THE TOP 10 CONSIDERATIONS WHEN DETERMINING A FUNGICIDE APPLICATION

The Type and Severity of Disease

  • are you trying to control a monocyclic or polycyclic disease?
  • what is the disease cycle of the pathogen?
  • if it is a seed or root disease that is likely to cause a problem, the decision to apply a fungicide must be made before planting, i.e. seed or soil treatment
  • remember, you aren’t going to ‘see’ the pathogen, your first indication that it is there is when symptoms develop, so you need to be ready to go!

Stage of the Crop

  • timing is everything! Apply when you’ll get your ‘biggest bang for your fungicide buck’. This means regular scouting of the field and knowing what disease you are dealing with. It pays to anticipate problems well in advance
  • typically, the earlier the disease hits, the more likelihood that damage will occur. Hence, applying a fungicide early will reduce additional build-up of inoculum
  • pay attention to prohibitive statements and withholding periods, (WHP) whether they apply to harvesting, cutting or grazing of the treated crop. The WHP could mean as many as 3-4 weeks prior to harvest, or in some cases there could be a total prohibition on grazing the treated crop.

The Resistance Rating of the Cultivar

  • refer to state guides for disease resistance ratings of cultivars
  • some crops are more susceptible at the seedling stage and become more tolerant as they age, e.g. against root diseases. Conversely, some crops become more susceptible once they reach the flowering stage, e.g. ascochyta blight in chickpea.

The Environmental Conditions

  • how much rain has been received in the past week? Is more rain forecast?
  • are there any relevant prohibitive statements on the product label?
  • fungicides are most effective if they can be applied before a rain event. If nearing the end of the period of effectiveness, i.e. 10 - 14 days for a some fungicides, you may want to consider application earlier if rain is forecast
  • disease risk can change in a matter of hours, depending on rainfall. The longer the period of time that favourable weather conditions are present, the more loss to disease can be expected. That is why it is essential to know the optimal temperature and moisture requirements for each disease.

The Agronomic Practices Used

  • check the field records and monitor the crop. What practices were used that may have increased or decreased disease risk?
  • are the plants weakened from any other stresses, environmental or agronomic, that could favour disease? For example, residual herbicides favour diseases such as ascochyta blight in chickpea because plants are weakened and maturity delayed.

Quality of Application

  • uniform coverage is essential for both seed and foliar treatments. For seed treatments, calibrate application equipment before each new seed lot to ensure proper mixing of product and application rate. Adding water may help coverage of seed, or putting through an auger again for mixing. Always follow label recommendations!
  • for foliar fungicides the best way to ensure good coverage is by using high water volumes.
  • application onto a wet plant (following a dew or light rain) will help distribute the product. Check the product label to see if spreader or sticker ingredients have been added or if it is recommended to add them.
  • there is limited information available on sprayer technology and fungicide application. Sprayer modification such as using split-application nozzles that have an angled spray pattern have been used for some diseases. The angled spray pattern improves coverage of vertically oriented heads such as for fungicide application against fusarium head blight. Follow label instructions!

Scouting and Accurate Identification of the Problem

To gain a full appreciation of the disease severity within a paddock it is important to view several locations. A fence line is not necessarily representative of the whole paddock. Accurate identification is also critical as many crop ailments are not caused by fungal pathogens and therefore will not benefit from a fungicide application.

Cost of Control vs. Potential Loss

  • what is the yield potential of the crop? The higher the yield and/or current market price, the greater the likelihood of a positive economic outcome from a fungicide application
  • use the two equations below to crunch some numbers to determine the ‘break-even point’ for a fungicide application. Try putting in different values for expected yield, expected yield increase and selling price:

Availability and Cost of Fungicide

A common question from farmers is ‘which fungicide is better?’ If you are applying a product at the right time and disease risk is present … the difference between individual products is splitting hairs.

Alternate Fungicide Chemistry

As discussed, it is important to avoid fungicide resistance from developing in a fungal population. Alternate fungicides with different chemistries whenever possible, (Table 12.1). In some cases, this is difficult to do since many fungicides are within the same chemical family, e.g. there is only one product for cereal leaf diseases that includes a product that is not a triazole. There is more choice for pulse fungicides.

 

NOTE: Not all active ingredients are registered for use on both cereals and pulses. Always check the product label before applying any agricultural chemical.

