Glyphosate is the most widely used herbicide ever developed.
It is a non selective, non residual, leaf absorbed, translocated herbicide. Its main uses are for total vegetation control (eg. before planing crops or in industrial areas) and controlling the seed set of annual weeds. It is particularly effective on perennial weeds. It is of low toxicity to mammals, birds and fish. It presents virtually no environmental hazard.
Some plants have become resistant to glyphosate.
7 APPLICATION METHODS AND TIPS:
Glyphosate is applied by hydraulic nozzles or CDA (Controlled Droplet Application) equipment mounted on air craft or ground vehicles for broadcast application. It is usually mixed with water. Its low toxicity (to the operator) makes it ideal for directed application using hand held equipment.
Various wick type applicators have been developed for applying concentrated glyphosate solutions.
Glyphosate is most effective when applied on warm, sunny days when the plants are growing vigorously.
Drought or nitrogen stressed plants are difficult to kill with glyphosate.
Plants covered with dust are often hard to kill because the glyphosate attaches to the clays before entering the leaf.
If plants have been heavily grazed or defoliated they should be allowed to regrow until the root:shoot ratio is around 1 before application of herbicide or the rate of herbicide may need to be increased to achieve effective control.
Whilst glyphosate is not regarded as a soil residual herbicide, it appears to reduce germination of grasses for a few days after spraying. This may be due to direct contact of the herbicide on surface seeds.
20 mm rain is required to wash residues from sprayed plastic mulch before transplanting as glyphosate residues may affect seedlings contacting the plastic.
Glyphosate reacts with calcium and other di and tri valent ions in water. 50 ppm calcium will reduce activity (Shea and Tupy, 1984). The ions form a complex chelate type structure with glyphosate which reduces absorption (Thelen et al, 1995). This antagonism may be reduced by adding crystalline sulphate of ammonia at a rate of 1 kg per 100 L of water.
Do not store in galvanised or mild steel containers as it will corrode them and glyphosate may react with zinc to form explosive hydrogen gas.
Rainfast in 6 hours.
Frost effects: Frost affected plants are more tolerant to glyphosate. Frost one day or more after spraying generally has little effect on performance.
Inversions: Avoid application during low level inversions as excessive drift may occur.
Delta T and relative humidity: Avoid application when Delta T is greater than
Wetting agents: Generally not required unless plants are very hard to wet of low rates of herbicide are being used with high rates of water. If the tank concentration of herbicide to water is less than 1:100 then additional wetting agent may be beneficial.
Pulse may increase the activity of glyphosate on broad leaved species but often reduces its activity on grasses. It may also improve the rainfastness on some species. It usually shows greatest benefit on large broad leaved species such as Bracken, Blackberry and Gorse.
On annual plants it is usually more cost effective to use extra glyphosate rather than adjuvants.
LI 700, Spraymate Activator and Wetter TX are recommended on some labels.
Spray oils: Rarely used unless the mixing partners requires oil.
Salts: Crystalline ammonium sulphate at 1-2 kg per 100 L spray mix is commonly used to reduce antagonism with di and tri-valent salts in the water, dislodge waxes on some plants and improve the uptake of glyphosate. In other countries ammonium nitrate or urea is used.
10 WATER QUALITY:
Hard water: Glyphosate IPA reacts (chelates) with calcium and other di and tri valent ions in water. 50 ppm calcium will reduce activity (Shea and Tupy, 1984). The ions form a complex chelate type structure with glyphosate which reduces absorption (Thelen et al, 1995). This antagonism may be reduced by adding crystalline sulphate of ammonia at a rate of 1-2 kg per 100 L of water. Acidifiers can also reduce the antagonism in some cases.
Salty water: Tolerates salty water. A 10-20% loss of activity can be expected with sea water.
Colloids: Avoid using cloudy water if possible. Cloudy water containing clay reduces the activity of glyphosate. It is bound strongly by clay particles and less strongly by organic matter. However chemical clearing agents often leave surplus ions in the water which also reduce activity. Don't use Alum or similar compounds to clear water as the di and trivalent ions can cause more antagonism than the clay they clear. Use ammonium sulphate or mechanical filtering. If a coin cannot be easily seen on the bottom of a 10 litre bucket full of water, then that water is likely to significantly reduce glyphosate activity.
pH: High pH is often associated with high concentrations of calcium ions which are antagonistic with glyphosate IPA. Altering the pH with acidifiers may not reduce the antagonism. Addition of crystalline sulphate of ammonia at a rate of 1 kg per 100 L of water is preferred in most cases.
