Information Sheet 24 Cabbage stem Updated Winter 2015

©Dewar Crop Protection Latest information Action – Neonicotinoid-treated seed cannot – Monitor beetle numbers before be planted following the restrictions and at emergence and spray the imposed in December 2013. emerging crop if there is – Cabbage stem flea beetle resistance evidence of high pest pressure. to pyrethroids has been confirmed in – Once cotyledons are through, the UK. refer to spray thresholds. – Crops are most vulnerable at – Pyrethroids should only be emergence if the growing point is applied when absolutely destroyed. Once cotyledons are necessary (to minimise the through, the crop is much more spread of resistance). tolerant to attack. Adult cabbage stem flea are about 5mm long and shiny Always read product labels, consider your local conditions and consult a professional agronomist, black with a hint of green/blue. if necessary.

Importance Risk factors Other flea beetles Cabbage stem flea beetle ( Early sown crops are more There are a number of other flea chrysocephala ) is wide-spread in the susceptible to cabbage stem flea beetles that are potential pests of UK and northern Europe. beetle attack. oilseed rape. These are the Wessex flea beetle ( Psylliodes Cabbage stem flea beetles migrate A warm autumn will favour egg laying luteola ), which attacks crops in the into oilseed rape crops during crop and early hatch of larvae, coinciding autumn, turnip flea beetles emergence. This is the stage at with smaller, more vulnerable plants. ( cruciferae, P. which the crop is most vulnerable as nigripes ), which attack crops in the beetles can feed on and destroy the autumn and spring, and the large growing point. Once the cotyledons ( P. nemorum ), are through, the crop is much more which attacks crops in the spring. tolerant of attack. Wessex flea beetle is most likely to be damaging in southern The beetles chew holes in England on early sown winter cotyledons and early true leaves, crops, whereas late-sown spring giving rise to ‘shot-holing’ crops are most susceptible to symptoms, which can result in turnip and striped flea beetles. stunting and poor plant vigour. If Pictured left top: Cabbage stem severe, beetle feeding can kill the flea beetle larvae damage to an seedlings even before they emerge. oilseed rape petiole.

Larvae also bore into leaf petioles Pictured left bottom: Adult and, later, into the main stems, cabbage stem flea beetle damage which can also affect plant vigour. (<10% leaf area).

Pyrethroid resistance and control without neonicotinoids The confirmation of cabbage stem Pyrethroid sprays should only be If required, insecticide sprays can flea beetles resistant to pyrethroids applied where there is evidence of be applied to control adult beetles (knockdown resistance, or kdr) in the high pest pressure at emergence or and/or larvae. Treatments applied at UK means that, for some, if thresholds are exceeded post full rate will kill susceptible adults pyrethroids may provide little or no emergence. To prevent resistance and larvae; residues on leaves kill control. from spreading, it is important to susceptible larvae hatching after spray only if absolutely necessary. application. In some situations, Kdr usually confers moderate Any applications must be made in reinfestation of adults can happen resistance to all pyrethroids applied the correct water volume and at the quickly after treatment. at recommended field rates. full recommended rate for the product selected. Repeat treatments should be avoided if possible. Assessing the need to spray adult beetles * The crop is most vulnerable at – Using water traps to check Consider applying a spray if: emergence, as beetles can feed on beetle numbers – Adults have eaten over 25% of leaf and destroy the growing point. – Assessing damage to volunteer area at the cotyledon–2 true leaf There are no spray thresholds at oilseed rape plants growth stage emergence but monitoring local Once the cotelydons are through, – Adults have eaten over 50% of the pest pressure will give an indication leaf area at the 3 –4 true leaf stage of whether treatment is necessary. an assessment of the loss of leaf area due to shot-holing can be – The crop is growing more slowly Monitor pest pressure by: used to determine the need for a than it is being destroyed. spray against adult cabbage stem – Checking the number of cabbage flea beetle. stem flea beetles in the previous crop's harvested seed Assessing the need to spray larvae * Water-trapping monitoring period to calculate an Set four yellow water traps on the average number of beetles/trap. A The larvae are predominantly soil surface in early September, two spray is justified if this average white, with numerous small dark on the headland and two in the field number of beetles/trap caught over dots on the back and three pairs of along a wheeling. Fill the traps with the monitoring period exceeds 35. dark legs. Fully grown larvae are water and a drop of detergent to about 6mm long and have a black ensure that any caught sink This has been shown to be head and a large black plate on the and drown. equivalent to the threshold of two upper surface of the hind end. larvae/plant. Do not spray if this Visit the traps regularly, weekly if threshold has not been reached. scalpel and count the number of possible, before emptying and larvae recovered. Samples are best resetting the traps. Each time a trap Plant dissection dissected by an accredited is emptied, the number of cabbage An alternative option to water- laboratory. stem flea beetles should be recorded trapping, though more difficult, is and added to the previous total for plant dissection. A spray is justified if there are more that trap. At the end of October, than two larvae/plant or more than remove the traps. A random sample of 25 plants 50% of petioles are damaged. should be taken from the field in late *HGCA recognises the need for further work on Use the total numbers of beetles October/early November. Dissect all thresholds. The information in this publication is caught in each trap over the whole leaf petioles and stems with a sharp based on current recommendations. Life cycle October: Eggs Further information laid at the base September: Adults Steve Ellis, ADAS of plants if mild. move to new crop, [email protected] mate and eat leaves. Newly hatched Sep Oct Caroline Nicholls, HGCA larvae may enter Nov [email protected] August: Adults plants and feed 'rest' in moist, Aug in petioles from HGCA Research Review 73: A sheltered places. Dec October to early review of invertebrate pest Adults are often April. Egg thresholds (HGCA, 2009) found in large Jan development HGCA Project Report 428: numbers in and larval activity Revised thresholds for cabbage harvested seed, Feb are inhibited by stem flea beetle on oilseed rape where they do temperatures ©Dewar Crop (HGCA, 2008) no harm. Jul Protection Mar below 3˚C. www.hgca.com/pests June-July: Adults Jun Apr March-April: Larvae HGCA Publications emerge and feed May feed on main stem T 0845 245 0009 on foliage. and can destroy the May: Larvae E [email protected] growing points. www.hgca.com pupate in soil.

Information Sheet 2 4 While the Agriculture and Horticulture Development Board, operating through its HGCA division, seeks to ensure that the information contained within this document is accurate at the time of Updated Winter 2015 printing, no warranty is given in respect thereof and, to the maximum extent permitted by law, the Agriculture and Horticulture Development Board accepts no liability for loss, damage or injury howsoever caused (including that caused by negligence) or suffered directly or indirectly in relation HGCA publications are free to levy payers to information and opinions contained in or omitted from this document. To join the mailing list, contact: [email protected] Reference herein to trade names and proprietary products without stating that they are protected does not imply that they may be regarded as unprotected and thus free for general use. No endorsement of named products is intended, nor is any criticism implied of other alternative but unnamed products. © Agriculture and Horticulture Development Board 2014. All rights reserved. HGCA is the cereals and oilseeds division of the Agriculture and Horticulture Development Board.