27 July 1998
Brown tips on wheat flag leaves
I HAVE noticed brown tips on the flag leaves of our wheat. We have
Reaper, Buster and Raleigh and there is no difference between any of them. I am aware of this problem in other areas, but wondered if anybody had any new
information – little seems to be known.
Darren Lovell, IACR-Long Ashton
IM studying crop growth and canopy structure as part of the Septoria epidemiology programme at Long Ashton. This involves extensive and detailed crop monitoring throughout canopy expansion and provides an insight into the interactions between crop growth and disease progress.
I have seen tipping on a range of cultivars subjected to several treatments, across four seasons. Here are a few factors that may give us an insight to the mystery:
- General Observations (Not based on assessment or analysis):
- Tipping occurs, predominately on the flag leaf regardless of fungicide;
- PGR treatments appear to increase tipping;
- There is a cultivar effect;
- There is a seasonal effect;
- Tipping is generally confined to the area of the leaf above the “crimping mark”.
- Leaf crimping:
This occurs when the ligule of the expanding leaf and the last fully expanded leaf come together in the culm and constrict the next emerging leaf. e.g GS37.
Leaf three is fully emerged, the ligule of leaf two is not yet visible but is just beneath that of leaf three, the flag leaf is just starting to emerging and is being constricted by the ligules of leaves 2 and 3. This constriction causes a crimping mark on the leaf tip, that in some seasons, or on some plants within the crop, can be severe enough to cause damage to the leaf. This site of damage is often associated with infections of Septoria.
However, even when Septoria is not present, senescence can be observed along this line. As the crop matures, this crimping mark becomes more evident. The leaf can be folded at this point as if it were creased. I believe that the cellular damage that is caused by this crimping may be responsible for a large proportion of leaf tipping.
Like leaf tipping, crimping is most evident on the flag leaf.
When PGRs are applied, stems are thicker and crop growth is slow, thus the two ligules are together for a longer period of time.
Cultivars that have a rapid rate of stem extension appear to experience less tipping, e.g in Cadenza. This cultivar has less crimping as the flag often emerges after the two ligules have passed and when if the two ligules do meet when the flag is emerging then it is for a shorter time.
If the weather is cold, the crops growth is slowed and the period of crimping can therefore be increased. At Long Ashton this year, the weather was relatively cool during the GS37 period and the crimping effect was more visible than in previous years.
If you combine these observations you start to get a convincing case. I am sure that there are other factors involved that will contribute to tipping and look forward to reading the views of others.