Controlling blossom blight challenging in alfalfa

BROOKS, Alta. — A hot and humid blossom period saved Alberta’s alfalfa seed crops from significant blossom blight damage this year, but research continues into the fungal pest.


Syama Chatterton of Agriculture Canada described the nature of the beast Nov. 27 to members of the Alberta Alfalfa Seed Commission. 


She said she plans to focus on whether alfalfa pollen can be infected in low humidity and investigate the role bees and other insects have on spore spread. 


Blossom blight can be controlled with fungicides, but alfalfa presents challenges.


“I think seed alfalfa is a little bit tricky to work with … because of such a long flowering period, so you have a fairly long time when your plant is going to be susceptible,” said Chatterton.


She debunked the myth that purple flowers are less susceptible than white. Resistant varieties are not an option either, she said, because the disease is so complex.


Blossom blight is the result of two pathogens, sclerotinia sclerotiorum and botrytis cinerea. 


“These are very generalist, broad spectrum pathogens that most plants don’t have resistance to,” she said.


The sclerotinia aspect, which is associated with white mould and stem rot, is the same type that wreaks havoc in canola and pulse crops. Sclerotia produce apothecia, the small mushroom-like fungi that emit spores.


Spread by wind, the spores can easily travel.


“Usually the first place they like to infect is flowers in bloom, and that’s because flowers have an awful lot of pollen associated with them that can serve as a nutrient source, and flowers are also usually in different stages of development and decay.”


The fungus releases spores at the beginning of the season.


The other part of the blossom blight complex, botrytis, is a fluffy grey mould of the same type found on strawberries, other fruits and pulse crops. 


In the right conditions, its spores can spread throughout the growing season, Chatterton said.


“Botrytis is also a very widespread disease. It’s probably the number one disease in the world in terms of what it can infect.”


Severe blossom blight will reduce the number of pods, the number of seeds per pod and seed quality.


Fungicide treatments are preventive rather than curative, so Chatterton said it is important to consider risk factors when making spraying decisions. 


Blossom blight thrives in cool, moist conditions.

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