The wettest seeds in a grain bin determine storability, not the average
grain moisture, cautions a Montana State University plant pathologist.
While the Prairies’ dry climate and cold winters generally reduce the
risk of mould damage to stored crops, this year’s late rain and weedy
fields have resulted in higher risk of storage moulds, said Barry
Jacobsen. There are three major factors involved in storage mould
damage, he added:
- The wettest seeds in a grain mass determine storability.
- Mould and insects are more active at higher temperatures.
- Damage to the seed coat will increase the risk of mould.
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Jacobsen said many people think average grain moisture is most
important for safe grain storage. However, it is the wettest seeds in a
grain mass, not the average grain moisture, that determine storability.
For example, if the average grain moisture is 13 percent but immature
grain or weed seeds are above 15 percent moisture, mould will grow on
these wetter seeds. They produce water and heat as they grow, enabling
surrounding seeds to be attacked and damaged as well.
Jacobsen said because mould and insects are more active at higher
temperatures, lower temperatures can make it safer for higher-moisture
grains.
Storage mould and many grain-storage insects generally are not active
below about 0 C, so commodities can be safely stored at higher
moistures.
For example, wheat can be stored almost indefinitely at 14 percent
moisture at temperatures below
4 C, but will mould in three to six months at temperatures between 15
and 21 C.
Agriculture Canada recommends that cereals be stored at a moisture
content of less than 12 percent. Canola is often infested by mites and
mould, and Agriculture Canada advises that it be stored at less than
eight percent moisture content.
Mould can raise nearby temperatures to as high as 60 C once it begins
to grow. It also produces fungal mycelia that crusts the grain
together, preventing air movement, so fans cannot effectively cool
areas of mould activity.
Jacobsen said damage to the seed coat also increases mould risk.
“The intact seed coat is a very effective barrier to invasion by
storage moulds. Damage to the seed coat by field moulds, insects,
improperly adjusted harvesting equipment or rodents will increase
storage mould damage.”
Field moulds such as fusarium, ascochyta, helminthosporium, alternaria
or claudosporium are not able to continue growing below 18-20 percent
moisture, but seeds damaged by these fungi are easily infected by
storage mould.
Other management practices important for safe storage are:
- Elimination of spout lines by cleaning the grain before binning or
using a spreader device. High moisture weed seeds commonly collect in
the spout line and mould problems often start at these sites.
- Control rodents and insects by thoroughly cleaning bins and using
preventative rodenticides and insecticides. Many storage insects feed
on the storage fungi, not the grain.
- Manage grain bin temperature to prevent moisture migration. Generally
this can be prevented by aeration to keep grain moisture within about 6
C of the outside temperatures.
- Be sure bins are tight with no leaks.
- Check grain bins on a regular basis for signs of heating, musty
odours, crusting or insect activity.
Agriculture Canada’s Cereal Research Centre in Winnipeg has an in-depth
report on grain storage on its website. For a link, go to
www.producer.com and click on news links.
