Pest Problem In Stored Grain

Press, Volume CIX, Issue 32032, 5 July 1969, Page 10

Pest Problem In Stored Grain

Bulk storage is now an accepted method of holding wheat on a large number of Canterbury farms. Although the method has many advantages, one risk is that of pest invasion.

A survey carried out in Canterbury over the last three years has shown that each year about one third of the silos and bins examined have signs of mite or insect infestation. In some cases they are severely infected. The situation this year promised to be more serious than in previous years because of the volume of poorly conditioned wheat harvested. However, no significant increase in the general infestation level was recorded, possibly because of unfavourable weather upsetting the pest’s life cycle in the field or the use of more effective pest-prevention procedures by the farmers covered by the survey, such' as attention to cleanliness and use of insecticides before bulking. Any signs of infestation, however, are potentially significant, especially at this time of the year. Any insects or mites present now could multiply rapidly over the next three to six months, resulting in tainted wheat.

Tainted wheat, especially in a year of surplus such as this, would probably be rejected by the miller. This might result in a loss of up to $3OOO to $4OOO to a farmer. This loss could be disastrous for the average farmer, making it essential that all people with bulk wheat check their grain immediately, and at least once a month thereafter and preferably more often. Checking bulk wheat is a simple procedure and is carried out using a sampling spear, a sieve made by soldering 1/8 mesh over a coffee tin, and a piece of white paper.

A sample is best taken one to two feet below the surface and in the centre of the hin or silo. Sieve the sample over the piece of white paper placed in a warm, draughtfree area.

If mites are present they can be seen as small pale yellow specks, about the size of a pin head, moving rapidly over the paper. If more than 20 mites per sample can be counted, fumigation ot the wheat is advisable. Insect pests are seen as large and distinctly darker organisms and are not usually as active as mites. If more than five

'insects a sample are seen, fumigation is again advisable. Fumigation is a very simple process, using chloropicrin at the rate of one bottle (cost $1.50 a bottle) for every 10 tons of wheat. Chloropicrin is sold under the name of Larvacide.

A single pipe can be used, which is pushed into the bin at various depths and small quantities of liquid poured down (at depths of 4ft and Bft in a 12ft silo). The treatment does not harm the grain and is usually highly effective. The cost in both time and labour is a very cheap insurance for a silo of wheat.

Helping to prevent the problem is also a simple, inexpensive procedure and should be carried out if only for hygiene’s sake. Remove any source of infestation from the storage

area—old sacks, hay, dog biscuits, etc. Keep the storage area scrupulously clean by vacuuming out dust and debris before wheat storage. A week before harvesting It is recommended that an approved insecticide, such as Premium Grade Malathion, be sprayed on to the silo or bin surfaces and preferably over the surroundings. It is absolutely essential, of course, to make sure the moisture content.of the wheat does not exceed 15 per cent and preferably is Ipwer. The

survey has shown that mites can cause damage even at 14 per cent moisture. Below 13.5 per cent, however, the risk of infestation and consequent damage is minimal. It must be emphasised that education in ways and means of bulk grain pest prevention and control is a key faetor in helping to re.‘duce the threat of pest damage. The whole problem of pests in farm bulk grain can be minimised by • people handling bulk grain applying the few simple precautions outlined above.

The writer of the accompanying article on the pest problem in farm-stored bulk grain is Mr R. A. French, field research officer (entomology) of the field research section of the Research Division. Department of Agriculture.