There are a number of key factors when looking to successfully control weeds.
During a cold spell like the past few weeks, growth slows and plants build their defences. This defence mechanism comes in the form of a waxy layer on the surface of leaves.
During a rapid phase of growth, leaves expand, new growth develops and their waxy layer narrows.
Herbicides landing on a weed must pass through its waxy layer before entering the plant.
A thicker waxy layer slows the herbicide molecule's entry into the plant. But the inclusion of a wetting agent (Torpedo 2, etc) will help the herbicide penetrate the waxy layer and improve its effectiveness.
In general, the growing conditions before the application of a herbicide are more important than after the herbicide has been applied.
Ideally, three days of good growth is needed before the application of a herbicide to achieve the best results.
Correct identification of weed species and weed size in all fields is essential. The selection of a general herbicide mix to cover all weed situations over a large area is a risky strategy.
Awareness of the weed spectrum in all fields is not just nice to know but can save growers money in the long term.
Generally, weed control in spring cereals should be completed by the early tillering stage of the crop.
In good growing conditions (three days before application), rates of herbicides may be reduced substantially – half rates have been shown to work successfully in many trials in Oak Park over the years.
Even though products such as the sulfonylurea (SU) Max range (Cameo Max, Ally Max, Harmony Max, etc) and Galaxy contain a number of actives which will control a broad range of weeds, there are situations which suit one herbicide over another.
A grower can reduce the effect of a product by doing any or a combination of the following: Reducing the dose rate; applying onto a very large weed; applying the product poorly; or by applying with too many other products in the tank, thereby reducing efficacy.
Sprayer calibration has to be correct, with the correct volume and nozzles appropriate to the prevailing weather conditions, target weed and product.
Water quality can also affect the efficacy of herbicides, especially where water is hard (excess cations – Ca 2+, Mg 2+, etc).
Herbicide formulations are optimised to overcome most of these difficulties.
However, where water quality is a problem, the addition of an of adjuvant (non-ionic wetter or wetting agent such as Torpedo, Activator 90) is recommended.
Weed control in beet is informative because poorly working nozzles are quickly found out as weeds appear.
This is generally not the case in cereals, as poorly controlled weeds can be masked in the crop for most of the season.
At the start of each spraying season and at regular intervals throughout, check that the output from each nozzle is + 5pc from the manufacturer's guidelines.
Replace worn nozzles immediately. Nozzle selection can also affect the eventual outcome.
Generally, sprayers are fitted with a 025-04 flat fan nozzle.
In most situations, these nozzles are robust enough to apply a herbicide in the correct droplet size to provide good control.