|ITIS 42236 (http://www.itis.usda.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=42236) 2002-09-22|
Crop management decisions require the knowledge of stage of development of the crop. In particular, spring fertilizers applications, herbicides, fungicides[?], growth regulators[?] are typically applied at specific stages of plant development.
For example, current recommandations often indicate the second application of nitrogen be done when the ear (not visible at this stage) is about 1 cm in size (Z31 on Zadok scale). Knowledge of stages is also interesting to identify periods of higher risk, in terms of climate. For example, the meļosis stage is extremely suceptible to low temperatures (under 4°C) or high temperatures (over 25°C). Farmers also benefit from knowing when the flag leaf (last leaf) appears as this leaf represent about 75% of photosynthesis reactions during the grain filling period and as such should be preserved from disease or insect attacks to insure a good yield.
|Several systems exist to identify crop stages (the Feekes scale, the Zadocks scale being the most widely used). Each scale is a standard system which describe successive stages reach by the crop during the agricultural season. Wheat spiklet with its three antheres sticking out|
Wheat is subject to more diseases than other grains, and, in some seasons, especially in wet ones, heavier losses are sustained from those diseases than are felt in the culture of any other culmiferous crop with which we are acquainted. Wheat may suffer from the attack of insects at the root; from blight, which primarily affects the leaf or straw, and ultimately deprives the grain of sufficient nourishment; from mildew on the ear, which operates thereon with the force of an apoplectic stroke; and from gum of different shades, which lodges on the chaff or cups in which the grain is deposited.
Viral diseases and viruslike agents
Harvested wheat grain is classified according to grain properties for the purposes of the commodities market. Wheat buyers use the classifications to help determine which wheat to purchase as each class has special uses. Wheat producers determine which classes of wheat are the most profitable to cultivate with this system.
Wheat in the United States Classes used in the United-States are
Hard wheats are harder to process and red wheats may need bleaching. Therefore, soft and white wheats usually command higher prices than hard and red wheats on the commodities market.
Much of the following text is taken from the Household Cyclopedia of 1881:
Wheat may be classed under two principal divisions, though each of these admits of several subdivisions. The first is composed of all the varieties of red wheat. The second division comprehends the whole varieties of white wheat, which again may be arranged under two distinct heads, namely, thick-chaffed and thin-chaffed.
The thick-chaffed varieties were formerly in greatest repute, generally yielding the whitest and finest flour, and, in dry seasons, not inferior in produce to the other; but since 1799, when the disease called mildew, to which they are constitutionally predisposed, raged so extensively, they have gradually been going out of fashion.
The thin-chaffed wheats are a hardy class, and seldom mildewed, unless the weather be particularly inimical during the stages of blossoming, filling, and ripening, though some of them are rather better qualified to resist that destructive disorder than others. In 1799, thin-chaffed wheats were seriously injured; and instances were not wanting to show, that an acre of them, with respect to value, exceeded an acre of thick-chaffed wheat, quantity and quality considered, not less than fifty per cent. Since that time, therefore, their culture has rapidly increased; and to this circumstance may, in a great measure, be attributed the high character which thin-chaffed wheats now bear.