Nozzle choice for autumn weed control
For Pre-Emergence
Where the target is the soil and the aim is to get as much sprayed as possible a drift reducing air-inclusion nozzle is ideal, especially a finer type (GuardianAIR) which offers more spray droplets. Inclining the spray from both sides using a Twin spray or alternating nozzle spray direction will offer the best spray distribution where soil surfaces are uneven.
Post-Emergence
A standard flat fan or VP nozzle includes more fine droplets than an air-inclusion type and this is preferred for post-em applications for small grass weeds. Looked at from above, even a high population of blackgrass plants does not present very much leaf area to receive spray droplets.
It is important to follow label recommendations on water volume and spray quality but equally important is the angle at which the spray hits the target soil or leaves.
Research carried out by Silsoe Reasearch Institute has shown that an inclined spray works much better, depositing twice as much spray onto 1-2 leaf blackgrass plants.
Field trials using an 03 flat fan VP nozzle with a 40 degree forward incline* have confirmed this.
The photo above shows blackgrass regrowth in the following crop of Linseed. Alternate boom widths were sprayed with the same product and water volume but through either a standard VP nozzle or one that was inclined at 40 degrees (Syngenta's Hawk nozzle). There is much less re-growth in the areas where the inclined nozzle was used, indicating that blackgrass control was much higher in these area - remember the only difference was the spray incline!
* An inclined VP can be achieved using Syngenta's Defy nozzle or a Hypro flat fan VP nozzle selected for the desired speed and water volume in a TwinCap. TwinCap offers the option of either two 30 degree inclined sprays (useful for maintaining finer spray quality at higher water volumes) or a single 30 degree inclined spray when used with a blanking nozzle.
Hypro TwinCap (EF3 version) part # 152607TC
Blanking nozzle part # 30KBLANK
For latest industry advice on autumn spraying see FWI academy.