Mild winters continue to sustain populations of aphids. 2016 is expected to be another high aphid year with accompanying levels of virus. Willow-carrot aphid principally over-winters as eggs on winter host and migrates onto carrot and parsnip for 5-6 weeks from May, peaking in early June. So this is the time to be vigilant. In addition, carrot growers now have significantly limited choices following restrictions on the use of pirimicarb (Biscaya and pirimicarb having been the main controls to date).
Willow-carrot aphid can cause two kinds of problems:
1. Crop losses from direct feeding damage, usually at very early crop stages
Symptoms include discoloured, distorted leaves, ‘honeydew’ and discarded skins. Last year, many crops were lost completely to aphid damage, particularly in East Anglia.
2. Transmission of viruses
- Parsnip yellow fleck virus - severe damage, stunting and black cores
- Carrot Motley Dwarf Complex (Carrot red leaf virus and Carrot mottle virus) - reddening or yellow mottling of leaves and stunting
- Carrot yellow leaf virus (CYLV) - recently discovered by an AHDB-funded project led by FERA’s, Adrian Fox. CYLV is strongly linked to root necrosis and impossible to detect in the field. Growers reported up to 50% loss of their marketable yield due to necrosis issues last season. A further complication is that Peach-potato aphid (Myzus persicae) is now known to be a vector of CYLV too. Biscaya is the only foliar insecticide available that will control this aphid on carrots.
- Carrot torrado virus (CaTV) – newly discovered but its impact and incidence is unknown.
Note: Pirimicarb (MAPP 17401) no longer approved for carrots. decis Protech has an EAMU* for use on outdoor carrots.
This extension of the authorised use provides for the use of Decis Protech in respect of crops and situations, other than those included on the product label. No efficacy or phytotoxicity data have been assessed and as such the ‘extension of use’ is at all times done at the user’s choosing, and the commercial risk is entirely theirs.
Limited aphicide options now available
- Recent restrictions to the use of pirimicarb has meant that there are now significantly limited aphicide options for carrot growers
- A recent, newer option for growers in particularly susceptible areas could be EAMU 0737/2016 70% w/w thiamethoxam as an neonicotinoid insecticide
What to do
Option 1: If a CNI seed treatment has not been used:
- At the first sign of aphids (nomally during May/June) apply Biscaya at 0.4 L/ha. Crops at the cotyledon stage are most susceptible
- Under high aphid pressure a max of 2 applications of Biscaya are permitted with a harvest interval of 7 days
Option 2: If a UK CNI seed treatment has been used (e.g. EAMU 0737/2016 70% w/w thiamethoxam):
- The first subsequent foliar spray should be with a non-neonicotinoid containing product with a different mode of action
- Only 1 single foliar application of a neonicotinoid can then be used. Biscaya could be applied as the second foliar spray
- Follow IRAC guidelines for insecticides
- Use different modes of action to prevent development of resistance
- Remember you only have 2 applications of Biscaya!
- Always check the CRD website for a product’s authorised rates and uses