Neil Sperry: Cause of 'tire tracks' on yard explored in depth

DEAR NEIL: About a month ago our lawn maintenance company mowed our grass. I noticed a spot that almost immediately appeared beneath our red oak. It was about 4 by 4 feet, and it looked like it had tire tracks going through it. A few days later we had our trees trimmed and the company dragged limbs from our yard. Many more of the spots appeared almost overnight, again looking like tire tracks. We sprayed with a fungicide and the grass began to look a bit better. One thing that showed up on Web searches was Ascochyta leaf blight. We've never had anything like this in 11 years of living here. I've known how to deal with chinch bugs from reading your columns, but this one has me stumped. Any suggestions?

Dear Reader: My challenge will be in answering without a closeup photo, and without a photo of the root system. You'll see as I outline the possibilities.

First, the oddball one. There may be a few people out there who are familiar with "heat tracking" caused by running heavy equipment, especially large mowers across lawns that are dry when temperatures are high. Michigan State University has an outstanding photo I found online several years ago. ( ) (You did not mention if the arborists brought any tired equipment onto your lawn.)

I am replying to your question within one week of your sending it, and I'm subtracting the one month you mentioned. That puts us back into early September when it was very hot. However, I'm going to mention that I have only seen heat tracking on bermudagrass lawns and not on St. Augustine such as you have. I'm going to take a pass on that possibility, but I felt I should mention it.

We had one week of cool weather back about the time you're referencing. That could have been enough to trigger the beginnings of brown patch (large patch) fungus. If the grass blades turn yellow, then brown, and especially if they are rotted at their bases and pull loose easily from the runners, that's the issue. The fungicide Azoxystrobin does a good job of stopping that fungus, just as it does for take all root rot and gray leaf spot.

I would even present the possibility of chinch bugs, although you say you know how to recognize their presence. I respect that, so I'll move on, plus it's getting late in their season.

This could even be damage of white grub worms, the larval form of June bugs. This is the precise time that their damage starts to show up. Pull on the dying grass. If it comes loose from the soil, runners, blades and all, and if it appears the roots have been chewed away, then dig a few 12x12-inch test holes 4 inches deep. If you see any of the white C-shaped larvae, always with legs and brown heads, those are the grubs and they're your proof of the cause. Imidacloprid applied and soaked deeply into the soil will stop them, but don't use it until you confirm their presence in numbers of 4 or 5 per square foot.

And, before I sign off completely on your questions, I'll address the Ascochyta leaf blight. It appears to be primarily a problem of Kentucky bluegrass and tall fescue, both cool-season turfgrasses. I can see why you would consider it a possibility when I saw its photos with the northern grasses, but I found no references to it affecting St. Augustine.

DEAR NEIL: Have you written about preparing the lawn for the winter? I have St. Augustine, and I'm wondering if I should aerate in the fall as well as the spring, and also if I should spread compost on the lawn in fall as well as in the spring.

Dear Reader: This will be a different answer than you expected. I don't think you should do either one either time. Core aeration (where you remove plugs from the soil) is somewhat damaging to the large stolons of the St. Augustine. Odds of your having (a) soil compaction due to pedestrian traffic or (b) a build-up of undecomposed organic matter known as thatch are very slight. They are not worth the gamble of the injury to the St. Augustine. We do aerate bermuda turf in Texas, but that's best done in April.

As for topdressing the lawn with compost: What is your reason? It decomposes and adds organic matter to the top of the soil surface. That's a good thing, but only for a short period of time. If you mulch your clippings, they will do the same thing. I'd rather see you invest your money and your effort into buying and applying a high-quality, all-nitrogen lawn food with 30 to 40 percent of its nitrogen in slow-release form. For St. Augustine, those applications should be made in early or mid-April, early June and early September.

DEAR NEIL: These azaleas are 3 years old. They have performed beautifully each year, but gradually this one began to die even though I have a sprinkler system. What might have happened? I will be very sad if I lose the others.

Dear Reader: Your photos only had about 100kb of resolution. I could only enlarge them to about 1 inch tall before I lost important detail, so obviously I couldn't see the individual leaves. I can only guess, but this plant probably got too dry. The sprinkler head that serves it could even be malfunctioning. Azaleas have very fine roots that would fill up that small amount of planting soil in just a few years. Then, when temperatures got high, their margins of error in watering would be razor thin. This plant was probably the first one to reach what is called the "permanent wilting point" – the point of no return from which a plant cannot recover even if it is soaked deeply. This does not appear to be the work of an insect or disease.

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