Control dollar spot disease in lawns

Dollar spot disease has the scientific name Sclerotinia homoeocarpa and attacks lawns from spring to late summer/beginning of autumn due to warmer temperatures preferred. Only the leaves of the grass are attacked by the fungal pathogen. Clear, straw-like spots form, which are initially about the size of a coin.

The causes are soil that is too moist and poorly aerated, persistently high humidity and a lack of nitrogen and potassium. With suitable preventive and countermeasures, dollar spot disease can be combated sustainably without chemical agents.

causes

In the case of dollar spot disease, lawns are primarily infected with the harmful fungal pathogen Sclerotinia homoeocarpa during the warm summer months. Especially on deep-cut lawns used for sport, for example on golf courses or soccer fields, the fungal disease has an extremely negative impact on the quality of the lawn. With suitable weather conditions and constantly damp grass, the fungus grows out with the mycelium and infects new and healthy growing leaf tissue. In doing so, it uses existing wounds and stomata on the grasses, and the fungus can also grow directly through the epidermis into the leaf tissue of severely weakened lawns. In particular, the following criteria promote infestation with dollar spot disease:

• permanently moist and poorly aerated soil
• Persistently high temperatures (25-30 °C), with cool and dewy nights
• severely dried out soils, which are then excessively watered
• extremely high humidity
• Lack of nitrogen and potassium
• Fungus survives as mycelium in infected grasses

Symptoms & Damage

Characteristic of dollar spot disease is the eponymous pattern of damage, which is caused by a fungal pathogen. Starting from the cutting height of the lawn, round spots in the shape of coins that are sharply separated from the healthy lawn surface initially form. The following aspects are significant in terms of symptoms and damage:

• Infestation period from May/June to September/October
• Although it bleaches the leaves of the grass, it does not affect the roots of the grass
• At the beginning of the fungal infection, single and yellowish spots of about 1-2 cm appear
• Diameter can increase up to 5-15 cm in the course of the disease
• With very high humidity and increased dew, whitish mycelium forms
• Mycelium parts are active particles of the fungal pathogen, also called aerial mycelium
• Dead grass turns yellow and straw-like

preventive measures

Since the fungal pathogen of the dollar spot disease is already increasing in resistance to the frequently shows the fungicides used from the specialist trade, this becomes more and more difficult after an outbreak fight. For this reason, it is better and more effective to avoid the fungus with suitable preventive measures than to treat it with chemicals afterwards. The following preventive measures render the pathogen Sclerotinia homoeocarpa harmless:

• balanced supply of nutrients and fertilizers
• additional administration of potassium at the beginning of summer
• Potassium increases the resistance of the epidermis and the stress tolerance of grasses
• It is essential to avoid prolonged drying out of the lawn and the soil
• water correctly, heavy watering before midday heat in the early morning hours
• Promotion of air circulation in the lawn
• get rid of morning dew quickly
• Check regularly for thatch
• Dismantle matted lawns promptly, scarify the lawn regularly
• Increase soil ventilation
• Periodically slit the lawn and then aerate, then sand
• prefer resistant types of grass when cultivating, for example bent grass
• comply with strict hygiene regulations
• Avoid transmission with devices and through shoes
• Clean all used objects meticulously after use

countermeasures

If only a few parts of the lawn are affected by dollar spot disease, there is still room for natural countermeasures:

• Remove infested areas of lawn over a large area
• aerate the entire lawn
• use a higher cutting height when cutting the lawn
• if there is a lack of nitrogen and potassium, fertilize until the end of July
• However, do not apply fertilizer later, excessive growth promotes the disease
• Strictly avoid entering areas that are already diseased on healthy lawns
• Regularly optimize already infested areas by reseeding with resistant grass varieties

Control with chemicals

If the dollar spot disease is already well advanced and has affected large parts of the lawn, the only thing that often helps is the use of chemical agents intended for this purpose. These are usually offered in a well-stocked DIY store or in a specialized garden store. However, the chemical agents should really only be used in an emergency and should never be used regularly, otherwise the lawn will develop resistance to them. The following active ingredients are suitable for actively combating dollar spot disease:

• carbendazim
• chlorothalonil
• iprodione
• propiconazole
• pyraclostrobin
• Thiophanate-Methyl

Editor's conclusion

Dollar spot disease is a nuisance and can quickly ruin a lush green lawn with unsightly and strawy patches. Regular lawn inspections during the warm summer months are therefore extremely important, as is constant maintenance during this period. With sufficient ventilation and sustainable fertilization, the immune system of the lawn is strengthened and infection is avoided in advance. Increased doses of potassium and nitrogen in spring and scarifying the lawn strengthen resistance and prevent the transmission of the fungal pathogen. In addition, strict hygiene regulations also prevent the transmission of dollar spot disease, and all equipment and footwear used must always be cleaned after use. However, if the infestation has already spread very widely, only chemical agents from specialist shops can help in cases of hardship.

Worth knowing about dollar spot disease in brief

How to spot dollar spots in the lawn

• The damage varies according to the growth height of the lawn, with straw-like patches, usually in a round shape, forming on the lawn.
• If your lawn is cut particularly shallow, you will recognize dollar spot disease by spots about the size of a coin.
• The higher the lawn height, the larger the spots, which can even work their way up to a spot size of 15 cm each.
• Another feature: discoloration where you can see delicate indentations in the form of a white web-like braid.
• Usually only certain types of lawn are affected: Bent grass species, annual meadow grass and red fescue species.

infestation and control

• The pathogen prefers higher temperatures between 25 and 30 °C.
• Dewy nights and increased soil drying lead to potassium and nitrogen deficiency with grasses.
• So it can also affect your lawn between the end of May and the beginning of October.

If this is the case, then you must act quickly: make sure that you do not transmit the disease to healthy lawns. This means you need to thoroughly clean your garden tools and remove all grass debris. Stepping on a healthy lawn from a diseased area should also be strictly avoided. Combat the Causes of Dollar Spot Disease:

• You can initially treat the lawn to a higher cutting height and ensure sufficient air circulation.
• Use chemical agents intended for this disease, which are offered to you in the hardware store or garden center.
• Only use them in emergencies and never regularly!
• Provide the soil with sufficient nutrients and provide the infested areas with new seed of a more resistant lawn variety.

Prevent

• For example, you can ensure that the soil does not dry out too much...
• ... and that you tend to fall back on sprinkling the lawn in the morning hours.
• An additional dose of potassium, which you carry out in the spring, can also strengthen the lawn.

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