Off the back of a cold winter and spring, the powdery mildew forecast in sugar beet is one of the lowest in recent years
Off the back of a cold winter and spring, the powdery mildew forecast in sugar beet is one of the lowest in recent years, according to the BBRO (British Beet Research Organisation), however fungicides still have an important role to play this season. Dominic Kilburn writes.The advice from BBRO lead scientist, Dr Mark Stevens (right) is that if yields are to be maximised after the difficult and protracted establishment seen across many crops earlier this season, growers must opt for at least one fungicide application, and possibly two, depending on when the crop is scheduled to be lifted. “Judging by the cold weather earlier in the year, powdery mildew is unlikely to be a major problem however it could be that we’ll continue to see more rust, as has been the case in recent years, and protection with broad-spectrum fungicides will also keep diseases such as ramularia and cercospora at bay,” he says.”The advice is that one spray should be applied for crops being lifted up to early October, and two sprays for anything that is going to be lifted later,” adds Mark.Three-spray programmes
While the BBRO currently has no recommendations for three-spray fungicide strategies, on-going trials work is attempting to determine whether there are sufficient benefits of a third application.Trials started in 2011 and repeated in 2012 included up to 21 different treatments based on broad-spectrum fungicides Escolta (cyproconazole + trifloxystrobin) and Spyrale (difenoconazole + fenpropidin).In addition, as well as comparing three-spray programmes against one- and two-spray equivalents (lifted in November and December), the three-spray treatments were compared as ‘early’ applications (applied monthly from late June), as well as when applied ‘late’ (from disease onset at the end of July, and then at the end of August and at the end of September).Commenting on the two seasons’ trials results, Mark says that, generally speaking, the trends in performance between the different fungicide application programmes are similar, although in 2011 the early three-spray programme lifted in November (97.9 adjusted t/ha) gave a 3t/ha yield improvement compared with a two-spray programme (94.9t/ha). However, when the trial was repeated in 2012, and lifted in December, the early three-spray programme didn’t provide an uplift in yield compared with the two-spray approach.”My thinking is that in 2011 the crop had a good start to the season with rapid canopy development and it was mature enough to cope with the fungicides. When they were applied on June 20th in 2012 there was only 80 per cent canopy cover as it had been cooler and the crop hadn’t grown sufficiently.
“We saw the same effects back in the 2005-2006 season when applying fungicides at the end of June there are the same physiological implications for yield,” he added.Mark points out that the late three-spray approach harvested in November in 2011 yielded equivalent to a two-spray programme while in 2012 it could only match the one-spray treatment.As well as November and December-lifted crops, Mark says that data from both years was also recorded in January lifted crops and, although the overall yield trends between treatments were similar, there was a noticeable jump in sugar content (17.2 per cent) with crops that received a late three-spray fungicide programme compared with one-, two- and early three-spray applications (16.2 per cent).”There is clearly a benefit from a late three-spray strategy for crops lifted after Christmas in terms of maintaining a good, healthy canopy and keeping disease out, and promoting higher sugar levels.”For the first time in 2012 he also trialled a four-spray programme on crops both December and January lifted which delivered a sugar content of up to 17.8 per cent.”When lifted late, the four-spray programme delivered a high sugar content,” points out Mark.
However, the four-spray December lifted crop produced the lowest yield out of all the treatments, while in January it was the highest yielding.
Fungicide trials at BBRO are continuing for this season and Farmers Guide will bring you more data as and when it is available. Growers are advised to opt for at least one fungicide application, and possibly two, depending on when the crop is scheduled to be lifted this season. Stick with two sprays
Adopting a two-spray fungicide programme typically adds more than 10t/ha to a later lifted sugar beet crop, yet around half of these are only receiving one fungicide spray and losing significant margin potential, says Bayer CropScience.There is now a strong body of evidence supporting the yield benefit of a two-spray strategy on crops lifted beyond the end of October. Bayer’s product manager for root crops Dr Albert Pineda estimates this accounts for around two-thirds of the national crop but, according to the most recent BBRO survey a third of growers still apply just one spray.”Successive BBRO trials have demonstrated the beneficial effects of fungicides in promoting yield; growers who do not adopt this knowledge are foregoing significant additional yield for little extra cost. Fungicides pay back their cost many times over,” he says.Across 32 trials performed by Broom’s Barn, British Sugar and Bayer CropScience, from 2007 to 2012 a single spray of Escolta (cyproconazole + trifloxystrobin) in July has boosted yield by an average of 8t/ha over untreated sugar beet. In two-spray programmes, a second spray in late August to early September has added a further 5.3t/ha on average.”With beet at 26.51/tonne a spray of Escolta costs a tonne of beet and, from these trials results, a two-spray programme can be expected to pay for itself and add around 11t/ha to yield putting almost 300/ha on the bottom line. This is a substantial return on investment,” says Dr Pineda.
Experience has shown that Escolta can provide up to six weeks protection so a spray in the second half of July, at the first sign of disease, should see a beet crop safely through to the time cereal harvesting is completed and oilseed rape crops drilled.A second application of Escolta around the beginning of September will then protect against rust while its combined strobilurin + triazole effects prolong photosynthetic activity, effectively building yield in to winter while protecting against frost,” says Dr Pineda.