Few would argue that it is more of a challenging task to correctly calibrate a vineyard sprayer than a broadacre sprayer. There is much to consider here but for vineyard application, one can note:

  • Type of equipment (airblast versus airshear)
  • Row and vine spacing, canopy height and trellising system
  • Table versus wine grapes
  • Contact versus systemic chemistry
  • Seasonal effects and weather at the time of application
  • Which convention to follow in order to determine the dilute volume required for a particular vine canopy

The Australian Wine Research Institute (AWRI) (1) states, “The water volume that produces coverage to the ‘point of runoff’ (where the vine canopy is thoroughly wet) is termed the dilute volume . This spray volume is the key to determining the amount of chemical that should be applied to a vine canopy to deposit a lethal dose. The label RATE /100 litres in conjunction with the dilute volume determines the amount of product that must be applied to a particular canopy whether dilute or concentrate spraying.”
The AWRI (1) in 2010 goes on to say that “Currently there are four options for determining the dilute volume required for a particular vine canopy:

  • Measure in-field dilute volumes by test spraying to run-off
  • Use estimates based on past experiences or regional best practice for similar situations
  • Use Vine-Row-Volume methods such as Unit Canopy Row (UCR) to give you starting points
  • Follow pre-existing Avcare recommendations.” (now CropLife)

Talking to Scott Matthew, Syngenta’s Senior Technical Lead – Viticulture, he, like AWRI in their studies, found that in field measurement of dilute volumes as per the first dot point is also yielding great results with Syngenta’s suite of fungicide products. Scott’s description of the point of run-off references the inside of the vine canopy (or the targeted spray area, if in fact, you are looking to control powdery mildew, your dilute volume must be worked out as point of run-off inside the canopy) and relates to the coalescence of spray droplets on the leaf or fruit surface.
Some of Scott’s tips for efficacious vineyard spray application (focus on powdery mildew) include:

  • The quantity or dose on the surface of the leaf, needed for an acceptable disease control, which for grapevines is worked out as a rate per 100L of water applied to the point of run-off
  • The % of leaf area to be covered in order to achieve control, the 5 of leaf covered needs to be higher for protectant fungicides than for systemic (xylem mobile) fungicide.
  • The thickness of the spray droplet residue (particularly for protectant fungicides like mancozeb and copper) must be durable enough to persist up to the next treatment given the breakdown by rain, wind, and UV light etc., 2010/11 estimates showed copper was only lasting 3-5 days
  • Identifying the Target – There are two spray targets we need to identify. Firstly the biological target (the pest that is to be controlled) and application target (a place where the pesticide spray must be deposited in order for it to work on the biological target for effective control)
  • Application timing – Slide 1 below shows what often happens in reality as opposed to what is ideal application timing

spray application timing • Protectant (Preventative) Fungicide (PF) versus Curative Fungicide Activity (CF) – Slide 2, PF’s are applied before the development of disease and prevent spore germination or penetration of the pathogen into the plant whereas CF’s are applied when the disease is already present, but symptoms are not yet visible. Note from slide 2 that powdery mildew takes only 6 days for incubation at 23 degrees Celsius. syngenta spray application Factors affecting Spray Application

  • Always check the product label for the Rainfast Period but as a general rule 2 –3 hours without rain after an application is needed for systemic fungicides to penetrate the leaf tissues as wel