This is a foliar disease common to onion growing areas. The disease causes leaf spotting and tip dieback, and can adversely affect the maturity and quality of the bulbs. Botrytis infection initially results in small, oval (1/4” in length), white spots on the leaves. These lesions often are surrounded by a halo of green water-soaked tissue. Leaf tissue within the spots eventually collapses and becomes tan coloured. Numerous lesions on a single leaf result in dieback of the entire onion top, giving severely affected fields a ‘blasted’ appearance.
Destruction of cull piles and rotation out of onions for at least 2-3 years are important to help prevent the buildup of inoculum and reduce the likelihood of severe epidemics. Because these cultural practices are only partially effective, and no blast-resistant varieties are available, onion growers must rely upon repeated application of protective fungicides for acceptable disease control.
Downy mildew is manifested by a purple-brown mold occurring in irregular shaped patches on onion leaves. The mold is as a result of spores produced by the fungus in wet or humid weather. Severely affected leaves collapse and die in a few days. The downy mildew pathogen overwinters in infected crop residue and in soil as resistant spore-structures. It is also possible for the pathogen to be carried with the seed. During the growing season, the disease is spread by wind. The disease is controlled through crop rotation and the use of disease-free seed. Protective fungicides can provide a moderate degree of control. If downy mildew is already established in a field, a systemic fungicide can be used to eradicate existing infections.
Symptom for purple blotch first appear as small tan spots on leaves. The lesions become sunken and rapidly expand rapidly up and down the leaf. Individual lesions 1/4” - 3/4” in diameter frequently are surrounded by a band of purple tissue. Numerous leaf lesions contribute to collapse of the entire top. Wounds occurring at or shortly before harvest provide sites for Alternaria infection of onion bulbs. Wind and rain are responsible for dispersing spores to other plants and fields. Tops are more prone to infection as plants mature. Under favourable conditions, an unprotected crop can sustain a substantial amount of infection in a few weeks. Crop rotation is important to prevent pathogen populations from building up to high levels. Rotations out of onions for 2-3 years are recommended. Most commercial onion crops must be protected from purple blotch by using repeated applications of protective fungicides.
Onion smut is a disease common to temperate growing regions, especially where onions are grown from seed. Most onions and related crops are susceptible to smut. Onion smut appear as Lesions with dark brown streaks running up and down the leaves. The streaks initially appear as long blisters on the leaf surface. As the lesions mature, they turn brown and contain a mass of dark powdery spores that give the tops a sooty appearance. Diseased leaves may bend or twist abnormally and usually are shed prematurely. Smut infected plants normally are stunted and produce bulbs highly prone to soft rot. Use of onion sets is recommended as they are rarely affected by the disease.
Yes, deworming can kill animal if not done well