Much of the following text is taken from the Household Cyclopedia of 1881:

Wheat mildew may be ranked as a wheat disease which affects the ear, and is brought on by causes somewhat similar to those which occasion blight, though at a more advanced period of the season. If this disorder comes on immediately after the first appearance of the ear the straw will also be affected, but if the grain is nearly or fully formed then injury on the straw is not much discernible. We have seen a crop that carried wheat that was mildewed where the straw was perfectly fresh, though, indeed, this rarely happens. A severe mildew, however, effectually prevents both grain and straw from making any further progress, the whole plant apparently going backward every day till existence in a manner ceases altogether. Something akin to mildew is the gum, which, in all warm moist seasons, attaches itself to the ear, and often occasions considerable damage. All these different disorders are generally accompanied by insects, and by minute parasitic vegetable growths, considered by many to be the authors of the mischief that follows. Their appearance, however, may justly be attributed to the diseased state of the plant; for wherever putrefaction takes place, either in animal or vegetable substances, the presence of these parasites will never be wanting.

Another disorder which affects wheat and is by several people denominated the real rust, is brought on by excessive heat, which occasions the plants to suffer from a privation of nourishment, and become sickly and feeble. In this atrophic state a kind of dust gathers on the stalks and leaves, which increases with the disease, till the plant is in a great measure worn out and exhausted. The only remedy in this case, and it is one that cannot easily be administered by the hand of man, is a plentiful supply of moisture, by which, if it is received before consumption is too far advanced, the crop is benefited in a degree proportional to the extent of nourishment received, and the stage at which the disease has arrived.

Some people have recommended the sowing of blighted and mildewed wheat, because it will vegetate; though certainly the recommendation, if carried into practice, would be attended with imminent danger to those who attempted it. That light or defective wheat will vegetate and produce a plant we are not disposed to contradict, but that it will vegetate as briskly, or put out a stem of equal strength, and capable of withstanding the severe winter blasts as those produced from sound seed we must be excused for not believing. Let it only be considered that a plant of young wheat, unless when very early sown, lives three or four months, in a great measure, upon the nourishment which it derives from the parent seed; and that such nourishment can, in no view of the subject, be so great when the parent is lean and emaciated as when sound, healthy and vigorous. Let it also be remembered that a plant produced from the best and weightiest seed must, in every case, under a parity of other circumstances, have a stronger constitution at the outset, which necessarily qualifies it to push on with greater energy then the season of growth arrives. Indeed, the economy of nature would be overturned should any other result follow. A breeder of cattle or sheep would not act more foolishly, who trusted that a deformed diminutive bull or ram would produce him good stock, than the corn farmer does who uses unsound or imperfect seed.

See also

• QoI
• strobilurins
• Powdery mildew