lawn disease

Asked May 15, 2018, 1:03 PM EDT

I get these dead spots (attached photos) in my lawn every year. I treat with spray lawn fungicide and Heritage G spread fungicide from May to August and it helps a little but I can't seem to cure it. Can you recommend an effective product to get rid of this desease once and for all? I adhere to all the right lawn care guidelines like mowing high, not watering late, only fertilizing in the fall. I've had a soil analysis and everything looks fine except Phosphorus is a little low. Thank you

Anne Arundel County Maryland

9 Responses

First of all, fungicides do not cure diseases. They are used to prevent them and to stop the spread. Fungicide applications by homeowners tend not to be very effective. By the time disease, symptoms are noticed it is too late to apply them. Homeowners usually get the timing of application wrong. Professional applicators monitor weather conditions and spray before they anticipate a problem. For this reason, we do not recommend that homeowners apply fungicides to their lawns at all. Most often they are not necessary. As of yet, we have not had any reports of diseases of home lawns even being active right now.
The photos you sent do not even look like a disease problem. Brown patch is the most serious disease of tall fescue but it is much too early for it. You mention the proper cultural practices to reduce the likelihood of diseases. But, do you apply weed and feed products in the spring to prevent crabgrass and to control broadleaf weeds? If so they need to be counted as fertilizer applications also. Do you have a sprinkler system? They can contribute to disease problems especially if they are set to run for a short while frequently during the week. Maybe there is something about this area that is causing the problem, like if it is an area that collects water. Again if these are current photos of your lawn this is not a disease.

I'm not sure my last response was sent because it said the soil analysis was in the wrong format so here it is again.... If not lawn disease, what is turning my grass brown in patches and what can I do to stop it? Attached are close up pictures of the grass blades that appear to have striping and spotting that I thought were disease. I've also attached my latest soil analysis.

Thank you,

Thanks for sending your soil report but unfortunately it will not shed any light on the brown spots in your lawn. Were these photos taken recently and please go into more detail about how you take care of your lawn. We need more information about your cultural practices. Information about the seed you use could be helpful too.

The pictures of disease on the grass blades were taken this morning. Can you identify the disease and suggest a treatment?

I haven't seeded this area in years. The grass is well established and is tall fescue. I mow weekly at a height of 4 inches and avoid watering except when absolutely necessary like during a long spell without rain. It has been quite wet lately with many strong thunderstorms and high humidity. I'm located in Arnold, MD.

From on-line research, I believe I may have red thread, brown patch and/or rust. Can you tell from the pictures of the blades, what it is?

This is not red thread, brown patch, or rust. The lesions on the grass blade in the first photo resembles dollar spot. But this disease is not serious enough on tall fescue to require fungicide treatment. As weather patterns change so will the disease pressure.
The following are some cultural practices to help with disease problems:
Maintain adequate N levels, increase mowing height, mow early AM to remove dew and maintain good soil moisture during dry periods in late summer (especially August and September).
If you are still interested in spraying a fungicide see the following publication which should provide some guidance for you

It sounds like the Nitrogen level is key. I've read that too much or too little N can both promote disease. So how do I know how much my lawn has since it's not on the soil analysis? How do I maintain the appropriate level of N?

Thanks for your patience today,

You hit the nail right on the head. Maintaining proper N levels is very important. Although too much N in the spring can make fescue lawns prone to brown patch.
Following this fertilizer schedule should provide your lawn with the proper amount of N for the year.

Good luck!

Given those fertilizer guidlines, it looks like a May application is in order. If I have an 8000 sq ft lawn and my soil analysis shows low P level with an index value of 38, and an optimum K index value of 89, and I need 0.9 lbs/1000 sq ft of N (27 lbs).....what ratio fertilizer should I use?


Yes, a fertilizer application sounds like it could help your situation. But the fact that we will be entering the time frame when brown patch will start to become active we would recommend an organic lawn fertilizer (there are many on the market). This would provide a slow-release form of nitrogen. But since the soil microbes will be active due to the moisture and warm temperatures it will most likely be able to provide the N you need now. Many organic lawn fertilizers also contain phosphorus and because of your soil test results this would be beneficial too. Don't be concerned that your soil is optimum in K, it only means you do not need to add more but again most lawn fertilizers contain K and it will not be a problem. We do not recommend specific brands or analysis of fertilizers (because manufacturers change this every year) as they do not differ enough to really make a difference and we try not to send people on a wild goose chase.
Lawn fertilizers manufactured to be used in Maryland will provide 0.9 lbs of N (if they are applied according to the label directions) because they need to conform with the Lawn Fertilizer Use Act of 2011.