PESTS OF STORED GRAIN

Press, Volume LXXI, Issue 21411, 1 March 1935, Page 9

PESTS OF STORED GRAIN

MEANS OF PREVENTION AGRirn.TTRAI. BULLETIN The February bulletin INO 68), of the "anicrburv Chamber of Commerce, prepared by Canterbury Agricultural Collet deals with the subject of •"ptftF. in Stored (srain." as follows: prc's of stored grain, such as weevils -nd" niitcs. ai 'c usually found in destructive numbers only when grain »-!<; "been stored for several months. I'ntii recentlv it has been the custom Jar farmers "to sell their wheat, oats, itp «oon after threshing, and consel iwitlv there have been few cases of Cse pests occurring in the farmers' I'hpds During the last two or three *r; son c however, the monthly increments "in prices have induced many ..rowers to hold their wheat for six T,r eifiht months, and as a result there have been several serious outbreaks of various pests, with considerable resultant loss to the holders. It is at this time of the year, when gram ?, 20 ing into store, that these outbreaks 'if wests can be combated, and so this hulle*in is issued now. to describe the nest-: and the precautions that should be taken to prevent their occurrence j;) serious numbers. Th'*re are three grain pests that occur more or 'ess commonly in New Zealand, and these will be described an turn. Weevils

(irau; weevils arc peihaps the com-r„i!if-t" and certainly the most destructive "f the pesls of stored grain j,-, \Vw Zealand. The adult weevils chc-lnut brown in colour, about of an inch long, and pos««s a": all weevils do, a long snout. Thc'v occur in wheat, oats, biscuits, etc " The female weevil with her knout bores a hole into the grain and ]av= a single egg in each of many Brains laying about 20 eggs a day, *nd often producing a total of 200 eg"s The grub that hatches out feeds on the interior of the grain, and in time hollows it out completely. No inark of its presence is seen on the surlace the hole that the parent bores bein" too smail to be seen. When all "the inside of the grain has been eaten the grub goes into a resting stage- and afterwards changes into a beetle still within the gram. It then teres it< way out of the grain, leaving a hole about the size of a pin's head. and ouite plainly seen. After emergjii" the adult weevil itself starts to cat th" mam. umiullv attacking broken grams, 'and even iii this stage doing considerable damage and producing noticeable quantities of dust. After a few davs the adult weevils pair, and fgg-lav]!.'.- a'.;ani commences a new cycle"

"Tin.- period covered by a generation. that i::. from the laying of an egg until the egg ha: hatched out and developed Into a weevil that is again laying eggs, is, in summertime, about six weeks. The period varies considerably with the temperature; no development taken place when the temperature is under about (JO decree.- F.. as it always is in winter, but with the return of spring, and especially in summer, the development proceed- apace, and the numbers increase rapidlv. Moisture as well as temperature affects the rate of breedin?, and line.* of wheat 'hat are oul of eondhion are especially liable to weevil attsck. There have been numerous destructive outbreaks of weevil* in grain ftores in New Zealand. There is one story of a wecvily town store being emptied of grain. ;md the weevils marching in such numbers towards another store that a hose war, used to war-h tlif-m off the footpath into the futtcr*. In ann'her weevily wheat v.'as tipped out on a beach and the weevils were seen marching back towards 'he stores on the waterfront. Althou'.'h these rases are extreme, yet ♦'we have b'>r>ii rnnnv serfou" losses from weevil attack, and no miller will veer* w'">at that show? anv sign of weevil. This i-~ parf'v he does rot wHi to infect r" the I'no= in thf ef er'» and the huilding itself, and partly h«>raii>-'e he ha* to h<->ld his when* through the summer, "-hen the v-eev'! breeds most nuickly, and therefore docs most harr.-.. Mites Wheat maes are not Insects but degenerate spiders, and in common with sll other spiders possess four pairs of lees. Mites are commoner than weevils, but are much less easily seen. The mite is white in colour, and is only the size of a pin's point. It is almost impossible to see it with the naked eye, but mitey wheat is usually very dusty and if the dust is riddled ot and held in bright sunlight the mites can perhaps be seen. Usually. however, a lens has to be used to make them visible. Mites attack not only wheat, but any kind of grain, as well as bran, hay. chaff, etc. Dusty eorncrs of a chaff house, or hav stored for a long time, or the chaff *>n the floor of an unswept stable, are almost sure to provide mites in quantity. A case occurred last year where a i table became so infected with mites thai horses could not be kept in it. Mites are also often found -n the timber of buildings, especially if they are rotten or infected with borer. Often the first sign of mites 33 their dropping on to floors leaving » white or brown dust that has continually to be swept up, or occasionally they arc first detected by a tickling sensation on the arms or face of people corning into contact with them. The mite does not go through a complicated life history as the weevil does. It lays '2O to 30 eggs on the surface of the grain and these eggs hatch out directly into mites again. The complete life cycle from egg laying of the parent, to egg laying of the offspring is passed through in 17 days in summer temperature, but it continues to develop, though at a dower rate even in winter. As with ■weevils S)i with mites, development is more rapid where moisture is present, find to stoie wheat that is at all out *f condition is an invitation to attack. The mite does; not bore into the main part of the grain, but bores into the cerui. and up to f>o mites can sometimes be found in the hole where the germ has been hollowed out. The mite also probably attacks the surface layers of the grain, reducing them to dust, and at the same time it produces an offensive smell, easily recognised by those accustomed to dealing with fctorcd grain. As in the case of weevils no miller accept a line of mitey wheat. simply brca,,-e he does not want 'Jther lines, or his store itself, to become infected.

