{"id":49317,"date":"2022-12-01T13:59:30","date_gmt":"2022-12-01T13:59:30","guid":{"rendered":"https:\/\/dev.metos.global\/?page_id=49317"},"modified":"2026-05-04T09:39:16","modified_gmt":"2026-05-04T09:39:16","slug":"disease-models-chilli-eggplant-paprika","status":"publish","type":"page","link":"https:\/\/metos.global\/en\/disease-models-chilli-eggplant-paprika\/","title":{"rendered":"Disease models – chilli, eggplant and paprika"},"content":{"rendered":"\t\t
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Chilli, eggplant and paprika <\/b>disease models\n<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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\u00a0<\/p>

Pepper is an important commercial vegetable crop worldwide. Production of pepper is often severely limited by one or more disease problems. This content describes the symptoms of several commonly observed diseases and the models used for its prediction in FieldClimate.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t

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ALTERNARIA AND TOMCAST -<\/br>Alternaria solani <\/em><\/a><\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t
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POWDERY MILDEW<\/br>RISK MODEL<\/a><\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t
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GREY MOULD -<\/br>Botrytis cinerea<\/em><\/a><\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t
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PHYTOPHTHORA BLIGHT -<\/br>Phytophthora capsici<\/em><\/a><\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t
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Alternaria and TomCast<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Alternaria<\/h3>

Alternaria solani<\/em>\u00a0occasionally causes leaf spot on pepper foliage.\u00a0Alternaria alternata<\/em>\u00a0may cause fruit rot, particularly following sun scald or blossom end rot. Sun scald on pepper fruit usually occurs when the foliage is sparse and the peppers are exposed to sunlight. The injury becomes tan and shrunken and may appear water-soaked. When Alternaria colonizes these lesions they become chocolate brown to black and the fungus may be evident by a felty, dark brown to black growth. Alternaria fruit rot may also occur post-harvest.<\/p>

The fungus\u00a0infects stems, leaves and fruits<\/u>. It may girdle seedlings causing damping-off in the seedbed. On the leaves, brown circular spots are often surrounded by a yellow area. Leaf spots have characteristic dark concentric rings. Leaf spots usually appear on the oldest leaves first and progress up the plant. As the disease progresses, the fungus may infect the stems and fruit. The spots on the fruit look similar to those on the leaves\u2013brown with dark concentric rings. Dark, dusty spores are produced in concentric rings. The spores can be seen if the spot is touched to a light-colored object.<\/p>

The fungus can\u00a0survive in soil and in infested crop and weed residues<\/u>. It may be seed-borne and\u00a0carried by wind, water, insects, workers and farm equipment<\/u>. The spores that land on plants will germinate and infect the leaves when they are wet. Spores can enter the leaf, steam or fruit. The fungus is most active\u00a0during mild to warm temperatures and wet weather<\/u>. The disease is worse during the rainy season. Early blight is most severe on plants stressed by a heavy fruit load, nematode attack, or low nitrogen fertility.<\/p>

The susceptibility of the most pepper varieties to Alternaria is very low. Therefore using the TomCast model needs to adopt the action threshold to the specific susceptibility of the cultivar. Eggplant is susceptible to Alternaria. For this plant the thresholds, originally used in tomato are more propriate.<\/p>

TomCast Model<\/h3>

The TomCast model is designed to evaluate the data of the first needed spray and the needed spray intersept. It is calculated on\u00a0base of hours with leaf wetness (or relative humidity more than 90%) and the average temperature during this period<\/u>. Every day is evaluated for this and every day gets a severity figure in between 0 and 4.<\/p>

To assess the date of the first spary and the date when a spray has to be repeated the\u00a0accumulated severity values are used<\/u>. On the normally low susceptible pepper cultivars a high value (40 and more) can be accepted. After an injury like hail susceptibility is much higher and the acculated severity values have to be reduced to 18 to 25. This threshold has to be applied in Eggplants too.<\/p>

Output in Fieldclimate: Severity values are accumulated regarding to favourable conditions of leaf wetness and temperature within this period (see tabel above). In Sum 24 Severity values have been accumulated within the observed time span of 10th of July to 27nd of August. In dependence of the cultivar (susceptibility) and of injuries the severity value a spray application is recommended at about 40 SV (not susceptible cultivar, no injuries) or at about 20 SV, when injuries are observed through hail or the cultivar is very susceptible to the pathogen.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t

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Powdery mildew risk model<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Powdery Mildew<\/h3>

Powdery mildew primarily affects leaves on pepper plants. Although the disease commonly occurs on older leaves just before or at fruit set, it can develop at any stage of crop development. Symptoms include patchy, white, powdery growth that enlarges and coalesces to cover the entire lower leaf surface. At times the powdery growth is present on the upper leaf surface as well. Leaves with mildew growing on the under surface may show a patchy yellowish or brownish discoloration on the upper surface. The edges of infected leaves may roll upwards exposing the white, powdery fungal growth. Diseased leaves drop from the plants and leave the fruit exposed to the sun, which may result in sunburning.<\/p>

Powdery mildew can be severe during the warmest part of summer and can cause heavy yield losses. The pathogen has a very wide host range and inoculum from one host plant species can cross infect other host plants. In California, powdery mildew inoculum can come from crops such as onion, cotton, tomato, all varieties of peppers, and weeds such as annual sow thistle and ground cherry. This powdery mildew pathogen differs from powdery mildew pathogens in other genera in that it primarily occurs inside the leaf rather than on the leaf surface. Cleistothecia (sexual spores) of the Leveillula perfect stage rarely occur in California, but asexual spores (conidia) are produced and disseminated by wind. In general, high humidity favors germination of conidia. Infection of plants can occur over a wide temperature range (64\u00b0 to 91\u00b0F or 18\u00b0 to 33\u00b0C) under both high and low humidity. Under favorable conditions, secondary infections occur every 7 to 10 days, and disease can spread rapidly. Temperatures over 95\u00b0F that commonly occur in the interior valleys of the state can temporarily suppress development.<\/p>

Risk Model<\/h3>