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Protecting sunflowers through the growth stages

May 7, 2019

This article looks at some of the agronomic issues we need to consider during the life of the sunflower crop, to give plants the best possible start, and to protect yield.

The vegetative phase

This covers the period from dry seeds, through germination to establishment, when the plants are photosynthesising, producing new leaves and are self-sustaining.

Although harvest can seem a long way off, yield can be won or lost at this point.

This also covers the stage before the seed is in the bag, how the parent plant was treated in the previous crop will influence the quality of your seed.

Unless you are a plant breeder producing your own seeds, you will have no influence over this stage.

Therefore, sourcing quality seed from reputable seed companies like Nuseed will guarantee your seeds have been produced to the highest standards and will go on to perform for you.

Select the best quality seeds

By using good quality seeds, you will have plants that will germinate quickly with vigorous growth, allowing them to withstand the negative impact of plant antagonists.

It’s often said the best herbicide is a well-established vigorous crop that can out-compete weeds.

Selecting varieties with inherent disease resistant traits is a great way of avoiding problems in the first place.

Nuseed varieties come with resistance to common issues such as Orobanche, multiple races of downy mildew, Sclerotinia head rot tolerance, and Phomopsis stem canker.

Give your seed the best start in life

This essentially comes down to three issues; soil temperature, soil moisture and soil fertility, get these right and you will be giving your seed the best start in life.

Soil temperatures

Don’t be tempted to start planting too early, sunflowers like the soil to warm up a bit first and will really appreciate it, and emerge quicker if you wait until soil temperatures reach a more comfortable 13oC.

Soil moisture

Retaining soil moisture so that it is available to the seedling, coupled with warm soils, really allows the emerging root to rapidly develop and start drawing in water, and the shoot to reach the surface quickly and start absorbing sunlight.

As climate change creates more volatile weather it’s likely that the current sunflower growing regions will become hotter and drier, and retaining soil moisture through conservation tillage and direct drilling will become increasingly important.

Soil fertility

Simply put, soil fertility is the ability of a soil to sustain agricultural plant growth and is a complex interaction between the soil type and what we do to it.

Growing a range of different crops, returning crop residues to the soil, utilising green manures, spreading animal manures, protecting soil structure, avoiding compaction and erosion, are some of the ways we can influence soil fertility.

Applying fertiliser is a good way of improving yields but they shouldn’t be used to compensate for poor soil fertility, appropriate and suitable soil management should be first and foremost in any decision-making process.

Looking after your crop

You bought the best seed and you carefully planted the crop, now you need to think about looking after your investment.

To do this well you need to consider many aspects of agronomy and crop management, but here we are going to focus on the effective use of pesticides and some first principles.

Weed control

As already mentioned, a rapidly growing healthy crop is a great way to combat weeds, but giving the crop a helping hand through that vulnerable stage, from emergence to the crop canopy closing over, is a good idea.

Weeds compete for moisture, nutrients, sunlight and space, and their effects are felt greater by the crop when seedlings are small.

The effect of weeds on yield varies depending on the species of weed and crop, but things you need to consider are;

  • Will the crop become more competitive as it develops?
  • How much moisture and nutrients will the weeds take from the crop?
  • Will weeds shade and compete for light?
  • How competitive are selected weeds?

Herbicides can provide effective economic control of weeds if used correctly, but for herbicides to work well you need to pay attention to the detail.

  • Crop agronomy – including adequate seed rates and plant spacing, suitable seedbeds, correct drilling date, suitable use of fertiliser, pest and disease protection.
  • Soil type – soil acting herbicides may not be recommended when soil organic matter is more than 10% as organic matter locks up the herbicide.
  • Consolidated seedbeds – help good spray distribution, encourage rapid and even weed germination.
  • Moist seedbeds – encourage weed root growth near the surface which results in early contact between roots and herbicide.
  • Weather – rainfall will wash herbicides into the root zone, weeds growing well will be more susceptible to herbicides, however, prolonged rainfall can cause leaching, humid warm air improves foliage acting herbicides, frost, low temperature, drought or drying winds may affect herbicide efficiency and increase the risk of crop damage.
  • Applying herbicides – use correct spray quality, low water volume (less than 200l/ha) produces high work rates but reduced efficiency, low volumes will control small weeds with an open crop canopy, high volumes improve weed control in thick crops or dense weed population, high pressure improves weed control in thick crops as it “pushes” spray into the crop.

Pests and diseases

Pests and diseases affect crops in a variety of ways, but the net effect is they will reduce yield and quality.

Yield depends on effective light interception by the crop, foliar diseases and leaf-eating insects reduce yield by reducing the leaf area and reducing the plant’s photosynthetic ability.

Therefore, maintaining the green leaf area during the yield forming period is crucial.

When thinking about insect pests and diseases, it’s good practice to follow the principles of Integrated Crop Management or ICM; to maintain crop yield and quality by keeping pest and diseases below economically damaging levels.

The idea is not for total control, but to maintain pest and diseases below economic levels, and to obtain optimum crop yields.

To follow the principles of ICM, and to use pesticides economically, consider the following;

  • Monitor the crop regularly, weekly or fortnightly, depending on the season
  • Identify the problem pest, weed or disease correctly
  • Determine if the pest, weed or disease is at an economically damaging level
  • Treat accordingly

If the recommended treatment is to use a pesticide, then ensure the correct chemical is chosen, that it is applied at the correct dose, through the correct nozzles and at the optimum time.

The following flow chart can be used as a checklist when making crop management decisions:

Survey and Assessment

As well as identifying the pest or disease, the severity and incidence in the field must be determined to assess the potential benefits from any control measures.

A diagnostic survey can be used to determine what combination of pests and crop plants exist in the crop being assessed.

Incidence

Incidence is assessed by counting the number of affected plants versus the number of healthy plants in a sample and is suitable for issues such as viruses, stem canker or sclerotinia.

Incidence = number of infected plants x 100
total number of plants assessed

Severity

Severity is assessed as a ratio of healthy to infected plant tissue and is useful for diseases which affect photosynthetic capacities, such as rusts and mildews.

Severity = area of plant tissue affected by disease x 100
total area

Thresholds

Thresholds are a good way to determine when is the ideal time to target insecticides for optimum economic benefit.

Spraying too early and the insect may not yet be present in enough numbers to justify the expense; spraying too late and the damage may already be done.

Thresholds change, depending on which insect is present, the larval stage of the insect, the growth stage of the crop, the ratio of the cost of control and value of the crop, and so on.

However, some basic principles to keep in mind are that regular crop inspections throughout the season allow you to monitor the arrival and development of insects, avoid the edges of fields, walk into your crop before taking counts, walk a representative area of your crop, and traps are available for some insect pests.

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