Archive Article: 1997/09/06
The real benefit of inputs and new technology comes under scrutiny in recent research at Harper Adams College and SAC. David Millar reports.
HALVING blight spray applications with no loss of blight control. Sounds good?
Of course it does. Such chemical savings are possible using weather monitoring stations to predict blight, but it may not be worth the £5,000 you have to spend on the kit.
Dr Peter Jenkinson, of Harper Adams, admitted at a college research seminar that most of this years forecasting trial plots had too much late blight to make them acceptable for pre-packing. The only consolation less was spent on fungicides in the disease-hit crops.
Not that the Harper Adams team didnt try to keep on top of blight in the British Potato Council-supported trial of decision support systems based on weather monitoring stations.
Acknowledging that blight pressure was high this year, spraying started before the crops met in the rows under the conventional system based on local farm practice.
The two decision support systems using software linked to either a Hardi Metpole or an Adcon weather station triggered their first sprays within a further two days.
Both weather stations work by monitoring temperature, rainfall and humidity in the crop. The Metpole also keeps track of soil temperature and moisture, transmitting the data back to the farm computer which assesses the blight risk and the need for a spray.
This years trials with the highly blight resistant Brodick, Maris Piper, Fianna and the weakly resistant Russett Burbank were late going in during mid-May and tuber initiation took place on 2 June.
Shirlan (fluazinam) was applied every seven days in the conventional practice trial, while another prophylactic system used five applications of Trustan (cymoxanil + mancozeb + oxadixyl) by 27 July, to be followed by Curzate (cymoxanil + mancozeb) and Brestan (fentin acetate + maneb). Shirlan was used with both decision support systems.
As expected, Brodick showed the least foliage blight infection, just 0.5% in the untreated plot on 27 July. It was well controlled by the six Shirlan sprays, and by the two further Shirlan sprays triggered by the Hardi monitor. Just 0.3% infection was recorded in the Brodick treated twice at the Adcons instigation and under the Trustan programme.
Spray applications were halved for the Maris Piper and Fianna plots. The 1% blight infection recorded in the Piper plot monitored by the Adcon was the lowest, while the Hardi system had the edge in the Fianna plots. Untreated Fianna showed an 8% infection and the Maris Piper 4.3%.
Results were recorded for the Russett Burbank but the blight pressure was so severe the plots were burnt off early, as were any remaining plots reaching 10% infection levels.
Although the work showed significant improvements in blight control, with fewer sprays, Dr Jenkinson acknowledged grower criticism that the infection present would have led to a supermarket buyer rejecting the crops. The weather stations and their decision support systems should be regarded as a further management tool – not a complete answer.
Although the Adcon system is less user-friendly than the Hardi equivalent, he pointed out that the picture of blight build-up created by the Adcon could be particularly useful if it could be tied in with accurate weather forecasting to get sprays on before infection occurred.
EARLY crop vigour and plant cover does not receive as much of a boost from farmyard manure (fym) as that of bagged ammonium nitrate, according to a new trial for the BPC.
Plots at Harper Adams College in Shropshire, at Hereford and at Chester, using differing nitrogen treatments, with and without winter-applied fym, will be taken through to yield with checks on quality and storage capability.
But the initial reaction from Dr Keith Chaney, of Harper Adams, is that the early release of nitrogen from the fym was limited compared with ammonium nitrate. But there are signs that more will become available from the fym plots during August.
YOU pay your money and nothing much out of the ordinary happens. Your potatoes go on growing whether or not a foliar nutrient or growth stimulant is applied, and yields are pretty much the same.
That doesnt stop a lot of salespeople and, it has to be said, a few growers from swearing by any of the range of seaweed-based and other growth stimulants on the market.
Lawrence Morrice, of the Scottish Agricultural College, doesnt share their views after trialling various products.
This years fully-replicated plots are still to be harvested and assessed but the Aberdeen-based researcher doesnt expect much change over last years limited experiment.
"My personal feeling, looking at the data, is that I am a wee bit sceptical about their consistency," he told growers at the SAC/SCRI/BPC open day at Dundee.
"You may think £8-10/ha is cheap, but you shouldnt apply things just in case there is going to be a benefit," he added.
In fewer than half of the trials carried out by SAC has there been a cost-effective benefit from using a foliar nutrient, and there can be differences between varieties and responses – even to favourable sprays.
The most consistent effect has come from a straight foliar phosphate applied at tuber initiation and repeated four weeks later. This £15/ha (£6 acre) treatment has increased yield sufficiently to cover costs in eight out of the 10 trials carried out since 1990. It also appears to increase tuber number which could be worthwhile in seed crops.
This years plots at Dundee have been treated with the commercial products Cropset, Fulcrum, Marinure, Yeald and PCC972. There were no visual differences seen in the plots of Saxon.
Last years more limited trial included other foliar products but there were no consistent benefits seen in that experiment.
"Some of these products have been shown to work in some situations," admitted Mr Morrice, "but they depend on variety and on timing – if the weather is against you, you are scuppered."
He pointed out that there was evidence that stressed or droughted crops which might benefit most from a foliar feed found it difficult to take up the applications.
GETTING the most from organic nitrogen already in soil growing potatoes could mean lower bills for bought-in fertiliser.
Last year, a number of commercial growers in the UK were asked to apply just 75% of their usual nitrogen estimate for their potatoes as basal fertiliser. Plant assessments were then made to determine how much, if any, nitrogen was needed in foliar form. Some needed no extra N and most were able to apply less in total than expected.
This year, the SCRIs Mark Young is repeating the experiment at Dundee where a crop of Maris Piper received a standard 150kgN/ha (119 units/acre), with alternative treatments of 50kgN/ha (40 units/acre) and 100kgN/ha (80 units/acre) to be topped up with foliar applications.
In fact, whole plant measurement of nitrogen uptake shows the 100kgN/ha treatment is likely to reach the crops optimum yield and no further N will be applied.
Sample digs show the 50kg/ha plot has 51 tubers per sq m and a yield of 38t/ha (15t/acre) while the 100kg/ha area is yielding 40.8t/ha (16.5t/acre) with 40 tubers/sq m, and 42.2t/ha (17t/acre) from the 150kg area with 43 tubers/sq m.
However, the gap in yield between the potatoes receiving nitrogen and those without is expected to widen considerably by the time the crop is ready to harvest.
FUNGAL seed treatments are likely to produce a better harvest of saleable tubers but not all varieties will give similar results to applied foliar phosphate. Some, like Maris Bard, are more influenced by seed spacing.
The SAC is piecing together several years of trials work with differing varieties, seed sizes and treatments. Pentland Squire is one of the more responsive to the various combinations of treatment. Rovral (iprodione) or foliar phosphate giving the most consistent responses.
Eric Anderson, of SAC, said that Maris Bard didnt respond so well to spray treatments but did to reduced tuber size and seed spacing.
This years trial with Lady Rosetta is producing the greatest number of saleable tubers from small (35-45mm) seed with Rovral treatment and drilled at either 14cm (5.5in) or 10cm (4in) spacings. The increase in saleable tuber numbers from early assessments is as much as 30% over other treatments.
Mr Anderson suggested growers of Lady Rosetta for seed consider treating with Rovral out of store, while ware growers should consider treatment with Gambit (fenpiclonil).