You’ve got to know when to hold ’em
Know when to fold ’em
Know when to walk away
Know when to …spray!
Kenny Rogers knew a thing or two about timing. But when it comes to spraying your crop with fungicide, is timing really all that important?
CCDM farming systems economist, Amir Abadi, says it is. Using a case study of a wheat paddock from WA’s Great Southern region, Amir has crunched the numbers using simulation modelling to determine how important timing and number of fungicide applications actually are in an average season.
According to Amir, timing is very important. About $60/ha important.
With the case study of a property in Katanning, Amir showed that in an average season and where inexpensive chemicals are available, then two applications at growth stages 31 and 39, or 25 and 39 will result in $110/ha benefit to the grower, when compared to no sprays at all.
Amir also showed that a single spray was still okay and beneficial to the grower, as long as the spray was timed at G39 – to protect the very important flag leaf.
“The key is to not lose photosynthetic area, as it’s the photosynthetic area that contributes to grain fill and, hence, yield,” he said.
“This is why the flag leaf is so important – if we protect it, and fungicide is applied not too long before or after it has emerged, growers could see around $60/ha profit in places such as Katanning in an average season, when compared to a scheduled spray on say, August 10, when the flag leaf has not yet emerged.”
Amir’s number crunching
In a nutshell, Amir’s number crunching shows:
- In a low rainfall season (Low GSR), it is not worth applying fungicide, as the grower will make a loss. However, in the average and above average rainfall seasons (Average GSR and High GSR), it is worth protecting your crop because in those seasons the crop is profitable.
- In an average rainfall season (Average GSR) the difference between a single spray at G31 (stem elongation) and G39 (flag leaf) was $54/ha, highlighting the importance of protecting the flag leaf and timing. High profit margins of more than $200/ha were seen at the single spray at G39, as well as when more than one spray was applied. Growers could make $110 per hectare profit with two applications, compared with not applying anything
- In a high rainfall season (High GSR), it is worth applying two fungicides, but there was little economic incentive to spray three times.
“It is clear from our economic research that when the flag leaf is out, at G39, it is worth protecting it, in average to above average rainfall seasons – the top three leaves are the most important economic asset of the crop – no doubt about it,” Amir said.
What about logistical constraints, when timing of application is just not possible?
Amir recognises the difficulty in moving around large properties in time to spray the flag leaf, however it is essential growers keep the flag leaf in mind.
“If we were to spray, say, on August 10, the crop might only be at G25, which means the fungicides will land on other leaves, not the flag leaf,” Amir said.
“From my research, they would still be a little better off than not spraying at all, but only by a marginal amount, of around $20/ha.”
Great for high rainfall regions, but what about for low rainfall regions?
Amir said in low rainfall regions, there is often little need to protect a wheat crop at all from disease, as leaf wetness is lower, making it less conducive for pathogens to take over the leaf.
“If you are in a lower rainfall region, you have to ask yourself how much leaf wetness duration should I expect after the flag leaf has emerged, as it is leaf wetness duration that determines the level of damage to leaves.
“This is why in higher rainfall regions, more than one spray is needed, but in lower rainfall regions, a single spray or no spray at all may be the way to go.”
Chemicals will not be cheap forever with fungicide resistance approaching
Amir also looked at a scenario when chemicals were more costly, say at $30 per hectare, as this could be the case in the near future with the development of fungicide resistance.
“If this is the case, then the most profitable strategy shifts to applying fungicide only once at G39. Again, coming back to protecting the most important leaf – the flag leaf,” Amir said.
“I realise it’s tempting to apply cheap chemicals prophylactically because they are so cheap and convenient.
“But if we can delay the onset of fungicide resistance, then we may be able to use the cheaper chemicals for a few more years, and we’ll all be better off, economically speaking.”
To listen to the Crop Disease Podcast related to this story, click here.
