Rigorous cleaning before harvest essential: M.A.F.

Press, 22 January 1982, Page 9

Rigorous cleaning before harvest essential: M.A.F.

Severe contamination by insects or mites in wheat consignments can result in rejection or significant financial penalties, according to two Canterbury-based entomologists with the .Ministry of Agriculture and Fisheries. Drs Ray French and Ken Somerfield. But contamination or infestation can be largely avoided by thorough cleaning of all equipment used to harvest and store grain before the harvest gets underwav, sav the M.A.F. officers.

They say that the necessity for rigorous cleaning down prior to harvest cannot be overemphasised, for it is the residues of grain from the previous season that are the most likely source of contamination of newly-har-vested grain in storages.

There have been a greater number of complaints from millers and bakers about contamination of grain and there is an increasing amount of bulk storage on farms for periods of months.

“The first step is complete cleaning of all harvesting machinery — header, auger and bins." said Dr French.

"Don't leave any part of the machinery untouched." he said.

"Thorough cleaning will usually entail using vacuum cleaners or brushes to reach any corners or places where grain from the previous harvest may have lodged.

“Any residue that is found and collected must be sprayed or burnt.

“The next step is to spray with suitable chemicals.

“It is essential to use a saturating liquid spray so that it literally runs down the machinery. A nozzle must be directed around all the nooks and crannies of the machinery." said Dr French. In New South Wales, surveys in 1970 and 1972 of headers, augers, trucking bins, mobile field bins and seed drills (141 machines in ail) showed that 24 per cent contained grain damaging insects.

The next area that should receive thorough attention is the storage silo. Obviously empty silos should be rigorously cleaned out. but in practice this is often hard to do.

Many silos have overhead or internal bracing beams which are high and difficult

to reach. A ladder inside the silo may be necessary.

Anything that is derived from cereals, such as bread, should be removed from the vicinity of the silos as well as all types of grain.

The entomologists have recommended that the ground for several metres around the silos should be sprayed with insecticide because grain is often left unattended in long grass and debris around silos and can present a source of infection. The best time to use insecticides is obviously before harvest begins so as not to risk contamination of the new grain. Conscientious work in this area before the harvest can save considerable financial penalties later in the year.

The main pests to be guarded against with such a regime as outlined above are the granary and rice weevils, which are called primary pests, and the sawtooth grain beetle, the rusty grain beetle, the flour beetle, which are secondary pests, and the mites.

The mites are particularly important to eliminate because they are the worst source of taint in flour, which can lead to complaints from bakers.

Dr French and Dr Somerfield said that a high moisture content in stored grain provided the ideal conditions for the breeding of pests. Although the legal maximum for storage of wheat is 15 per cent moisture. 13 to 13.5 per cent is a much more desirable figure to aim at.

In Canterbury surveys conducted by Dr Somerfield, 80 per cent of all pest infestations of wheat occurred when the moisture content was over 15 per cent.

Around 95 per cent of al) infestations occurred in wheat above 13.5 per cent. The two entomologists said there are several publications in the Aglink series put out by the M.A.F. which deal with grain storages and insect infestations and these are available from the Ministry's Victoria St office in Christchurch.