Technical
In areas in close proximity to traffic, plants lay down thicker waxy cuticles to reduce moisture loss during prolonged dry spells, while debris and dust builds up on the leaf surface, physically preventing efficient uptake.
Foliar disease, such as leaf spotting, mildew and rusts, and pest infestation like aphids also reduce the effective target area of leaf.
CLIMATE FACTORS Temperature Moderate temperatures (15-25O
thunderstorm will cause wash-off and would require re-spraying.
Light
Best results come from morning applications due to the long light period, before darkness stops the movement around the plant.
The quickest results are seen in high light intensity, long days which maximise the movement throughout the plant.
C) favour
efficacy. Low temperatures or light frost give a slow, but good kill. Spraying can continue in November/December as long as the frost will lift during the day, but symptoms may take four weeks to show in winter.
Hard/long-term frosts, when the plants go floppy and the metabolism shuts down, will lead to poor uptake and poor performance.
High temperatures can also cause stress in the target plants, shutting down the stomata, leading to poor uptake.
Avoid spraying in the hottest part of day during a heatwave. High temperatures, combined with low water volumes, can mean droplets evaporate very quickly, resulting in scorch and poor translocation within the plant.
Humidity
High humidity or light drizzle leads to good control, as long as run-off is minimal. It is acceptable to spray in the morning on dew or in fog, so long as it dries out in the day. Avoid spraying in the evenings where there is a high risk of run-off from night rainfall.
Rainfall
Rain before spraying, leaving wet leaves, is not a problem, but rain after spraying, before uptake, can lead to very poor results (40-60% of control without rain). Most other glyphosate formulations require 6-24 hours of dry weather after spraying but, for Roundup ProBio and Roundup ProVantage, Monsanto support one hour on annual grasses and couch and four hours for all broad leaved weeds.
The type of rain which occurs soon after spraying may also make a difference: up to 2mm in a short shower or light drizzle will have only a minimum effect and will not require a re- spray. However, 4-8mm of frontal rain or a
“ 126 I PC JUNE/JULY 2015
Slowest results are from evening or night application and run-off can still occur from rainfall overnight if the glyphosate was not taken up before dark.
Do not bury or cover weeds for at least five days after treatment as this will cut out light and stop translocation of glyphosate to the growing points, especially in perennials, and will lead to poor control.
Air movement
Spray when the wind speed is Force1-3, (1.2- 6mph) and wind direction is away from susceptible vegetation. Glyphosate is non- volatile and will not lift from target areas in high temperatures, but avoid temperature inversions where cool air is trapped under warm air. Droplets can behave in unpredictable ways and move away from the target area.
APPLICATION FACTORS Volumes
Hydraulic sprayers can be used at 80-250 l/ha; lower volumes usually give best results. Run-off occurs at around 400l/ha. Take care when mixing with residuals where high water volumes are recommended.
The volume range for standard CDA sprayers is 7.5-40l/ha in carrier oils or water. They can also be used neat through shrouded ULV sprayers like the Mankar.
Follow labels for volumes for other specialist uses, e.g. selective weed wipers, stem Injection, cut stump.
Volume/rate interaction
Low rates lead to a low concentration of glyphosate and surfactant. Higher rates in high water volumes (>250l/ha), still produce droplets with a low concentration of glyphosate, and both of these can lead to poorer results, especially in conjunction with
hard water or other sub-optimum conditions.
Low water volumes give good results, providing the correct nozzles are used, but rates should not be cut. High temperatures and low volumes together can cause problems and there is less margin for operator error in low volumes. Correct calibration is vital for swath width and boom height as well as walking speed. Halving boom height doubles the application rate.
SPRAY QUALITY Conventional
- Medium-coarse BCPC (200-400 microns). Use low drift, flat fan, even-spray nozzles or Polyjet/anvil nozzles for knapsacks
- Avoid driftable fines (< 100 microns) by never using cone nozzles and fit pressure regulators to avoid over-pressurising hand pumps
- Larger drops have a longer liquid phase which helps direct uptake through stomata
- Use droplets on finer side of medium for optimum wetting of hairy plants like nettles.
CDA - Medium BCPC (200-300 microns)
All equipment should be properly serviced and calibrated to ensure efficient application. Dose rate
Make sure the correct dose rate is chosen for the most difficult to kill target weed. If all other factors are optimal, lower dose rates may work, but sub-optimum dose rates will give less reliable results, especially if other conditions are also less than perfect.
Hard water
In many areas of central and eastern England, mains water is ‘hard’ and contains high levels of dissolved calcium, magnesium ions. Glyphosate can be locked up (chelated) by these ions, reducing the actual dose rate. The effects are most obvious where low rates and high water volumes are used
CONCLUSIONS
Knowledge of the ideal conditions can help maximise satisfaction by ensuring spraying takes place only when as many factors as possible are conducive to best results, and can prevent wasteful applications when conditions don’t favour a satisfactory kill.
The type of rain which occurs soon after spraying may also make a difference: up to 2mm in a short shower or light drizzle will have only a minimum effect. However, 4-8mm of frontal rain will cause wash-off and would require re-spraying
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