Main Objectives
This pest is known to be more problematic in Mediterranean areas where its incidence and reports of damage are usually associated with warmer and drier climates. Unfortunately, we have limited information on its life cycle in UK sugar beet crops, but it is likely that adults can both over-winter and/or migrate into crops during the spring from mainland continent populations. Subsequently, caterpillars (larvae) feed on the leaves and crown causing direct feeding damage, loss of older leaves and a negative impact on the development of new leaves. In 2022, a number of generations developed, particularly in the Bury St Edmunds area, but it is not clear how many generations are possible, although this could ultimately be temperature/rainfall related. Pheromone monitoring of adult moths provides an opportunity to track this pest in the future and provide an early warning system for the industry (cabdirect.org).
There are limited data available regarding their control. Pyrethroids have been suggested but appear to have given limit or no control in the UK in 2022 presumably as the larvae are protected within the petiole or crown as they feed. One of the most widely suggested and effective methods of control is irrigation or heavy rain events which presumably drown the larvae in situ.
Stevens, M, Orman, K., Towler, E & Wright A (2023). Beet moth: has summer 2022 introduced a new threat to the UK crop? Sugar Beet Review 91, (1) 11-14.
Management and Mitigation Cool, wet weather usually deters beet moth development, and heavy rain events and/or irrigation usually drowns the caterpillars. There is the potential for a foliar applied insecticide to be used but this will require large water volumes to penetrate the canopy. Therefore, results may well be variable as it is the caterpillar within the heart leaves that the insecticide needs to target. Experiences with pyrethroids in the UK to date are variable and limited and this is re-enforced by comments from Europe. Use of pyrethroids will also impact any beneficial insects too. There are a few products (e.g., Cythrin) that have general caterpillar control on their label. It is important that recommendations are followed on the label. In many cases, this includes the use of high-water volumes. It is important to keep all remaining and future leaves as green and healthy as possible for as long as possible to mitigate the impact of beet moth damage.
Ploughing down beet remnants that have been impacted by beet moth may well help to decrease the risk. Manage spoil carefully from cleaning and loading operations to avoid contamination back on to sugar beet land. Soil under maus clamps may have a higher pest burden, as soil and tops dry and are dislodged during loading. These areas need to be recorded, ideally ploughed and monitored.
It is difficult to predict whether this pest will now establish in the UK, or whether 2022, due to the hot dry conditions, was a one-off scenario. However, it will be important to continue to monitor this pest in future years and identify any suitable control strategies as insecticides applied to the crop appear to have had little effect once the larvae are protected within the crown of the beet or their petioles.
BBRO will address the following areas:
- Monitoring larva & adults via pheromone traps
- Control – the role and efficacy of insecticides alongside water volumes and wetting agents
- Overwintering survival, is it possible?
- Future risk – can we model/predict the threat?
