Time for spray program planning
By Brandy Rawnsley
Each season brings new challenges. The forecasts are pointing toward a wetter year, which are more conducive to fungal disease. Having some appreciation of what problems may arise under these circumstances, and how various fungicides work, will help pave the way to a successful crop management strategy.
Correct timing requires an understanding of the disease and how the fungicide works. Mode of action (MOA) refers to how the fungicide acts on the fungus. If only one mode of action is regularly used on a crop, the single control method increases the risk of a fungus becoming resistant.
Before selecting any fungicide, consider what disease may pose a risk to your crop. Powdery mildew, downy mildew and Botrytis are key viticultural diseases. Get to know what conditions promote disease and think about those parts of the vineyards that are more susceptible.
Most fungicides are protectants, which stop fungal pathogens from entering and infecting the plant. Protectant fungicides need to be applied before disease development.
Fungicides move on and within the plant in different ways. Contact fungicides protect the surface of the leaf but do not penetrate into the plant. THIOVIT JET®, applied just after budburst, provides excellent early protection against powdery mildew because it has both contact and volatile activity.
When shoots are rapidly growing, consider fungicides that move in the plant to protect new growth. Most demethylation inhibitor (DMI) fungicides, such as TOPAS 100EC®, have local systemic or translaminar activity; That is, they move across/within the leaf. Other local systemic products move outwards as the shoot grows via the xylem (including AMISTAR® 250 SC).
Application interval is critical to get the most out of your chosen fungicide. Some products require a 7-10 day spray interval for good control, whilst others offer up to 21-day protection (including MIRAVIS® and REVUS®). Increased spray interval provides greater flexibility in terms of time, labour and peace of mind.
Application timing should be aimed when the plant is most susceptible to infection. For instance, Botrytis grey mould requires a wounding site to infect the plant, one key time when this occurs in grapes is at as cap fall when the flowering process causes tissue damage. For this reason a botryticide like SWITCH® is best applied at the 80% cap fall timing.
To achieve the best disease control, consider season weather forecasts. Sticking to the same program each year can be expensive and ineffective. Product labels provide essential information such as target disease, product rate, spray interval, withholding period, number and timing of applications to assist in product selection.
Selecting reputable products based on sound knowledge and good advice will ensure disease doesn’t get the better of you this season.
Dr Belinda (Brandy) Rawnsley is a Syngenta Technical Services Lead for Viticulture and Horticulture