Stage 1: VE to V6

Establishment phase

Problems at this stage can be caused by any number of interacting factors.

First, determine the extent and severity of any problems as this will help eliminate some of the possible causes. Is the problem confined, patchy, localised or widespread? Is there a problem with emergence? If so, have a dig where there are gaps to find out what proportion of missing seedlings are due to skips and what proportion of seeds are dead or just slow to germinate.

Check for small/weak plants. Are there any problems with abnormal development of slow-germinating seedlings? Try to find out what has caused them to lag behind. Other than size is there anything abnormal about them? Were they late emergers? If so why? Check seed-soil contact and their roots. Have they been affected by some pest, disease or other factor(s) or were they simply weaker plants/seeds?

If you are concerned about the level of establishment, undertake plant counts to assess stand establishment, including abnormal and chewed seedlings, skips, doubles and dead seeds. Do this in at least 10 representative locations across each field. If emergence is variable across the field split it into zones. Look closely for signs of root burning (fertiliser placement) in emerged plants, and insect or disease damage in abnormal, emerging or dead seeds/seedlings.

Try to understand what is going on. Remember that seed is a living organism and there may be differences not only between hybrids but also different seed lots of the same hybrid.

Despite strict quality control measures implemented by all leading seed companies, there are natural differences in germination % and vigour between seed lots and just like seed companies, growers must accept that there will be differences between seed lots and hybrids. Furthermore, some treatments are tougher on the seed than others. It is recommended that seed be sown in the same season of purchase to mitigate any issues that may arise from carryover seed.

One of the biggest and often overlooked causes of poor emergence is waterlogging. The process of imbibition (seed rehydration) causes trauma to the embryo and the rate at which this happens can have a marked effect on the embryo’s ability to overcome the cellular damage that occurs.

 

If conditions are near optimal during the imbibing and germination period, then emergence will be close to the germ % (germ test result) on all but the lowest vigour seed lots.

High-vigour seed lots are less likely to have problems in cold and/or wet conditions than lower-vigour seed lots. At present, there is no standard seed vigour test for maize which makes it impossible to compare vigour test results from different seed companies.

The following section details what to look out for during the crop establishment phase.

SKIPS (NO SEED OR SEEDLING)

Planter error

Dig for seed where there are skips to determine if seed is present or not. If there is no seed, check planter settings and maintenance prior to next planting.

Rodents or birds

Check for damaged and/or partly eaten kernels. If the problem is severe and widespread, consider replanting worst affected areas. In future consider preventative measures including seed treatments, baiting and/or population control.

SEED LOOKS NORMAL BUT HAS NOT IMBIBED (SWOLLEN)

Cold, dry

In the future either "plant to moisture" if the soil is dry, ensure adequate moisture is present before planting or irrigate after planting.

Poor seed-soil contact, cloddy soil

In the future check seed-soil contact when planting, adjust down force, press wheels and/or residue managers if necessary. Revise tillage practices or soil conditions at cultivation if the soil is cloddy.

Dead seed

If suspected dead seed is greater than 10% request an inspection from your seed supplier.

SEED HAS IMBIBED (SWOLLEN) BUT NOT GERMINATED

Unfavourable soil conditions

Cold, wet soil.

Fertiliser or pesticide injury

Residual herbicide damage or excessive fertiliser too close to seed.

Dead seed

If suspected dead seed is greater than 10% request an inspection from your seed supplier.

SEED GERMINATED BUT DIED BEFORE EMERGING

Seed rot

Check seed treatment used, this should include fungicide; but several species of bacteria may also be involved. Seed rot tends to be prevalent in cold or very warm, wet soils, and/or where high rates of raw manure have been applied.

Fertiliser injury

Seed may have germinated but roots appear stunted or burnt. In-furrow (pop-up) fertilisers with high salt indexes are the most risky; it is safer to apply these fertilisers 5 cm below and 5 cm to the side of the seed.

Pests

Slugs and black beetles can chew the growing point (shoot meristem) beneath the soil. Closely inspect the damaged seedlings for signs of chewing.

SEEDLING TWISTED/TANGLED UNDERGROUND

Unfavourable soil conditions

Crusted, cold or cloddy soil. A cloddy soil can allow light to penetrate the soil disrupting normal “spike” emergence.

Seed planted too deep

Aim for 4-5 cm planting depth with good seed-soil contact; only plant shallower if the soil is already damp and rain is forecast in the first few days after planting. Do not plant shallower than 3 cm as there is an increased risk of nodal root development problems during the establishment phase.

Chemical injury (tatters)

Can be caused by pre-emergent herbicides including acetachlor and metolachlor especially in very light, or cold/wet soils where seedling emergence is delayed; pre-plant incorporation of these herbicides may increase risk in some situations (e.g. light and/or cold/wet soils).

SLOW, UNEVEN EMERGENCE

Unfavourable soil conditions

Cold, dry, wet, cloddy or crusted soil.

Seed planted too deep or too shallow

In the future pay attention to seed depth placement in different areas of the field while planting, especially where soil conditions change.

