Delta T - Half-life of a droplet

It's a really curious question, what is the half-life of a droplet? That question is full of interesting studies that we will review in this Greenkeepedia entry.

Drift during the spraying of pesticides is a danger to the biodiversity of the environment. It affects plants, soils and surface water, and depending on how the activity is carried out, the effect can be greater or lesser. As explained in the greenkeepedia entry on spraying, the factors affecting drift are atmospheric, technological and chemical.

Why are we interested in knowing the half-life of a drop?

All studies on the half-life of a droplet aim at effective spraying and explain why products should be applied under suitable weather conditions.

In general, to minimise drift it is desirable to spray large droplets such as rain or heavy rain, although if the Delta T-index is too high even these droplets will lose effectiveness. The shape and size of the droplet depends mainly on the nozzle and the suction pressure.

It is the science of psychrometry that determines the behaviour of water and air masses. Depending on the humidity in the air and its temperature, it is possible to determine how much water the air mass requires and how long the water will remain atomised in the atmosphere.

Wind speed is another determining factor in determining the optimal application conditionsv and modifies the Delta T.

Carrancio, L. and Massaro, R.A. 2018.

It is not only the droplet size that determines the quality of the spray, but also the type of pattern in the spray nozzle. Spray technology is very varied and there are nozzles that apply in the form of a solid cone, hollow, flat fan or with an air stream that accompanies the droplet to the target.

Drift increases with wind speed and height above the ground when spraying.

Bode, L.E., Wolf, R.E.. Techniques for Applying Postemergence Herbicides. Univ. Illinois, Urbana, IL. 5 pp. Undated.

The droplet size depends on the type of nozzle, the working pressure and the surface tension of the solution. A small nozzle with high pressure and low surface tension produces small droplets that increase the risk of drift.

Bode, L.E., Wolf, R.E.. Techniques for Applying Postemergence Herbicides. Univ. Illinois, Urbana, IL. 5 pp. Undated.

The type of product to be applied also affects the drift as different solvent types, density or surface tension lead to different droplet sizes.

Many times lowering the working pressure results in larger droplets. The impact is very significant as increasing the droplet from 20 to 200 microns increases the droplet life from 0.7 seconds to 65 seconds, making it easier for the droplet to contact the target. The use of adjuvants such as wetting agents also allows for larger droplets that wet more of the leaf.

The disadvantage of increasing the droplet size is that the plant surface area impacted by the active material is reduced.

To ensure that the application is effective, you need access to real-time information from the Delta T, which is why we have the best weather station for tractors. WatchDog has a weather station designed for safe spraying. By means of a small ultrasonic station on the tractor and a display inside, we know in real time if it is the right time to make the application by means of the Delta T calculation.

If you want to know more about the half-life of the gout and the usefulness of the Delta T Index please contact us at info@tiloom.com.