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WEEDS, FUNGOUS DISEASES AND INSECT ENEMIES.
316. Weeds.—Maize differs from the other cereals in that the grain as it goes to market does not contain weed seeds, nor is there any danger of adding such seeds to the soil when the maize is planted. There are, therefore, no distinctive weeds of the maize crop, but weeds that chance to infest the soil may occur in the maize field. Fields are not infrequently cultivated in order that the cultivation incident to the maize may partially or wholly eradicate existing weeds. This, in fact, is one of the purposes of a systematic rotation of crops. Besides the injury that all weeds do, some are more troublesome than others, either through their tenacity, their immediate injury to the young maize plant, or through the inconvenience which their presence involves. Among the more troublesome weeds of the maize field may be mentioned:
(1) Foxtail (Chamoeraphis).
(2) Bindweed (Convolvulus).
(3) Cocklebur (Xanthium canadense Mill., and X. spinosum L»),
(4) Spanish Needles (Bidens Hpinnata L., B.connata Muhl., and B.Jrondosa L.).
317. Foxtail.—There are two species of foxtail; one known as Pigeon grass (Chamoeraphis glauca (L.) Kuntze), and the other known as Bottle grass (Chamoeraphis viridis (L.) Porter). So far as actually reducing the yield of grain is concerned, these foxtails are probably the worst weeds that infest the maize fields. They are annuals, varying from a few inches to two feet or more in height, with dense spiked heads, yellow in Pigeon grass and green in Bottle grass. The heads are less dense and the bristles longer in the latter. Their abundance of seed, produced almost under any environment, which is evidently stored in the soil for considerable periods, makes it almost, if not quite impossible, to eradicate it permanently.
318. Bindweed.—There are a number of species belonging to the Morning Glory family which may infest cultivated fields; the most serious are the field bindweed (Convolvulus arvensls L.), imported, and the hedge bindweed or morning glory (Convolvulus septum (L.) Willd.), native. Both are perennial vines, with extensive underground stems, which make them practically impossible to eradicate. They may be greatly reduced by thorough cultivation. Where they are a serious pest, it is desirable to cultivate the field two years in maize, in order to reduce their injury to succeeding grain and grass crops. Good results have been obtained by using sorghum or rye as a smother crop. They do their chief injury by winding themselves about the cultivated plants. When a badly infested field is to be planted to maize, it is desirable to delay plowing until the weather is favorable for a rapid growth of maize. By this time the bindweeds will have started in the unplowed land. By plowing and immediately planting, the maize will get well started before the bindweeds have recovered from the plowing. The land should be kept harrowed, so as to prevent, as far as possible, the growth of other weeds, until both maize and bindweeds have a good start. If the bindweeds are now cut off with a hoe, and the land thereafter kept cultivated in the usual manner, no further serious inconvenience will be experienced from the bindweeds.
319. Cocklebur is also a branching annual, belonging to the Aster and Daisy family. It grows from one to two feet high, and is especially distinguished for its large spiny burs, which are so serious an inconvenience by clinging to the bodies of our domestic animals. Each bur contains two seeds, only one of which grows the first year, the other remaining dormant until the second year, unless the plant of the first seed has been destroyed, when, as shown by McCluer, the second seed may germinate. The plants usually grow in such limited numbers that those which escape destruction through ordinary methods of cultivation may be pulled by hand.
320. Spanish Needles, Stick-tights, Beggar's Ticks.—These are branched annuals belonging to the Aster and Daisy family (Compasitae), growing two to four feet high, with brown, thin, flat seeds, two to four downwardly barbed awns. These weeds do their principal damage by the seeds adhering to animals and clothing. Reasonably careful cultivation will destroy them.
321. Fungous Diseases.—The more important fungi which attack the growing maize plant are as follows:
(1) Maizesmut (Ustilago zeae (Beckm.) Ung.).
(2) The bacterial disease of dent maize (Bacillus cloacae Jordan).
(3) The bacterial or wilt disease of sweet maize (Pseudomonas steward).
(4) Maize rust (Puccinia sorghi Schw.).
(5) The leaf blight fungus (Helminthosporiumgraminum Rab.).
The maize smut is the only disease that has assumed any widespread economic importance.
322. Maize Smut differs from the smut of the other cereals in its mode and source of infection, making its appearance upon any part of the plant above ground; although the ears and tassels are the portions chiefly infected. Formerly it was thought that infection was largely by means of smutty seeds. It is now pretty well agreed that the principal and perhaps the only source of infection is from the flying conidia produced by the germination on the ground of the myriad spores of the smut boil. Warmth, moisture and soluble food material are very essential to the germination of the spores and the spread of the disease. Naturally, therefore, as the season of active growth progresses the conditions favorable to spore germination increase and the number of pustules is increased as the foliage, tassels and silk increase to afford a suitable matrix for the conidia. The abundance of silk and the great amount of nourishment in the grains explain the enormous development of the smut boils, which often attain the size of a man's head. The infection is purely local; the disease does not spread, as is shown by the appearance of the smut boils at the point of infection two to three weeks after the conidia have made their entrance into the host. Thus, it is seen that infection may take place at any time in the growing season, and the longer the season of growth, the greater the infection is likely to be. It is reported that sweet maize is more susceptible to the disease than the ordinary field maize; estimates on the percentage of infection of the latter have been variously stated at from five-tenths to twenty-six per cent. It therefore follows that the extent of infection depends considerably upon five factors: (i) seasonal conditions, a rainy season tending to keep much of the conidia washed out of the air, while much dry weather is fatal to the germinative powers; (2) the thickness of planting, the moisture held by the plants being increased as the foliage is multiplied; (3) the presence of decayed vegetable matter; (4) manure, which may be infested with spores; (5) the degree of maturity of the different parts of the plant. The only practical method of prevention, so far as known, is to gather all smut pustules as they appear, care being taken to prevent scattering the black powder (spores), two or three times in the growing season and destroy them by burning or placing in boiling water. Great care should be taken, also, in seeing that, as iar as possible, the manure for the maize field is free from spores. Experiments have shown that the hot water treatment used for smut of oats and wheat is of no avail in combating maize smut; this is explained by the fact that inoculation of the host comes not from the seed but from the flying conidia which alight upon the growing plant. Maize smut has been fed to cattle in numerous instances in large quantities for a considerable period of time without apparent injury.l
323. Bacterial Disease.—There has been observed in Illinois and other North Central States a bacterial disease of maize, which not only does considerable damage to maize in some localities, but it is supposed that the germ which causes the disease in maize is able to cause a sudden and fatal disease in cattle,
IFor detailed study of maize smut, see Ind. Rpt. 1899 (12), pp. 84-135; also Farmers' Bui. 69; Kan. Bui. 62; Ohio Bui. 78.
