Compiled by JP le Roux

Good crop protection starts with a good sprayer. Last month we discussed the parts of sprayers and what a farmer should consider when he buys a sprayer. In this issue we discuss different nozzles, and next month we compare costs of draw, hitch and self-propelled sprayers.

Nozzle types

Various overseas companies manufacture a wide range of nozzles, each with its own purpose and application.

Flat-fan nozzles

Flat fan nozzles are used on most farms for the broad cast or strip application of herbicide on well-prepared soil.

Broad cast application with flat-fan spraying

Flat-fan nozzles are mounted evenly on the spray bar. The spacing of the nozzles depends on the specific spray angle of the nozzle and the height of the spray bar from the ground. The spray bar must be placed at a specific height above the ground so that a 30% overlap is obtained on the sides of the spray patterns between nozzles. A code number on the nozzle indicates the spray angle and delivery volume of flat-fan nozzles. For example, the number 80 in the code number 8004 on the nozzle, indicates that the specific nozzle sprays out the mixture at an angle of 80°. The last two digits in the code, namely 04, indicate the delivery of the nozzle which in this case will be: 4 US gallon per minute at a pressure of 40 pounds per square inch.

Flat-fan nozzles with different spray angles and delivery volumes are available from suppliers.

Strip spraying with flat-fan nozzles (Evenly)

Code numbers on these nozzles are followed by an “E”. This means that unlike the ordinary flat-fan nozzles, equal quantities of the mixture are delivered across the entire spray width of the spray pattern of a nozzle and therefore do not allow for overlapping with other nozzles. The whole spray width is uniformly covered by the one nozzle.

The “E” type nozzles should not be used for broad cast applications.

Cone type nozzles

Of the cone type nozzles, the following two are of great importance:

Hollow cone nozzles

As the name indicates, the spray pattern of this nozzle is in the form of a hollow cone. It is important to note the manner in which the nozzles should be assembled. Hollow cone nozzles are suitable for the application of fungicides and insecticides, and also for foliar feeding of plants. The fact that it sprays in the form of a hollow cone, results in different droplets reaching the target at different angles of incidence. In this way, better intrusion and covering are obtained in dense leaves. For example, hidden insects and fungi can also be targeted easier. Hollow cone nozzles are particularly suitable for the application of contact as well as systemic plant protection agents. The application of one, two or three nozzles per row and their placement will depend on the size of the plants as well as the density of the leaves.

Characteristics of hollow cone nozzles:

• Droplets reach the target from different angles, which improves leaf wetting (especially in dense leaves).

• Fine droplets are usually formed, which improves invasion and wetting, but also increases the danger of drifting.

• Works at pressures of 300 to 500 kPa.

Full cone nozzles

By changing the core or swing plates of the nozzle, the spray pattern of a nozzle can be changed from hollow to full. A full cone nozzle is suitable for the post-emergence control of weeds and insects in crops by broad casting or strip spraying. This nozzle works at pressure levels of between 300 and 500 kPa.

The follow-up spraying of weeds in standing maize is a good example of the use of full cone nozzles. Full cone nozzles can also be placed right above the maize rows to wet a specific target on the plants, such as the cups of maize plants infected with maize stalk borers. If the caterpillars have not moved too deep into the cups, they can be effectively controlled by correct placement of hollow nozzles over the rows and the application of enough spray to effect droplet formation inside the cups.

Floodjet nozzles

This type of nozzle can be used efficiently for herbicides that have to work in the soil and, to a lesser extent, for pre-emergence weed control. In other countries, the nozzles are used to apply liquid fertiliser, but they are mostly used in orchards in South Africa, especially for applications under the leaves of trees.

Properties of flood beam nozzles:

• Work at low pressure of 100 to 200 kPa

• Deliver large droplets with little drift

• Relatively large nozzle openings that do not clog easily

• Deliver a broad spray width

Note

The application of the right nozzles, the right placement, pressure, and delivery are aspects that farmers still largely neglect, and which will eventually lead to poor control and a waste of expensive chemicals. When in doubt, ask an expert. A good harvest will compensate for any trouble or cost to get the right advice.

Next month we shall discuss air assisted boom sprayers and compare the costs of hitch, draw and self-propelled sprayers.

We thank Koos le Roux, compiler of the Mechanisation Guide for the article.