Farmers and others who apply agrochemicals as part of their husbandry practice must attempt to achieve the optimal level of performance from the products used while taking care of the crop and environment around.

This means an increasing need for professionalism in the way we use agrochemicals and this article aims to help operators understand these other factors.

The first step in any disease, weed or insect control programme is to select the correct product for the job in hand. However, we must remember that this is only the starting point because the level of control achieved is also very much influenced by other factors.

Good pest control is dependent on a combination of the following:

1. Product choice.

2. Spraying operation.

3. Crop.

4. Weather conditions.

1. Product choice

Assuming the correct active ingredient is chosen, does your product have a good formulation? A good formulation can improve the performance of a product against the target pest, as well as causing fewer physical problems such as nozzle blockage when mixed in the sprayer. When more than one pesticide is to be tank-mixed, the tank mixing sequence shown in Table 1 should be followed.

When filling the sprayer, it is good practice to have the batches of spray laid out in the sequence that they are to be added to the sprayer. This way there is less chance of adding the wrong product to the tank and causing crop damage.

2. Spraying operation

All boom sprayers over 3m wide must be tested by 26 November 2016. This testing process will help ensure that sprayers are in good working order and ready to apply pesticides safely and accurately.

Spraying technology has come a long way since the early days, with developments such as active suspensions, bigger tanks, wider booms, improved boom suspension, faster forward speeds, lower water volumes, specialist nozzles, computer-controlled instruments, GPS guidance, etc. However, owning a sprayer fitted with all the latest technology does not guarantee success.

When spraying, the aim is to place as much of the spray on the target as possible while keeping off-target drift to a minimum. Nozzle choice and boom height are key in this regard.

Nozzle choice: The spray nozzle is the ultimate control unit on the sprayer. If the nozzle is worn or blocked, the spray distribution is adversely affected and application is compromised. The main nozzles used in modern farming produce a flat-fan distribution pattern.

Flat-fan patterned nozzles are classified as conventional flat fans, low-drift flat fans, low-pressure air induction (AI) flat fans and high-pressure AI flat fans. There are similarities and differences between these nozzle classifications.

Nozzle similarities: All ISO-rated flat-fan nozzles are colour-coded relating to their orifice size and output flow rate. For example, yellow nozzles are always an 02 size with a flow rate of 0.8 l/min at 3 bar pressure. A blue 03 size has a flow rate of 1.2 l/min at 3 bar pressure.

The most common sizes used on farm sprayers range from an 025 to an 04. There are smaller and larger nozzle sizes available, but these are not generally used. The numbering on these nozzles – 110 03 – describes the fan angle of 110° and the nozzle size 03 refers to its flow rate at three bar pressure. The higher the number, the bigger the flow rate at any given pressure.

Growers who use lower water volumes generally tend to use nozzles sized 025 or 03 (120-150l/ha). Those using higher water volumes opt for 04 or 05 sizes. Smaller orifices require better liquid filtration to prevent nozzle blockage.

Nozzle output charts are available for the different sized nozzles and show the application rates in l/ha at different forward speeds and pressures (example in Table 2).

Forward speed can be calculated simply. Mark out a run of 100m in a field to be sprayed. Record the time taken to travel the 100m and use the average of a few runs. Divide 360 by the time taken (in seconds) to drive the 100m and this gives your speed in km/h. Do this with a half-full sprayer and at the intended spraying speed.

Nozzle classifications relate mainly to the droplet size profile they produce. The smaller the droplet size, the better the coverage of the target. However, fine droplets increase the amount of off-target drift.

The conventional flat-fan nozzle produces the smallest droplets and, as a result, the most drift. High-pressure air induction nozzles produce the largest droplets and reduce drift relative to conventional nozzles by 90%. However, when choosing a nozzle, select one that combines good coverage with good drift reduction. The Hypro Guardian Air nozzle is one such nozzle reducing drift by 75% compared with a conventional fan jet while also giving good target coverage.

