Disease Management in Cereals

Once fields are properly scouted, data can be used to determine insect control options. Course of action should be started only when you are fully armed with up-to-date, accurate information writes Thomas Kipkorir

Wheat and Barley farmers rank disease as one of the top factors limiting wheat and barley yields on their farms. Disease management is a key component of high-yielding wheat. Some diseases, such as take – all disease, must be managed proactively and cannot be controlled once they are established. Other diseases, such as foliar diseases caused by fungi, can be managed by the timely application of foliar fungicides.

Scouting for disease
Scouting for disease is very important for two reasons. Yearly scouting helps you to build an on-farm database that can be used to select appropriate disease management tactics for future crops. Scouting also helps you determine if and when to spray fungicides. Once fields are properly scouted, data can be used to determine disease control options. Course of action should be started only when you are fully armed with up-to-date, accurate information.

Most wheat producers have their total disease management program in place once the seed is in the ground. By that time, decisions have been made relative to crop rotation, tillage/ seedbed preparation, variety selection, seed quality, seed treatment, planting date, seeding method, seeding rate, and soil fertility. Individually and collectively, these decisions can play an important role in influencing which diseases develop, their severity, and their effect on crop yield and weight. Because pre-plant and planting decisions are important in the management of wheat diseases, you need to understand how they affect disease.

Variety selection
Decisions relating to variety selection are, perhaps, the most important decisions in managing diseases. Every commercially available wheat variety has a unique range of reaction to common diseases. Which and how many varieties are planted determines the potential for certain diseases. Failure to consider the implications of variety selection in managing diseases is a costly mistake made by many wheat farmers. Select two or three varieties with the greatest amount of available resistance to the diseases most common in the growing region. It is important to plant more than one variety for this key reason: it is common for a single disease to severely damage a single variety of wheat or barley. When multiple varieties are planted, your risk level is reduced. Planting more than one variety, especially when different maturities are represented, also can help with the logistics of harvesting.

Crop rotation
Crop rotation helps in the management of wheat pathogens that survive between wheat crops in wheat residue. When a crop other than wheat is grown in a field, levels of wheat pathogens decline. This occurs simultaneously as the residue of previous crops deteriorates. Reduced levels of pathogens can translate into reduced disease pressure the next time wheat is produced. Rotation is helpful in the management of hidden diseases, such as Pythium root rot, and destructive diseases, such as take- all. Rotation of fields out of wheat and barley is the only practical means of controlling take- all disease. Rotation also can reduce infections by the fungi Stagonospora and Septoria. However, spores’ blowing into fields from neighboring fields reduce the effect of rotation on these diseases. Maize is generally a good nonhost crop to grow in rotation to wheat.

Tillage / cultivation
Ploughing wheat residue hastens the breakdown of residue that harbors certain disease organisms. This can help reduce levels of take – all and foliar diseases, such as Septoria leaf blotch and tan spot. For fields in a maize rotation, tillage prior planting maize should cause a significant decline in surviving wheat stubble. The year between wheat crops in this rotation also helps, except where high levels of the take- all fungus exist. In those cases, two or more years between wheat crops may be required. To achieve the highest possible yields, sufficient stands are very necessary.

To achieve the desired stands, excellent seed germination and development of seedlings is required. Using high- quality seed treated with a broad – spectrum fungicide and good planting techniques help good stand establishment.

Excess stands, however, encourage foliar and head diseases by reducing air circulation and light penetration into the canopy later in the season. Calibration of the equipment ensures achievement of sufficient but not excessive stands.

Nitrogen fertility
Too much nitrogen in the previous crop can encourage excessive growth that can increase problems with barley yellow dwarf and most foliar disease caused by fungi. Increased problems with barley yellow dwarf are as a result of an extended period of aphid activity when stands are dense. The same situation encourages infection and carry-over of foliar diseases, such as leaf rust, powdery mildew, and leaf blotch complex.

Fungicide application
All fungicides must be applied within specific growth-stage. Fungicides provide the greatest benefit when plants are protected from disease between flag leaf emergence and soft dough. The most critical stage is typically from mid head emergence through flowering. This is the period in which fungicide applications are often most beneficial.

Thomas Kipkorir Is The Country Manager, Crop Protection And Health Business At Basf.