Take home messages

• Correct growth stage identification is critical for chemical application to work effectively.
• Crop growth stage development can tell you if a plant is growing abnormally in time to make corrective action.
• Grazing crops at the wrong growth stage can be very detrimental to yield.

Cereal identification

At the seedling stage, all cereal crops can look the same, but small differences for alert eyes can easily tell them apart.

Looking at the auricles (the clasping structures at the base of the leaves where they join the stem), wheat and triticale are small and hairy, cereal rye has a very small non-hairy auricle, barley is big and bare and paler in colour, and oats have none. The ligule (the see-through membrane surrounding the unrolling leaves at the base of a leaf) is small on wheat, notched and small on rye, medium size on barley and quite large on oats. When plants are very small, it can be quicker to dig up the plant and observe the remnants of the seed. This is the only way to tell triticale from wheat, where triticale seed is twice the length of wheat and darker in colour. In the early stages of growth, oat and wild oat leaves twist in an anti-clockwise way (when viewed from above), where the other cereals all twist clockwise.

Cereal growth stages

Leaves (Z11-19)

For consistency, just the number of leaves growing on the main stem are counted for a growth stage. Easier said than done. Up until leaf three, it’s easy as there will only be three leaves on a plant. The first leaf is easy to find (if not eaten) and characterised by a short leaf and a blunted tip (even when dead), all other leaves will have a pointed tip. Once you get four leaves, the presence of tillers can confuse the count. To find the main stem on any size plant, hang it upside down, clasp your hand around all the leaves and tillers and run your hand down, the main stem will be attached to the last leaf that you feel. Monitoring leaf emergence allows you to assess if the plant is growing normally and when a plant has six leaves on the main stem, you know it’s close to getting to the start of stem elongation and then the first node stage. A new leaf forms every 100 accumulated degree days (called the phyllochron) and this practically means about one every fortnight in winter and a leaf a week in spring. A hundred degree days is not set in stone, as counterintuitively, earlier sown crops have more degree days between leaves, while crops sown later than June, have less degree days between leaves. Estimating leaf emergence rates based on temperature forecasts can be quite handy for planning fungicide protection of upper leaves. The number of potential leaves a plant can grow on the main stem is determined by the variety and the sowing date. It can vary from just five for a spring wheat sown in summer to 14 in a winter wheat sown in March. The total number of leaves on the main stem is set very early after germination. Many herbicides have a minimum number of leaves required for earliest application and this can be two, three or four leaves on the main stem. Some herbicides have a maximum number of leaves required for application, as crop damage can occur if the plants are older when sprayed.

The emergence of the last leaf, the flag leaf, signifies no more leaf production and the start of booting where the head rapidly starts growing in size. Many herbicides have a cut-off for application at this time.

Tillering (Z21-29)

The first primary tiller should be easily visible forming at the base of the fourth leaf when the plant is around four true leaves. The second tiller will form at the base of the second leaf and the third tiller will form at the base of the third leaf. The fourth tiller is likely to form at the leaf sheath of the first tiller and is called a secondary tiller. The fifth tiller is likely to form at the leaf sheath of the second tiller. Further secondary tillers can form at the base of the first leaves of the tillers. Early planted winter habit cereal crops and some spring feed barleys can sometimes develop tertiary tillers, where tillers start developing in the leaf sheaths of the secondary tillers. Knowing this timing and behaviour allows you to notice when tillering is not happening and potentially make remedial N applications to boost mid-tillering. The third tiller will usually be appearing at about the six-leaf stage and close to the start of stem elongation in normal sowing time spring wheats.

Sometimes you can see a tiller forming below the first leaf and these are called coleoptile tillers, more common on winter habit types and with deeper sowing. This will appear to be growing from the seed. Counting of total tillers (mainstem plus tillers per m2) can be used to assess nitrogen response likelihood.

There are primordia for tillers formed at the bases of many other leaves and these are suppressed by the dominance of the first formed tillers. When the mainstem and tiller heads are killed off by mowing, grazing, frost or hail we get ‘regrowth’ (technically new growth) of those little undeveloped tillers (moisture permitting), once the first formed tillers are removed.

The main stem is attached to the fine primary root system, which is the first developed and grows to the greatest depth from the seed. Each tiller formed has to grow its own root system and these are the stouter secondary roots which anchor the plant and do much of the surface nutrient scavenging. The last tiller formed will therefore have the weakest secondary root system. This is why, when you see tiller death due to moisture or nutrient availability, the smallest tiller is the first to die. Later sown crops are prone to easier tiller loss due to a less developed secondary root system. Some herbicides can only be applied during the tillering phase. Early tillering would be described if one to two tillers are present, nominally a four-leaf plant. Mid-tillering when two tillers are present, a five-leaf plant. Late tillering would be when there are three or more, but a node is not visible, around a six-leaf plant. You need to be careful with this identification, as missing tillers (due to early nitrogen stress or waterlogging) can mean the plant is actually older and at a more advanced growth stage than what it appears.

Nodes (Z30-34)

The visual and tactile appearance of the first node indicates the start of stem elongation has occurred and in theory, this marks the end of tillering. In practice, small tillers that have formed, that are barely visible, can still grow and form heads. The small head has already been formed and from this stage on, will start setting the number of spikelets high and the number of florets wide that will be available for flowering. Practically, in normal sowing time varieties, the start of first node on the main stem is somewhere around the presence of the sixth to seventh leaf on the main stem. The presence of nodes is best found by splitting the stem in half with a sharp knife. The node first starts at crown level and will then start to be moved up by subsequent expansion between the node growth plates. The first node is not counted until the gap below it is greater than 1cm and the second node is not counted until the gap between it and node one is greater than 2cm. In practical terms, when the node is a few centimetres above the ground, it’s prone to being grazed by sheep and when it’s 5cm off the ground, it’s edible by cattle. The timing of stock removal in grazed crops to prevent severe yield loss is predicated on the first node growth stage not being eaten. If it’s removed, this necessitates firing up of the baby tillers to reshoot, which are rarely as large or capable of yielding as high, but are capable of a salvage situation.