Variable planting depth

Usually caused by excessive planter speed and/or uneven soil surface. In the future check seed depth uniformity during planting and adjust planter/speed as required.

Poor seed-soil contact

In the future check seed-soil contact while planting when soil conditions are changeable and adjust planter set-up if necessary.

Low seed vigour

Talk to your seed supplier if you are concerned and other causes are unlikely.

SEEDLING PROBLEMS FROM VE TO V6

By now the crop has emerged and the transition from seed reserves to photosynthesis progresses as rapidly as development of the nodal root system allows. A delay in the development of the nodal root system will cause a corresponding delay in the transition from seed reserves to soil nutrient uptake. During the early part of this transition the seedling is particularly vulnerable to attack from soil borne pests and diseases. Various pests and diseases can affect the mesocotyl (the thin “stalk” between the seed and the growing point) which can have a marked effect on the rate of nodal root and seedling growth and development. Seed fungicide treatments or in-furrow applications help to protect the seed and young seedling from fungal attack but in some conditions and for some pathogens, this protection may be inadequate. Furthermore, bacteria are not deterred by fungicides and chewing insects or birds do damage before they are controlled or deterred by some seed treatments. This highlights the importance of ensuring your crop protection plan is well thought out prior to ordering the seed.

SEEDLINGS UPROOTED

Birds/rodents

Common culprits are pheasants, pigeons, pukekos and rats. If the problem is severe and widespread, consider replanting. In the future consider preventative measures including seed treatments, baiting and/or population control.

SLOW, UNEVEN PLANT GROWTH

Unfavourable growing conditions

Cold, dry, wet, or compacted soil.

Starter fertiliser placement problems

Check for patterns in row vigour/growth across the field. Are they systematic and related to planter passes? Is the fertiliser blocked, placed too close or distant from the seed furrow? Starter fertiliser should be placed 5 cm below and 5 cm to the side of the seed furrow. In the future check fertiliser placement during planting, focusing on headland/turning exits to help identify issues.

Herbicide injury

Check for patterns across the field, focus on sprayer overlaps around headlands and uneven contour. Check the chemicals used, label application rates and timing.

Nutrient deficiency

Usually associated with other symptoms including discoloured leaves (see Discoloured leaves ). If a deficiency is suspected, collect plant tissue samples to determine the nutrient balance.

Insects, slugs

Check for insect and/or slug damage. Apply remedial action if necessary.

Variable planting depth

Check uniformity of seed depth and root development. Planting too shallow can affect nodal root development especially in dry, loose, cloddy soil and/or windy conditions. In the future ensure a correct and even planting depth is achieved and adjust speed and downforce if necessary.

Low seed vigour

Talk to your seed supplier if you are concerned and other causes are unlikely.

DISCOLOURED LEAVES

Nutrient deficiency

The most common nutrient deficiencies are N, P, K, S, Mg and Zn at this stage (see Leaf Abnormalities for specfic symtoms). Usually, N, P, K, S and Mg availability can be adequately forecast in soil tests. Collect plant tissue samples from affected and normal areas to analyse for a deficiency. Apply remedial action if the deficiency is widespread and necessary.

Frost and cold temperature stress

This includes frost and near frost events. Frosted plants will appear burnt, pale and weak. Check the growing point (below the ground) for damage. Usually worse in low-lying areas. Plants usually recover providing the frost is not too severe or late. Widespread, severe frost at V4 or greater may require replanting. Quantify the affected area and severity and seek advice before making the decision to replant.

Large temperature variations

Cool nights and warm days promote shoot growth over root growth which can limit nutrient uptake, making shoots appear pale and/or unthrifty.

High rainfall and wet soils

Perfect conditions for nutrient losses (leaching and denitrification). Collect tissue samples to determine any deficient nutrient(s) and try to correct any deficiencies if it is economically viable and possible.

Compaction

Affects root growth and nutrient uptake. In the future reduce and alleviate compaction with deep ripping and limit wheel traffic before and after planting. There are a multitude of crop management systems that can minimise the risk or severity of compaction.

Disease

Diseases such as anthracnose can cause yellowing and blotchy patches (lesions) on the leaves of young plants. Most prevalent in wet conditions, particularly ponded areas. Plants will usually recover but may be prone to stalk rot during the grain drydown period. Monitor affected areas during this period.

Insects and slugs

Chewing may be accompanied with chlorosis (yellowing) or other pigmentation (e.g. purpling) and general unthriftiness. Apply control measures if damage is widespread. In the future consider the merits of preventative control measures.

Herbicide injury

Leaves may appear pale, bleached and/or scorched. Symptoms are usually worse in overlap areas so focus on headland and contoured areas. Always check chemicals, the compatibility of mixtures used and application rates/calibration before spraying. Some herbicides can interact with some insecticides including seed treatments so again, check compatibility before spraying.

Fertiliser injury

Leaves can appear pale, bleached and/or scorched. Check roots for signs of damage as well as starter fertiliser placement and application rate.

Mechanical injury

Includes tyre damage and machinery. Check roots and shoots for damage. If the damage is significant or widespread ask the question “how do we avoid the same problem in future?”.

