Cereals 2024 Week 9-B Growth Regulation in Cereals

lodging occurs when the forces of gravity pulling stem to ground are greater than those keeping it standing

key parameters are – stem strength – crown roots

stem lodging, root lodging or a combination of both stem and root lodging

A greater lodging force

– height of stem – weight of stem (and ear

– bending or breaking of stem bases

• stem diameter, • stem thickness, • degree of lignification

modern wheat varieties have short, thick stems and the forces required to break/bend stems are usually far in excess of the self weight moment in most crops

-lodging due to stem failure is not very common in wheat crops – the occurrence of stem disease, eyespot can also lead to stem lodging

barley crops are much more prone to this type of lodging as they tend to be taller with weaker stem bases

the ability of the cereal root system to keep roots anchored in the ground depends largely on the thick basal regions of the roots - crown roots, which only extend a few cm’s into the soil

– number and spread of crown roots – crown root length and strength

root lodging occurs when the crown root system rotates through the soil profile under a high lodging pressure (overturning force)

1- decrease crop height 2-* increase stem strength – increase stem diameter – increase stem thickness 3* increase root anchorage – by increasing crown root volume – by having firm seedbed characteristics? Growth regulators

1* use the ‘standing power’ ratings when choosing varieties – shortness of straw – strength of straw 2* site factors – fertility of the field – site aspect : is it exposed to wind effects 3* sowing date – most relevant to winter wheat, e.g. higher lodging risk with early sowings unless sowing rates are reduced significantly

As Fertiliser rate increased the higher % of lodging occurred

• plant growth and reproduction is controlled by hormones – key ‘growth’ hormones are auxins, gibberellins and kinins • PGRs can be used to manipulate the internal hormone activity of the plant

1- in cereals the gibberellin hormones increase internode length and anti-gibberellins stop this 2-chlormequat (CCC) is a growth retardant which inhibits gibberellin synthesis 3- this activity was observed by Tolbert (1960) and over the last three decades, the use of CCC for straw shortening has been an integral part of the crop management in cereals 4- CCC has shortening and strengthening effects – the time of application will determine the effect with earlier timings giving more strengthening and later timings giving more shortening

1- timing is very important – key timing is before GS 31 (first node) – temperature is critical (5-60 C air temp.) 2- rate will depend on timing and on crop – lower rates used on spring-sown cereals – typical rate is 1.5-2.0 l/ha of 75% CCC , - ~3 l/ha of 46% CCC 3- in high risk situations a split appl. may be used – 2/3 of the total dose at GS. 22-23 (mid-tillering) – 1/3 of the dose at GS. 30-31 4- on Winter Oats a split-appl. is used with GS 31-32 and GS37 timings

1- Ethephon inhibits auxins and is sold as Cerone – commonly used on winter barley at GS 32-45 2- Mepiquat chloride inhibits gibberellins and is sold as Terpal – key timing is GS 32 to GS 37-39 on wheat and barley 3- trinexapal ethyl is sold as Moddus and has uses on winter cereals – claims for its performance in reducing both stem and root lodging risk – variety profiling for risk of stem and root lodging and product timed accordingly 4- Meteor is a chrormequat-based product with imazaquin added to increase performance and also the spray- window

Lodging levels were extremely high on many of the heritage lines. • All were salvageable but caused a lot of mechanical problems. 4 breakdowns due to lodging, all attributable to older genetic material.