Dissipation of soil-applied sugarcane herbicides in organic soils Calvin Odero Certified Crop Adviser CEU Session

Outline Everglades Agricultural Area (EAA) –Organic soils Sugarcane –Taxonomy, crop cycle Weeds associated with sugarcane –Broadleaf, grass, and grass-like weeds Weed management in sugarcane –Preemergence and postemergence herbicides Soil herbicide dissipation –Terminologies (degradation, dissipation, persistence) –Factors affecting herbicides dissipation Soil, climatic, and herbicide properties Soil-applied herbicides in sugarcane –Pendimethalin, atrazine, metribuzin Field dissipation of pendimethalin in organic soils of the EAA Field dissipation of atrazine and metribuzin in organic soils of the EAA

Everglades Agricultural Area (EAA) 700,000 acres of land –Major crop - sugarcane –Other crops - winter vegetables, rice, sod –Dominated by organic (muck) soils Sugarcane acreage –325,000 acres on organic soils (Histosols) –92,000 acres on mineral (sandy) soils (Spodosols & Entisols) Source:

Organic soils Formed several thousands of years –Organic matter production exceeded decomposition –Flooded sawgrass prairies south of Lake Okeechobee High soil organic matter content (up to 85%) Soil depth –6 inches to over 4 feet

Organic soil subsidence Drainage of soils resulted in –Oxidation & mineralization of large quantities of organic N –Microbial oxidation account for 50 to 75% of the subsidence Subsidence rates –Estimated using transect lines from the bedrock 1924 – 1967: 1.12 inches/year 1967 – 2009: 0.55 inches/year Reasons for decline –Maintenance of high water table, BMPs –Increasing recalcitrate of remaining soil organic matter –Increased mineral content (CaCO 3, sand, clay) 9 foot post driven into the bedrock at the EREC in 1924

Sugarcane Giant grass Family: Poaceae Tribe: Adropogoneae Saccharum officinarum L. –‘Noble cane’ with long, thick, heavy, juicy & sweet stalks Other species –S. barberi –S. robustum –S. sinese –S. spontaneum Commercial clones are typically 3-part hybrids

Sugarcane Perennial crop, harvested annually Planting season –Mid-October to end-December First year crop is plant cane, successive years are ratoon or stubble crops Harvest season –Mid-October to March/April Typically replanted every 3 to 5 years Planting Following fallow period after final ratoon ‒ Crop rotation (winter vegetables, rice), flooding, fallow Successive ‒ Replanting several weeks after the final ratoon

Sugarcane planting

Common broadleaf weeds in sugarcane Common lambsquarters * Spiny amaranth * Common ragweed * Common purslane Alligatorweed American blacknightshade Common lambsquarters Spiny amaranth

Common grass and grass-like weeds in sugarcane Fall panicum * Guineagrass Goosegrass Crowfoot grass Crabgrasses Bermudagrass * Almum sorghum Elephantgrass Yellow nutsedge * Purple nutsedge Fall panicum Bermudagrass

Weed management in sugarcane Major cost associated with sugarcane production Weed management methods –Mechanical cultivation, herbicides, cultural (crop rotation) Herbicides are most commonly used Preemergence Atrazine Metribuzin Pendimethalin Postemergence 2,4-D Dicamba Ametryn Atrazine Metribuzin Mesotrione Asulam Trifloxysulfuron Halosulfuron Mechanical cultivation Crop rotation (Sweet corn) Glyphosate

Herbicide application in sugarcane

Terminologies Several related terms with respect to the residence time a herbicide remains in a given portion of the soil matrix Degradation: substantive change in the molecular makeup of a given herbicide, with a component of the parent molecule removed by some process to form a metabolite or metabolites Dissipation: sum of all possible outcomes of the parent herbicide –Non-alteration of chemical form of the herbicide Volatilization, movement off-site, leaching, surface runoff –Chemical alteration of the chemical form of the herbicide Chemical or microbial degradation Persistence: length of time a herbicide remains active in the soil –Can be considered a negative connotation Damages to rotational crops, contamination of surface water and groundwater –Allow for residual weed control Half-life: amount of time required for dissipation of one half of the original amount of herbicide applied Source:

Herbicide families with their persistent members Herbicides vary in their potential to persist in soil

Soil factors affecting dissipation Physical –Composition Relative amounts of sand, silt, clay, organic matter –Herbicidal activity is affected by Adsorption, leaching, volatilization Chemistry –Soil pH, CEC, nutrient status Triazines and sulfonylureas Microbial activity –Microbes (bacteria, fungi) and their relative numbers –Affected by Moisture, pH, oxygen, mineral nutrient supply

Climatic factors affecting dissipation Moisture and temperature –Degradation rates affected by both factors Chemical and microbial decomposition increase with higher temperatures and moisture levels Sunlight –Photodecomposition Dinitroanilines (pendimethalin, trifluralin)

Herbicide properties affecting dissipation Chemical properties –Water solubility, vapor pressure Susceptibility to chemical or microbial alteration or degradation Leaching depends on –Water solubility of the herbicide –Herbicide-soil binding properties –Soil physical characteristics –Rainfall frequency and intensity –Herbicide concentration –Time of herbicide application Volatilization –Higher vapor pressure Thiocarbamates, dinitroanilines Herbicide’s chemical structure –Dictates degradation in soil by microbial or chemical means

