» Growth

Weed and chemical control
Important principles for herbicide applications
Principles for controlling leaf diseases
Animal pests / Nematodes
Basic fertilising
Organic fertiliser
N-fertiliser

Weeds and chemical control

Weeds are wild plants which have become adapted over the years to the changing conditions on soils used for arable farming. In addition to "normal weed growth", there is also now a trend towards special weed growth, which is usually very difficult to control and which can often only be inadequately fought using existing herbicide systems. Early identification of the weed spectrum is vital for its economical and environmentally-compatible control. It is therefore important to optimally match the herbicide mix, application volumes and application conditions to achieve a high degree of weed control without damaging the sugar beet.

Herbicide agents

The herbicide agents Phenmedipham, Desmedipham, Metamitron and Ethofumesat are usually the basis for sprayed applications, and are mixed with other agents depending on the presence of specific key weeds. The Arbeitsgemeinschaft zur Förderung des Zuckerrübenanbaus in Norddeutschland e.V. (ARGE Nord) (Joint Venture for the Promotion of Sugar Beet Cultivation in North Germany) carries out tests to investigate the consequences of spraying herbicides on some very tough weeds, and uses this information to develop more effective and cheaper weed control strategies which are in the interests of the users.

Grasses

A wide spectrum of products is available to control grasses. A splitting method is recommended when controlling millet varieties. When millet emerges, it is possible to integrate a grass herbicide in the NA treatment. The application amount can be reduced by around 30 per cent in this case when the grasses are still poorly developed. But this means leaving oil out of the herbicide mixture.

Important herbicide application principles

• Observe the relevant regulations when applying herbicides and pesticides.

• Apply sparingly with precise dosages depending on the actual type of weeds being controlled

• The application technique should ensure a high distribution accuracy

• Avoid herbicide losses and reductions in effectiveness by spray drift

• Apply herbicides in weak sunlight in the early morning or late evening hours, and not at temperatures exceeding 25 °C

• Take the sugar beet growth into consideration (tolerance and agent absorption)

• Do not spray herbicides or pesticides when the wind speed is faster than 3 m/s

Bolted sugar beet

Sugar beet is a biennial plant which means that the flowers and seeds are only formed in the second vegetation year. If temperatures remain low for a long time (total cold period) and the light intensity is high in May/June, it is possible for the plants to experience a bolting stimulus (vernalisation) in the first vegetation year, and start to form seed bearers. If the bolted sugar beet is not removed, it produces a large number of seeds which are capable of germination for many years, and during subsequent rotations, can grow as weed beet within the properly planted sugar beet, and again lead to the formation of bolted sugar beet. The bolted sugar beet is undesirable for many reasons:

• Bolted sugar beet competes with ""normal" beet for nutrients, water, and light, and can considerably reduce the yield of the neighbouring plants depending on the density of the bolted sugar beet

• Bolted sugar beet forms seed bearers with the potential to produce large numbers of seeds. When these beet seeds fall onto the ground, they are capable of germination and grow as undesirable weed beet in subsequent sugar beet rotations. These always produce bolted sugar beet and always grow in all of the crops planted in the affected area even after many years.

• bolted sugar beet forms very strong, weedy and fibrous stems which grow higher than the actual crop and can significantly hinder harvesting

• The bolted sugar beet collected at the same time as harvesting can cause problems which negatively affect the pre-cleaning of the sugar beet as it is harvested

• The ability to process the sugar beet in the sugar factory can be hindered by the bolted sugar beet

Bolted sugar beet must be removed from the beet crops before the seeds mature (in other words  before the beginning of August). The tendency of sugar beet to produce bolted sugar beet is also dependent on the variety, and this trait is assessed in the sugar beet variety tests co-ordinated throughout Germany. The results should be used to preferentially select varieties which have a lower tendency to produce bolted sugar beet.

Basic information on leaf diseases

Sugar beet can be infected by numerous leaf diseases. The size of the damage depends on:

• The population density of the pathogen

• The phase of development of the sugar beet when it is first affected

• The aggressiveness of the pathogen with respect to sugar beet plants

• The resistance of the plants to each of the pathogens

• Weather conditions

1.    Fungal diseases

Leaf diseases have increased considerably in recent years. Depending on the time of infection and the way the infection progresses, losses in beet yields of up to 40 per cent can occur when the sugar beet is affected by the following fungal pathogens:

• Cercospora leaf spot (Cercospora beticola),

• Ramularia leaf spot (Ramularia beticola),

• Powdery mildew (Erysiphe betae),

• Beet rust (Uromyces betae)

These losses can be reduced or even avoided by implementing suitable measures.
The ability to treat this problem varies depending on the specific fungal leaf disease.

Symptoms

The symptoms of the different fungal diseases can be very similar.

