Spider Webs on Lawns

The following question was sent to the P&PDL diagnosticians here at Purdue University:

Question: Last summer I noticed what looked like many spider webs in my grass in early morning dew. I lost a lot of my yard. Yesterday I noticed the same thing. I heard it is a fungi caused by wet nights. Other than not overwatering what can I do now and in the future to minimize the damage. I have lived here 7 years and am just starting to have this problem.

Answer: It is very difficult to diagnose a disease with the limited information given but the disease that you describe could be one of two summer diseases that look similar but occur under very different maintenance systems.

The most common disease is dollar spot that tends to affect Kentucky bluegrass and/or perennial ryegrass lawns that are somewhat low in nitrogen. Though the exact amount of nitrogen needs of a lawn varies with soil type, location in IN or the nation, if it is irrigated or not and so on. Generally for lawns, Purdue recommends between 2 and 4 lbs of actual nitrogen/1000 sq ft. If you apply 2-3 lbs or less of nitrogen per year, there is a very good chance it is dollar spot. The most effective control for dollar spot is to apply slightly more N over the course of the year with most of it in the fall. This disease is also common on lawns where the clippings are bagged which robs nitrogen from the lawn.

The other disease could be pythium which attacks mostly perennial ryegrass lawns that receive ample nitrogen and may actually be too green and succulent for this time of the year. If you apply 4 lbs of nitrogen or more/1000 sq ft, you may be dealing with pythium. The most effective control for this is to reduce the amount of nitrogen that you apply over the course of the year.

-Zac Reicher