“Does this look infected? Disease in turf

Disease of turfgrass is another perennial problem for the Florida lawn. We have high humidity, heavy rainfall, and other factors that contribute to outbreaks of disease. However, there are definitely helps to reduce the amount of disease that impacts our lawns.
The first help to reduce turfgrass disease is an understanding of something called the “Disease Triangle.” There are three sides to the Disease Triangle: Susceptible Host, Proper Environment, and the Pathogen itself. All three parts are necessary for a disease outbreak.
A susceptible host is simply a plant or variety of turf that is susceptible to the disease. For example, Large Patch is common in St Augustine grass so therefore St Augustine grass is a Susceptible Host for Large Patch Disease.
Likewise, Proper Environment is the second side of the Disease Triangle. The pathogen needs the right conditions to grow and thrive so if there is high humidity, high precipitation, clouds/shade, stress on turf, high amounts of Nitrogen, then all of these ingredients are part of the Proper Environment for the disease to grow and spread.
Lastly, the pathogen itself must be present for disease outbreak. If the pathogen is in the soil and then the conditions are right, that pathogen will grow and spread and damage your lawn.
As the saying the goes, “An ounce of prevention is worth a pound of cure.” This saying is vitaly important for maintaining a healthy lawn. The best way to prevent a fungus outbreak is to keep the factors that cause the outbreak to a minimum. Sadly though many people lack the knowledge or understanding of how to keep the fungus out of their lawn.
Proper irrigation is probably the single most effective measure you can take to prevent a fungus outbreak in your lawn. You should definitely install a rain shutoff sensor if you have an irrigation timer. And if you have a rain sensor, make sure it is working properly.
Part of proper irrigation setup is to make sure that shaded areas do not get overwatered. If there is an area with heavy shade, adjust that zone so that it is getting less water, only as much as needed. Also, during the Winter months, irrigation can be reduced since the days are shorter and the plants/turf are not growing so much.
Another ingredient that can exacerbate disease in your lawn is the over application of Nitrogen. Everyone wants a nice, green lawn but when you apply heavy amounts of Nitrogen to get a dark green lawn you run the risk of inviting a disease. Therefore it is imperative that the nitrogen you are applying be at least 50% slow release and that you apply at the recommended rate. If you are spraying the lawn with a liquid form of Nitrogen, then do so at a lower rate.
The best way to prevent disease in your lawn is to make sure you do not overwater the grass. The second best way to prevent disease is to use a very, very slow release nitrogen fertilizer. What I recommend is that you purchase a 5 month slow release nitrogen and apply it 3x per year. You may need to apply it heavier than a 3 month slow release product in order to get enough Nitrogen to the turf, but if it is a heavily coated 5 month product then you do not have to worry about too much quick release Nitrogen that causes problems.
So apply the 5 month product about 2-3x per year heavier than you normally would your 3 month product. Then between applications, you will want to add some potassium and other nutrients since these are likely not coated and will not last as long as the coated Nitrogen. Products like K Mag or Sulpo Mag are good additions to make in between the slow release Nitrogen applications.
If you plan to add micronutrients to your lawn, it is better to apply these as a foliar spray. There are different forms of micronutrients but the main products in a liquid form are sulfates, glucoheptonates, citrates, or other chelated sources such as EDTA. Keep in mind that all fertilizer has the ability to stain and so you want to keep the applications to the grass area. If you do get fertilizer on a hard surface, rinse it off immediately. Or if it is granular, blow or sweep it back into the grass.
Now that you are aware that quick release Nitrogen can increase your odds of getting a disease in your lawn, let’s look at some common diseases and how to avoid/treat them.

Take All Root Rot/Patch
Take All Root Rot or Patch (also known as Bermudagrass Decline) is a disease caused by Gaeumannomyces graminis var. graminis and affects all warm-season lawns including St. Augustine grass as well as Bermudagrass. Outbreaks usually coincide with our rainy season, Summer and early Fall. Stress such as scalping the lawn with a mower or heavy traffic can increase the presence of the disease. This root pathogen attacks the root structure of the turf and so prevents the normal function of the plant. Roots are first diminished and weakened and so the disease can be undetected for a time. The area affected by Take All Root Rot will appear as weakened, yellow/orange (chlorotic) patches that can range in size from a few inches to a few feet in diameter. Pulling up pieces of turf and observing/smelling the roots can help identify the diseases. If you suspect you may have Take All Patch, then consider sending a lab sample to confirm the presence of disease. Treatment involves reducing the irrigation and treating with a fungicide. Since the root system is diminished, apply the fungicide as a foliar spray. Make sure you follow the label exactly. And if you experience recurring outbreaks of the disease, you may want to use a fungicide as a preventative.

