Viral diseases in turfgrasses are generally not economically significant and often go unnoticed. Symptoms are usually mild and do not result in plant death. However, there are exceptions. St. Augustine Decline, caused by Panicum mosaic virus, can cause significant damage to St. Augustinegrass. Ryegrass Mosaic, caused by Ryegrass mosaic virus, can harm ryegrass. Lethal Viral Necrosis, associated with sugarcane mosaic virus and bermudagrass latent virus, affects ‘Floratam’ St. Augustinegrass. These viruses have been identified, but their impact and management in turfgrasses require further research.
Causal agents
Viruses in turfgrasses are classified into different groups based on characteristics like size, shape, nucleic acid type, host range, and transmission methods. Some virus groups known to cause diseases in turfgrasses include:
- Potyviridae
- Rhabdoviridae
- Tombusviridae
- Luteoviridae
- Tenuiviridae
- Reoviridae
- Sobemoviruses
Primary Hosts
Stenotaphrum secundatum and Lolium spp.
Disease Cycle
Viruses in turfgrasses are transmitted through various means, including insect vectors, soilborne vectors, physical activities, seed transmission, and plant sap. Insect vectors such as aphids, beetles, mites, and leafhoppers transmit viruses while feeding on infected plants. Soilborne vectors like fungi and nematodes move through the soil and infect nearby plants. Some viruses are transmitted through physical activities like mowing or transplanting infected sod, while others can be transmitted through infected seeds or plant sap.
The spread of plant-infecting viruses can be influenced by the presence and behavior of specific vectors. Virus reservoirs in alternative hosts, asymptomatic hosts, or neighboring lawns can contribute to reinfection and repeated failures. The true extent and impact of viruses in turfgrasses require further research for better understanding and management.
Epidemiology
Viral diseases in turfgrasses spread through vectors, such as insects or soilborne organisms, as well as by physical means like mowing or sap transmission. Insect-vectored viruses can be widespread or concentrated in specific areas. Regular insecticide treatments can reduce virus transmission. Soilborne vectors are influenced by soil conditions. Mowing and mechanical activities can physically spread viruses, so avoiding those activities when turf is wet is important. Infected seeds can also transmit viruses.
Virus-infected plants serve as reservoirs, leading to reinfection of newly established and/or neighboring lawns. Effective management involves vector control, cultural practices, and virus-resistant cultivars.
Symptoms
Viral infections in plants can lead to a variety of symptoms. One common symptom is the yellowing or chlorosis of infected leaves, which can occur in localized areas or even affect the entire plant. Another characteristic sign is the presence of a mosaic pattern on the leaves, with light and dark green areas intermingling.
Infected plants often display reduced growth and a stunted appearance, with limited overall development. Additionally, viral infections may cause excessive tillering, leading to the production of an increased number of side shoots or tillers. Lastly, necrotic spots or patches can form on the leaves, resulting in tissue death. These symptoms collectively serve as indicators of viral infections in plants and highlight the impact of these pathogens on plant health and growth.
Credit: John Kaminski/Penn State University
Signs
Viruses vary in shape and size, but expensive, high-powered scanning microscopes are required for positive identification.
Management
Cultural practices are key to managing viral diseases in turfgrasses, as they focus on creating unfavorable conditions for virus transmission while promoting overall turf health. Chemical control options are limited, with insecticide treatments targeting insect vectors and nematicides controlling nematode-vectored viruses.
Cultural
Cultural practices play a crucial role in managing viral diseases in turfgrasses. These methods focus on creating unfavorable conditions for virus transmission and promoting overall turf health. Strategies include:
- avoiding mowing when the grass is wet to minimize sap transmission
- maintaining well-drained soils to reduce the activity of soilborne vectors
- implementing proper irrigation practices to prevent waterlogging
Additionally, the impact of viral disease on infected plants can be minimized by the following strategies:
- promoting overall plant health
- balancing fertilization
- controlling fungal diseases
- using virus-resistant cultivars
Chemical
Chemical control options for viral diseases in turfgrasses are limited. Insecticide treatments can be effective in reducing virus transmission by insect vectors, while nematicide applications can help control nematode-vectored viruses. However, it’s important to use these chemicals judiciously and follow proper application guidelines.