Tank life: Many months in clean water.
Trace elements. Glyphosate combines (chelates) with di and trivalent ions. Calcium, copper, iron, magnesium, manganese and zinc seriously reduce the effectiveness of glyphosate. This chelation is related to pH and acidifiers can be used to reduce problems with hard water. Slightly salty water and phosphates have little effect on glyphosate activity.
Compatible with ammonium sulphate, ammonium nitrate, urea, Flexi-N. Slightly salty water and phosphates have little effect on glyphosate activity.
Some chelated trace elements may be compatible.
Spraying oils and non-ionic wetting agents are usually compatible with glyphosate. Glyphosate increases the absorption of imazethapyr (Spinnaker) Starke and Oliver 1998.
Plant hormonal herbicides, like 2,4-D, generally reduce the absorption and translocation of glyphosate.
Slight antagonism between glyphosate and glufosinate has been reported for Goosegrass Eleusine indica (about 5% less control at marginal rates), however these mixes at higher rates also gave the highest absolute levels of control.
Generally slightly antagonistic with wettable powder formulations of pesticides.
Tank mixes with residual type herbicides such as substituted ureas, triazines, or others may decrease the activity of glyphosate. The addition of crystalline ammonium sulphate will assist to overcome the antagonism with triazines.
See HerbiGuide Compatibilities button.
Carrier volume: 25-1000 L/ha. Lower water rates give slightly better kill providing the spray is distributed evenly to each plant.
Nozzles: 1100 Flat fan preferred.
Pressure: 150-400 kPa.
Droplet size: Medium to coarse (ASAE S527) droplets are recommended on some labels. Use finer droplets for young grasses or when using low water volumes.
High Volume hand sprays:
Nozzles: Spraying systems D6 or similar.
Pressure: 400-700 kPa.
Glyphosate can be applied by range of low volume equipment such as gas guns, splatter guns, sprinkler sprayers, CDA applicators and wipers. When using this equipment the concentration of herbicide must be increased to apply similar amounts of active ingredient per square metre as would be applied by conventional application.
Carrier volume: 20 L/ha minimum with micronair equipment. Increase water volume to at least 30 L/ha and use larger droplets if the temperature is greater than 250C. Don't apply when temperatures are greater than 300C. Avoid application when relative humidity is less than 35%
13 SPRAYER DECONTAMINATION:
Clean soon after spraying to reduce the risk of forming dried deposits that may be difficult to remove.
Remove filters and clean separately. Triple rinse with water or water plus 0.25% wetting agent and run through boom.
Remove filters and clean separately.
Rinse with water and drain.
Quarter fill the tank with an alkali detergent (eg 500 mL or g of Drive, Dynamo, Omo, or Surf per 100 L water) and circulate for at least 15 minutes then run through boom. Rinse twice with water.
14 HERBICIDE RESISTANCE:
In 1996, annual ryegrass populations tolerant to glyphosate were discovered in Australia. Practices to reduce the development of herbicide resistance should be integrated into systems reliant on glyphosate.
Crops tolerant to glyphosate can be produced by genetic engineering.
15 REPLANTING INTERVALS:
16 WITHHOLDING PERIODS:
Allow 1 day before grazing or disturbing annual weeds and 7 days before grazing or disturbing perennial to allow maximum translocation and weed control.
17 RE-ENTRY PERIOD:
Wear protective clothing if in contact with the crop before the spray has dried.
18 PROTECTIVE CLOTHING:
Overalls, boots and washable hat. Use gloves and face shield when handling the concentrate.
Soil texture: Little effect.
Soil pH: Little effect.
Soil organic matter: Little effect.
Soil moisture at application: Best results when soil is moist and plants are actively growing. On dry soils use the HerbiRate module in HerbiGuide to estimate the rate required under dry conditions.