ISuok-lice of Wheat nook-lice are not such common T«fis on commercial lines of wheat as the two previously mentioned, but a * w cases of their attack were observed last season, and they very frequently infest samples of wheat stored ifi bottles as specimens. The louse is n *t in shape.', while and brown in <»iOuj. and about one-twelfth of an yxn long. It is thus easily .seen and » especially noticeable from its rapid woijon which makes it quite diilicult w catch, This book-louse feeds on any kind of Ve fctablc mailer. It is common in . n books, whose bindings it eats, fm m dried specimens in museums. *nc-se arc places where it is easily ,ia\ hui n "'most certainly lives in wa deposits of hay, chaff, and stored jsrain, w that it is likely to be found it y corners °f sheds and stores. .J} aoes less harm than weevils or ffiS W b,y eatin u 8 °£ ly the outside SiT™ 0I «5e grain, but here again no li«T^ r . or merchant would accept a fe» . wheat obviously infected, for ** spreading the pest through his There are several other pests of grain - but the three described JWMwa commonest and the most in " Mode of Infection *tJ2W hese pests comes from noS„!, fr ° m "othing. Each is pro!Fßh2?* by br *«iing from eggs laid ZuZ pCsts of ,hc "ame kind. The ** sue so small that they can be,

blown about in dust, and the infection is often carried by mice, rats and birds. Wherever grain is stored, therefore, it is likely to become infested with these pests from other and older stores of grain or hay or chaff, where the pests have had time to multiply and become numerous. But such modes of infection are relatively slow. Only a few insects or mites would be carried by such means, and although they multiply rapidly in warm weather they do so slowly during winter, and at any rate they have to be present in large numbers before their presence is noticeable and deleterious. Under local conditions this mode of infection, though certain to be effective in the long run, would never cause trouble during the eight or nine months grain is usually held. Before serious injury can result there must be a nearer and more concentrated source of infection, and this is usually found in some old neglected bags of grain that have been undisturbed for years, lying in the same shed as that in which the new grain is to be stored. Part bags of grain, or grass seed, or chaff, or bran, and such like feeds, are often left lying in odd corners, not used because they are too small, and not thrown away because they may come in useful. Such material is usually swarming with weevils and mites, which, when the shed is filled with new grain, rapidly spread to the new feed provided for them. In the dark and quiet of the shed and during the warm days of autumn the pests crawl all over the new stacks, and multiply rapidly for a time at least. In addition to such sources of infection, grain, etc., left in threshing machines, seed cleaners, chaff cutters, and even the dust in corners, or on unboardeel floors where chaff and such litter accumulates, or hay stored in a shed left over from one season to the next, are frequently the means of providing a dense army of pests to infect new grain coming into store.

Means of Prevention All the pests mentioned can be killed even when lines of grain are badly infected, but the means of doing this are usually beyond the farmers' province. Lines of mitey wheat are sometimes cleaned up by riddles and blasts, a method occasionally used being to run the mitey wheat through a threshing machine. If pests are to be killed in the store fumigation must be resorted to, carbon bi-sulphide being the material that is cheapest and most effective. To use it, however, the store -must be made practically air tight, by plugging up all holes, and pasting strips of paper round doors and windows. If only part of the store is to be fumigated, air-tight, tarpaulins hung over the sacks to be treated will confine the gas, but they must enclose the sacks very completely. Carbon bi-sulphide is highly inflammable and explosive, •nd notice should be given to fire insurance companies beforesit is used. These details indicate that to clean lines of grain already infected is difficult, dangerous, and laborious. It is much easier and simpler to avoid infection. The means of doing this have been j sufficiently indicated. They are simply not to store new grain close to where old grain or hay or chaff, has been lying during the preceding summer. Collect all part bags of seed and feed, and if there is no immediate prospect of using their contents otherwise, boil them up for the pigs. i Sweep out the shed thoroughly, and if , the floor is not sound, spray cracks and corners with a strong solution of sheep dip. Do not use old bags which may be infected with the eggs of mites or insects for new grain, nor store such bags near new grain heaps. Infected bags will become clean if they are hung over a fence and exposed to the weather for a week or so, and they will be safer if they are used for potatoes, instead of for grain or chaff. Do not stack new grain close to old stores of chaff or hay, or even close to stables where old chaff litters the floor. Be especially careful with any grain in the least out of condition. The moisture tends to generate heat, which helps the rapid development of the pests. If these precautions are followed grain will rarely become injuriously affected by any of the pests mentioned before it is sold in the ordinary course of farm practice. Stored grain should, however, be examined periodically, especially for excess dust, and at the first signs of infection it should be disposed of to the best advantage. Copies of this Bulletin may be obtained from the Secretary, Canterbury Chamber of Commerce, P.O. Box 187, Christchurch.