For more information about current trade names of these fungicides, refer to CropLife Australia’s current Fungicide Activity Group Table. Information presented in this table is drawn from the Fungicide Resistance Action Committee, (FRAC) and CropLife Australia.

CropLife Australia is involved in FRAC and promotes the responsible use of pest management methods to ensure sustainable agriculture.

 

Table 12.1 Fungicide chemical groups for resistance management and related information Adapted from CropLife http://www.croplife.org.au/

Activity
Group
Code
(FRAC Code
Chemical Group Mode of Action Active Ingredient Type of Activity 1Risk
for
Resistance
1 Methyl Benzimidazole
Carbamates (MBC)
  • Benzimidazoles
  • Thiophanates
Inhibition of mitosis and cell
division
Carbendazim
Thiabendazole
Thiophanate-methyl
Systemic with
apoplastic mobility
(protectant, curative)
High
2 Dicarboximides Inhibition of lipids and membrane
synthesis
Iprodione
Procymidone
Systemic with
apoplastic mobility
(protective, curative)
Medium to High
3 Demethylation
Inhibitors (DMI)
  • Triazoles
Inhibition of sterol biosynthesis
in membranes
Cyproconazole
Difenoconazole
Epoxiconazole
Fluquinconazole
Flutriafol
Propiconazole
Tebuconazole
Triadimefon
Triadimenol
Triticonazole
Systemic with
apoplastic mobility
(protectant, curative,
eradicant)
Medium
4 Phenyl Amides (PA)
  • Acylalanines
Affect RNA synthesis Metalaxyl
Metalaxyl-M
Systemic (protectant,
curative)
High
7 Carboximides /
Oxathiin
Inhibits mitochondrial
respiration (SDHIs)
Carboxin
Oxycarboxin
Systemic (apoplastic
mobility)
Medium
11 Quinone Outside
Inhibitors (QoI)
  • Strobilurins
Inhibition of
mitochondrial
respiration
Azoxystrobin
Azoxystrobin
Famoxadone
Systemic activity with
apoplastic + acrepetal
mobility (protectant,
curative)
High
12 Phenylpyrroles(PP) Affect proteins involved in
membrane permeability
Fludioxonil   Low to Medium
14 Multi-site contact
activity
  • Inorganics
  • Dithiocarbamates
  • Phthalimide
  • Chloronitrile
  • Phosphonate
  • Triazine
Act as general toxifiers with
several sites of action (sites
may differ between group
members)
Captan*
Chlorothalonil
Copper
Metiram
Mancozeb
Sulphur
Thiram
Zineb
Contact
(protectant)
Low
17 Hydroxyanilide Inhibition of tubulin formation
during mitosis
Fenhexamid^   High

* Permitted use only (PER81406) ^ Permitted use only (PER14211)

This chapter was prepared by Penny Pearse1, Provincial Plant Pathologist, Saskatchewan Agriculture and Food, Regina, Canada ppearse@agr.gov.sk.ca

Further Information

More detailed information can be obtained from: DEDJTR AgNotes Series www.vic.gov.au/graindiseases

DEDJTR chemical use information http://agriculture.vic.gov.au/agriculture/farm-management/chemical-use

Cereal Seed Treatment Guide (SARDI) www.pir.sa.gov.au

Victorian Cereal Diseases Guide (AG1160) www.vic.gov.au/cerealdiseaseguide

Victorian Pulse Diseases Guide www.vic.gov.au/pulsediseaseguide

Victorian Winter Crop Summary www.vic.gov.au/victorianwintercropsummary

CropLife Fungicide Activity Group Table 2015 www.croplife.org.au

CropLife Fungicide Resistance Management Strategies 2015 www.croplife.org.au

Wallwork H (2015) Cereal Seed Treatments (SARDI) www.pir.sa.gov.au, http://www.pir.sa.gov.au/ data/ assets/pdf_file/0005/237920/cerealseedtreat2015_web.pdf

Wallwork H (2000) Cereal Root and Crown Diseases www.grdc.com.au/bookshop

Wallwork H (2000) Cereal Leaf and Stem Diseases www.grdc.com.au/bookshop

Australian Pesticides & Veterinary Medicine Authority www.apvma.gov.au

APVMA Public Chemical Registration Information System https://portal.apvma.gov.au/pubcris

 

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