By Gilba Solutions Pty Ltd

02/27/2022 It is increasingly commonplace in the turf industry for Managers to try and do the right thing in relation to monitoring the environmental impact and using lower risk inputs, whether these be for example fungicides or fertilisers. Gone are the days of the mercuric fungicides!
This is an admirable approach but a major issue is that there is little by way of good information on the non-target impact of preventative (or curative for that matter) programmes. Spraying to manage one disease can in fact encourage other diseases.
In 1995 Eric Nelson discussed the non-target effects of fungicides in depth. The actual manner in which this disease enhancement occurs depends on the specific environment in which applications are made. The main reason this occurs is that by spraying to deal with a fungal pathogen, you in turn cause a reduction in competition from other non-pathogenic antagonistic microbes. This reduction leads other pathogenic species to proliferate and become the main disease causing fungi.
Microbial void
Ever had ongoing issues with pythium sp? It appears that pythium sp are very good at filling this microbial void. The same situation occurs with brown patch. Antagonistic bi-nucleate Rhizoctonia species are commonly detrimentally affected by fungicide sprays. Population reductions in these naturally occurring disease controls result in an actual increase in brown patch!
On occasion Turfgrass Managers experience times when a fungicide allows a particular disease to become more severe or when a second disease occurs soon after a fungicide has been applied to control the initial issue. Many companies promote preventative programmes in relation to disease management but give very little by way of technical information of what impact fungicide applications may actually have on beneficial organisms. The table below shows the impact of commonly used turf registered fungicides on the severity of turfgrass diseases.
Fungicides that increase the severity of turfgrass diseases
Fungicide
Leaf spot
Dollar spot
Rhizoctonia sp
Pythium sp
Possible effect on Trichoderma sp
Chlorothalonil
Yes
Yes


Negative
Etridiazole

Yes
Yes

Negative. Need 10-14 day interval pre or post application
Iprodione




Negative. Need 10-14 day interval pre or post application
Mancozeb
Yes




Metalaxyl


Yes


Propiconazole



Yes
Negative
Thiram
Yes
Yes
Yes



Many companies promote p







I am by no means suggesting that Managers stop using fungicides but I do suggest that when adopting a spray programme be aware of the implications of this approach. If issues develop and continue to occur then alternative options such as cultural control etc. should be examined.