Table: Description of fungal leaf diseases

Cercospora (Cercospora beticola)

Ramularia (Ramularia beticola)

Powdery mildew (Erysiphe betae)

Beet rust (Uromyces betae)

In the early stages, Cercospora and Ramularia can be confused with bacterial leaf spot disease (Pseudomonas) (see 2.: Bacterial diseases).

Control/Preventative measures

Factors which increase susceptibility:

• irrigation

• frequent sugar beet rotation

• strong infestation of neighbouring sugar beet in the preceding year

• weakened plants (as a result of humidity, Rhizomania, lack of nutrients, structural damage)

Individual factors are not ranked because they can be superimposed, and because their effect on the course of the infection can vary depending on the specific conditions during the growing year. Seriously infected neighbouring crops can also raise the infection potential if these infected crops are not turned over during ploughing.

Control thresholds

Treatment thresholds for Cercospora and Ramularia were defined for Germany after undertaking tests for several years. These thresholds describe the infection of the infected leaves in per cent after which the infection can give rise to economically measurable damage. The leaf-tear method is used to measure the infection threshold: the middle part of a leaf is torn out of a randomly selected leaf from 100 randomly selected plants. A leaf is defined as being infected when only a small symptom is found.

The optimal control time depends on the following damage thresholds:

*take the fungicide waiting times into consideration The azoles and strobilurines approved for sugar beet can be used to control the infection!

Leaf disease monitoring

When using fungicides, the right application time is more important than the product used. To assess the course of infection early on, leaf disease monitoring is carried out at around 300 locations every year in the LIZ area (Middle and North Germany). This involves investigating representative fields on a weekly basis to determine the degree of infection with leaf diseases. The results are published in the internet. If the threshold values are exceeded at the monitoring sites, farmers should carefully check their own fields for fungal infection and undertake fungicide control measures when necessary.

2.    Bacterial diseases

Bacterial leaf spot disease (Pseudomonas) The bacterial leaf spot disease (Pseudomonas) occurs after the leaf has been mechanically injured. This can be the result of very heavy rain or hail. Pseudomonas can therefore appear as early as May before the crops cover the ground, and cause damage to the small growing plants.

Symptoms

Table: Description of bacterial leaf spot disease

Bacterial leaf spot disease (Pseudomonas)

Control measures

Pseudomonas cannot be controlled. In plants that have been only slightly infected, the symptoms go away as the weather becomes dryer. In the case of strongly damaged plants, measures to reduce the stress on the plants or revitalise the plants should be carried out: such as a protective herbicide measure or additional leaf fertilising. It is important to diagnose Pseudomonas accurately because of the danger of a false diagnosis (confusion with fungal diseases) and therefore the unnecessary and uneconomic application of a fungicide.

3. Viral diseases

Virus yellows (viral beet yellowing)

Sugar beet production can be affected by ""Virus yellows" which can lead to yield losses of up to 50 per cent and reduce the sugar content by 2 per cent. Promoting factors

• mild winter, dry, warm spring

• conditions which favour the growth of aphids

• retarded growth of the young sugar beet plants

The ""virus" itself cannot be controlled and is primarily transmitted by the green peach aphid and much more rarely by the black bean aphid

Symptoms

Table: Description of virus yellows

Virus yellows

Control measures

Systemic insecticides incorporated within the pellet mixture protects the beet from aphids and are therefore the most effective protection against virus yellows. The alternative is to carry out separate insecticide treatments at the right times.

Animal pests / Nematodes

White beet cyst eelworms (Heterodera schachtii)

Appearance and damage symptoms

Infected beet can be identified by the retarded growth and the wilting of clusters of plants. The main root remains stunted and there is a tendency for more lateral roots to form which gradually form a felted mass and have the appearance of a root beard. Lemon-shaped cysts up to 1 mm in size are visible on the lateral roots.

Biology

The eggs can survive for over ten years in the resistant cysts. The larvae developing from the eggs leave the cysts above temperatures of 8 °C and penetrate the fibre roots. The substances exuded by the roots of the host plant stimulate the larvae to hatch. Mature animals capable of reproduction form once they have ingested enough food. After fertilisation by the male nematodes, the females harden and transform in the subsequent weeks into brownish lemon-shaped cysts. This cycle can be completed after only five to six weeks under ideal conditions, so that two to three generations can develop per vegetation period. Moist-warm weather and the cultivation of cruciferous plants (such as rape, cabbage, spinach or non-resistant oil radish and mustard) create highly favourable conditions for nematode reproduction.