Some herbicides can only be applied during the stem elongation stage and some must be stopped being applied once the crop reaches first node.

The second to third node stages are critical when considering timing of fungicides. At the second node stage, the flag -2 leaf is fully out but flag -1 and the flag leaf are still inside and get no coverage, in fact, the flag leaf is only a few millimetres long. At the three-node stage, flag -1 is fully unfurled and the flag leaf is still hidden and about one week out from unfurling.

Booting (Z41-49)

Once the flag leaf is fully emerged and until the first awns appear is called booting. The head is progressively pushed upwards by expanding internodes. The head increases in size and final floret number and spikelet height is being determined. Awn peep is the final application timing for a few herbicides. Severe frost at early booting can lead to complete head sterilisation in cereals. In barley, flowering occurs inside the boot before the head has emerged and frost damage at late booting can cause floral abortion.

Ear emergence (Z50-59) and flowering (Z60-69)

In wheat, about a week to ten days after awn peep, the ear will be fully out and start flowering. This is the critical time for flowering frost in wheat.

A wheat crop flowers in the middle third first, then the bottom third and then the top third. Frost at this stage can often take out different thirds of the head depending on its severity. The appearance of the anthers hanging outside the florets indicates that the crop has actually pollinated some days earlier.

Canola growth stages

Leaves

Counting canola leaves is one of the easier jobs in crop growth stages. When a leaf is fully unfurled to the sun, it is counted. The heart shaped cotyledon leaves that arise as the first things out of the seed are not true leaves. If the plant is cut/eaten off below the cotyledons, the plant can’t regrow new leaves or shoots and dies. Normal spring varieties might produce 10 to 15 leaves before the start of stem elongation, while winter varieties might produce up to 30. At higher leaf numbers, some of the older leaves have been shaded, senesced, died and fallen off. Some herbicides are able to be applied up until the six true leaf stage. Like wheat, leaf emergence rates in canola are driven by accumulated temperature and a new leaf in a normal sowing time crop takes 80odays. This can be useful in estimating the time to herbicide application windows opening or closing.

Stem elongation

The stem will start elongating by pushing the flower buds up by expanding internodal joints. There will be a leaf at the start of each node. The flower bud will be hidden at the early stages and the leaves need to be pulled back to see it. Eventually the developing flower buds will be visible but surrounded by leaves and this is called the green bud stage. Some fungicides use this stage as a cut-off. Subsequent node expansions will push the flower head above and eventually the green buds will turn yellow, indicating they are close to flowering at the yellow bud stage.

Flowering

Canola is an indeterminate plant and will continue to flower if temperature and moisture conditions are suitable. This makes the start of flowering easy, with the first visible flower opened. Some herbicides cannot be applied after this stage. The end of flowering will be when no more open flowers remain on the plant. ‘Flowering’ can be a short or long process, depending on variety and season. Generally, the longer the plant flowers for, the more it might yield. Canola can branch from the leaf axils joining the stem but when assessing flowering stages, only the main stem is considered. Usually, the branches are behind in their development.

The number of open flowers on a plant can be an important determinant of fungicide timing. The following flowering stages are when 50% of the plants in the paddock are exhibiting the following flowering amounts: 10% bloom is when the plant has around 10 main stem flowers open; 20% bloom is when there are 14–16 main stem flowers open; 30% bloom is when around 20 main stem flowers are open; and 50% bloom is when greater than 20 main stem flowers are open. Some fungicides can’t be applied past the 50% bloom stage.

Pulse growth stages

Leaves

Lupins (and navy, adzuki, mung, soy bean) start life differently to the other pulses, as they push their cotyledons above ground. Lupins are very vulnerable if the young plants are removed below the cotyledons as they can’t regrow. Lupins, where the stem is removed above the cotyledons, can regrow from the cotyledons but always at a decreased yield potential. In the early growth stages, the number of fully emerged true leaves attached to stem petioles are counted to determine the growth stage. Only count a leaf if it’s fully unfolded. Eventually, the main stem growing point reaches the reproductive stage and a green collection of flower buds sits at the top, called the big bud stage. Many herbicides have growth stage restrictions for application of two, four, six, and eight true leaves, and some finish at the big bud stage pre-flowering.

All other pulse crops (lentil, chickpea, pea, faba bean) send their first leaves up and leave the cotyledons in the ground. Leaves are attached to the stem and appear alternately on each side of a node. Only count a leaf if it’s fully unfolded. The growing point of new nodes and leaves is constantly being pushed up by elongating nodes. Many herbicides have requirements for starting or stopping application at the two to eight leaf, branch or node stage. These pulse crops also have small leaf like growths called scale leaves above ground level and before the first node. These are not counted as leaves or nodes. One to two branches can form from these scale leaves and are a point of regrowth if the main shoot is removed. Branches can also form at the nodes.

Useful resources

Identifying cereal seedlings

Using the growth stages of cereal crops to time herbicide applications

Fungicide management and timing - keeping crops greener for longer in the high rainfall zone

GRDC GrowNotes™ Canola section 4 plant growth and physiology

A visual guide to key stages in the growth and maturity of field pea 

Contact details

Dale Grey
Epsom VIC 3551
0409 213 335
dale.grey@agriculture.vic.gov.au
@eladyerg