Developing Crops
Wheat normally needs between 110 and 130 days between planting and harvest, depending upon climate, seed type, and soil conditions (winter wheat lies dormant during a winter freeze).
Optimal crop management requires that the farmer have a detailed understanding of each stage of development in the growing plants. In particular, spring fertilizers, herbicides, fungicides, growth regulators are typically applied only at specific stages of plant development.For example, it is currently recommended that the second application of nitrogen is best done when the ear (not visible at this stage) is about 1 cm in size (Z31 on Zadoks scale).
Knowledge of stages is also important to identify periods of higher risk from the climate. For example, pollen formation from the mother cell, and the stages between anthesis and maturity are susceptible to high temperatures, and this adverse effect is made worse by water stress.
Farmers also benefit from knowing when the ‘flag leaf’ (last leaf) appears, as this leaf represents about 75% of photosynthesis reactions during the grain filling period, and so should be preserved from disease or insect attacks to ensure a good yield.
Several systems exist to identify crop stages, with the Feekes and Zadoks scales being the most widely used. Each scale is a standard system which describes successive stages reached by the crop during the agricultural season.
Diseases
There are many wheat diseases, mainly caused by fungi, bacteria, and viruses.
Plant breeding to develop new disease-resistant varieties, and sound crop management practices are important for preventing disease.
Fungicides, used to prevent the significant crop losses from fungal disease, can be a significant variable cost in wheat production.
A wide range of organisms infect wheat, of which the most important are viruses and fungi.
The main wheat-disease categories are:
- Seed-borne diseases: these include seed-borne scab, seed-borne Stagonospora (previously known as Septoria), common bunt (stinking smut), and loose smut. These are managed with fungicides.
- Leaf- and head- blight diseases: Powdery mildew, leaf rust, Septoria tritici leaf blotch, Stagonospora (Septoria) nodorum leaf and glume blotch, and Fusarium head scab.
- Crown and root rot diseases: Two of the more important of these are ‘take-all’ and Cephalosporium stripe. Both of these diseases are soil borne.
- Viral diseases: Wheat spindle streak mosaic (yellow mosaic) and barley yellow dwarf are the two most common viral diseases. Control can be achieved by using resistant varieties.
Pests
Wheat is used as a food plant by the larvae of some Lepidoptera (butterfly and moth) species including The Flame, Rustic Shoulder-knot, Setaceous Hebrew Character and Turnip Moth. Early in the season, birds and rodents can also cause significant damage to a crop by digging up and eating newly planted seeds or young plants. They can also damage the crop late in the season by eating the grain from the mature spike. Recent post-harvest losses in cereals amount to billions of dollars per year in the USA alone, and damage to wheat by various borers, beetles and weevils is no exception.
Rodents can also cause major losses during storage, and in major grain growing regions, field mice numbers can sometimes build up explosively to plague proportions because of the ready availability of food.
To reduce the amount of wheat lost to post-harvest pests, Agricultural Research Service scientists have developed an “insect-o-graph,” which can detect insects in wheat that are not visible to the naked eye. The device uses electrical signals to detect the insects as the wheat is being milled. The new technology is so precise that it can detect 5-10 infested seeds out of 300,000 good ones.
Tracking insect infestations in stored grain is critical for food safety as well as for the marketing value of the crop.
