With uncertainty around the future of metaldehyde, more growers are making the switch to ferric phosphate for the flexibility it offers.
The active has become an integral tool in slug control due to its strong efficacy and environmental profile.
Geoffrey Bastard, Certis’ Regional Technical Specialist, outlines his top tips for those looking to maximise their ferric phosphate applications.
1. Field history
Start by thinking about the field history, the previous crop, the soil type and weather conditions.
These all need considering on a field-by-field basis before doing anything else.
For example, this year’s dry and warm conditions mean that on very light ground slug populations may be non-existent, but on heavier land that’s had rainfall, slug populations will be active.
Be aware that slugs can quickly repopulate and thrive at the first onset of rainfall.
Taking a total field perspective will help to develop a holistic approach and maximise slug control.
2. Assess slug pressure
Ferric phosphate should always be used as part of an integrated pest management (IPM) approach, and monitoring for slug pressure before application is vital.
To make sure you get the most out of applications and apply at the right time, monitor slug numbers using a slug mat or a simple piece of plastic with layers mash underneath. Place traps overnight and check early in the morning when slugs are usually active.
For OSR crops, the treatment threshold is four or more slugs to justify slug pellet applications. For information on crop specific slug thresholds visit the AHDB website, www.ahdb.org.uk.
3. Pellet choice
It’s important to choose a high-quality ferric phosphate pellet that spreads well and is durable.
The four main characteristics that come together to form a good pellet include size, which should be between 2mm and 3mm, uniform shape, crush strength over 3kg and a density over 0.7kg/L.
Taking all of this into account I would recommend a high quality, wet process pellet, such as Sluxx HP, as it is uniform, durable, rainfast and has anti-moulding properties. This all means that the pellet will spread well and survive in the field without leaching, even after rainfall.
Ensure that pelleters have been specifically calibrated to the ferric phosphate pellet with a maximum width of 24m to ensure good coverage.
If using both ferric phosphate and metaldehyde on-farm, ensure that both the setting for spread pattern and rate are correctly adjusted between the two products.
To achieve this, carry out a calibration test on both products and ensure that the operator is trained in the different spread patterns, dose rates and how to adjust settings accordingly.
Finally ensure that baiting points and pellet dose rate are relevant to the slug pressure in each individual field.
Application of ferric phosphate should only occur once thresholds have been reached.
The active can be used on all arable crops and should be applied with a maximum dose of 7kg/ha. In high pressure cases, up to 4 applications of Sluxx HP can be made as long as the maximum total dose does not exceed 28kg/ha/crop.
6. Be aware of the mode of action
Although both ferric phosphate and metaldehyde essentially do the same thing, kill slugs, their mode of action differs.
With metaldehyde, growers are used to seeing dead slugs and slime trails on the surface, but with ferric phosphate slugs migrate underground to die.
Therefore, when assessing treatment efficacy of ferric phosphate, monitor the crop for damage rather than looking for dead slugs.
A recent Harper Adams study showed that 50 to 60% of slugs that ingested Sluxx HP pellets (ferric phosphate) retreated below the soil surface within the first 24 hours. After two to three days, virtually every slug had died underground.