Large Patch/Brown Patch
Large Patch (aka Brown Patch) is caused by the pathogen Rhizoctonia Soloni and affects all warm season turfgrass, especially St Augustine and Zoysia. Large Patch is mostly observed in the Winter months when temperatures stay below 80F for an extended period of time. As with most disease, excessive rainfall or irrigation can trigger an outbreak.
Roots are not generally affected by this Large Patch disease but you will notice discolored leafs with a soft, dark rot at the base of the leaf blade. The leaf blade will easily pull away from the rest of the plant and you will notice a foul smell. Usually the patch starts small (1ft in diameter) and then can grow substantially. You will notice a yellowing of the turf, then brownish color of the patch, and then a straw-like color as the disease kills the turf. The edge of the ring may appear dark and wilted while there may be some healthy blades of grass in the center of the ring.
The best way to prevent Large Patch is to keep irrigation to a minimum and use a quality slow-release Nitrogen fertilizer. Additional applications of Potassium may help reduce disease pressure. If an outbreak occurs applications of a fungicide can usually control further damage. Follow the label of the fungicide.

Dollar Spot
Dollar Spot is caused by Sclerotinia homoeocarpa. The disease appears as white to straw colored lesions or spots with dark colored borders on the blade. On older, taller blades the spots can be shaped like an hourglass. Affected areas appear as small, circular patches about the size of a dollar coin. While Dollar Spot can be a serious issue, it usually does not kill the turf as other diseases will.
Some strains of bacteria have shown the ability to reduce Dollar Spot. These include B. Subtilis (Companion), B. Amyoliquifaciens (Double Nickel), and B. Licheniformis (EcoGuard). Products such as Abound combine several strains of Bacteria that have shown some efficacy against the pathogenic fungi.

Pythium Root Rot
Pythium affects all warm season turfgrass anytime of the year. Stressed turf and compacted soils can see an increase in Pythium occurrence. Like TARR (Take All Root Rot), Pythium is a root disease. However unlike TARR, Pythium can show up anytime of year, especially in areas of compacted soil.
Pythium is a root disease that affects and discolors root hairs. There is a noticeable thinning of the roots. You will notice a weakening of the turf, which will include a yellow, light green, or brown discoloration. Not only will the turfgrass be weak and thin, noticeable are the presence of either small or large irregular shapes or “patches.”
While Pythium Root Rot does affect turfgrass quality, it rarely kills the turf. Good cultural controls can reduce the impact of Pythium. Make sure to cut at the proper height. Install a rain sensor to ensure that irrigation stops if rainfall is present. Limit Nitrogen applications to recommended rates. Use a quality slow release fertilizer if needed. Extra applications of Potassium may reduce the occurrence of Pythium.

Rust
Rust affects mainly zoysiagrass and St. Augustine grass and mainly in late Fall to early Spring. Symptoms of Rust develop from small yellow specs to orange colored spots on the leaf. While Rust disease will cause thinning, yellow areas in turf, it will not kill the turf. It is advisable to water in the morning to reduce additional moisture on the leaf blade throughout the day.

Gray Leaf Spot
The hot, humid, and rainy summers of Florida create a favorable environment for Gray Leaf Spot, the most common fungal disease for St. Augustinegrass. Gray Leaf Spot is marked by small, oblong lesions on the turf blade. The lesions appear olive or brown with a dark ring surrounding the lesion as a border. If severe, the turfgrass will thin out and appear diseased.
Symptoms will often occur in St. Augustinegrass in the Summer, especially after applications of Nitrogen. Stressed, compacted areas are also susceptible to the disease. Also, Summer applications of Atrazine can cause an onset of Gray Leaf Spot.
Make sure that your fertilizer program is well-balanced to include Potassium, Magnesium, Sulfur, Calcium, and micronutrients. Reduce the use of quick release Nitrogen fertilizers.
Irrigate in the morning and cut the grass at the proper mowing height, as high as possible for St. Augustinegrass.
Gray Leaf Spot is rarely fatal to the turf but can cause an unsightly and unhealthy lawn. Regular proper cultural practices reduce the impact of Gray Leaf Spot include proper mowing height, using slow release Nitrogen at the proper rates, and proper irrigation practices. If chemical control is needed due to a history of the disease, prevention is preferred over treating once the disease is present. Early applications of fungicides, strictly following the label, will often prevent severe outbreaks.
The availability of bio-fungicides are increasing and there are some hopeful research projects ongoing that propel these novel ideas to the forefront of treatment options.

Anthracnose
Occurrence is notable in Spring and Summer when temperatures and humidity rises. Anthracnose appears on the leaf surface as dark lesions with a yellow “halo” surrounding the spot. Look for small yellow patches of turf that indicate the presence of anthracnose.
As with other disease, prevention is key. Cut grass at proper mowing height, use slow release Nitrogen if needed at proper rate, irrigate earlier in the day.
Chemical fungicides are effective means of controlling outbreaks. These chemicals include azoxystrobin, propiconazole, T Methyl, myclobutanil, etc. Make sure the label is followed and the correct number of applications are made to reduce fungicide resistance in future outbreaks.