Quality = Effectiveness + Safety
Spray oils vary considerably in quality. It is important to understand how they differ so you can use the right oil in the right circumstances.
The quality of the spray oil you use will define two things:
- Safety: How safe it will be to the fruit, tree and environment.
- Effectiveness: How effective it will work in helping control fungal disease and pests.
So how do we determine how safe and effective a spray oil will be? Below is a checklist that provides an effective guide to ensuring product quality.
A Quality Checklist
How can product quality be ensured? Here's a seven point checklist to follow.
| ITEM |
DISCUSSION |
EXAMPLE - BIOPEST |
| 1. Virgin oil |
Spray oils should originate only from a virgin oil, NOT recycled oils |
Produced from a virgin medicinal-grade iso-paraffinic mineral oil |
| 2. Registered |
Products should be registered with the NRA for the intended use |
Registered with the NRA for a variety of applications |
| 3. Paraffinic content |
Paraffinic content provides the most pesticidal efficacy. Products should contain at least 62% paraffinic molecules for use in pest management |
74% paraffinic molecules |
| 4. Purity |
A spray oil's purity should be at least 92% This can be measured by USR (or UR) - UnSulphonated Residue. Impurities are a key cause of plant and yield damage |
USR (UR) purity at over 98% |
| 5. 'Weight' of the oil |
Measured by carbon number. An oil's weight will influence its effectiveness and appropriateness for intended use. |
An nC24 rated oil |
| 6. Surfactant quality |
This can have a significant impact on mixing and spraying. |
Uses a premium surfactant package. |
| 7. Product support |
What support does the product have? |
- Ongoing research into use in cotton and horticulture
- Extensive supporting data and documentation available |
Measuring Product Purity
Impurities are generally a grower's worst enemy when applying spray oils. Impurities, when exposed to sunlight, oxidise and form acids on the leaf and fruit surfaces and in certain conditions 'burn' the plant.
So how can we measure purity?
A widely accepted measure is Unsulphonated Residue level (USR or UR). Base oil quality and the level of product refinement will determine a spray oil's USR. This measures the absence of potentially damaging impurities (referred to as aromatics and other unsaturates) in oils.
A simple indicator of purity is the clarity of the product. For example BIOPEST's clarity is a clear sign of its quality and purity. The next time you open a drum of oil, check its clarity. Is it 'water clear'?
Paraffinic Oils
Paraffinic Oils Regarded As The Most Effective In Pest Management
The superiority of paraffinic oils (over vegetable, pine and other mineral oils) for controlling a variety of pests and diseases has been evidenced in a number of crops. The following paragraphs aim to explain why this is the case.
Not All Paraffinic Oils Are The Same
For an oil to be regarded as a paraffin, or paraffinic oil it should contain at least 62% paraffin chains. BIOPEST contains not less than 74% paraffin chains, making it a uniquely effective product.
Understanding 'Active Constituent'
Spray oils are required to list the amount of active constituent in the product on the product label. For example BIOPEST 's contains is 815g/L of paraffinic oil.
What does this mean? It means that by weight, BIOPEST contains 815g of paraffinic oil in every litre of product. It is less than 1kg because of two things:
- Specific gravity: The specific gravity of most spray oils is less than one. If an oil's specific gravity is say 0.815, this means that 1L of oil weighs 0.815kg. Hence 1L of product contains 815g/L of paraffinic oil.
- Surfactant: The surfactant used may take up between 1%-3% of the weight of the product, or up to 15% as in the case of Crop Oil Concentrates (COCs) such as SACOA ENHANCE Spray Adjuvant.
In terms of pest and disease management what is important in this measure is the type of oil used. Is it a paraffinic oil?
Summary
So how well a spray oil works as a pesticide is influenced by its paraffinic content. That is, the pesticidal/fungicidal efficiency of an oil increases as the paraffinic content in the oil increases.
There is another factor that influences a spray oil's effectiveness - the size of its molecules. This is because how long an oil remains on the insect or on the foliage depends greatly upon its molecular size. .
The Importance Of A Spray Oil's 'Weight'
How long a spray oil remains on a pest or foliage will strongly influence how effective it will be. And how long it remains will depend greatly upon its molecular size or 'weight'.
Why is this? Because a 'heavier' oil has greater 'sticking' power and will take longer to evaporate (volatilise).
How is this commonly measured? Whilst a number of measures can be used - viscosity, boiling range and carbon number - carbon number is the most practical measure to use and is illustrated in the diagram below.
Carbon number (e.g. nC24) measures the number of carbon atoms in each molecule of oil and is used to indicate an oil's molecular size or 'weight'. Common carbon number values of spray oils are nC21, nC23, nC24 and nC25. An example of its relationship to efficacy is illustrated in the diagram above for summer pest spraying programs.
The Tradeoff Between Efficacy and Plant Safety
So heavier oils are optimal for efficacy but they also carry a greater risk of plant or fruit damage. This greater risk of plant damage is because if the oil persists longer on the plant surface, then so will the potentially damaging impurities in the oil (aromatics - refer above). |
