With the reduction in fungicide availability in the amenity market, greenkeepers and groundsmen are looking at alternative methods of disease suppression.
There are a few products now being looked at as a way of keeping disease at bay such as phosphite, salicylic acid, biostimulants, Plant Growth Promoting Rhizobacteria (PGPR’s) and compost teas. Another method which has gathered momentum is the promotion of micronutrient packages containing elevated levels of metal ions such as Copper (Cu) and Zinc (Zn). Using metal ions to reduce disease is not new of course – iron has been used for almost as long as turf has been prepared.
Iron has well-known benefits in reducing disease – but I think we’ve all seen the drawbacks from over-application of iron to turf. Black layer, reduced microbial activity, iron pans blocking drainage and increased thatch build-up are some of the issues of excess iron applications. Small amounts of chelated iron are sensible, but like most things, applying excess amounts, particularly in granular fertilisers, is something that can be liable to cause long-term issues. Keep an eye out for Fe percentage on your granulars and ask if you really need, 6, 8 or 10% Fe adding into your soil. I carry out hundreds of soil tests every year and iron levels are already very high in 90% of them due to historical applications.
There is no doubt that Cu and Zn can reduce disease activity – copper was a key part of the now-banned Bordeaux Mixture which was used as a fungicide for many years. The reason for the banning of Bordeaux Mixture does give cause for concern – over-use led to contamination of soils and surface run-off into water sources which had the potential to kill aquatic life.
Used sparingly at very low doses, you may not see a significant build-up of metal ions in your soils, but I do think it is worth keeping an eye on levels in your soils to ensure we are not storing up a long-term environmental issue.
Other than pollution, what other issues can we see from excessive use of metals? Well, there is plenty of research suggesting increasing metal concentrations in soils leads to reduced microbial activity (Nwuche &Ugoji, 2008). Many turf managers are going down the road of improving soil health, adding in biostimulants and organic amendments, trying to encourage a thriving, diverse microbial community. We need to be careful we’re not spending money on one product encouraging good soil biology, then spending more money undoing the good work with another product. There is also research showing a decline in both shoot and root growth as these metals accumulate in soils.
Studies on the effects of metals in the soils of forests have shown decreased leaf litter decomposition where metal contamination has taken place (Freedman & Hutchinson, 1980). It isn’t a great leap to put this in context of a golf green environment and to be concerned that a reduction in natural thatch breakdown could be a possible knock-on effect of increased uses of metal ions as disease suppressors. Slowing down microbial activity will naturally slow thatch breakdown too.
I was at a seminar last year where the speaker made the point that natural disease resistance in many turf surfaces had been reduced by the constant, regular application of fungicides knocking back the healthy soil microbes. Could we get to the same stage with metals? All the research would suggest that excess applications may have a long-term knock-on effect on soil microbial populations.
I am not dismissing the use of these substances out of hand. Just as fungicides still have their place in a well-designed Integrated Turf Management Plan, so these products can too. What I would be concerned about is becoming reliant on metals and getting into a situation where you are applying every few weeks to keep disease at bay.
As with almost everything we apply to turf, the poison is in the dose. Everything can have a positive and negative impact. For example, in the good old days of insecticides for turf we could kill a lot of leatherjackets and chafer grubs with relative ease, but you would also be killing some beneficial soil life too. The same applies to fungicides; we can kill pathogenic fungi, but we must also accept that some beneficial soil life is killed too. Nature can deal with stress and small amounts of stress can be a positive thing. What turf cannot withstand is constant stress. If we start relying on metals to control disease we could be heading towards an unhealthy soil and constant stress, and turf quality will drop.
If you are integrating these products into your management programme it may be worth expanding the range of nutrients you test for in your soil tests. Standard soil tests do not check for micronutrients like zinc and copper, so asking your lab to include these would be a good starting point to ensure we are not getting levels up to those which can potentially cause problems for our soil health.
There is very little research going into the long-term effects of products that are being used in modern turf management: not just metals, but substances like chitosan and saponins too. What effect are these treatments in autumn having on the turf the following spring and summer? Is there more drought stress and anthracnose as a result? Hopefully not, but the concern is we may be addressing our disease issues in autumn, but are we just kicking the can down the road?
Geoff Fenn BSc (Hons) UK Technical Manager
Nwuche, C. O., and E. O. Ugoji. “Effects of heavy metal pollution on the soil microbial activity.” International Journal of Environmental Science & Technology 5, no. 3 (2008): 409-414.
Freedman, Bill, and T. C. Hutchinson. “Effects of smelter pollutants on forest leaf litter decomposition near a nickel–copper smelter at Sudbury, Ontario.” Canadian Journal of Botany 58, no. 15 (1980): 1722-1736.
