moisture Soil adsorption: Month yr average in Dry soils typically adsorb greater than moist soils Treflan applied to dry soil can be tightly adsorbed Avoid applying to dry soil October November December January February March April Keep rainfall, irrigation records May Total

22 Often asked questions 1. Why do we have rotational restrictions on herbicides? 2. What are the most common problems? 3. What factors influence carryover? 4. What methods can growers use to reduce carryover potential?

23 5 rules how to avoid problems 1. Plan ahead for crop rotation, ask question 2. Keep detailed herbicide records- years 3. Read the label, look at rotation restrictions label is the law! 4. After application have already been made, try some type of bioassay use crop transplant or seed about to plant! 5. First year renters, get cropping details for at least 2 years!

24 Options to reduce impact 1. Scout fields vegetables will be grown 2. Keep them clean throughout the year Spray with contact herbicide when not in crop Will reduce the weed seed load over time 3. If residual herbicides are used in rotational crops, deep tillage usually helps to dissipate herbicides But this can promote erosion and the need for greater nutrient management 4. Avoid compacting soil, prolongs carryover issues

25 Options to reduce impact 1. Ensure seedling stress is minimized a) Keep ph & fertility optimum b) Avoid planting in cold wet soils 2. Plan for appropriate rotational crop a) Plant crops with reduced rotational issues 3. Maintain proper soil ph 4. None of this is easy, but good planning can save time, money, and prevent potential crop failures

26 Thank you Vegetable producers for support College of Agriculture and Environmental Sciences

27 Question????