Put simply, blight can be fatal to a potato or tomato crop. Through a combination of farming best practices, great care and treatment with a systemic fungicide such as Demildex, the problem of blight can be a thing of the past. Copper oxychloride Demildex is a highly effective fungicide, useful for treating potato and tomato blights amongst a wide array of other fungal plant diseases.
Blight in tomatoes and potatoes, commonly known as late blight is a nightmare for most farmers of these crops. It can wreak devastating damages to plantations and farmlands. Its catastrophic effect is so great that it was identified as one of the major contributory factors leading to the Irish potato famine in the middle of the nineteenth century.
Although there are early and late blight conditions, late blight is the most common form of blight infection.
Early Blight
Early blight is caused by Alternaria solani, a fungus. Overwintering in nightshade plants, conidia are produced asexually in the spring which are transmitted via wind, water or rain to uninfected plants. The weather conditions in the springtime are ideal for transmission: moist and not too warm. The fungus penetrates the plant through stomata or via direct injection, whereupon the fungus can grow, producing lesions. In potatoes, a yield reduction is typically experienced. The symptoms are lesions on stems and concentric circles on leaves. In the case of tomatoes, infection is through openings caused by growing cracks or by those created by insects, in addition to direct injection through stems. Concentric circles are again a feature on leaves and defoliation can occur.
Defoliation can lead to a degree of sun scalding to the fruit, which will lead to spoilage and further cracking and proliferation of the fungus. In all cases, the fungus can produce more conidia which is easily spread. A. solani also has similar and profound effects on other plants in the family Solanaceae, including peppers and aubergines. A. solani can additionally cause ‘dropping off’, where seedlings and seeds are weakened before or after germination.
Late Blight
Late blight is by far more destructive to a potato or tomato crop than early blight. Herein, strategies to manage the transmission and proliferation of late blight will be discussed.
The organism responsible for late blight is oomycete Phytophthora infestans. An oomycete is a fungus-like eukaryotic microorganism, and is treated in a similar way to as if it were a fungus.
Oomycetes are highly aggressive. They can affect all plant parts and can potentially cause quick diebacks and deaths. This organism spreads its infection through sporangia and zoospores.
Sporangia, known in the singular as sporangium, is mostly formed on infected foliage and then dispersed through water and wind media. The organism strongly favours moist and cool environments, with the production of zoospores typically occurring at temperatures below 15 °C - i.e. typically in the springtime. A legion of zoospores can be formed and enveloped within a sporangium. They can then swim in both films of water in the soil and on the plant's leaves in a bid to infect the plant's parts. Lesion growths typically are most efficient in the summer months, when temperatures exceed 20 °C.
Late blight in potatoes will cause the crop to defoliate. However, if the disease arrives after the tubers are formed and ripe for harvest, little to nothing is lost.
If the tubers are infected, they develop some reddish-brown granular markings on the flesh and brown discolouration on the surface. The tubers may seem solid but are bound to develop soft rot. This soft rot is caused and quickened by an invasion of bacteria that can cause tissue breakdown, often appearing ‘corky’ throughout the flesh. It should be noted that there are little to no known problems of consuming lightly blighted potatoes - the major problem lies with failed and rotted crops.
In tomatoes, dark, water-soaked lesions are formed on leaves with the lesions gradually growing from the leaves/margins of the plant towards the centre. Lesions then develop into brown, dark patches which become brittle as soon as they dry out. These lesions also develop in the stems and fruits of the crop.
Blight in potatoes are potentially caused by diseased potatoes dumped on the farm or infected seeds, and unharvested potatoes abandoned to rot in the soil all of which have the potential to grow the following season.
Proper Sanitation
Asides from planting resistant varieties, proper sanitation and maintenance of the growing area is one of the most important preventive measures against blight in potatoes and tomatoes, as potato hulls (including ‘seed potatoes’ from the previous growing season) and tomato seeds are usually the main culprits of blight infections as they may not always show signs of being infected by the blight causing pathogen. Infected parts need to be burned, buried or composted before planting in the spring.
When burying potato hulls, make sure that they are buried deep in the soil and they are covered with soil or plastic to block out any light that might help them photosynthesise and grow. When burning, pile them up in thin layers over combustible materials. Old specimens and infected plants can also be exposed to the extreme freezing temperatures of winter, if appropriate.
In general, if the last option is chosen, it is recommended that the field in which exposure of the chopped cells to freezing temperatures should not be used for growing potatoes or tomatoes the following year - though growers may wish to include this technique as part of crop rotation and leaving fields fallow. Other nightshade plants should not be planted in a field that has been recently vacated by blighted potatoes, tomatoes or other crops.
Blight Treatment for Potatoes
If few leaves are affected by blight, targeted removal and disposal of the infected leaves to limit the spread is often very effective. Otherwise, for a more severe infection, growers may have to cut off all affected foliage and stem and either burn or compost them. Removing the foliage from the infected plant helps prevent the disease from spreading and sinking into the tubers, as long as they are well converted with the soil. Then, leave the crop for a while – about two weeks – to let the blight spores on the surface die and the potatoes develop a much thicker skin.
You may also spray your crops using copper fungicides, one of the most effective of which is copper oxychloride. Copper oxychloride Demildex - a specifically developed fungicide - should be applied every 10 to 14 days following heavy rainfall or when the infection is rapidly increasing across the farm area. If possible, it is recommended that the fungicide is applied such that there are 12 hours of dry weather following application.
For powdery copper fungicides, apply a thin layer of fungicide powder on both top and bottom of the leaves using pressure duster. You should reapply the fungicides every three to ten days until all blight symptoms vanish and the disease is cured.
You can also spray the infected tomato plants with baking soda spray. These sorts of sprays are good for killing fungal organisms and do a brilliant job of treating blight. They are also friendlier than copper fungicides.
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