Tomatoes grow well during warmer weather, and that is expected since they are subtropical plants native to western South America and Central America. In cool to temperate climates tomatoes are grown as annuals, since they start to decline as temperatures drop in late autumn to early winter.
Often in mid to late summer, even if the plants are quite healthy, it’s often observed that the lower leaves yellow and curl, then the leaves drop. The leaf loss slowly creeps upwards until the plant is completely defoliated, and with no leaves the plant quickly dies off.
This decline is not temperature related, it’s caused by a tiny pest, the tomato russet mite, which can be stopped. By eliminating this pest, the productive season of tomato plants can be extended well into the cooler seasons, until they finally succumb to the colder weather.
Tomato Russet Mite
The tomato russet mite (Aculops lycopersici), a member of the Eriophyidae family of mites, is a tiny sap-sucking pest approximately 0.15-0.2 mm long and 0.05 mm wide. They are so small they are not visible to the unaided eye, and a hand lens or jewellers loupe is needed to see these mites.
They reproduce very quickly, and their populations can grow quite large in number before any damage is noticed. They do not produce the noticeable fine webbing which identifies the presence of red spider mites.
Plants Affected by Tomato Russet Mite
These pests attack tomato, chilli and capsicum plants.
Tomato russet mites attack the lower leaves first, which yellow and curl, then dry and fall off. The stems also discolour (bronze) from the pest attack. These mites move upward to feed as their population increases, and leaf loss continues moving upwards as a result.
As the sap is sucked from the plant, the green growth is weakened, flowering is reduced, and the plant’s overall health and vigour decline. If left untreated, the pest will eventually suck all the sap from the entire plant and kill it.
The tomato russet mite populations grow more rapidly under warm, dry, windless conditions, making infestations worse. They prefer locations on target plants which provide them with adequate shelter and humidity.
How the Pest Spreads
Due to their small size, tomato russet mites are spread by the wind, and are also carried on clothing, in removed garden debris, on tools and machinery, and even on other pest insects such as whitefly and aphids.
Management of Tomato Russet Mite
Tomato russet mite can be managed with both cultural controls and organic-gardening approved chemical controls. Combining both increases the effectiveness of pest control measures.
Cultural controls are integrated pest management (IPM) practices which disrupt the environment of the disease, reducing establishment, reproduction, dispersal, and survival. These cultural practices are the most effective methods currently available for control of white leaf spot in organic farming systems.
The following cultural controls can be used to reduce tomato russet mite:
- Planting location – do not plant downwind of infested plantings as this pest is carried by the wind.
- Plant hygiene – check that seedlings are not infested with the pest before transplanting.
- Sanitation – clean tools and equipment after working in infested areas, take necessary precautions with clothing sanitation to avoid pests hitching a ride to new areas.
The tomato russet mite, and other pest mites can be effectively controlled by using wettable sulphur, a miticide which is approved for use in organic gardening.
Wettable sulphur is a colloidal form of elemental sulphur that is designed to be sprayed. It is used to eradicate pest mites and is also used as a fungicide. It’s a fine yellow-brown powder which dissolves in water and is very effective at controlling this pest. From my own experience, after spraying, the leave fall ceases and the plants take on a healthier, greener colour if they had a mottled green colour previously.
How to Use Wettable Sulphur to Control Mites
- Use 2-3g wettable sulphur per litre of water when spraying for for tomato russet mite and red spider mite, 2.5-5g per litre for grape leaf rust mite and grape leaf blister mite.
- Shake bottle frequently during spraying
- It’s important to spray all parts of the plant, including the undersides of leaves, stems, buds and flowers.
- Repeat application at 2 week intervals, usually two to three sprays two weeks apart will be sufficient.
Know the Difference Between Sulphur Garden Products
Note that wettable sulphur is not the same as lime sulphur, a liquid fungicide and pesticide which is used to spray fruit trees in winter.
Granular sulphur or agricultural sulphur is elemental sulphur which is mixed into the soil to reduce the soil pH and make it more acidic. It’s insoluble in water (can’t be dissolved in water), and therefore cannot be used for spraying. It’s a soil amendment product and can’t be used to treat tomato russet mite.