Monday, August 24, 2009

White mould can be one devastating soybean disease.And it all starts as just a small spore thats released from these inverted appearing mushrooms on the soil surface.As the black sclerotinia seed from a previous soybean crop germinate they produce these inverted mushroom like structures at the soil surface.At just the right time these fruiting bodies release large numbers of ascopores into the soybean canopy.If a spore lands on a wet dying petal that remains moist for 2-3 days the infection process is on its way.( Photo - Courtesy of the Pioneer Agronomic Photo Library - DesMoine,Iowa )
Once the thread like infection strand has penetrated within the stalk the growth of white mould mycelia begin their process of shutting down the plants phloem and xylem network ( in other words they block off the plants water and nutrient plumbing devices that feed the upper plants leaves )The end result is a wilting death to the upper leaves.
Once infection has occurred at a flowering node the white cottony mycelial growth will begin both its downward and upward ascent of the plants stem.
It doesn't take long for the mycelial threads to develop black fruiting bodies called sclerotinia.
These seed like structures( sometimes referred to as rat turds by farmers )can be already seen formed in the above photo.( Double click on the shot and you should be able to detect several )
As growth progresses white mould can spread quite profusely throughout the canopy as seen by the amount of stem infection these plants display.
Yield losses from severe white mould ( 50% plant infection can approach 15 - 20 bu / acre )All companies are well aware of what white moulds potentially devastating impact can be. Research is being conducted in several arenas to help overcome it.
In the meantime if a grower is seriously plaqued with WHITE MOULD all he can do is follow these helpful suggestions.1) Do not over fertilize a field either with commercial nutrients or manure.Excess foliage growth and leaning soybeans can lead to more white mould development because of more humid and darker shaded canopies 2)Select above average white mould tolerant narrow line soybean varieties with exceptional standability to avoid early season lodging 3)If posssible grow strong yielding but earlier maturity soybean lines for your geography.Earlier maturing varieties will not grow as big and lush by the time they flower and so they can often avoid white mould infection because of greater air movement and sunlight penetration into the lower canopy.4)If possible consider widening your row spacing and reducing your seeding rate.Soybeans should always be seeded according to their seed size.If you are planting a small seeded variety you may be dropping too high a plant population.Consider moving to a 20 inch or wider row spacing and dropping only 150,000 seeds per acre.6)You might consider using atrazine in your corn crop prior to rotating to soybeans.There is some evidence to indicate that the L-isomer of atrazine controls a percentage of the germinating sclerotinia and 7)You might want to consider cultivating wide row soybeans.There is evidence to show that when cultivation is done when sclerotinia are germinating a percentage can be controlled through soil disturbance.
Bottom line is that we will inevitably see some white mould show up in soybeans when we experience lush moist growthy years.
When its all said and done I don't mind seeing some white mould in a soybean canopy.When you see white mould its making a statement that growth has been strong and lush and that yields are likely going to be favourable due to better pod set and larger seed sizing.It reminds me of the grower who once called me to come look at his mouldy soybean crop.After examining the field for an hour or so I left him telling him that I'd have to get back to him to see how they were going to yield.His reply was that a he couldn't afford to grow a soybean that moulded like the one he had planted.I just said that we'd have to wait and see.A call came back to me about a month later.It was the same farmer.He said he'd called because he wanted me to know just how the field had turned out.I replied with, " well,whats the verdict " His comeback was that as much as he'd once stated that he couldn't afford to grow the variety, he now indicated that with what it had yielded he couldn't afford not to grow it.The moral of the story is that we probably shouldn't be too quick to judge how things will turn out when it comes to white mould.They sometimes aren't near as bad as we think.

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