Hybrid differences

Some hybrids are naturally darker or lighter in colour than others. Providing the crop looks uniform with healthy roots and shoots, subtle differences in colour should not be of concern. Take notes on differences in colour between hybrids for future reference.

Drought

In dry conditions plants may take on a pale and/or greyish tinge, which is usually accompanied with leaf rolling; particularly during the heat of the day (see Leaves rolled ).

LEAVES ROLLED (PINEAPPLED)

Drought

Leaf rolling can occur in very hot conditions, even in seemingly moist soil. More often leaf rolling will occur when the soil is approaching the critical soil moisture deficit where water uptake cannot service transpiration requirements. If possible, apply irrigation before this point to avoid reducing nodal root development which may affect yield.

Insects

Insects feeding on roots reduces water uptake causing leaves to wilt. Check roots for damage.

Mechanical root damage

By side dressing or weeding implements. Check roots for damage.

LEAVES COILED, TWISTED, LADDERED OR WHIP-LIKE

Herbicide injury

Certain pre and post-emergence herbicides can cause leaves to curl or twist. Sometimes this is a temporary phenomenon, whereas at other times the problem can last for weeks, reducing the yield potential of affected plants.

Temperature variation

Alternating hot and cold weather induces alternating periods of fast and slow growth, this can cause developing/emerging leaves to become entangled.

Mechanical damage

This is often caused by crushing of the leaf whorl from tractor tyres etc.

Hail or frost damage

Damage to the leaf whorl can cause leaves to become entangled.

Nutrient imbalance

Calcium deficiency can cause leaves to entangle and become laddered. It is rare but collect tissue samples if there is no other logical explanation.

LEAVES CHEWED, SHREDDED OR MISSING

Slug/insect damage

Slugs, Argentine stem weevil (ASW), or cutworm.

Animal grazing

Common culprits are hares, stock and birds.

Wind or hail damage

Wind causes abrasion of leaves on the soil surface. Hail damage is usually accompanied with ponding and/or soil splashing onto leaves and into whorls.

LEAVES PALE, SCORCHED, SPOTTED, STRIPED OR DEAD

Wind damage

Most common on exposed lighter textured (sandy) soils in high wind-run areas.

Nutrient damage

Most commonly N, P, K, S, Mg and Zn. Collect plant tissue and soil samples from affected and normal areas for analysis. If the deficiency or imbalance is widespread seek advice on remedial action.

Disease

Anthracnose (prevalent in ponded areas) or bacterial wilt (prevalent in cool, wet soils).

Herbicide injury

Spray drift from neighbouring crops or overlaps (check headlands and contoured areas).

Hybrid differences

Some hybrids are more susceptible to the possible causes of leaf scorching, spotting or striping; and because one hybrid doesn’t show any symptoms this doesn’t mean that another hybrid will be unaffected by a potential causal agent.

PLANTS WILT, FALL OR DIE SUDDENLY

Insect damage

Argentine stem weevil (ASW) larvae, cutworm or black beetle. Check for signs of insect chewing above and below ground.

Disease

Phythium seedling blight (damping off) or bacterial wilt.

PLANTS BROKEN, LEANING OVER OR SNAPPED OFF

Uneven planting depth

Shallow planted seed may not develop a strong nodal root system and may be prone to falling/leaning. If the problem is widespread consider mounding the soil around the base of the plants to provide an opportunity for nodal roots to develop (effective before V4).

Insect damage

Common culprits are cutworm (plants chopped off) and Argentine stem weevil (ASW) larvae (plants wilt from the growing point with an accompanying hole in the stem at or just below ground level). Cutworm can be controlled by spraying a synthetic pyrethroid while ASW can be controlled by seed applied insecticide Poncho®.

Herbicide injury

Especially caused by 2,4-D or similar (auxin-type) products followed by a strong wind event. These products can make plants brittle and susceptible to lodging and green snap.

Wind damage

Severe winds can cause plants to fall or snap. If nodal roots have properly developed it is unlikely that plants will fall at this stage unless the soil is very loose and/or wet. More common is green snap where plants snap off above ground level once the stems start to elongate.

PLANTS ABNORMAL WITH MULTIPLE TILLER AND/OR STUNTED MAIN SHOOT

Insect damage

Most common culprit is Argentine stem weevil (ASW) larvae but other insects cannot be discounted.

DAMAGED, CHEWED OR ABNORMAL ROOTS

Herbicide injury

Particularly phenoxy-type products such as dicamba can affect nodal and brace root development. Typically, this is only a problem if applied too late (after V6) or at higher rates. Some hybrids are more susceptible to these herbicides so check tolerance to phenoxy herbicides before application. If concerned ask your seed supplier.

Insects

Particularly black beetle.

Mechanical injury

Commonly caused during side dressing or other post-planting tillage operations.

Compaction

Planting or field operations when too wet can cause sidewall compaction. Check for horizontally restricted root systems.

Fungal damage

Crazy top - occasionally occurs in the Waikato and Northland but is generally rare and control measures are unnecessary.

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