Common summer diseases on lawns: dollar spot and brown patch

The management of fungal diseases on turfgrass, private ornamental, sports lawns and urban lawns is a key area for aesthetic and functional success.

High spring-summer temperatures, high humidity due to the high frequency of watering and fertilisation that a lawn requires, puts a strain on the ability of the manager or owner to be able to exactly identify the cause of the problem of lawn stains, yellowing, necrosis, burns at an early stage, and act consequently, possibly with particular attention to the environment, the health of the lawn users themselves and their own.

The importance of environmental factors

As already mentioned in the article dealing with autumn-winter diseases, environmental factors are important distinguishing features in recognising the problem. Some plant diseases, as well as the biological cycle of insects, are in fact ‘seasonal’, i.e. very much influenced by the environmental factors at this time of year.

Climatic changes that have characterised recent years, with slightly higher values at different times of the year than the average values recorded in previous years, can anticipate problems, and some pathologies that used to occur in summer can appear in the late spring-early summer period.

As we are now in the summer period, which from the point of view of temperatures actually began in spring, two of the most common fungal diseases typical of this period will be described.

Dollar spot

The first pathogen that can appear in the course of the season, starting in late spring, is Sclerotinia homeocarpa, recently reclassified as Clarireedia homeocarpa, also known as ‘dollar spot’, because of the size of the typical initial symptom, a circular spot, the size of a coin, precisely, a dollar. (photos 1 and 2)

Favoured by mild thermal conditions, high relative humidity and abundant dew, the fungus penetrates directly through the epidermis, stomata or small wounds. Unlike many fungal diseases, favoured by excessive nitrogenous fertilisation, which makes the leaf tissues weaker and more susceptible, in the case of Sclerotinia one of the prevention systems is regular and frequent nitrogenous fertilisation, which, together with other actions, such as the regular supply of iron-containing fertilisers, irrigation or wetting in the early hours of the morning, aeration of the soil, make it possible to contain fungal infection. Defence can be applied using antagonistic fungi, in particular Trichoderma gamsii, asperellum, harzianum that are active ingredients of some commercial products that can also be used in ornamental lawns, turfgrasses and sports facilities. The action is mainly preventive. This is why it is advisable to apply the product by wetting before optimal disease conditions occur, i.e. in spring. The colonisation of the soil by strains of this antagonistic fungus has multiple actions, both in terms of containing the pathogenic fungi, competing for nutrients and space, otherwise occupied by the pathogens themselves, and stimulating rooting and vegetative development of plants.

Rhizoctonia

The other most common summer disease, which has higher temperature conditions than Sclerotinia h., is Rhizoctonia solani, also called ‘brown patch’. The symptom is represented by circular patches that soon become quite significant in size, up to 50-60 cm in diameter, and beyond, depending on the herbaceous species, brownish-brown in colour, with a frequent whitish, or diffuse yellowish halo. (photos 3 and 4)

Effective preventive actions can be: wetting early in the morning hours, good drainage, and balanced fertilisation, with particular attention to the need for potassium fertilizing. Trichoderma spp. can also be used for rhizoctonia, keeping in mind, however, that since it is a fungus, i.e. a living being, it too has optimal conditions for development, and in situations of very high temperatures, it may reduce its growth and thus its activity. When autumn temperatures return and also optimal conditions in the following spring, it will restartsume development, so a good treatment with Trichoderma will in any case lead to an increase in the concentration of antagonistic fungi, improving soil conditions, with actions to reduce future pathogen development.

The advantages of these increasingly widespread and applied biological methods today are not only related to the fact that these are organisms naturally present in the soil, not chemical ones, but also to the possibility of apply a single product on several diseases, so even if we are not able to exactly recognise exactly which fungal disease it is, we can use these fungi that can be defined as ‘broad spectrum’.