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Forestry Fact Sheet No 5

Introduction

The fact sheet aims to provide some background information to assist in the effective spraying of farm forestry plantations.

Importance of Weed Control

The aim of weed control is to minimise the competition between weeds and trees for limited resources, such as water, nutrients and sunlight, in the first two years after planting. Weed control also plays an important part in fire control and access.

Weeds can have an adverse effect on the survival and growth of trees and may also result in less wood production over the rotation.

Generally, the larger the weed free area around the new tree, the greater the growth response (blanket weed control as in Figure 1 except when there is a need for erosion control). For the first two years after planting the roots of the tree are relatively close to the surface and therefore in close competition for moisture with other plants using the same zone.

In areas where there is a high risk of erosion, weeds can provide benefits such as soil stabilisation. It is important to note however, that these benefits are the result of concentrating the weeds left in a strip in between the rows of trees, leaving a weed free zone for the trees to grow in (Figure 2).

 

Figure 1 Blanket weed control	Figure 2 Strip weed control

 

The three critical components of successful weed control are:

• Timing of the operation;
• Area and position of weed control; and
• Length of control.

Timing involves looking at the best time to kill the weeds based on their growth and the season, and in relation to the time until planting.

Weed control in forestry is usually carried out in several operations throughout the year. These are classified below:

Preliminary

This is carried out in the spring (preferably) or autumn, prior to planting, with the aim to stop the set of seed and to remove the larger, well-established and more difficult weeds (such as Sorrel). This application is carried out as a blanket operation containing a knockdown and with little residual.

Pre-plant

This provides knockdown and residual control in pines and is carried out before, during or after the planting. It can be either blanket or strip, depending on the site. For eucalypts this operation is carried out before planting because the residual chemicals currently available (Oust and Simazine) both require a six-week withholding period after spraying before planting can proceed.

Post-plant

This should generally not be required in most cases if the two prior treatments were carried out effectively; however it is needed if weeds grow back in the first spring after planting.

Second-year

Spraying in the second year extends the period of weed-free conditions until the second autumn after planting, building on the gains of successful weed control in the first year.

Application of Chemicals

Methods

Spraying operations are of three types:

• Manual spot-spraying using a knapsack, spray-gun or weed-a-metre;
• Strip-spraying using either a 4WD motorbike, small boom spray or manually with a knapsack (liquid/granule); and
• Blanket-spraying using either a large boom spray, or aerially.

The most appropriate type for a particular site will depend on factors such as terrain, soil type, weed problem, drainage lines, proximity to neighbours and layout of planting. Blanket-spraying in the first two years is best under most conditions. However strip-spraying is suitable:

• On very exposed sites where winds are severe;
• On light sandy sites where soil erosion and sand blast will occur; or
• In situations where retained grass may provide and alternative food supply for grasshoppers insect pests such as cockchafer beetles and weevils.

When strip-spraying it is important that the trees are planted in the middle of the sprayed strip. With eucalypts, where spacing is usually 4m x 2.5m, strip-spraying should leave a minimum 2m wide strip free of weeds. With pines the spacing is usually 2.5m x 2.5m, therefore a minimum 1.5m wide strip should be free of weeds.

In the second year blanket-spray weed control should occur on all sites as soils will be stable enough even on all erosion prone sites. Due to phsyiological differences it is possible to spray directly over pines without damaging them; however eucalypts must be sheltered from any contact with herbicides.

Environmental Conditions

It is important that environmental factors such as wind, temperature, humidity and rain are taken into account when considering spraying.

Wind

The most important factor is wind. It is vital that the chemical lands exactly where it is supposed to and not in the neighbour’s property. Therefore windy days should be avoided. By contrast, on dead calm days sprays can be carried long distances because of temperature inversions; so dead calm days should also be avoided (Table 1). As well as damaging neighbouring properties spraying in these conditions leads to increased costs as respraying will be necessary.

Table 1 Wind Speeds : Guidelines for Spraying Farm Chemicals

Approx. Windspeed	Description	Visible Signs	Spraying Recommendations
Less than 2km/h	Calm/Inversion	Smoke raise vertically	Avoid Spraying
2-3.2km/h	Light Air	Direction shown by smoke drift	Spraying inadvisable
3.2-6.5km/h	Light Breeze	Leaves rustle,wind can be felt	Ideal Boom Spraying Ideal Mister Spraying
6.5-9.6km/h	Gentle Breeze	Leaves and twigs in constant motion	Avoid Boom Spraying (Especially herbicides) Ideal Mister spraying
9.6-14.5km/h	Moderate	Small branches moved, raises dust or loose paper	Boom Spraying Inadvisable Ideal Mister spraying

Temperature/Humidity

High temperatures (>25°C) and low humidity (<50%) increase the likelihood of drift due to the decrease in droplet size due to evaporation . Large droplets are less likely to drift than small droplets, as they are airborne for a shorter period (Figure 3). Minimal drift is especially important in strip-spraying and in eucalypt plantations. Increasing temperature also increases volatility and therefore the chances of vapour drift, especially with ester formulations.

 

 

 

 

 

 

Figure 1 Droplet risk while spraying.

Rain

Most chemicals require a rain free period, however some soil active chemicals can be sprayed in the rain (check the label before spraying).

Mixing Chemical

• Do not leave a tank mix of spray overnight and expect it to be effective the next day because chemicals have varying half-lives, which will influence the effectiveness of the chemical over time.
• The same applies to lunchtime stops - empty the spray tank, refill with water then have lunch before adding the chemical.
• Each night make sure the tank is cleaned out before finishing.
• At the end of the spray program make sure the tank is thoroughly cleaned.
• When using a mix of solid and liquid formulations, always add the solid chemical before the liquid to allow the solid to mix sufficiently.

