Arable
Early drilled rape minimises damage
from flea beetle • Crops sown early August fare best • Most growers wait too long to drill • More rape lost this season than last
G
rowers are drilling oilseed rape increasingly early in a bid to avoid damage from
cabbage stem flea beetle, confirms a study.
Crops sown in the first week
of August 2018 had little or no pest damage, according to Simon Kightley of independent agrono- mists NIABTAG, who analysed over a thousand responses sub- mitted by rape growers from all over the UK.
But later crops suffered, with damage increasing weekly in crops drilled throughout Au- gust and into September, when the combined effects of flea bee- tle and drought produced severe damage or crop write-off in 71% of reported fields. Most of the rape for harvest
2019 was drilled around the fourth week of August – a bit later than ideal, with many growers wait- ing for rain. At this time, 53% of crop had zero to mild pest dam- age whilst 23% was severe or a write off, according to this survey.
Peak migration
“This coincided with the peak migration of flea beetle into the
crop.” says Mr Kightley. The find- ings suggest that very early sown rape crop can limit damage by flea beetle by avoiding peak pest inva- sion times, he adds.
“This pest is one of national sig- nificance and we no longer have the neonicotinoids or reliable help from pyrethroid insecticides to fall back on,” Mr Kightley explains. “Any cultural control method is worth considering.” Research conducted by NIA-
BTAG over four years shows that drilling rape before 10 August will avoid the worst of the flea beetle invasion. “This is providing that other stresses such as the heat or soil moisture do not slow down crop establishment.” Nearly four times as much win- ter oilseed rape was lost in au- tumn 2018 compared to autumn 2017, according to the Kleffmann Group, which surveyed 403 UK rape growers. It estimated an orig-
“
Light leaf spot risk remains ex- ceptionally low in East Anglia this spring, according to the lat- est update from Rothamsted Re- search. Each spring, the autumn fore- cast is updated to take account of winter rainfall. As January and February were relatively dry, and because December was not par- ticularly wet, the overall risk has
8 ANGLIA FARMER • APRIL 2019
Any cultural control method is worth considering
inal planted area in autumn 2018 of 581,030ha of winter rape.
Failed crops
Some 68 farmers reported failed crops amounting to 6.28% of the total original planted area. This represents 36,000ha lost. In the 2017/18 season, the percentage loss was just 1.62% so autumn 2018 was almost four times more hostile to rape survival.
The survey also revealed a
clear difference in failed crops by breeding method. In conventional varieties the area lost was 7.52% (21,000ha) of the area planted.
Of the restored hybrid varieties, some 5.16% of the crop planted (15,000ha) were lost.
The south-east region had the highest area of failed crop at 12.60%, followed by Yorkshire and the Humber Region at 9.75%. Be- tween these extremes were the East Midlands (3.5% loss), south- west (4.34%), West Midlands (5.34%) and East Anglia (7.29%). Reasons for crop losses were varied and included cabbage stem flea beetle damage, poor estab- lishment and a lack of moisture which hindered germination in some areas.
Overall light leaf spot risk remains relatively low
reduced in the final forecast. The regional forecast high- lights the proportion of the win- ter oilseed rape (OSR) crop, with a disease resistance rating of 5, predicted to have more than 25% of plants affected by the disease by the spring. The forecast does not show total incidence. Jon West, who manages the forecast at Rothamsted Research,
said: “Light leaf spot symptoms have already been observed at some monitoring sites. Although it is a relatively low-risk year, a high incidence can still occur in some crops.”
It is the first season since
2013/14 that no regions have fall- en into the highest risk category (>60%). In East Anglia, the risk forecast is exceptionally low, with
the forecast predicting even low- er disease pressures than the rel- atively low-risk 2013/14 season. The highest risk is forecast to be in the West Midlands and Wales regions. Historically, light leaf spot risk is more serious to- wards the north of England and in Scotland. The 2018/19 risk in these regions can be described as moderate.
Drilling rape before 10 August is best to avoid flea beetle, says Simon Kightley
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