Identifying Wheat Stages for Fungicide Application
Timing of fungicide application to wheat is critical.
- [John] Control of various leaf diseases of wheat with fungicides has been practiced for many years.
But more farmers are applying fungicides in recent years because of the availability and effectiveness of newer products that provide some control of another serious disease that these older products did not, Fusarium head blight, also known as head scab.
Both types of control require careful application timing but at different stages of growth of the wheat.
The goal of this video is to help wheat farmers and field scouts identify when wheat is entering these critical growth stages.
Foliar diseases, such as powdery mildew, will first be seen on the lowest leaves of wheat plants.
Even if disease is present early in a season, spraying is not necessarily recommended at this time.
Instead, monitor the progress of these diseases.
If they continue to move upwards on the plant, then protection is recommended before yield losses occur from damage to the upper leaves.
Fungicide applications for foliar diseases are most effective when applied soon after the last leaf, the flag leaf, has begun to emerge.
So the question is, with leaves unfurling from inside the stem, how do you know when a leaf emerging on a wheat plant is, in fact, a flag leaf?
Here is a way to tell if the flag leaf is emerging instead of one of the lower leaves.
Collect a few wheat plants.
Dig them out so the lowest parts of the stems remain intact.
Pick out the more advanced stems.
The first thing to look for is the first node that forms on the stem.
This should be somewhere between one and three inches above the soil line.
Strip off the lowest leaves to reveal the first node.
Once you strip off the leaf that was located just above this first node, fully revealing it, there will be three more leaves left on the plant between the first node and the flag leaf.
If you only see three leaves, then the flag leaf has not yet emerged from the whorl.
When you see the fourth leaf emerging, then you know that this is the flag leaf.
Another method that you can use in conjunction with counting leaves, is to look for the formation of the third node.
You will be able to feel the third node just above the second node if the flag leaf is beginning to emerge.
And if you cut the stem open just above the third node, you will be able to see the early stages of the head beginning to develop.
If the disease has progressed up the plant and reaches action threshold guidelines, a fungicide application should be made when the flag leaf is from half to fully emerged.
The next important growth stage to know for fungicide application is flowering, as it is critical to apply fungicides for head scab control early in the flowering period, and strobilurin class fungicides commonly used for leaf diseases should no longer be applied once the wheat is beginning to flower.
Wheat heads begin to emerge about 10 days after the flag leaf is completely out of the stem.
After heading, flowering begins in as little as three days, but could be up to 10 days depending on the temperature.
The emergence of anthers on the wheat heads shown in this photo, is the sign that it is flowering.
It is critical to know when wheat begins to flower, because the flowering stage is when head scab infection occurs, therefore, fungicides for head scab control have to be applied at the onset of flowering before infection by the pathogen.
It is essential to know when flowering is beginning, because it only lasts about five days.
These photos were taken with a time lapse camera, showing the progression of flowering over the course of five days in May of 2016.
And remember, well-timed applications of fungicides are only part of a comprehensive wheat disease control strategy that supplements the use of resistant varieties, balanced nitrogen rates, and minimizing the risk of infection from the preceding rotational crop and residue.