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5. Improve application techniques and diagnose spray failures

Diagnosis and correction of spray failures

Skilled insecticide application will improve chemical effectiveness, reduce the risk of resistance, reduce crop losses, and probably reduce the quantity of chemicals and labour required to do the job.


A. INSECTICIDE RESISTANCE

Diagnosis:
Insect samples can be tested for resistance by NSW Agriculture. Contact ….

Corrective action:
To reduce the risk of increasing the level of resistant insects in the pest populations:

• Set up a chemical rotation plan of effective chemicals from different chemical groups (save some chemicals with shorter withholding periods for harvest time)
• Don’t mix chemical groups together. Use one at a time and rotate after 3-4 back to back applications. Use 3 consecutive sprays of a single group if a key pest like WFT is breeding in the crop. Vary the spray interval to fit the life cycle of the pest.
• Don’t spray more often than you need to. This can promote resistance more quickly
  

Make sure that you get good coverage to get the maximum kill

Many pest control failures are not due to resistance and are in fact correctable. Before testing for resistance it is worth making sure that other factors (as covered in the information below) can be eliminated as causes of pest control failure.

B. POOR SPRAY CALIBRATION AND COVERAGE

Spray calibration calculations: It is vital to have the right amount of active chemical in the right volume of water (or other carrier) for the pest, the crop area and the plant growth stage to be treated. Although no growers regularly get this wrong for standard conditions many labels only give rates for standard applications of high or low volume sprays. So growers are often guessing how to interpret labels for spray applications that the label is not designed for, e.g. foggers ! A chemical applied as a conventional spray will probably behave very differently as an aerosol (fogger) or if applied through drippers. Correct droplet size is often critical for contact sprays. If the droplets are too small and conditions are very dry the chemical may dry out before contact and not be adequately absorbed.

The consequences of occasionally or consistently getting applications wrong can be very great. Under-dosing can encourage resistance in WFT (and other pests) by not killing off partially resistant strains. Just bumping it up a bit is not a good idea either. Guessing can lead to residue violations and plant damage.

Spray coverage: Insecticides, especially contact insecticides, require thorough coverage of fine droplets to be effective. For small, secretive insects like thrips this is critical. Growers found it was very useful to run a dye to test spray coverage. We used a fluorescent night dye with different spray jets, pressures and hand movements. The variation in results was dramatic! Growers made corrections for worn and oversize spray jets, increased or decreased pressure as required, modified their hand movements and then checked the results. Generally too much chemical was being applied in oversized droplets and not enough care was being taken to penetrate foliage in larger plants.

A wet plant is not necessarily a protected plant! Many growers reduced chemical output and improved pest control as a result. If you haven’t tested coverage you will probably be as surprised as they were by the results.

Diagnosis:
Check that the spray equipment is set to deliver correct volumes to the target area (calibration)

Check coverage efficiency using a coloured dye at different pressure settings, jet sizes and delivery patterns (with hand held equipment) to detect weaknesses in spray coverage of the crop – under leaves, on the far side of rows, low on the plant etc.

* Methods for setting and checking differ depending on equipment used, i.e. spray boom, hand held gun, aerial application, misters, foggers etc

Corrective action:
Correct the size and distribution of spray droplets by adjusting jet size, pressure and movement through the crop to get the most even and close packed distribution of spray drops possible. This may require:

• Changing jet size to get a better spray droplet size
• Replacing jets every 12 months (worn jets become oversized, making droplets too large and uneven to give good coverage and they waste a lot of chemical through inefficient application)
• Increasing or reducing tank pressure to vary droplet size and air pressure driving spray into the crop
• Making sure that your movement of the spray nozzles is achieving good coverage from top to bottom, between plants and under leaves by altering application patterns (not too many rows at once etc.), speed through the crop and hand movements
• Modifying the design of hand wands to get better penetration of the crop (number of jets, length, angle etc.)
  

Avoid run off with most insecticides as this often leads to leaf burn and can actually leave less chemical on the leaf for insects!

C. INCORRECT CHEMICAL RATE:

Diagnosis:
Make sure you check the label against your crop, pest and equipment! Under dosing can reduce pest kill and increase the risk of resistance. Overdosing is an unnecessary threat to the health of workers and consumers and is not likely to improve results in most cases and can lead to residue violations.

Corrective action:
Check the label for the rate for your pest, method of application (high or low volume), crop type and crop area. You may wish to make adjustments for changes in leaf area at different stages of crop maturity if you want to conserve chemical use on younger plants

D. POOR UNDERSTANDING OF KEY CHEMICAL PROPERTIES, (mode of action etc.)

Diagnosis:
Sometimes a spray application appears to fail, or does fail because the grower may not fully understand how a new chemical works on the insect, or that it may break down quickly under certain conditions. Some new chemicals take time to kill, or work only on specific life stages of the pest. Some are systemic, or partly system and others need direct contact. Some last as an effective killing residue for a period of days while others do not. The chemical may not be effective, or may appear ineffective if not applied in a certain way. This can be difficult to diagnose without specific information about each chemical and its key properties and potential weaknesses.

Corrective action:

• Look for details on the label
• Consult information provided here on some chemicals under “C. Key chemical properties” (pages 34-50)
• Get expert advice
  

E. UNSUITABLE PRODUCT FORMULATION FOR YOUR NEEDS:

Diagnosis:
Check the label! The same chemical may be available in different formulations that can require different mixing procedures. They also may have different application and coverage properties, storage requirements and different compatibility with other additives.

Corrective action:
Make sure that the formulation of the insecticide you have purchased is suited to your spray equipment and methods of spraying.
 

6. Check for potential weaknesses in your insecticides

Pesticides are chemicals that need certain conditions to work effectively. If they are not used correctly this can lead to poor results sometimes for reasons other than resistance. Greater knowledge of the mixing and application guidelines for each chemical will help to avoid various potential causes of failure.

Chemicals properties summarised include:

Pesticides are chemicals that need certain conditions to work effectively. If they are not used correctly this can lead to poor results sometimes for reasons other than resistance. Greater knowledge of the mixing and application guidelines for each chemical will help to avoid various potential causes of failure.Please seek additional advice to confirm any decision prompted by information contained here because:

• Not all risks and benefits are fully covered
• This list does not rate resistance levels
• Impact on beneficial insects is noted in some cases
• Pesticide group is noted in the list above

7. Further Information and Expert Advice

 Advice on chemical permits and chemical use:

Australian Pesticides and Veterinary Medicines Authority (APVMA):

• Permits: http://www.apvma.gov.au/permits/permits.shtml
• Registrations: http://services.apvma.gov.au/PubcrisWebClient
  

Pest Genie
Permit trials: AgAware Pty Ltd,03 5439 5916; 0407 393 397
PIRSA legislation on farm chem. use:
Virginia Horticulture centre: 8282 9200 (Stacee Brouwers)
Your preferred reseller

Advice on spray coverage

Your preferred reseller
Commercial consultants
ChemCert course – via VHC 8282 9200

Insect and disease diagnostics:

Your preferred reseller
Commercial consultants
SARDI (Insects: Tony Burfield 0401 120 857, Plant diseases: Barbara Hall 8303 9562 or Kaye Ferguson 0437 297 585)

Advice on using beneficial insects

Biological services 8584 6977
Commercial consultants
SARDI Tony Burfield (0401 120 857)

General agronomy

VHC 8282 9200 (Stacee Brouwers)
Your preferred reseller
Commercial consultants

Insecticide resistance testing

NSW DPI: Sample via SARDI (Tony Burfield: 0401 120 857)