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Refinzar for roots?

Refinzar for roots? Ben Burrows

With a number of the major manufactures launching SDHI fungicides in recent years, most are claiming that these chemicals are having a plant heath benefit – but whilst this may be the case, what does it mean for crops in the field? For cereal fungicides, Syngenta and Bayer both believe their SDHI molecules increase plant greening and now DuPont has launched an oilseed rape fungicide that is said to promote rooting.

Refinzar (penthiopyrad + picoxystrobin) is targeted by DuPont for Autumn phoma control, but increased plant rooting is also seen to be a significant side benefit. Independent research by Dr. Stephen Rossall from the University of Nottingham found that against other treatments, root mass was significantly increased when Refinzar was applied full rate at the 4 leaf stage. These experiments were carried out both in controlled environments and again in the field – but the increased rooting didn’t always result in more yield. So what’s the point?

This Autumn I have been carrying out a trial at Chilton Candover, Hants on early Phoma Leaf Spot control, but as a side project I wanted to see whether I could replicate the improved rooting in a real field situation. A field of Campus oilseed rape was sprayed with 0.5 l/ha Refinzar at 5 leaf (Oct 19) and a section of untreated tramline was left.

Much of a difference? Not to the bare eye…

In the original research, the entire dry root mass was measured, but as the soil was moist, I opted to carefully dig up plants and then measured the length of taproots after washing.

Whilst I was measuring the roots in the field, I wasn’t really seeing a difference between the treated and untreated. However once I went through the data, I discovered that the taproots were on average 2.6cm longer where we sprayed Refinzar than the untreated. The difference was also enough to be statistically significant which lends further credibility to my result! Of course, this is just one experiment and we need to consider that other factors may have played a part – but we were indeed able to get the plants to increase their rooting using the SDHI.

Taproot Graph
…but the data shows increased taproot length where Refinzar was sprayed

But we come back my original question, why bother trying to enhance rooting if we don’t always see a yield response? A plant with larger root mass is likely to be capable of taking on more water – crucial during a period of drought as well as scavenging more for nutrients. OSR has a huge demand for Phosphate and because P is highly immobile in the soil, we need to ensure that the roots can find it. Yes, oilseed rape is at £250/tonne – but if we are already going through to control Phoma Leaf Spot, then surelyan increased rooting benefit can only be a good thing.