This years high blight pressure severely tested one growers ability to comply with Natures Choice guidelines. Heres how he did it.
PLANS for a radically revised blight control programme were abandoned this year. But Chris de Jong at Babraham Farms still managed to comply with Tescos input specifications.
Blight is a constant threat to the 60ha (150 acres) of irrigated potatoes on the 623ha (1,540 acres) arable farm near Cambridge. The crop includes Desiree, Fianna and Saxon for prepacking, and Maris Piper grown on a chipping contract.
"Traceability is fast becoming a vital component in the production of all our crops," says Mr de Jong. "To comply with Tescos Natures Choice scheme we now have full traceability in potatoes going for pre-packing. This year we planned to modify our blight control strategy to rely on cheaper products. The extreme blight pressure forced a re-think."
Until this season blight control revolved around systemic fungicides. The plan for 1997 was to use mancozeb-based Dithane for the first treatment before switching to Trustan (cymoxanil + mancozeb + oxadixyl), which has both systemic and protectant activity.
After two sprays, applied while the crop was still growing vigorously, Dithane was scheduled to return at the full canopy stage. A tin-based product was planned for the end of the season to protect tubers.
As planned, the first Dithane spray went on as soon as the plants were as big as a lettuce and before tops met in the row. But as blight started to threaten, Trustan was used for the next three treatments at the maximum allowed at 10-day intervals.
Then Curzate (cymoxanil + mancozeb), which has some kick-back activity, was used for the next four sprays before the switch was made to the fluazinam-based Shirlan. Brestan (fentin acetate + maneb) was used for the last two treatments.
"We had intended using a lot more Dithane early on to keep costs down, possibly alternating with Curzate to keep the fungus guessing," says Mr de Jong.
"But because of the huge threat we could not risk it. We managed to maintain a 10-day spray interval even in the wet June, but were prepared to go closer if the worst came to the worst.
"This is the first season we have grown for pre-packing under Tescos Natures Choice scheme and, despite blight, we were able to work within the strict protocol."
The variety line-up for 1997 was changed to suit market need, and to match the farms ability to deliver quality produce. Piper and Fianna were used for chipping last year with Sante, Desiree, and Saxon for pre-packing.
This year the acreage of Piper was cut back and Fianna, now for packing, expanded. Sante was replaced by an increased acreage of Saxon. There were 15ha (37 acres) of Saxon, and 23ha (57 acres) of Desiree.
"Sante seems to do well, but end-users prefer Saxon," says Mr de Jong. "As supermarkets like the appearance and taste of the locally-bred variety our acreage was stepped up. According to NIAB, its in-built ability to cope with blight is not as good as other varieties, but we like it and it is popular with our customers."
Because of the soil type – sandy loam and chalk – at Babraham, tuber dry matters in recent years have been high, averaging between 23% and 25%. This increases the risk of bruising so careful choice of variety and gentle handling at lifting is essential.
According to Anglian Produce, the company which markets the farms crop, Saxons tubers from test digs in recent years have averaged 20.8% when Desiree was 23.7% and Sante 24.6%.
Ideally Mr de Jong would like to dig potatoes with less than 20% because the difference in susceptibility to bruising between 20% and 23% is enormous.
To minimise damage a careful watch is kept on tubers during lifting. A miniature tv camera mounted on the harvester and a monitor in the cab shows the driver the level in the trailer so the drop height can be reduced.
The main lesson from the 1997 season is the need for flexibility with blight control to cope with actual conditions. In future the installation of an in-field weather station could improve fungicide targeting and give potential for cost cutting.
This year a 12ft high radio relay mast was installed on a high part of the farm. So data gathered by a neighbours Adcon weather station could be sent down the line to a central base, allowing management decisions on actual conditions and individual crop needs to be made.