On Crops: Bulb onions, leeks, chives, garlic and shallots
Worldwide, in humid temperate climates
The tips of onion leaves shrivel and fall over, and pale green to yellowish oval spots form further down the leaf. Early in the morning, the spots may appear purplish as the fungus matures, or as the colonies are invaded by other fungi. Constant dampness from rainy weather, heavy fog, or crowded plants is needed to trigger an outbreak of onion downy mildew, which reproduces rapidly at 13 C (55F). Plants that have been damaged by hail may be infected when spores enter the moist, wounded tissues. Warm, dry weather often curtails this disease.
Onion plants are weakened by downy mildew but seldom killed. Bulbs may be small, with soft outer layers.
Choose a sunny, well-drained site for onions, and control weeds that threaten to crowd the plants. Rotate onions to a fresh site to prevent disease buildup, and water early enough in the day so that onion foliage is dry by afternoon. Gather up and compost onion debris so that the fungus cannot overwinter in onion tissues buried in the soil.
Clip off and compost affected leaves, and weed the bed to admit more sun to the planting. Set aside bulbs from affected plants for short-term consumption, because they tend to rot in storage.
Katika mimea: Bulb vitunguu, leeks, chives, vitunguu na shallots duniani kote, katika hali ya hewa ya unyevu, ncha ya majani ya vitunguu kuharibika na kuanguka juu, na pale kijani kwa rangi ya manjano madoa spots kuunda zaidi chini ya jani. Mapema asubuhi, madoa hayo yanaweza kuonekana kuwa na rangi ya zambarau wakati uyoga unapokomaa, au wakati makoloni yanapovamiwa na uyoga mwingine. Unyevu wa kawaida kutoka kwa hali ya hewa ya mvua, ukungu mzito, au mimea iliyojaa unahitajika kuchochea mlipuko wa kuvu la vitunguu, ambalo linazalisha haraka kwa joto la 13 ° C (55 ° F). Mimea iliyoharibiwa na mvua ya mawe yaweza kuambukizwa wakati spora zinapoingia kwenye tishu zenye unyevunyevu na zilizoumia. Mara nyingi hali ya hewa ya joto na kavu hupunguza ugonjwa huo. Mimea ya vitunguu hupunguzwa nguvu na kuvu la uvimbe lakini mara chache huuawa. Matofali yanaweza kuwa madogo, yenye tabaka la nje laini. Chagua mahali penye jua na mahali penye maji mengi, na uondoe magugu yanayoweza kuharibu mimea hiyo. Pindua vitunguu kwenye eneo jipya ili kuzuia ugonjwa usikue, na umwagie maji mapema sana mchana ili majani ya vitunguu yawe kavu alasiri. Kukusanya na kuunganisha mabaki ya vitunguu ili kuondoa kuvu katika tishu za vitunguu zilizozikwa katika udongo. Kata na kuyeyusha majani yaliyoathiriwa, na kuondoa magugu kwenye kitanda ili kupanda kuonyeshe jua zaidi. Weka kando bulbs kutoka kwa mimea iliyoathiriwa kwa matumizi ya muda mfupi, kwa sababu huwa na kuoza katika kuhifadhi.