'Many modern tomato varieties have made growing outdoor tomatoes easier because of earlier ripening and improved disease resistance,' says Simon Crawford. (Image credit: Future / Annaick Guitteny) Grow blight resistant tomato varieties Ensure potatoes and tomatoes are not planted in the same soil for successive years. Clear as many old potatoes as possible from a plot, ' advises Simon Crawford. 'Proper composting of plant waste is of paramount importance and ‘plant dumps’ must be eliminated in garden and allotment situations to reduce infection. We've found that history will repeat itself,' says Tammy Sons 'Tomato blight spores can stay in the ground for for 3 to 4 years. Never plant tomatoes in soil or compost that has previously contained diseased plants. Plant tomatoes in a disease free location.Try to water the soil only and keep the leaves and plants dry. This is to avoid the plants sitting damp all night. This avoids leaves resting on damp soil, and also helps air circulation and speeds the ripening of tomatoes by providing them with maximum sun exposure. Remove lower leaves as the fruits develop.'Bush varieties grown in pots can be trimmed and partially supported with a bamboo cane to avoid a dense mass of foliage,' says Simon Crawford. Support bush tomato plants with a stake to keep their leaves off the soil, or tie up cordon tomatoes regularly with soft twine to improve air circulation. Likewise, pick a well ventilated spot for growing the tomatoes outside. If growing tomato plants in a greenhouse or polytunnel, avoid these becoming too humid by keeping them well ventilated. So learn how to prune tomato plants properly. 'Environmental control must focus on reducing the likelihood of leaves remaining wet for an extended period, so trimming foliage and side-shoots to maximise air movement and ensure the evaporation of surface moisture is essential,' explains Simon Crawford. The following environmental controls can help to prevent the occurrence or spread of tomato blight: Chlorothalonil has been withdrawn, mancozeb is likely to be withdrawn (in 2023 or 2024).(Image credit: Getty Images) Environmental controls for tomato blight However, against Alternaria species, fungicides available include: QoI (strobilurin fungicides) and alternatively, hydrogen peroxide, potassium bicarbonate or copper-containing products such as Bordeaux Mixture for organic crops. Most potato ‘blight’ information actually relates to ‘late blight’ caused by Phytophthora infestans. There are reports of differences in susceptibility of varieties to early blight but resistance information is currently not included in the AHDB potatoes variety database.įungicides: According to the label, these usually need to be reapplied every 7-14 days. Remove Solanum species such as nightshade and potato volunteers. Increase row separation slightly to improve ventilation. Irrigate crops early in the day so the leaves remain wet for as short a period as possible or use drip irrigation. If possible add mulch to prevent dispersal of spores. Removal of as much crop debris as possible after harvest and leave at least a 3-year separation in cropping of potatoes on the same land. It can also be encouraged by hedgerow plants or weeds such as nightshade ( Solanum family). The disease can be spread to new locations on infected seed tubers. solani (above, right) have a long tail, compared to those of Alternaria alternata (above, left) which are much shorter and rounder and also infect potato crops. Symptoms appear in 2-6 days after infection depending on temperature. In particularly warm and wet conditions (20-30☌), this can take only a few hours. The spores germinate to infect crops in wet conditions via wounds, stomata and direct penetration of leaves. These are produced in humid, damp conditions, typically close to the ground or on diseased leaves during prolonged wet or humid weather, and are dispersed by wind and rain. The fungus survives in soil and crop debris and is spread by many cycles of infection by asexually-produced spores (conidia). On potato tubers, lesions appear as dark, dry, shrunken patches on the skin, extending into the tuber. Girdling of the stem by this kind of lesion can cause death of the plant. On stems, lesions appear as dark patches of collapsed tissue giving a darker, shrunken zone. Symptoms often appear first on older leaves near the ground as dark brown spots surrounded by a zone of yellowing or chlorosis. Early blight is caused by the fungus Alternaria solani, which infects both potato and tomato crops, along with other species of the Solanum family, causing yield losses due to reduction in green leaf area (early senescence) and direct infections of fruits and tubers.
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