Turf disease detection XIII-Copper Spot

The Copper Spotalso known as zonate leaf spotis a disease that mainly affects species of the genus Agrostiswith the highest incidence in Agrostis canina (velvet bentgrass) y Agrostis capillaris (colonial bentgrass). However, the pathogen responsible for this disease can also cause zonate leaf spot in other grass genera, such as Cynodon, Zoysia and various species of the family Poaceae.

Disease cycle

The causative agent of the Copper Spot is the fungus Microdochium sorghi (formerly known as Gloeocercospora sorghi). This fungus produces asexual sporodochiawhich are fruiting bodies that emerge through stomata in the leaf epidermis.

Conidia, which are the reproductive spores of the fungus, are:

• Hyaline (transparent).
• Filiformes (needle-shaped).
• With one to seven septa.
• They range in size from 1.4 to 3.2 μm wide by 20 to 95 μm long, with an average of 2.4 μm by 83 μm.

These spores develop inside a gelatinous matrix and, when present in large numbers, acquire a salmon colour characteristic.

In addition, small black sclerotia0.1 to 0.2 mm in diameter in necrotic lesions on leaves.

Relationship of the disease cycle to management

The biological characteristics of Microdochium sorghi directly influence the strategies for managing the Copper Spot. Some key points are:

1. Spore production in gelatinous matrix
   The gelatinous matrix surrounding the conidia facilitates their dispersal by water, such as raindrops or irrigation. Therefore, avoid overwatering or sprinkler irrigation at night hours is essential to reduce the spread of the disease.
2. Presence of sclerotia
   Sclerotia act as resistance structures that allow the fungus to survive under adverse conditions, such as periods of drought or extreme temperatures. This makes it necessary to remove infected leaf debris during mowing to reduce the amount of inoculum available.
3. Absence of sexual stage
   The lack of a sexual stage indicates that the genetic variability of the pathogen is limited, which could facilitate the effectiveness of targeted fungicides.
4. Mass production of spores
   The ability to produce large numbers of conidia on infected leaves underlines the importance of maintaining healthy turf and reducing plant stress.

Epidemiology

The Copper Spot develops in warm and humid climatic conditions, the optimum temperatures for infection being those ranging from 20 and 30°C. This disease is particularly detrimental to turfgrasses fertilised with excess nitrogen or grown on soils highly acidicwith a notable impact on Agrostis canina.

1. Survival of the pathogen
   The fungus Microdochium sorghi survives adverse climatic conditions and overwinters in the form of sclerotia o mycelium housed in the thatch (accumulated organic layer) and infested leaves.
2. Germination of sclerotia
   When soil temperatures are above freezing temperatures on a sustained basis 17°C (62°F), the sclerotia germinate and form sporodochia. These produce conidia during warm, moist periods, ready to infect nearby leaves.
3. Infection and spread
   Conidia can either penetrate directly into the leaves or enter through the leaves through the stomatacausing leaf necrosis. In infected areas, new sporodochia develop and produce more conidia, accelerating the infection cycle.
4. Conditions favourable to the disease
   The development of the disease is particularly rapid in the presence of condiciones ideales de humidity prolongada on the leaves, as is the case with persistent dew, frequent rainfall or watering at night.

Symptoms and signs of Copper Spot

The Copper Spot manifests itself as scattered, circular patches of affected turf, with a diameter of 3 to 8 cm. These patches have a orange to copperwhich is a hallmark of the disease.

At foliar level:

• The leaves within the patches show small lesions of red to brownwith a waterlogged appearance.
• These lesions can grow and coalesce, affecting entire leaves.
• Unlike the dollar spotThe margins of the patches in the Copper Spot are more diffuseThis makes it easier to differentiate between the two diseases.

In wet conditions, the patches of Copper Spot can be extended in the direction of the cutting or rolling a propagation pattern similar to the one observed in the Microdochium patch. Furthermore, although both diseases can coexist, differences in the colour of the lesions and the margins of the patches are key to distinguish between the two. Copper Spot from dollar spot.

Copper Spot management

Cultural practices

1. Elimination of morning dew. Removing the spray through cutting, rolling or dragging helps to reduce the wet period on the leaves, making it more difficult for the pathogen to spread.
2. Improved air circulation. Pruning trees or install fans can increase air circulation, reducing periods of prolonged leaf wetness.
3. Fertilisation management. Limit the use of water soluble nitrogen sources during periods of disease activity. Apply a maximum of 12 kg N/ha in a single application.
4. Management of the Soil pH. Maintain a pH between 6 y 7. It stands out for being one of the few that is favoured by soils with Low pH. In soils with pH less than 5.5Lime applications can be beneficial in reducing the severity of the disease.
5. Avoid mowing wet grass. Do not mow infested turf when the leaves are wet to prevent the spread of spores.

Chemical control

Fungicides effective in controlling the Copper Spot include:

• Azoxystrobin
• Chlorothalonil
• Fluazinam
• Combinations such as:
  • Azoxystrobin + Chlorothalonil
  • Propiconazole + Chlorothalonil
  • Iprodione + Thiophanate-methyl

It is advisable to rotate fungicides to prevent pathogen resistance and to follow the manufacturer's instructions on dosage and frequency of application.

Is your lawn not looking as it should? Find out if it is being affected by plant pathogens with a Phytodiagnosis analysis. This report provides you with accurate information on the presence of the main agents that can damage your lawn, helping you to make quick and effective decisions.

References:
https://turfpestlab.psu.edu/pest-profiles/copper-spot-zonate-leaf-spot/

For more information, please contact us at agro@tiloom.com.