Cabbage Stem Flea Beetle larvae in huge numbers
Variety – Nikita
Location – Thame
Date – 04.04.2016
Cabbage Stem Flea Beetle are renowned as one of the biggest threats to UK oilseed rape crops and can cause complete crop devastation. Above is a photo from a field over in the West. The threshold recognised by AHDB is now 5 larvae per plant however, there have been many reports from across the country well exceeding those levels. The larvae can be readily found in the stems and petioles.
The high numbers of larvae being seen are likely to be a result of a warm autumn which is believed to encourage egg laying. A recent report from FERA has suggested levels of CSFB larvae are the highest they have been since the 1990’s. The larvae can be easily found within the rape plants in the field. They are predominantly white/beige with small dark dots on the back and three pairs of dark legs. Larvae may grow up to about 6 mm long and have a black head and dark back end.
Whilst it is now too late to do much about CSFB larvae this season, growers will need to ensure they are proactive in controlling the adults this autumn. The high levels of larvae are likely to result in huge adult populations next season.
Although it is recognised that there is some Kdr resistance to pyrethroids, there is very limited chemistry for use against CSFB so HALLMARK ZEON remains the best option for control of susceptible populations.