Weed beet and bolters
Tractor hoeing before weed beet reach the four leaf stage is very effective in removing up to 70% of weed beet (i.e. those between the rows). In some situations two passes of the tractor hoe may be required. In many crops it is now getting past the stage when hoeing is an option.
Bolters are starting to show in crops and given the weather conditions we have experienced this spring we would expect that many more will appear over the next few months.
For populations less than 1000/ha it is worth walking through fields and pulling out any bolters/weed beet, at this stage they can be left in the field. When weed beet or bolters commence flowering they should be removed from the field. Each bolter or weed beet left can produce up to 1500 viable seeds. Therefore every effort should be made to remove bolters and weed beet in your current sugar beet crop.
Check sugar beet crops that are still open for any late flushes of broad-leaved weeds in particular volunteer oilseed rape. See last week s Advisory Bulletin for control suggestions.
Continue with control measures for volunteer potatoes and thistles where present.
Aphids Myzus persicae
1120 M.persicae were caught at the 30 aphid trapping sites between 13-19th June. However, over half of these (625) were caught at the Stetchworth site in the Bury area. If conditions permit, winged aphids will continue to migrate into sugar beet. If the crop has less than 12 leaves apply Biscaya when the threshold of one green wingless aphid per four plants is found; the threshold increases to one green aphid per plant above this growth stage.
The use of Biscaya (M15014) is only for the control of aphids, principally peach potato aphid (Myzus persicae). Applications should be made via horizontal boom sprayer in a minimum water volume of 200 litres per hectare.
This authorisation has been granted for the 2012 season in exceptional circumstances due to the unseasonal weather conditions which have affected crop development early in the season, and the developing high numbers of aphids including MACE resistant populations.
No more than two sprays of Biscaya may be made to sugar beet crops, and no later than the end of July.
The good news is that none of the first batch of 265 M. persicae tested was found to contain virus.
Cercospora leaf spot
We have confirmed the presence of cercospora on one sugar beet sample that was sent into the Plant Clinic last week from the Newark area. We would welcome samples of any suspected cercospora cases to be sent into Broom s Barn. Cercospora (Photo 1), can be positively confirmed under the microscope as the spores of the fungi are easily distinguishable from other diseases. It is early in the season and surprising to find cercospora as it tends to favour high temperatures and long periods of high humidity. Samples should be sent to the BBRO Plant Clinic, Broom s Barn Research Centre, Higham, Bury St Edmunds, Suffolk. IP28 6NP.
Photo 1. Cercospora (lesions 2-3 mm across)
Variety choice for 2013
For the majority of situations, sugar yield remains the main factor upon which to base variety selection. History shows that the top 6 yielding varieties typically account for around 80% of the market place and this rapid adoption of the best yielding varieties has underpinned the recent rises in sugar beet yields. We recommend that growers continue with the policy of selecting the highest yielding varieties for their situations. The top 6 yielding varieties on the recommended list for 2013 are
Bolting remains a risk from very early drillings although in an average spring, this risk falls away rapidly once the first week of March has passed. Choose varieties with a lower number of bolters for very early drillings.
Beet Cyst Nematode (BCN) tolerance
BCN tolerant varieties can provide significant yield advantages when grown in BCN infested fields. However, they yield significantly less than conventional varieties when grown in the absence of the pest. Therefore it is essential that any at-risk fields are soil sampled to test for the presence of BCN. Since their introduction to the UK market place, beet cyst nematode tolerant varieties have taken around 5% of the market and we could see this moving to 8-10% in the near future. Soil testing is the key, and we encourage everyone finding BCN to grow tolerant varieties. Four BCN tolerant varieties are available - Thor, Pitbull, Annouschka and Sentinel.
All material on the list is partially resistant to rhizomania. Isabella KWS contains two genetic resistance mechanisms compared to the more conventional single gene approach. Strip trials have shown that varieties with this enhanced mechanism can offer greater resistance to the AYPR strain of rhizomania. As such this variety may have a particular role to play in these situations. Outside of such conditions, its yield is below that of the control group.
Around 5% of the UK crop is still grown without an insecticide seed treatment, and this is mostly where a granular nematicide is being used to overcome docking disorder caused by free living nematodes. Common practice has been to monitor these crops for aphids and to apply a foliar insecticide as required. However, the prevalence of aphids carrying MACE resistance in the UK has left us with no effective foliar aphicides and as a result, crops grown without an insecticide seed treatment are now at significant risk from virus yellows. We therefore recommend that ALL seed is ordered with an appropriate seed treatment.
Two BASIS points in total (not per bulletin) have been allocated for the period between 01/06/12 and 31/05/13 reference CPD/24888/1213/a. In order to claim these points please contact Jessica at BASIS registration on Jess@basis-reg.co.uk. Tel 01343 301206
For technical queries contact the BBRO helplines:
Pam Chambers , email@example.com 07887 628357
Colin Walters firstname.lastname@example.org 01733 422088
Caution : this information is based on results of experiments and experience but cannot constitute a recommendation.
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