Herbicide Carryover Katie Jennings David Monks and Steve

Herbicide Carryover Katie Jennings, David Monks, and Steve Meyers NCSU Department of Horticultural Science

Sandea herbicide label Rotational restrictions

Rotation Restrictions with Herbicides Registered in Other Crops Herbicide Atrazine Valor Envoke Sandea Classic Harmony GT XP Callisto Sencor Staple Cotoran Vegetables > 1 year 8 to 18 months 210 to 540 days 2 to 12 months 9 to 30 months 45 days 18 months 4 to 18 months 10 to 12 months 8 to 9 months

What is a Residual Herbicide? • A herbicide that provides extended weed control. – Preemergence or Postemergence • Herbicide activity is only beneficial for the time it is needed; longer activity can cause injury to subsequent crops.

Herbicide Persistence • The amount of time that a herbicide or a metabolite remains active (present and available) in the soil. – Varies with environmental conditions, soil type and soil characteristics, and cultural practices. • Half-life of a herbicide is the amount of time it takes to decompose 50% of the herbicide to an inactive form. – Determined under standard conditions in the lab. – Half-life in field will vary depending on environmental and soil conditions.

Herbicide Half-Life Herbicide Atrazine Reflex Stinger Sandea Pursuit EPTC Days 60 120 -240 40 25 -30 60 to 120 7 -14

Factors Affecting Herbicide Carryover Environment • Increased rainfall tends to reduce the likelihood of carryover to another crop. – Irrigated crop – Under flooded soil conditions less microbial activity occurs. • If rainfall is low then there is an increased chance of carryover to a follow-crop. – Less microbial degradation occurs under limited moisture conditions.

Factors Affecting Herbicide Carryover Soil Characteristics • Soil p. H – High p. H may decrease herbicide degradation. (sulfonylureas) – Chemical degradation slows and less tightly adsorbed to soil particles making more available for plant uptake. • Soil organic matter – tends to increase adsorption. • Soil type.

Factors Affecting Herbicide Carryover Herbicidal Characteristics • Herbicide rate • Herbicide persistence – Varies by herbicide and can range from a few days to a few years. – Influenced by soil type, soil p. H, climatic conditions, and cropping systems.

Factors Affecting Herbicide Persistence Plant uptake Detoxification Harvest removal photodecomposition volatilization Surface runoff leaching Chemical decomposition Soil adsorption Microbial degregation

Herbicide Bioassay 1. Collect field soil from the top 2 to 3 inches and mix thoroughly (sample various places). 2. Plant several crop seeds that are known to be highly susceptible to the herbicide of concern. 3. Thin to 1 plant per pot after emergence. 4. Place pots in natural light if possible. 5. Evaluate for herbicide injury symptoms.

Herbicide Bioassay Field 1. Some labels require a field bioassay. 2. Crop must be grown to a specific growth stage, some to maturity. 3. Herbicide specific.

ACCase Inhibitors Graminicides (Poast, Select Max) • Persistence is short to moderate. – Rotation restriction is often 120 days or less. • • • Adsorption is low to moderate. Leaching is low. Microbial degradation is high. Chemical decomposition is low to moderate. Photodecomposition is low to high.

ALS Inhibitors Sulfonylureas • Persistence is short to long. – High p. H – sulfonylurea rotation restriction is long. – Low p. H – imidazolinone rotation restriction is long. • • Adsorption is low. Leaching is low to moderate. Microbial degradation is moderate to high. Chemical decomposition is very high (decreases as soil p. H increases). • Photodecomposition is low.

Dinitroanilines (Prowl, Sonalan, Treflan, Curbit) • Persistence is moderate. • Adsorption is high (increases with increasing om). • Leaching is low. • Microbial degradation is moderate to high. • Chemical decomposition is low. • Photodecomposition is moderate to high.

Photosystem I Inhibitors Bipyridyliums (Paraquat and diquat) • Persistence is very long. – Inactivated. • • • Adsorption is very high. Leaching is low. Microbial degradation is low. Chemical decomposition is low. Photodecomposition is moderate. • Minimal risk.

Photosystem II Inhibitors Triazines, Uracils (Atrazine, Sencor, Sinbar) • • • Persistence is moderate to long. Adsorption is low to high. Leaching is moderate to high. Microbial degradation is moderate to high. Chemical decomposition is low to moderate (> at low p. H). • Photodecomposition is low. • Rotational restrictions can be greater than 2 yr in some cases; often greater at high soil p. H.

PPO Inhibitors Triazilone(Sulfentrazone, Carfentrazone, Flumioxazin) • • • Persistence is short to long (sulfentrazone). Adsorption is moderate (sulfentrazone) to high. Leaching is low to moderate (sulfentrazone). Microbial degradation is moderate to high. Chemical decomposition is low. Photodecomposition is low to high.

Sulfentrazone Injury to Vegetable Crops Bell Pepper 6 WATr 1 Onion 12 WATr Snap bean 4 WAP 1 Tomato 6 WATr Watermelon 4 WAP Squash 4 WAP 6 1 b 3 b 1 b 1 b 1 c 0 c 12 9 a 4 b 1 b 2 b 8 b 20 b 24 10 a 13 a 15 a 5 a 18 a 36 a Rates (oz/A) 1 WATr = weeks after transplanting and WAP = weeks after planting. Pekarek, Monks, Garvey, Jennings, and Mac. Rae. 2010. Weed Tech. 24: 20 -24.

Synthetic Auxins (Banvel, 2, 4 -D, Stinger, Tordon, ) • Persistence is very short to short with exception of some (moderate to long). • Adsorption is low. • Leaching is low to high. • Microbial degradation is high (soil moisture and temperature are important). • Chemical decomposition is low. • Photodecomposition is low. • Rotation restrictions fairly short with exception of Stinger and Tordon.

Herbicide Carryover Growth regulator type herbicides • Aminopyralid, clopyralid, fluroxypyr, picloram, triclopyr • Crop residue • Mulch – grass clippings • Manure

To Minimize Carryover Potential in Manure, Clippings and Compost • Check with source of manure, clippings, and compost. • IF you can’t determine whether these herbicides were applied do not use manure, compost, or clippings near sensitive crops including tomato unless you conduct a bioassay. • A bioassy involves potting up suspected material

Herbicide Carryover to Vegetables is a Great Concern for Growers ‘Heritage’ bell pepper ‘Athena’ cantaloupe ‘Amelia’ tomato

Stinger Carryover to Vegetable Crops • Tomato and pepper – Crop injury on foliage. – Misshapen fruit. – Reduction in yield. Nontreated Stinger

Risk Points 1) Previous herbicide history. e. g. , rental property 2) Overlap of herbicide spray at the ends of the rows. 3) Misapplication. e. g. , miss target rate 4) Late applications 5) Sprayer contamination. 6) Read label. 7) Keep historic records for each field. 8) Crop failure.

Off Target Movement of Herbicides

Off Target Movement of Herbicides 1) Growth regulator type herbicides 1) Dicamba and 2, 4 -D 2) Herbicides that cause chlorosis (yellowing) of foliage 1) Glyphosate (Roundup)

Growth Regulator Type Herbicides • Twisting of stems. • Cupping and twisting of leaves. • Leaves can become thick and leathery. • Distorted fruit.

Glyphosate Injury • White/yellow discoloration at the base of new leaflet. • Cupping and twisting of leaves. Photos Courtesy of Virginia Polytechnic Institute.

Questions? ? Contact Information Cell: 919 -740 -4500 Email: katie_jennings@ncsu. edu