called the corn-stalk disease. The first indication of the disease is the dwarfed condition of the young plant. This commonly occurs in spots of various sizes, and is found in rich places, rather than in those of poorer quality. The young diseased plants, besides being smaller than the healthy ones, are uniformly yellowish in color, the lowest leaves showing worst. Affected plants are easily pulled from the ground on account of the death of the lower roots. The inner tissue of the low;;r part of the stalk has a uniform dark color, while on the surface there are brownish corroded spots. After midsummer the leaf-sheaths become spotted with various sized patches of a watery-brown, half rotten in appearance, which are most conspicuous from the inner surface. The ears are at least occasionally affected. Internally, in the worst stage, the whole ear is reduced to a moist state of corruption. Very often these ears subsequently become mouldy, penetrated through and through by a close, very white, felt-like fungus. These mouldy ears are, in certain seasons, very numerous, and are readily recognized by the husker. No remedy is known. There appears to be in a considerable number of cases more injury on land which has been planted with maize the preceding year.
324. Bacterial Disease Of Sweet Maize.—Plants affected by this disease wilt and dry up very much like plants suffering from lack of moisture, except that there is little or no rolling of the leaves. Diseased plants are intermingled with healthy ones. The woody strands of the plant are filled with a multitude of short, yellow bacilli, which, when the stem is cut across, exude as a yellow viscid substance. The disease is confined to sweet maize, and is most destructive to early varieties. It is disseminated chiefly by means of the germs which cling to the seed. No remedy is known. The principal measures of prevention are selection of seed and the planting of resistant varieties.1
325. Maize Rust is found wherever maize is grown, but principally in regions of considerable rainfall. The rust does not differ materially in appearance from rusts of other grasses, particularly Pueciniagraminis of wheat and oats; the surface of the affected leaf and sheath displays small oblong or elliptical spots, which contain reddish-brown spores. Kellerman has shown that only the uredo and teleuto stages may be included in the life cycle, although Arthur has identified the aecidial stage on oxalis.2 It passes the winter in the teleuto stage. Though fungicides are effective, the rust is of such little economic importance as not to warrant treatment. Pammel reports decreased yields of sweet maize due to the rust. The rust also occurs on sorghum and Uredo stage or red teosinte. rust on maize
leaf Disease 32^* The Leaf Blight Fungus has been reported in produced by in- maize, causing extended or elliptical brown (dead) areas in the oculation by leaf blades, not distinguishable by the unaided eye. The disease Kellerman is of little economic importance.
1 N. Y. (Geneva) Bui. 130.
3 Botanical Gazette, July, 1904.
327. Insect Enemies.—Two hundred and fourteen species of insects are known to be more or less injurious to the maize plant. Insect injuries are more common and more extensive in the Southern States than in the Northern States. Except, however, for those insects which attack the young plant and make replanting necessary, destruction of the crop is seldom complete. The larger number of the injuries to maize occur after plowing up grass land of long standing, or are due to continuous culture of maize upon the same land several years in succession. Some of the insects also pass a portion of their life on or can use weedy plants for food. Generally, therefore, the most effective remedies against insect attacks are short and systematic rotations, accompanied by clean culture of the maize field and the surrounding territory. Where the land is neither in grass nor maize more than two years in succession the attacks of insects are comparatively limited; except, perhaps, in the case of certain migratory insects, such as the chinch bug, locusts and army worms, whose increase in numbers has been brought about by special conditions. The insects of most economical importance to growing maize are as follows:
(1) Wireworms (Elatcridxe).
(2) Cutworms (Noctuidae).
(3) White grubs (Lachtiosterna spp.)
(4) Corn root worms (Diabrotka longicornis Say and D. 12-punctata Oliv.).
(5) Corn root web-worms (Crambus spp.).
(6) Corn root louse (Aphis maidi-radkis Forbes).
(7) Corn bill bugs (Sphenophorus spp.)
(8) Corn ear-worm (Heliothis armiger Hubn.).
(9) Stalk borers (Noctuidae and Pyralidae), (10) Chinch bug (Blissus Uucoptirus Say) (151).
The insects most injurious to the stored grain are the same as those affecting stored wheat. (156)
328. Wireworms are the larvae of the large family of click beetles or "Jumping Jacks," eight species of which are known to be injurious to maize. 1 The worms vary in length from one-half to one and one-quarter inches, have a hard,