We thought the slugs were bad, little did we know how much damage that the tiny winged hoards of whitefly could do! It took a while for us to notice this infestation, and weren’t as repetitive with the treatments as we probably should have been, so the tomato plants were a little stunted and didn’t produce much this year, lesson learned!
The whitefly (quite literally a tiny white fly) is a sap-sucking insect that is often found in thick crowds on the undersides of leaves. When infested plants are disturbed, great clouds of the winged adults fly into the air. Both nymphs and adults damage plants by sucking the juices from new growth causing stunted growth, leaf yellowing, and reduced yields. Plants become weak and susceptible to disease. Young nymphs overwinter on the leaves of host plants. In late spring adult females deposit 200-400 eggs in circular clusters on the undersides of upper leaves. Whiteflies develop from egg to adult in approximately 25 days at room temperature. Adults may live for one to two months.
Here’s what we discover about whitefly treatment:
Companion planting: There are some plants that deter whitefly, so mixing them in with the plants susceptible to attack can be a big help. These include Artemisia ( mugwort, wormwood, sagebrush, etc), basil, marigold (French marigold are tipped to be good for this purpose), peppermint, and thyme.
Sticky traps: We’d only heard about these being used for aphids, but apparently they can be useful for whitefly too. You can also make your own sticky trap by coating something yellow with vaseline; an upturned yellow plastic cup on a stick does for example.
Water: Hosing off plants with a strong stream of water can help to reduce pest numbers and minimise the amount of insecticidal spray needed.
Natural insecticidal spray: Hosing off may reduce the number of adults but it won’t do anything for the larval stages. If you’ve got a whitefly infestation, it needs treating fast and regularly till the lifecycle is interrupted and ended. Here are a few natural insecticidal sprays that we’ve heard of:
- For a very simple insecticidal spray, mix 1 tbsp of soap and 2 tbsp of oil with 2 cups of water in a spray bottle. The oil smothers them while the fatty acids in the soap dissolve the insects’ exoskeleton, causing them to dehydrate.
- Garlic, onion, chili, and horseradish are all naturally pest repelling. Make a spray by mixing one or a combination of these (crushed) with water. Leave to brew overnight, then strain and spray on the plant to repel pests.
- If you grow rhubarb, simply boil the leaves in water for 20 minutes, and when cool strain into a spray bottle.
- Organic neem oil can be sprayed to kill eggs, larvae, and adults. Mix 1 oz/ gallon of water and spray all leaf surfaces
- For a stronger spray mix 8 ounces of Hydrogen Peroxide, a gallon of water and 8 ounces of sugar together.
These need to be applied to the whole plant but especially the underside of the leaves! Repeat every 7-10 days until there is no sign of whitefly.
Natural predators: These include ladybugs and lacewing larvae, which feed on their eggs and the whitefly parasite which destroys nymphs and pupae. It’s always a good idea to attract natural predators to your growing space. Supplying the right environment is a good start, or in emergencies, they can be purposefully released, for best results, release them when pest levels are low to medium.
Note: Ants feed on the honeydew that sucking insects produce and will protect these pests from their natural enemies. So if you also have ants, think about how to deal with them too.