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Locating nozzles away from rotor tips.

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Placing the spray boom as far forward as possible.

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Orienting nozzles backward and spacing for uniform patterns.

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Using low nozzle pressures.

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Using larger orifices in the
nozzles.

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Spraying when winds are light and the air is cool, about 4 a.m.

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Using herbicides that do not produce damaging vapours.

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Using buffer zones, particularly around water

You can also modify the solution with additives that produce more viscosity (adjuvants), or with an invert emulsion system, which will apply a mayonnaise-like material. They both have disadvantages, though, in either needing specialised equipment or mixing techniques.
If you're trying to increase the volume of solution over a particular area, you're better off tinkering with the nozzles than reducing speed or raising spray pressure. This will help to avoid small droplets, or 'fines', that are more likely to drift. There are some crops, however, that require good coverage and small droplets, which is the opposite. This is where you need to be a bit of a chemist as well as a pilot to satisfy the customer.
Vapour drift is a similar effect arising from evaporation.
Accurate records are essential, not only as aids to the business but also for later complaints of drifting. It's helpful to note such items as nozzle size and spacing, wind velocity and weather conditions, rate of application and time on task, together with a diagram (which you should have made anyway, for planning purposes—many pilots use an aerial photograph and keep a log of the tracks flown with a marker).

Seeding
When a pipeline, or similar, has been laid, the countryside has to made to look attractive again as soon as possible. A large hopper full of grass seed is used to do this, and you will get to do a series of runs over the pipeline to spread it.

The hopper is basically a large fibreglass bucket that weighs about 300 lbs. It has a large petrol motor on the bottom, about the size of the average lawnmower engine, with a gate that is opened and closed from the cabin, and the important thing to remember is to positively switch off after a run, otherwise you will drop the seed everywhere. In other words, just letting go of the On button doesn’t automatically stop the flow.
The other point is that, like a longline, it is attached to the helicopter in two places, that is, the hook and the electrical cable, and the latter has to be pulled out by ground staff or you will strip the cables when the hook is released.
If you have a lot of ground to cover, think about placing the seed on a truck and operating from various points around the countryside, which will save a lot of dead flying time. Lastly, depending on the machine and how far you have to fly, it’s not uncommon to top up with fuel after every delivery.