SIMULATION modelling tells growers it’s all about timing when considering the best time to spray fungicides to get profitable returns.
Centre for Crop Disease Management researcher Amir Abadi spoke at the recent Grains Research and Development Corporation Grains Research Update in Perth recently on how growers could improve profitability of wheat through tactical use of fungicides.
Using risk-adjusted analysis of the economics of disease management, Dr Abadi said the model showed that using seasonal conditions to inform decisions on timing and number of applications of fungicides improved profitability when compared with a scheduled crop protection approach.
Dr Abadi posed the question, does timing of the chemical protection at stem elongation make a difference to return on investment with fungicide?
He said that applying fungicide to the flag leaf, between July and September, was the most effective way to protect the plant and get the most out of the chemical application.
“The wetness around during winter will help to produce the growth of fungi and the flag leaf, which the fungi grows on, impacts the grain fill towards the end of the season,” he said.
The window of flag leaf can be quite broad and many growers may ask how do they know the exact time to apply the fungicide.
In a medium rainfall farming system, when tactical decision making is a practical option, optimal treatment is a single application at flag leaf emergence (Z39) in average to above-average seasons.
However if applied at Z25 and Z30, the model predicts a below average crop with most fungicide treatments having a negative to very poor return on investment.
“I would like to emphasise that there is no set date to spray fungicide,” Dr Abadi said.
“It’s about reading the crop there and then deciding if its flag leaf is established enough to benefit from fungicide.
“If you protect the flag leaf you will get a longer grain fill time and prevent yield losses of up to 1.5 per cent.”
Research data from Dr Abadi showed fungicide, if applied correctly, would save 80 kilograms of grain per 10 millimetres of rain if you sprayed around growth stage 39.
Dr Abadi said it was possible for growers to see an improved net benefit of $80 per hectare if the flag leaf was protected from rain events.
“Economically significant infection levels occur in high rainfall seasons, particularly during late winter and spring when key crop growth stages coincide with weather conditions that extend leaf wetness duration on major yield contributing leaves, including the flag leaf,” he said.
“Fungicides, when used preventatively, offer some protection against significant yield loss if severe infections occur.
“When below average seasons are expected, funds will receive higher returns in other uses or in future seasons.”
Dr Abadi said, according to the simulation modelling, spraying on a fixed date like August 10 every year would only protect the crop 65pc of the time, whereas spraying when the crop was ready would pay off 100pc of the time in one way or another.
“The tactical adjustment to fungicide application in response to seasonal conditions improves long run profitability of the wheat production,” he said.
“A deliberate approach that allows flexible management of diseases permits alteration of the number and timing of fungicide treatments and improves return on investment to fungicides.”
He said when logistics and management resources allowed for some flexibility, making tactical adjustments to the fungicide program, in response to seasonal conditions, could save money in the long-run.
However, it is worth bearing in mind that this type of tactical response doesn’t come with a guarantee of success in every season.
“This technique improves the likelihood of success but it doesn’t attempt the impossible task avoiding the rare situations when a good decision may have undesirable consequences,” Dr Abadi said.