ALLIUMS (Onions, Garlic,and Leeks)

SCLEROTIM CEPIVORUM-also known as ALLIUM ROOT ROT 

Plant pathogen-Sclerotium Cepivorum FUNGUS

Host- alliums, Onions, garlic, leeks; Occurs all around the world where alliums are grown.  

Ideal growing conditions- The fungus thrives in cool weather and is found in the soil as small round structures called Sclerotia, These can live in the soil for decades and affect any allium planted there. 

Symptoms: One of the first things you will notice in the Allium is the foliage lacking luster.  The leaves will appear stunted and starting to yellow; eventually the older leaves will die.  In cool weather mycelium  growth will appear around the base plate and eventually covering the entire bulb, it looks white and fluffy.  The fungus can create very small hardened fungal bodies, sclerotium bodies, these will appear in the fluffy white growth.  Mycelium can grow outwards from the roots of one plant to the roots of a neighboring plant, and it is by this method that the pathogen can move down a planted row.  

Prevention: The most effective controls for white rot are avoidance and sanitation. Once a field is infected, chemical treatments are necessary to produce onion or garlic crops.  If S. Cepivorum is found in soil do not plant Alliums there for over ten years. Possible sifting methods to remove mycelium but seems extremely labor intensive.  On garlic, the disease is commonly introduced into the field on seed cloves. The best way to prevent disease from gettin onto your land is to only buy seeds from a trusted seed seller.  However, the fungus is vulnerable at temperatures above 115°F, thus dipping seed garlic in hot water will greatly reduce the amount of pathogen and is a good preventative measure, although it may not completely eradicate the fungus. Also, temperatures above 120°F may kill the garlic, so careful temperature control is essential.  

BOTRYTIS LEAF BLIGHT

Host- alliums, Onions, garlic, leeks at early bullbing stages

Pathogen- fungi Botrytis squamosa

Symptoms: First occur on oldest leaves, atiny oval white or yellow spot, Blight, Slighty sunken into the leaf and surrounded by a silver halo.  If you slice the leaf open you can find the lesion goes all the way though the leaf.  Botrytis can easily be confused with Leaf fleck, ozone injury and leaftip dieback. 

Environment-   favorable environmental conditions, high rainfall, extended periods of leaf wetness, high relative humidity, and moderately warm temperatures 50 F-75 F, can result in reduced onion bulb growth and yield.  The Squamosa fungi, compacted as sclerotic bodies,  can live in debris piles and lay dorment for a long period of time, idea conditions for spore production include wet with low winds.  Debris piles should be properly disposed of to prevent spreading. 

Prevention: proper two year crop rotation practices, and healthy seeds. To reduce the incidence and severity of botrytis leaf blight, cull piles should be destroyed, seed fields should be planned well apart from commercial onion production fields, and volunteer onions should be rogued. At harvest, severed onion tops should be removed from the field and destroyed. Fungicides are used instantly in commercial farms. 

Soft Rot:

Caused by the bacteria: Erwinia carotovora.

Symptoms:  At first the bacteria accesses the allium tissues through the bulb neck as the plant becomes mature, it becomes water logged; later becoming a decomposing slimy mess. It infects and rots certain scales or layers of the allium bulb flesh and emits a foul odor, remember> stink=bacteria.   

Environment: Alliums stored in a warm environment can become affect by E. carotovara.  Plants that have been damaged or bruised can also be affected.  These affected plants can easily spread infection by contact with other alliums.  

Management: Cultural controls.