Pendimethalin Dinitroaniline herbicide –PRE control of annual grasses, certain broadleaf weeds Chemical and physical properties –Crystalline orange-yellow solid with faint nutty odor –Low water solubility (0.275 mg L −1 ) –Low mobility and leaching potential –Strong adsorption to soil colloids and OM (K oc = 17,200 L kg −1 ) –Low volatility (vapor pressure = 1.25 × 10 −3 Pa) Characteristics are attributed to –High potential for hydrogen bonding in particular to organic, lipophilic and proteinaceous substances Use rate increases with increasing soil OM

Pendimethalin Degraded primarily by soil microorganisms Undergoes photodecomposition Persistence influenced by edaphic and climatic conditions Degradation is faster under anaerobic, warm and moist conditions Half-life –42 to 101 days under laboratory conditions –44 days in the field Depends on soil temperature and moisture Bioavailability decreases with increase in soil organic matter content

Field dissipation of pendimethalin Location –Belle Glade, FL in 2011 and 2012 –Dania muck soil, pH of 7.1 and 6.6, OM of 68.1 and 73.9% Design: RCBD, 3 to 4 replications Pendimethalin treatments –Oil-based formulation (Prowl 3.3 EC) –Water-based formulation (Prowl H 2 O) 2, 4, and 8 kg ha −1 plus a nontreated control Soil sampling –7, 14, 21, 28, 35, 42, 49, and 56 days after treatment –Four soil cores, 0 to 10 cm in depth Pendimethalin in soil was determined using a GC-MS

Environmental conditions at herbicide application Odero and Shaner, Weed Technology 28:82-88

Summary Rate of dissipation of oil- and water-based pendimethalin formulations was very similar Initial amount of pendimethalin in the soil was higher with the water-based compared to the oil-based formulation –Lower volatility of the water-based Lower half-life values for both pendimethalin formulations under field conditions –Climatic and edaphic conditions –Absence of incorporation following application Conclusion Growers on organic soils will not observe long residual activity of pendimethalin irrespective of the formulation when applied under dry soil conditions with no incorporation

Triazine herbicides Important in weed management in sugarcane Atrazine (s-triazine) is the most widely used –>70% of the sugarcane acreage in the US –Offers consistent performance, low cost, residual weed control, flexibility in time and method of application, compatibility with other herbicides, crop safety Metribuzin (asymmetrical triazine) is also used in sugarcane Both used for PRE or early POST for control of broadleaf weeds and certain grasses Efficacious residual weed control depends on their persistence Both have half-lives of up to 60 days under field conditions Relatively low adsorption on most soils Sugarcane growers have observed reduced residual activity of atrazine on organic soils of the EAA

Atrazine Persistence in soil attributed to the halogen, methylthiother, and N-alkyl substituents on the s-triazine ring which impeded microbial degradation but Adaptation of bacterial communities able to utilize atrazine as a C and N source has occurred –Soils with repeated atrazine use –Enhanced degradation Pseudomonas sp. strain ADP and Nocardioides sp. strain C190 able to metabolize and rapidly degrade atrazine have been isolated Enhanced atrazine degradation has been reported –Colorado, Mississippi, Ohio, Tennessee –Australia, Canada, Europe, South America Fields with a history of repeated atrazine use

Atrazine and metribuzin Enhanced atrazine degradation reported across the full range of sugarcane production areas –Using laboratory incubation dissipation studies –Atrazine-adapted soils were cross-adapted with ametryn (chloro-s-triazine) but not with metribuzin Lack of cross-adaptation of atrazine and metribuzin shows that metribuzin could be a viable alternative for use in sugarcane soils with enhanced atrazine degradation

Field dissipation of triazine herbicides Location –Belle Glade, FL in 2011 and 2012 –Dania muck soil, pH of 7.1 and 6.6, OM of 68.1 and 73.9% Design: RCBD, 3 to 4 replications Herbicide treatments –Atrazine , 4.48, and 8.96 kg ha -1 –Metribuzin , 1.12, and 2.24 kg ha -1 Soil sampling –7, 14, 21, 28, 35, 42, 49, and 56 days after treatment –Four soil cores, 0 to 10 cm in depth Herbicide extraction –Toluene (total amount of herbicide in the soil) –Water (readily bioavailable fraction in the soil)

Odero and Shaner, Weed Technology 28:

Summary Atrazine dissipated more rapidly than metribuzin under field conditions on organic soils Atrazine half-life values in these s-triazine-adapted organic sugarcane soils were up to 60-fold lower than previous estimates of 60 days under field conditions depending on atrazine rate and use history This implies that residual weed control by PRE atrazine in sugarcane grown in the EAA is up to 60-fold lower in these s- triazine-adapted soils The non-symmetrical triazine herbicide metribuzin had relatively longer half-life values under field conditions at the labeled use rate for sugarcane in the EAA compared to atrazine, implying that metribuzin is the better alternative for PRE weed control in sugarcane grown on organic soils of the EAA exhibiting enhanced atrazine degradation

Take home message Dissipation of pendimethalin on organic soils is influenced by climatic and edaphic conditions Enhanced atrazine degradation occurs on organic soils under field conditions, resulting in shorter residual atrazine activity

Contact Information Calvin Odero Everglades Research and Education Center 3200 E Palm Beach Road Belle Glade, FL