Environmental stresses or All brown spots in the lawn are not chinch bugs
By Laurie E. Trenholm

Do you ever get the feeling that homeowners, who look to you for advice on how to care for their lawns, have an actual attention span of about one nano-second and can only assimilate info in that somewhat brief time period? And that much of what you give them as advice really comes across as lah-de-da-de-da? For instance, here is an actual phone conversation that I had with a homeowner recently that I promise I am not making up:

Homeowner: Hello, I got this number on-line and I want to speak to the lawn expert guy.
Me: That would be me. How can I help you?
Homeowner: A woman! I can't believe they have a woman for a lawn specialist! What do you know about lawns?
Me (smiling): Some days more than others. How can I help you?
Homeowner: I knew it! That's why I listen to my barber. He KNOWS about lawns and things like that.
Me (still smiling): OK, so what can I help you with then?
Homeowner: My barber said that the brown spots in my lawn are from chinch bugs and that I should apply insecticides and fungicides too just to be sure. And he knows about this stuff.
Me (sigh, not much smile left): So how long have you been following this advice?
Homeowner: Well, let's see, I guess its since around February. You know, back when it first started to warm up. So I've been applying these things all along and I still have the same brown spots. He also told me I should ... blah, blah, blah, blah ...
Me (only slightly exasperated, no longer smiling): Sir! Excuse me! If I promise not to cut your hair, will you PLEASE listen to me for your lawn advice??????

HAVE YOU EVER HAD A CUSTOMER LIKE THIS????????????
Hopefully, by the time a homeowner e-mail or phone call gets to me, the person on the other end will listen to what I have to say and may even have some intention of following what I suggest. And over the years that I have been fielding lawn questions, I've pretty much devised a stock set of questions to ask NO MATTER WHAT THE PROBLEM IS THAT THEY'RE CALLING ABOUT. Why do I do that? Because, by the time someone sees a visible problem like disease or dollarweed or thinning grass, there's something else going on than what they're seeing. Disease, insects, and weeds are called biotic or living pests and they can be treated with pesticides. However, these pests are generally secondary to another problem, that we call an environmental pest. And if the environmental pest isn't treated, all the pesticides on the planet won't cure the visible problem. Sometimes it takes some detective work to figure out the real culprit, so get out your sleuth trenchcoat and let's talk about the questions we should all be asking.

ENVIRONMENTAL STRESSES
These stresses fall into several different categories, some of which are cultural practices that we can alter and some of which are due to the environment and may or may not be correctable. Some of the most common stresses on lawns are listed below:

 

While this list is not all inclusive, it covers the major problems that will be seen in lawns. Let's look at each of these separately.

IRRIGATION
This was the topic of a previous article. In a nutshell, sprinkler systems need to be adjusted seasonally or turned to manual and water applied only when grass begins to show signs of wilt. They need to be calibrated so that the proper amount of water is applied. Brown spots in the lawn can be from broken sprinkler heads, so it's important to watch the system run once in a while.
Saline water is another issue that is becoming more common. As long as this growth continues in Florida, it will remain an issue as we deplete water resources and experience more salt water intrusion. This injury often looks like drought stress and excessive salts can injure shoots, roots, or both. St. Augustine grass has pretty good salt tolerance and as long as it gets supplemental rains to flush the salts out, it will usually be OK, but this problem should be on your radar screen.

SHADE
Do you ever long for a nice shady spot in the hot dog days of summer? Well, so does the grass Ð to some extent. St. Augustine grass will actually do better in up to about 35 percent shade as opposed to full sun. In heavier shade than that, however, its growth habit is altered as the leaf blades become longer and skinnier as they try to reach for light. At the same time, the grass loses density as it puts its growth into the leaf blades Ð hence the thinning that is typical of shaded areas. The grass also receives different wavelengths of light under trees than what it needs for best growth Ð of course, the trees take up those wavelengths! So growth is further altered. And then imagine a crowded living environment, where grass roots compete in the soil with tree roots for space, water, air and nutrients. So what biotic problems can result from shaded environments? The primary problems are disease, due to increased soil moisture and reduced air movement in shade, and weeds in the thinned-out areas, especially those that love moist soil! So, while you can apply fungicides and herbicides to control these biotic problems, your customer really needs to be educated about whether turf can grow correctly in a shaded area.

SOIL CONDITIONS
Ah, Florida soils. Many of the lawns you maintain are literally sitting in a sandbox and require frequent watering and fertilization. Others may suffer from Builder's Special, consisting of top soil that may have been dredged from the bottom of a lake with no regard for pH or compaction. In many cases, you may have both in one yard.
Now don't you think we should at least be soil testing for pH and trying to get a handle on what soil conditions are like on your properties? Might make combating these stress and pest problems a lot easier over time. Aerifying might be necessary if soil is compacted or not draining well.

TRAFFIC
Dogs, kids, cars Ð St. Augustinegrass doesn't like much of any of them. This is one stress you're probably going to largely ignore, but there are a couple things you can do to reduce the problem. More leaf tissue reduces damage, so increasing mowing heights can help. Watch out for compaction, this is where it will happen. Watch weed control in this area. If grass is still growing but struggling, higher nitrogen will make it recover better and may help it to hang on. Potassium should be increased too Ð apply a 1:1 N:K ratio in these areas. If the grass is worn away in these areas, it will not recover unless traffic is eliminated or re-routed.

FERTILIZATION
This was also the subject of a previous article. Under-fertilized lawns start to look like Sanford & Son and are probably not the look your clientele expect. However, over-fertilization likewise is not the best answer, for while green is what we all strive for (of course I mean grass, not money) too much N often sets you up for less stress resistant grass, disease, insects, etc. If you want cosmetic green, don't forget about iron.
Fertilization timing is also important. If it's the end of the day and I'm tired, I'm not going to drink a cup of joe and lawns in the northern part of the state that are going into dormancy don't want to be fertilized late in the year either. This discussion gets into some pretty heavy duty physiology that keeps me animated, but is a topic for another day. One other often overlooked issue with fall fertilization is the fate of the nitrogen Ð how can semi-dormant roots take up the fertilizer applied? Well, we don't think they can and that large amounts of the fertilizer may leach into the groundwater, but that research will not be starting until next year. Stay tuned for the answer to that one!

MOWING
Have you ever seen a seashore paspalum lawn that got scalped? Not pretty as it turns reddish brown as disease sets in. Pretty soon you're reaching for the Heritage! This is a classic example of the stress-disease complex and can happen in other grasses too. Scalping eventually will wear the grass out, as it uses up all its reserves in regrowing. This leaves it susceptible to insects or disease damage. And we all know what dull mower blades do Ð they leave the light on for the insects and disease to find their way into the leaf.

HERBICIDE INJURY
Ooops Ð you're probably all pretty familiar with this one. Read the label, train the techs, try a new combo in a corner and see what happens. You may or may not be able to grow your way out of this one, but one thing not to do Ð don't apply any more pesticides!

So remember, living pests often occur because of environmental or cultural conditions. Simply applying a pesticide or fertilizer will not stop the problem, although it might mask it for a while. Remember to look for what the cause of the actual problem might be and try to educate your clients about what their options are. And I promise, I am not making any of this up!

Trenholm is associate professor of environmental horticulture and turfgrass specialist at the University
of Florida-IFAS, Gainesville.