Turfgrasses are more or less like humans in terms of immunity. With proper maintenance, enough food, and managed stress levels, they can defend themselves from pathogen attacks or all other diseases.
Identifying common diseases of cool season grasses.
Like with humans, very few disease or problems can occur on a turf that is healthy and well-maintained because the immune system is functioning optimally. On the other hand, turfgrasses that are stressed and have slow growth can immediately fall ill. So, maintaining proper cultural practices like mowing, irrigation, and fertilization is an absolute must.
However, even the healthiest and most well-maintained turf can suffer severe stress when exposed to extreme weather conditions. The hot and humid environment during an Alabama summer can trigger major disease outbreaks on cool-season grasses. While cool weather and not enough sunlight during fall, winter and spring can cause warm-season grasses to become highly susceptible to diseases.
Pathogen attacks during stress times are undeniably troublesome and can negatively affect the overall health and appearance of landscape turfgrasses in the long run. Common diseases like red thread, dollar spot, and leaf spots are relatively easy to address with proper management practices.
We have compiled 5 of the “least-wanted” diseases that require an integrated approach, proper cultural practices, and perfectly timed fungicide applications.
Brown Patch
A foliar disease that produces large, tan-colored lesions on the foliage that expand to blighted circular patches of turf up to several feet in diameter. This is the most common summer disease on cool-season grasses usually affecting tall fescue, Kentucky bluegrass, and perennial ryegrass.
Rhizoctonia solani, the brown patch pathogen, starts to become active in the spring or early summer when temperatures are above 60 degrees Fahrenheit. But it is most aggressive when temperatures reach more than 90 degrees Fahrenheit plus high humidity. This disease is most destructive in the transition zone where these conditions persist for a couple of months.
What to do?
Though curative applications can reduce brown patch by halting further disease activity, they are slow because of the effect of extremely high temperatures on cool-season grasses. And so, preventive fungicides are often needed to prevent and stop unacceptable damage especially in the transition zone. It’s best to initiate the applications in the spring or early summer when low temperatures consistently exceed 60 degrees Fahrenheit and repeat on a 21- to 28-day interval, depending on the product selected.
Large Patch
Large patch is caused by a different strain of the pathogen Rhizoctonia solani that is specific to warm-season grasses. Turfgrasses, centipedegrass, zoysiagrass and St. Augustine grass, which are the most popular warm-season grasses, are the ones that are highly susceptible to this disease.
The pathogen infects the basal portions of the turf plant and tan or reddish-brown lesions can be evidently seen on the leaf sheaths before the entire tiller is killed. If left untreated, the disease expands to blight large circular patches of turf, that may sometimes cover 10 feet or more in diameter.
What to do?
Limited cultural practices can prevent the development of this disease because it’s mainly weather-driven. And so a preventive fungicide program is your best option. The pathogen becomes active in the fall when the soil temperature drops below 60 degrees Fahrenheit and so this is the best time to apply a fungicide. Generally, two applications in the fall and one in the spring are needed to ensure your turf stays healthy. You can’t rely on curative applications for this disease because the turf is dormant or semi-dormant.
Pythium blight
This disease is all about stress. Turf managers refer to Pythium blight as a hot and wet weather disease and that’s true on cool-season grasses.
What to do?
You will have to provide good soil drainage and sound irrigation practices because Pythium blight requires long periods of leaf wetness. Be sure to irrigate deeply and infrequently to wet the entire root area. Repeat when the turf first starts to show signs of drought stress. Please note however that daily irrigation is unnecessary and may do more harm than good by contributing to the disease’s activity in most situations.
For sites with a history of Pythium blight development, consider applying a preventive fungicide program when the weather conditions are conducive to the disease. In general, if you’re already treating brown or large patch, it is no longer necessary to apply a special fungicide specifically for Pythium blight.
Spring Dead Spot
This is a devastating disease of bermudagrass and it can also affect zoysiagrasses. The culprit? The pathogen Opiosphaerella which weakens the turf and makes it more susceptible to freezing injury during winter dormancy. This results in circular patches of infected turf failing to green up in the spring.
What to do?
Recovery from this disease is very slow. At times, you may need to take the entire growing season working to get turf to spread back into the affected areas. Applying extra fertilizer is the natural tendency but isn’t recommended because can make the disease be more aggressive. What you have to do is, break up the mat of dead turf with regular aerification or spiking, apply fertilizer and irrigate on a light and frequent basis to help the stolons roots.
Fungicides can manage spring dead spots but should be applied preventively. Since this disease attacks during winter, apply a systemic fungicide in the fall. This way, the plant is protected during winter dormancy.
The most effective control options for this disease is the combination of DMI fungicides, or DMI + QoI combination products (such as Headway fungicide). Depending on the severity of the disease, two or three applications prior to dormancy is typically recommended.
Fairy Ring
The most complex and difficult turfgrass disease to manage. Caused by a neighborhood of 60 different fungi (and more), fairy rings, however, don’t infect the turf but grow in the thatch and soil using the organic matter as a food source. The fungi indirectly cause symptoms on the turf by changing the chemical or physical properties of the soil.
Type II fairy ring symptoms can cause a ring of greener, more quickly growing turf by releasing nitrogen in the soil profile. While Type I symptoms, or also called as rings of dead turf, are the result of water-repellent substances that are remnants of Fairy Ring growth.
What to do?
For fungicides to be an effective cure for Fairy rings, they need to be applied preventively. Even before the symptoms are expressed. Please note however that fungicide won’t get rid of excess nitrogen in the soil or re-wet the hydrophobic soil.
The most effective products are QoI, DMI, and SDHI fungicides. Keep in mind though, that not all fairy ring fungi are sensitive to the same fungicides. Therefore, some trial-and-error is typically needed to determine which products would be best.
It is important to always read and follow label instructions because some products may not be registered for sale or use in all states or counties.
Still unsure how to deal with your turf that’s suffering from any of the above? We’d be glad to help! Give us a call and let’s get to work!