Individual nozzle output should be checked regularly during the season. One simple way to do this is to hold a calibrated cylinder under each nozzle for a minute and record the output at the set operating pressure. If the nozzle output varies by 5% from the application chart (Table 2 or equivalent), change the nozzle. A set of Hypro Guardian Air Nozzles on a 24m boom costs approximately €200.

Boom height: The spray boom should be set 50cm above the target for 110° fan nozzles. At this height, drift is reduced significantly and coverage in the crop is better than where booms are set higher. At this height, each nozzle fan is also meeting the second next fan, ensuring that everything is being hit twice from different spray angles.

If the boom is set too low, uneven application will occur because of insufficient overlap of nozzle outputs across the boom. This can show as a castle wall effect with uneven heights following differential amounts of product.

Spraying speed is influenced by the size of the field, levelness of the seedbed, wet or dry soil conditions, wind speed, crop thickness, boom stability, etc. Keeping the boom stable is essential for even spray application and drift reduction. If the boom is bouncing around when spraying, slow down.

3. Crop

There are many different crops grown in Ireland – cereals, oilseed rape, field beans, peas, potatoes, brassicas, carrots, grass, etc. These crops have different canopy structures and need different nozzle choice.

A fan nozzle spraying vertically is a good choice for spraying barley post stem extension while the potato nozzle, where the fan of spray is angled at 30° from the vertical, is preferable when spraying potatoes at full canopy.

As crops develop and grow, penetration of spray down into the crop canopy becomes more difficult. If the spray cannot penetrate the canopy to hit a target below, control will be reduced. A typical example of this challenge can be seen in the ease of spray penetration in the different canopies in Figure 1.

Barley crops need to be dense, with high ear counts (1,000/m2) required for high yields. Wheat crops need not be so dense (approximately 600 ears/m2 optimum) and excessive density makes spray penetration and disease control more challenging. A more open crop canopy allows better penetration of spray (see Figure 2).

Early removal of grass and broadleaved weeds is important before the crop gets too dense. Grass weeds and broadleaved weeds present a small target when sprayed at up to the three-leaf stage, so nozzle choice can be critical.

At this timing, air induction nozzles can produce droplets that are too big to provide good weed coverage of tiny leaves. Using the Defy 3D nozzle, where the spray is angled, will increase weed coverage and reduce drift. The use of excessive water volumes on small targets has a negative effect on control as the large droplets associated with high water volumes do not stick very well to the fine-leaved grass weeds.

Choose a nozzle that operates best at 2-3 bar pressure range. Increasing the pressure will increase drift, even with air induction nozzles, and it does not improve penetration and coverage.

4 Weather conditions

Weather around the time of application can influence how a pesticide performs. Avoid spraying when temperatures are very low or very high and where there are big extremes between daytime and night time temperatures. Wet crops at time of application should also be avoided.

Wind can reduce the amount of active ingredient reaching the target and increase drift. If spraying near a surface water body, avail of the STRIPE options to decrease the buffer width required. Table 3 describes the wind speeds at which spraying should be carried out and appropriate measures to avoid undue risk. Wind speed can also be measured at boom height using a hand-held anemometer.

Wind speeds of between 2km/h and 6km/h are recommended. Be wary of spraying during calm conditions due to temperature inversions which can lead to drift. It is advisable to have a nozzle body on the sprayer that can hold more than one nozzle.

A good nozzle choice for cereals would be a Defy 3D and a Hypro Guardian Air nozzle. Choose the same colour for both nozzles as this allows a simple switch when conditions dictate. If you need to spray a crop such as potatoes, which requires higher water volumes, include an 04 or 05 potato nozzle on the holder.

Conclusion

It is important for farmers to maximise the return on the inputs they use to grow their crops. This is especially relevant this year with the prospect of even lower grain prices. The performance of agrochemicals is very much about getting the basics right. This involves selecting the right nozzle to balance coverage and drift, choosing a sensible forward speed for boom stability and setting boom height at 50cm over the target for 110° fans.

To read the full Crop Protection Focus Supplement, click here.