Water Quality

Make sure the water is clean. Rainwater is best. Do not use dam water. If bore water is used it should be allowed to settle so the soil particles settle out.

The pH of the water can also play an important role in the effectiveness of the chemical mix. Some chemicals become susceptible to degrade at certain pH levels. It is therefore vital that you are aware of your water’s pH and use buffering agents to keep the pH within the desired range.

Recording

When spraying you should always record:

• Date;
• Weather conditions (temperature, wind speed and direction);
• Chemicals used and rates; and
• Target weeds (or pest).

This ensures you have some protection against prosecution in case of drift and allows you to assess and understand any failures that may occur.

Aerial Spraying 

Communication and planning between the farmer and agent or operator is essential for safe, effective aerial spraying. If possible, consider combining your spraying program with your neighbour to save time and money. For helicopter spraying a nearby water supply is required.

 

 

 

 

 

 

 

 

Figure 4 Fixed Wing aerial sprayer

The aerial sprayer will need a detailed map, which clearly indicates the following:

• Crop and area to be sprayed;
• Nearby susceptible crops;
• Beehives;
• Powerlines;
• Houses, fences, roads (school bus routes);
• Dams, watercourses and water tanks;
• The nearest town or settlement and the distance from the spray site;
• Livestock; and 
• Direction of north (orientation of map).

Neighbours must be notified of your intention to spray and what chemical is to be used. The aerial spraying operators should also record what chemical was sprayed, how much was sprayed and when it was sprayed. The operators map their flight paths using Global Positioning System (GPS). This provides an accurate map of the area sprayed.

Spray Equipment

Nozzles

Nozzles should be spaced along the boom to create a double overlap (Figure 5). If this overlap is not achieved, uneven weed control can result. Ineffective weed kill is a common problem when the double overlap is not achieved.  

As nozzles produce different spray patterns, the type used will depend on the chemical that is being sprayed and the target weed or pest. The height of the boom above ground and pressure used also affect the spray patterns.

The most commonly used nozzle types are flat fan and cone. Cone nozzles concentrate the liquid on the outside of the spray pattern and produce small droplets. These are commonly used to apply contact herbicides.  Flat fan nozzles produce a large range of droplet sizes,                            Figure 5 Fan spacing and overlap
resulting in good plant coverage and are generally used in broadcast
herbicide application.

Low drift nozzles can also be used. They create large droplets and have a narrow fan angle, which will reduce the chance of spray drift. If using low drift nozzles the spacing along the boom will need to be changed to maintain double overlap (see Figure 5).

Nozzles are made from various materials. The material used will influence the durability and time it takes for the nozzle to wear out.These materials are, in order of durability: ceramic,stainless steel, nylon and brass.The cost varies considerably among these, with ceramic up to three times that of nylon or brass nozzles.

Calibration

Equipment must be calibrated correctly to ensure the exact amount of chemical is applied. When calibrating, the nozzle outputs should be within ten percent of each other. One method of calibration is:

Calculating rate of output of spray unit

 

You need to know:

 

Number of nozzles = N

Output of nozzles (ml/sec) = O

Width of boom (m) = W

Tractor speed (m/sec) = S

 

Output (litres/ha) = NxOx10

                                 WxS

 

For example:

 

Output of each nozzle = 300ml/30 sec

                                     = 10ml/s

Number of nozzles = 8

Width of boom = 2.0m

Tractor speed = 100m/55sec

                         = 1.818 m/s  

 

Output (litres/ha) = 8x10x10

                                2x1.818

 

Output (litres/ha)    = 220 litres/ha

 

If the output of your nozzles is unknown then you can calculate it by measuring the amount of water, in millilitres, you into a bucket in one minute and dividing by 60. This will give you your output in ml/s.

 

An alternative method is to fill the tank with a known amount of water. Spray this out while travelling at the spray speed while timing how long it takes to empty the tank. Measure the area sprayed in the time to work out the output (litre/ha) of the spray unit.

 

Calculating amount of product required

 

Need to know:

Tank size (litres) = T

Application rate (litres or g/ha) = A

Output of spray unit (litres or g/ha) = O

 

Amount of product required per tank = T x A

                                                                 O

 

For example:

Tank size = 50 litres

Application rate = 3 litres per ha

Output of spray unit = 220 litres/ha

 

Amount of product required per tank = 50 x 3 
                                                                220

                                                            = 0.68 litres
 

Legislation

The National Registration Authority (NRA) controls chemical registration, distribution and sale. Each state controls the use of chemicals through State Acts.

In South Australia the acts involved are:

• Controlled Substances Act
• Dangerous Substances Act
• Occupational Health Safety and Welfare Act
• Agricultural Chemicals Act
• Animal and Plant Control Act

All these have associated regulations. There are also Codes of Practice and Australian Standards. It is recommended that you complete a Farm Chemical Users course, run through your local TAFE,to make you aware of all the legislative requirements.

Safety

Before spraying, seek advice on the herbicides /insecticides and application rates to be used. Read the label, contact PIRSA Forestry or spraying contractors for advice. When spraying make sure that you:

• Follow the directions on the label; and
• protect yourself using the recommended safety equipment (Figure 6).
  Figure 6 Safe chemical handling using appropriate Personal Protective Equipment.

For further information contact PIRSA Forestry

 

 

Disclaimer: While this publication may be of assistance to you, the government of South Australia and its officers do not guarantee that it is without flaw of any kind or is wholly appropriate for your particular purpose. The Government therefore disclaims all liability for any error, loss or other consequence that may arise from you relying on any informa­tion in this publication.

 

 

Last Revised February 2008