~ Pablo Picaso
While Picaso had a great take on the color yellow, few of us appreciate yellow in our turfgrass. And since I've been getting a lot of calls and emails lately about yellowing St. Augustine, I guess it's time to look again at all its possible causes and methods for dealing with each situation.
Lately, the questions are mostly related to a chartreuse color ... or a faded green. Sound familiar? It's possible that all the recent rain we've experienced has leached out all the nutrients — especially iron, something lawns normally need to be deep green.
But first, let me get the most obvious out of the way: If you have not done the summer fertilization — maybe because you thought it was too hot or too wet — there's your answer. Remember, it's never too late to do the right thing. So you can and should apply fertilizer per my schedule.
Now ... while excessive moisture may be to blame, a number of other things could also be the cause. In my lawn fertilization schedule, I address the possibility of yellowing in July and August. Most often it's a nutrients deficiency ... either iron chlorosis or nutrient lock-up. You may notice the discoloration under tree canopies, especially those of pine trees and crape myrtles. GardenLine listener Irene Moulder sent me this picture of a good example.
So, here's what I recommend for chartreuse or pale-green grass. First, approach it as if it's iron chlorosis - a need for iron and soil acidifier. Put down any iron-acid combo you can find and water it in.
Here are some products you've heard me recommend for iron treatments:
- Dr. Iron from Monterey
- Iron Safe (if still available) by Lillie Miller
- Nitro-Phos Iron & Soil Acidifier
- Hi-Yield Iron Plus
- Actino Iron
- Any liquid iron-soil acidifier
If you don't see a significant green-up after two weeks, you likely have a nutrient lock-up. Apply a soil-activator/microbial treatment to the afflicted areas. Hopefully, if there's a phosphorous lock-up going on, this treatment will help release the right nutrients.
These are products I recommend for such treatments:
- Medina Soil Activator
- Medina Plus
- Lady Bug Terra Tonic
- Soil Mender Foliar Plus
If cost is no object, you can do an iron treatment and a soil-activator treatment together. I prefer applying iron first and soil activator second, both on the same day because I want to judge results quickly.
But what if neither of these treatments works? It could be the dreaded St. Augustine Decline - SAD. Frankly, there is no cure for it. Some fungicides work a little bit, but none are effective at complete control.
But the yellowing could also be the start of take-all patch. With that, the grass more or less thins out ... we often refer to it as "melting away." But if you catch it early, in the yellowing stage before the melt, you can control it. (By the way, if you have a lot of nutgrass in the yellowing areas, that's a harbinger of take-all patch.)
The last possibility ... something that causes a "yellowing tinge" ... would be gray leaf spot. The timing is way off for that predicament, though. Normally, it hits in the spring right after a high-nitrogen fertilizer application is followed by drenching rains. Most people who follow my schedule don't ever have this problem because they use controlled slow-release fertilizers with ratios like 19-4-10, which is NOT a high-nitrogen fertilizer (like, for example, a 29-3-4).