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Growth stage 30-31

Course: Lodging control in cereals | Last Updates: 7th October 2015

 
Pete Berry (Dr)
Principal Consultant
ADAS High Mowthorpe
Biography >>
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Growth stage 30 marks something of a turning point for wheat as the crop shrugs off its winter tillering and starts a surge of spring growth. Management changes too, and best results from nitrogen, growth regulators and fungicides come from well-timed applications at GS30-31.

But identifying these key stages is not easy. You need a sharp knife and a keen grasp of the changes the plant is going through.

What are the key early growth stages to identify?

GS30 is close to the point when a wheat plant switches from producing leaf primordia (vegetative growth) to developing its ear (reproductive growth). The stem begins to elongate and it starts a period of rapid growth. This means it suddenly requires a lot more nutrients.

It usually coincides with the end of tillering. The plant will have reached its maximum number of tillers and is likely to lose up to around 50%. This shouldn't be a problem as many crops have more than 1000 shoots/sq m at this point, but will only need 500 shoots to head.

A crop will reach GS30 towards the end of March, although for some varieties in the south this may come in the first half of the month. GS 31 usually follows about two weeks later. But this depends on the weather and the variation is huge – it can be anything from a few days to a full month.

During these growth stages the plant builds tissue at the base of the stem. If there are few resources available for each tiller, e.g. because there are many shoots/m2, the resulting shoots are thin and weak and will be at high risk of stem lodging.

It's important to identify these growth stages, as they will be key timings for growth regulator applications and fungicides. The nitrogen you apply at this stage will also have a significant effect on the plant's early spring growth.

How do you identify GS30?

This is also known as the "ear at 1cm" or "pseudo stem erect" stage. It's the position of the immature ear that's crucial – you need to confirm that it has started to lift away from the base and that the stem is elongating.

Take at least six plants from the field to get a representative sample and dissect them carefully (see diagram). Make sure you are dissecting the main shoot, not a tiller. You should be able to identify the immature ear – no longer than a few millimetres.

The plant is at GS30 when the distance between the tip of the ear and the base of the plant is greater than 1cm.

How do you identify GS31?

This is more complicated. You need to dissect the plant, as before, and find the first node (see diagram). This will form just below the ear. If there is no node, the plant is still at GS30. If the first internode – the distance between the first node and the base – is less than 1cm, the plant is still at GS30.

The plant has reached GS31 when the first internode is at least 1cm long. You may already be able to identify the second node, which will appear above the first node. The plant remains at GS31 until the second internode – the distance between the first two nodes – reaches 2cm long.

The first node should not be confused with the tillering node or basal node which appears occasionally. This may appear just above the base, but will not extend to more than 1cm above the base (see diagram). In this case, the next node that appears will be the first true node. The first internode would be the distance between the first node and the tillering node.

How do you assess lodging risk?

Along with the varietal standing power, lodging risk is related to Green Area Index (GAI) – the area of leaf cover/sq m of soil surface. At GS30, a GAI above 1 represents a higher-than-average lodging risk. A GAI above 1.5 is high risk at GS31. As a rule of thumb, if half the ground is covered by crop at GS30, the GAI is 1. There are more accurate ways to assess this, such as taking a sample or using a photographic assessment tool, such as BASF's Canopy Assessment Tool (CAT).

What will growth regulators do?

Plant growth regulators (PGRs) applied at early stem extension inhibit the production of giberellic acid, which promotes cell elongation. Different PGRs affect different stages of biosynthesis of giberellic acid.

PGRs applied during this crucial period in the crop growth act on the stem cells near the base, preventing them becoming too long and weak and so ensuring the stem is shorter. It is worth noting that if chlormequat is applied after GS31, there is an increased risk of higher residues getting into the grain, although these are very seldom above the maximum residue limit.

How do you ensure success with PGRs?

Lodging risk is a combination of crop height, stem strength and root anchorage. So choosing a variety from the HGCA Recommended List with a high lodging resistance and establishing the crop to ensure good root anchorage and stem strength using appropriate plant spacing are key to keeping it standing.

Early PGRs that inhibit gibberellic acid biosynthesis generally work best at GS30 or GS31 when the crop is actively growing. A split dose, at GS30 and GS31, will bring even better results. If there is a high lodging risk, PGRs applied at these stages may have to be followed up with extra applications later on, including PGRs which produce ethylene which are effective at shortening the upper internodes

Watch videos of Pete Berry giving a step-by-step guide on how to identify growth stages 30 and 31 plus tips on managing lodging risk this season. Go to www.fwi.co.uk/identifying-gs30

Three Golden Rules

  • Dissect – you need a sharp knife to assess the growth stage correctly
  • Identify – correct detection of nodes and internodes will tell you the stage
  • Assess – you need growth stage, crop GAI and varietal lodging resistance to determine lodging risk
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