Control

The damage threshold is defined as 500 eggs and larvae per 100 ml soil. There are currently no approved chemical control measures. A preventative measure is to completely exclude the host plants (goose-foot varieties and cruciferous plant varieties) from the crop rotation cycle. Sugar beet should only be planted on the same field every fourth year. Reducing the nematode infestation should mainly focus on biological control measures, which means the cultivation of nematode-resistant oil radish and mustard varieties. The control measures can be up to 90 per cent successful under optimal conditions and lead to significant improvements in yield in the subsequent beet crops. Sowing the seed early on after harvesting the preceding crop early on is a basic requirement for achieving high success levels. Another nematode control method is to plant resistant sugar beet varieties. However, cultivating these varieties is only prudent when the infestation density reaches at least 1200 eggs and larvae per 100 ml soil, because the resistant varieties will produce lower yields than nematode-tolerant varieties when the nematode infestation is lower.

Basic fertilising

Fertiliser is applied to guarantee the proper supply of nutrients to crops. A priority here is to determine the volumes of nutrients actually required. A balanced nutrient composition is particularly important to guarantee the good growth of healthy plants. Growth is limited by the nutrient in shortest supply. "Minimum tonnes", Justus von Liebig The fertiliser requirement of a crop can be determined by using either a soil analysis method or by determining the nutrient balance (over one or six years, depending on the nutrient). As a general rule, when the soils contain adequate nutrients, all that is necessary is to compensate for the nutrients extracted by the plant (nutrient balance). This ensures that the crops are supplied with the amount of nutrients they require. The following points must be taken into consideration when determining the amount of fertiliser required:

• Careful sampling when undertaking soil analysis

• The properties of the location (mineralisation)

• Size of the yield

• Nutrient recycling

• Proportion of organic matter in the soil

The type of fertiliser required is generally based on the aforementioned parameters. The more accurately the data is measured, the more precisely the nutrient requirements can be determined.

Organic fertiliser

Organic fertilisers are defined as farm fertilisers (stable manure, slurry, liquid manure, dried excrement), straw and green fertiliser, and domestic waste (compost and sewage sludge).

Farm fertiliser and straw

Average constituents of farm fertilisers (based on fresh mass)

D = dry mass FM = fresh mass

If farm fertilisers are used regularly and/or in large quantities, it is essential to analyse the constituents and the dry mass.
The fertiliser regulations define the volume and application times stipulated for farm fertilisers.

Green fertiliser

Green fertiliser is essentially a soil improvement measure which functions via the effect of the roots on the soil and the addition of organic matter. In addition to nitrogen binding (cultivation of leguminous plants), nematodes can be controlled by also selecting the type of crop to be planted (mustard, oil radish) and resistant varieties. When calculating the amount of fertiliser required by the main crop, take into consideration the amount of nitrogen applied for the green fertiliser.

Domestic waste

The average constituents of domestic waste are listed in the following table: Average constituents of domestic waste

D = dry mass, FM = fresh mass

The amount of fertiliser applied in this form is restricted by legislation. The sewage sludge regulations require the sludge and the soil to be analysed. This regulation specifies that the application of sewage sludge must comply with the stipulated limits for specific heavy metals. This regulation also restricts the total volume of sewage sludge to only 5 t dry mass per hectare per three years, independent of the constituents (corresponds to approx. 17 t fresh mass). Up to 10 t compost dry mass (corresponds to around 13 t FM) per hectare and year is the maximum which generally avoids any overfertilising.
The exploitation of the nitrogen in the subsequent year varies between 10 - 15 per cent in the case of compost, and up to 17 per cent in the case of liquid manure and spring applications. Exploitation is reduced by around 10 - 20 per cent if the fertiliser is applied in autumn. The remaining nutrients should be incorporated almost completely in the fertilising plan. In the subsequent years, the total exploitation of the nitrogen in sewage sludge, compost and stable manure can be expected to be up to 50 per cent.

N-fertiliser

The nutrient nitrogen (N) is an important growth factor, as well as being an important sugar beet quality parameter.

Deficiency symptoms

Colouration of the plants from light green to a light yellow colour. The light colouration starts on the older leaves which then wilt and dry up. The leaves point rigidly upwards and have elongated leaf stems.

Measuring the N-fertiliser requirements

When applying mineral nitrogen fertilisers to sugar beet, make sure that the amount added during each application is adjusted to the specific location. Assessing the amount of fertiliser required depends on a range of factors. The amount of nitrogen required in the soil which can be taken up by the plants is primarily determined by the size of the yield. During the vegetation period, sugar beet absorbs around  40 kg nitrogen per ten t of beet and leaves. The nitrogen content in the soil can be measured using the Nmin method. Another means of determining the location-specific N-fertiliser demand is crop-related balancing. Nitrogen fertilising depending on the soil type

When determining the N-fertiliser requirements, it is also important to take the following into consideration:

• the availability of the nitrogen (this depends on other factors) and

• boosting the yield of exploitable sugar