Phloem Mobile FACTORS EFFECTING HERBICIDE EFFICACY. Xylem Mobile. Illustrations: xylem and phloem. Stem Characteristics. Direction of Flow 4/18/2013

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1 Phloem Mobile FACTORS EFFECTING HERBICIDE EFFICACY phloem the living tissue of plants that primarily functions to transport metabolic compounds from the site of synthesis or storage to the site of utilization With herbicides we consider movement via the phloem from source to sink Source the point of herbicide entry in the plant Sink the site of high metabolic activity where the herbicide expresses it s toxicity new tissue root storage seed production Xylem Mobile Illustrations: xylem and phloem xylem the non-living tissue in plants that functions primarily to conduct water and mineral nutrients from roots to the shoots flow is driven by the negative pressure potential in the xylem created by the loss of water from the leaves Transpiration stream movement with water from soil into roots and up in the plant for PS and cooling Injury on older tissue first ytalab99/smilaxrotmaturephloemxylem300lab.jpg Direction of Flow Stem Characteristics location of the growing point? dicots terminal bud above ground grasses growing point below ground or protected by leaf whorl until late growing stages of development phloem.jpg 1

2 Contact and Retention Morphological features Leaf characteristics leaf orientation leaf area pubescence cuticle thickness, wax Spray Characteristics surface tension of the droplets resistance of a spray droplet to spread droplet size based on nozzle orifice size, impact drift and retention spray volume the total amount of spray solution (gal)/acre spray droplet characteristics can be manipulated by adding adjuvants Adjuvants (WCG p.134) Cuticle Barrier Nonionic surfactant improve retention by spreading droplet, more contact with leaf surface Oils loosen/dissolve cuticular waxes vegetable oils petroleum oils methylated seed oils Fertilizers condition water and aid movement into cell sulfate source nitrogen source Cuticle wax is mainly non-polar (not charged), so non-polar herbicides are absorbed more quickly Recall discussion of amines vs. esters Polar herbicides require surfactants oil-based surfactants help to penetrate the cuticle (lipophilic) Rainfall too soon after application can limit absorption, but dew in the morning may aid absorption rainfall acts to wash herbicide from leaf dew acts to rehydrate dried herbicide, or acts as free moisture if spraying in the morning to increase volume Soil applied herbicides Absorption is affected by placement shoot absorbed herbicides chloroacetamides carbamothioates oxyacetamides root absorbed herbicides dinitroanilines Absorption is generally easier through the roots compared to the cuticle no cuticular barrier but still must pass membrane herbicides enter via mass flow with water and nutrients through the root hairs Water Quality (WCG p. 76, 136) Common problems with water quality dirty water: soil and organic matter dissolved chemicals bicarbonate (HCO 3- ) Ca 2+, Mg 2+, Fe 2+ Common remedies for poor water quality add fertilzer adjuvant (NH 4 ) 2 SO 4 = AMS to overcome hard water other chelating compounds have not worked as well ph adjusters Basic ph blend: Quad 7 or Renegade make more acidic, does not affect herbicides usually, mainly used for insecticides 2

3 Factors influencing susceptibility of plants to herbicides Plants growing rapidly are most susceptible Susceptibility often decreases with age or maturity Older plants more difficult to control than younger ones Rosettes controlled but bolted plants are more difficult Mustard and dandelion, any stage Rosette technique (p. 102 WCG) use tillage to control Canada thistle until mid July (day length less than 15 hours) emerging shoots do not bolt when day length is less than 15 hours (remain in rosette stage) apply translocated herbicide mid September to early October clopyralid glyphosate Technique can be applied to any rosette weed When to Treat Mature Perennials When to treat leafy spurge? When carbohydrate reserves are low during flowering, or treat during the bud stage Generally, when carbohydrate reserves are being stored (translocate with sugars); with exceptions Lym and Messersmith 1991 Leafy spurge research found that despite carbohydrate movement to the roots in the fall, there was no increase in picloram translocation When plant is preparing for winter Lym and Messersmith 1991 for maximum translocation to the leafy spurge roots, best time to treat the plant is during the flowering period data also showed better results when applications were made under high humidity data also showed a slight increase in translocation if applications were made during a cool period followed immediately by hot weather What is Influence of Physical Injury or Environmental Stress HERBICIDE RESISTANCE s G_LMQRbPtXZQ2n4i6VVQy3v_IA=&h=1280&w=960&sz=564&hl=en&start=4&um=1&itbs=1&tbnid=GZJckeYMEYmzhM:&tbnh=150&tbnw=113&prev=/images%3Fq%3DKochia%26um%3D1%26hl%3Den%26s a%3dn%26rlz%3d1t4adfa_enus366us366%26tbs%3disch:1 3

4 The Competition Rages On Herbicide resistance Selection pressure Herbicide resistance categories Target site Non-target site Weed Science Society of America definitions Herbicide tolerance: The inherent ability of a species to survive and reproduce after herbicide treatment. This implies that there was no selection or genetic manipulation to make the plant tolerant; it is naturally tolerant. Herbicide Resistance: The inherent ability of a plant to survive and reproduce following exposure to a dose of herbicide normally lethal to the wild type. In a plant, resistance may be naturally occurring or induced by such techniques as genetic engineering or selection of variants produced by tissue culture or mutagenesis Herbicide 101 Mode of action Site of action Chemical family MODE OF ACTION: Amino acid synthesis inhibitors SITE OF ACTION: Acetolactate synthase enzyme HERBICIDE CLASS: sulfonylurea (SU) imidazolinone (IMI) Triazolopyrimidine sulfonanilide (TPS) sulfonylamino-carbonyltriazolinone (SACT) rigid ryegrass (Lolium rigidum) Weed has extensive cross and multiple resistance to many herbicides, over ten sites of action and families of herbicides Australia, Chile, France, Iran, Israel, Italy, Saudi Arabia, South Africa, Spain, Tunisia, and USA R is Increasing need stewardship Owen et al When does herbicide resistance occur? (Zimdahl 2007) One or several of the following factors may be true The herbicide has a high degree of control of the target species. It is very effective The weed s seed has a short life in the soil seed bank The herbicide has a long soil persistence The herbicide is used frequently; annually for many years or more than once per year for several years The herbicide has a single site of action The herbicide s rate is high Herbicides are not tank-mixed Christoffers et al Objective: evaluate wild mustard cross resistance evaluate possible introgression of resistance from herbicide resistant canola Studied two wild mustard (Sinapis arvensis) seed lots from Cass County, ND to confirm resistance and evaluate the resistance mechanism resistant (had survived herbicides) confirmed susceptible Christoffers et al Weed Sci. Target-site resistance to acetolactate synthase inhibitors in wild mustard (Sinapis arvensis) 4

5 Table 5. Treatment list Table 6. Percent visual control 14 DAT and biomass accumulation 28 DAT Herbicide Class untreated check -- thifensulfuron ethametsulfuron sulfonylurea (SU) triflusulfuron imazamethabenz imazamox imidazolinone (IMI) imazethapyr flumetsulam triazolopyrimidine (TP) cloransulam flucarbazone sulfonylamino-carbonyltriazolinone (SCT) Treatment Visual control susceptible (S) Visual control resistant (R) Biomass (S) Biomass (R) % g untreated check thifensulfuron ethametsulfuron triflusulfuron imazamethabenz imazamox imazethapyr flumetsulam cloransulam flucarbazone LSD (0.05)