What are they:
You will most likely notice whitefly around your tomatoes, though they can attack any tender, sappy plants. Whiteflies are sap suckers related to aphids and mealy bugs, though they are not a single species. Not only will they weaken your plants with their parasitic feeding, they can also introduce digestive enzymes that causes plants to weaken, growth to slow and reduce resistance to disease. Honey dew left behind as a waste product in turn limits photosynthesis, encourages sooty mould and attracts ants. Furthermore, they can act as vectors for viruses and can lead to fungal problems.
Whitefly will need to be addressed on multiple fronts to tackle each stage of the life cycle. Eggs are laid on the underside of leaves, while both nymphs and adult flies feed on the plants’ sap. You will probably find an integrated pest management approach, using several tactics at once will yield the best response with a low environmental impact. This may mean reducing damage to an acceptable level, rather than complete elimination.
What to look for:
- The first sign of white fly will likely be seeing the little buggers flying out of your plants. Be sure to check the undersides of leaves as this is where they will typically hide. You may find sudden, previously hidden, swarms when the plants are disturbed during watering or by brushing against the plants.
- Failure to thrive: Slow growth, slow/unripening fruit, unreliable production.
- Yellowing or yellow/white mottling, wilting and leaf loss.
How to treat them:
The best line of defence is a diverse and healthy garden with good soil and well watered, happy plants.
- Companion planting flowers such as marigolds, alyssum and nasturtiums can help attract beneficial predatory insects whilst also helping to bring in bees and pollinators.They also add a pretty pop of colour (good all round). As with most things, prevention is better than a cure.
- Whiteflies thrive in warm, moist, humid conditions. Their numbers will likely decline as the weather cools. Thinning out particularly affected plants and leaves can remove some of the critters and will also increase airflow which helps lower humidity as well as protecting against fungal diseases. Always be careful disposing of affected materials, it is a good idea to freeze or burn waste to ensure the flies do not just take a vacation before returning.
- Disturb the little beasties… shake them a bit, blast them with jets of water, make your garden an unpleasant place (for them) to be. This will need to be a sustained effort over a number to days.
- Take it to the next level and get out the vacuum to suck up the marauding horde, just make sure to be gentle around your plant babies. This is best done in the morning. It may be best to use an old or bag style vac, to avoid a filter clogged by your victims
- Mulching can help create a physical barrier to emerging nymphs, with the added benefit of helping your garden bed retain moisture and keeping weeds manageable. It will also make it less likely that eggs will overwinter in the soil.
- Whiteflies are supposedly attracted to yellow. You can buy or create sticky traps by thinly coating a yellow object with some tree guard pest barrier of dishwashing liquid. Be sure to place your traps near heavy infestations and bear in mind they will not differentiate between friend and foe. Please note that sticky traps that do not have a cage around them are now illegal in Victoria as small birds or bats may stick to them.
- Insect exclusion netting may be effective if used early. Remember that netting can trap pests inside as easily as they can exclude them and will also prevent beneficial insects and pollinators from doing their job.
- Insecticidal Sprays:
- Soapy water spray– minimal ecological impact
- Eco-oil – unlikely to harm beneficial bugs or pollinators, organic
- Neem oil – less targeted and quite a broad spectrum poison
- Pyrethrum should be treated as a last resort. It requires targeted application as it will indiscriminately kill most insects it touches. Also, the adaptability of whiteflies means they can build up tolerance to various chemicals.
Whatever spray you choose, be sure to cover both the top and underside of the leaves and stem. Check the weather forecast: it is best to spray when there is no wind, rain or extreme temperatures forecast. Consider the time of day, oil-based sprays can cause leaf burn in the heat of the day. Add a drop of gentle soap to assist in emulsifying oil mixes. Always check the product label and wash any produce (food you grow) that has been exposed to treatments, regardless of how mild or harmless you think it to be.
Regardless of the approach(es) you take, be mindful of the impact your treatment plan has on the rest of the ecosystem in your garden/veggie patch.