Thursday, 25 February 2021
Wayne Brough, AHDB Knowledge Exchange Manager for ornamentals, highlights some of the key take-home messages from the recent AHDB/Bedding and Pot Plant Centre webinar ‘Why am I having difficulty controlling aphids in my crop?’
1. Take time to plan your integrated pest management (IPM) approach to aphid control
This is required to achieve good levels of pest control, maintain plant quality and minimise the risk of pesticide resistance developing.
2. Start clean and stay clean
Ensure production areas are cleared up, swept clean and disinfected (as appropriate) before production starts. Ensure weeds within the growing structure are removed as they can act as hosts for aphids. They can create both a ‘pest bridge’ between crops and allow aphid colonies to build up undetected.
3. Know your aphid species
It’s not essential, but it helps to know which aphid species you are dealing with as they do vary in their tolerance to plant protection products. Get a copy of the AHDB Crop walkers’ guide for bedding and pot plants to help.
4. Scout crops early
Don’t leave crop inspections until after transplanting. Risk-assess incoming young plant material by both aphid susceptibility and the source of the plant material.
Post-transplanting, don’t rely on yellow sticky traps to give an indication of aphid populations, scout crops looking for the first signs of aphids in shoot tips and on the underside of leaves.
The presence of aphid cast skins and honeydew mean control could be getting out of hand.
5. Let the biological control agents work for you
When temperatures in the growing structure permit, begin introductions of parasitoids. Aphidius species are active hunters and will often find very low levels of aphids in the crop before you can. As the season progresses and the risk of aphid outbreak increases, you may need to start introducing predators more suited to dealing with small colonies of aphids. These are usually Aphidoletes, but other biocontrol agents are available.
Why am I having difficulty controlling aphids on my crops?
Watch the webinar
6. Make use of free biological control
Encourage native beneficial insects onto the nursery. This can be done with managed areas of perennial nettles, for instance, around the periphery of growing structures. On these plants, the common nettle aphid will develop (no threat to crops), which will attract ladybirds and a range of native parasitoids.
7. Watch out for hyperparasitoids
Unfortunately, these minute wasps parasitise the parasitoids and reduce levels of aphid control. Look out for rough-edged exit holes from mummified aphids and try to overcome any issues using a mix of parasitoids (commercially available) or focus on predator release.
8. Match the plant protection product applied to the need
Many factors will impact the choice of product, including;
- The aphid species present
- Whether biological controls are being introduced
- Time of the year
- Crop development
- Level of aphid infestation
IPM-compatible, contact-acting products like Spruzit (pyrethrins) or physical products like Eradicoat, Flipper or Majestik (maltodextrin or fatty acids) can be useful to treat aphid hotspots. They are also helpful where aphid colonies may impact plant appearance, in shoot tips and flower buds for example.
Systemic products like Sequoia (sulfoxaflor) and Mainman (flonicamid) can be used in high pest-pressure situations where plants are actively growing and where there may be a complete crop canopy. If used, note the impact of these products on Aphidius and Aphidoletes and adjust introductions accordingly.
9. Note the Insecticide Resistance Action Committee (IRAC) codes on products to manage potential resistance
Avoid using products with the same IRAC code sequentially – this can lead to tolerance or even resistance, especially with insects which have a short life cycle and many generations within a single season.
10. Integrate aphid control into a more holistic IPM programme
This should cover both pest and disease control within all crops on your nursery.
Wayne has worked at AHDB for 10 years and has spent 33 years working within the ornamentals industry. Prior to joining AHDB, Wayne worked at ADAS as the Horticulture Segment Manager, managing a team of six consultants and delivering consultancy on bedding plants, pot plants and hardy nursery stock.