Archive Article: 1997/10/18
FOR there to be extra problems this year, there has to be inoculum in the store to begin with. If the grain store was clean before being filled then the risk is no higher than at any other time. Various insects and beetles are brought in at harvest which dont matter too much so proper identification is worthwhile before applying pesticides.
However, temperatures need to fall below 12íC before storage beetle pests and grain weevil stop breeding. Hot spots in the grain store will favour the rapid development of infestations by insects such as the saw-tooth grain beetle.
Above 18íC it will proliferate and as these beetles run around in the grain they create more heat which is retained in their bodies to generate their own heat source and yet more hot spots.
It is important that growers monitor for these hot spots and check for the presence of beetles.
Cooler nights mean it should be possible to reduce the temperature inside stores steadily but care has to be taken when the nights are also damp. The main risk is bringing in an excess of cool air which creates condensation and wet surfaces inside the store. Moist grain is particularly susceptible to mite attack which may eventually require treatment with a surface-applied pesticide such as Actellic.
Mites are very affected by the relative humidity (RH) of the air inside the store. Once it falls below 65%, the mites lose moisture to the air and will shrivel and die.
A normal grain stack at 15% moisture content will have the surrounding air at an RH below 65, but once the grain moisture content rises above 16% growers should be considering the relative humidity. For oilseed rape, the critical moisture level is about 7%.
Mike Lole,
ADAS Plant Clinic, Wolverhampton.