Beet cyst nematode (BCN, Heterodera schachtii) can cause yield losses of up to 75% in the UK on heavily-infested soils with populations of more than 40 eggs/g soil. There are indications that infestations of BCN have become more prevalent in recent years (e.g. an increased number of samples into the BBRO plant clinic) creating the need for an up-to-date re-assessment of the importance of BCN and this is currently being investigated in a joint BBRO project (10/02). BCN populations are currently being affected by:
- an increase in the growing of alternative hosts such as oilseed rape and other brassicas within the sugar-beet rotation, which could increase nematode numbers.
- a decrease in the use of granular carbamate pesticides and change in main active ingredient used - less than 10% of sugar-beet crops are now treated compared with 56% in 1990; and
- longer growing seasons which give more time for additional generations of BCN to be produced within the time-frame of a single beet crop.
Historically, the pest has been controlled by wide crop rotations and possibly indirect pesticide use. These approaches are no longer mandatory or available, but BCN-tolerant sugar-beet varieties (e.g. Annouschka KWS, Sentinel, and Thor and Pitbull in 2013) are now available to growers that offer new approaches to combat the pest. These varieties have not been fully evaluated in terms of (a) the level of infestation at which they become economic to use and (b) their impact upon the buildup of BCN populations, but, again, this is part of the remit of the existing BBRO project.
However, the significance and importance of oilseed rape and other brassica species in sugar beet rotations is increasing. An appreciation of these rotational issues and the implications of other control strategies for different nematode species are urgently required. For example, certain growers in East Anglia are now growing a five year rotation of rape, cereal, beet, cereal, rape and, because of current high prices, this is becoming increasingly common. In addition, green manures of various mustard species (e.g. Caliente Mustard or Melotop fodder radish) are being deployed on farm between July and August to improve soil health, or to try and provide alternative strategies to control potato and/or beet cyst nematode via the interruption of their life cycles or biofumigation, or a combination of both strategies. Therefore, it is critical that the appropriate brassica varieties are adopted on farm in order to prevent an indirect acceleration of the populations of these (or other) nematode species.
Outcomes / Key Message For Growers And Industry
Sept 2013 – Jan 2015
Six cover crops (barley, oilseed rape, Accent mustard and Decapo & Colonel radish) were initially intended to be drilled at four timings; September, October, January and February. However, reliance on the selected farm to sow the cover crops alongside unfavourable weather conditions lead to only the first two timings being completed. Over the course of the trial four BCN samples were taken and analysed by Dr David Crump (Nemco Ltd). These were timed at cover establishment, mid cover crop, beet establishment and beet harvest. Overall, the data showed a sharp rise in BCN mid cover crop, only to reduce gradually until harvest of the beet; ending in a pf/pi lower than 1.0; generally large variations in BCN numbers were recorded. The beet drilled included tolerant varieties Mongoose and Pamina, and susceptible varieties Cayman and Bullfinch. As expected the tolerant varieties yielded on average 25adjusted t/ha more than the susceptible (57.3t/ha compared to 82.9t/ha). However, the beet yields were highest following barley and lowest after the mustard cover crop.
Sept 2014 – Jan 2016
In September 2014 cover crops were drilled successfully, but was subsequently destroyed by pigeon damage, as such, the trial was failed and no sugar beet were drilled for harvesting in the 20015/16 campaign.
Sept 2015 – Jan 2017
An additional host grower was found and the protocol simplified. The BCN cover crops used were Colonel, Decapo, Contra, Defender and Baracuda (all oilseed radishes). However, due to weather constraints only one site was drilled in September (near Garboldisham). At this site BCN samples have been taken at Cover crop establishment and Sugar Beet drilling, using GPS sampling for analysis by Nemco Ltd. This has established an initial population of BCN as well as levels of BCN following the cover crop period. BCN tolerant beet has now been drilled over the trial area and further BCN sampling will be conducted before the end of the season.
Project superseded by PhD study with University of Nottingham.