This Summer Illustrates the Need for Two Applications of Preemergent

Let’s face it folks, this has really been a sucky summer. June was like July, July was like August, and August has been as horrible as usual. This tropical weather has placed turf under massive stresses from diseases and weeds. Cool season turf species (fescue, bluegrass, ryegrass) would rather take a prolonged siesta, but we water and fertilize it to keep it actively growing. Stressed turf simply can’t grow aggressively enough to combat these invaders. In contrast, weeds like crabgrass and yellow nutsedge love this crap! Both these weeds are evolutionarily-advanced “C4” species, meaning that they can thrive when temperatures get above 95F.

A quote often attributed to the great Green Bay Packers coach, Vince Lombardi, is appropriate at this point, who said, “The best defense is a good offense.” You’re thinking, what the hell does a legendary football coach know about turf? Well duh! Healthy, thick turf prevents weed seedlings from germinating. On the other hand, weak turf allows sunshine to hit the soil surface, stimulating weed seed germination. Lush turf, especially those swards mowed appropriately high in the summer, casts too much shade upon the soil surface, thus inhibiting weed germination.

These photos illustrate numerous issues, the first of which is dreadful application! Notice the very clean line of demarcation, which proves the effectiveness of the preemergent herbicide. The applicator (supposedly a PRO!) either ran short of product, or simply forgot to apply the herbicide on both sides of the sidewalk. The very uniform lines of control suggest an advanced spreading device. The homeowner needs to fire their asses! Find an LCO (Lawn Care Operator) that uses Dimension™ herbicide! But what if this was DIY? If this is the case, numerous explanations are offered. Probably the best guess is that the homeowner did not heed our advice to make a “double pass” application. He/she set the spreader setting too “heavy”, resulting in him not having enough product for the last 2 or 3 spreader swaths. Boo, hiss! Set your spreader on a “low setting” that allows you to make a double-pass application of every product. But wait! There’s another problem here. START every application along the edges of your concrete and asphalt surfaces, and in the street median. Make those passes first. Then start your double pass application. Pass 1 goes down at a certain direction and Pass 2 goes out at 45 to 90 degrees different. Turf growing along hard paved surfaces suffer from the highest weed pressure. So hitting these areas first ensures at least 2 passes with the spreader, and hopefully even 3 passes. The radiant heat load from paved surfaces increases the soil temperature in the adjacent soil. As a result, crabgrass germinates a full 10 to 14 days ahead of the rest of the lawn. In these areas the crabgrass seedlings grow sufficiently large that even Dimension herbicide can’t control them. These weeds simply germinated ahead of the preemergent application. The double whammy comes from the heat stress this turf suffers from in this area (reread the prior paragraph).

Another best practice is to make TWO applications of a preemergent herbicide, “just-in-case!” This was a “just-in-case” year! Heavy rainfall and high temperatures contributed to high microbial activity. Soil microbes actually “eat” pesticides—and they were quite hungry this year. Most LCO’s only make a single application and hope for the best. Many of them wait for the homeowner to call and bitch about crabgrass escapes. Care to guess what percentage of customers don’t even bother to complain?

Astute turf tenders wonder why the crabgrass in this image is chlorotic (yellowish) compared to the normal green color. It’s obvious that either the LCO or the homeowner has attempted to rectify the problem with a postemergent herbicide. Based upon the degree of chlorotic and bleached tissue, the herbicide applied was probably Tenacity® (mesotrione). This is a very new tool (3rd year of sale) for weed control in turf. It controls key broadleaf weeds and problem grassy weeds in cool season turf. It will damage bermudagrass and zoysiagrass and repeated use can actually control bermudagrass, if tank-mixed with Turflon® (triclopyr) herbicide. The best thing about Tenacity is that it doesn’t interfere with reseeding so it can be used now.



10 thoughts on “This Summer Illustrates the Need for Two Applications of Preemergent

  1. your article re: preemergents suggests seeing photos when in fact I didn’t
    see any photos… your information is great, but as I read I looked for the
    photos….I could picture what you were suggesting in my mind 🤔


  2. Hi there. Saw you on the morning show. Great info. Much I follow quite well such as the grab grass early then dandillion later. Also the info about the lawn mower blade being sharpened, Guilty! Went and had done today. Bought a second one like you suggested👍🏻. So, my question. You mentioned I believe something called “brown patch”. I believe that me. Is there anything I can do? It seems like you mentioned that the products we use have to much nitrogen in them. Is this warm weather really showing that’s true? It has not happened to me in years past. Usually much cooler with ALOT more rain. I thought it was the start of fungus until I heard you mention that description🤔


    • Hello No-name! Glad you enjoyed the segment. Brown Patch is a disease caused by Rhizoctonia solani and it really is the Achilles Heal of turf-type fescue. One of the worst contributors to this nasty disease is to apply too much nitrogen after mid-May. Too much nitrogen is described as more than 0.2 lbs of ACTUAL NITROGEN per 1,000 sq ft. That’s not much N! I recommend that Milorganite (organic N) be used in May and June. Conversely, there are very, very slow release commercial formulations that are sold by professionals, which you won’t find in the hardware stores. Excessive nitrogen leads to succulent turf, which predisposes the turf to brown patch. But it’s not the only thing you can do. For example, as I stated, mow as high as you can and keep the blade sharp. Collect the clippings during an outbreak. Water only in the morning–watering late keeps the grass wet through the night, allowing the disease spores to germinate and grow. The single best fungicide for brown patch is azoxystrobin, available in the Scott’s fungicide product. It’s best to use this stuff PREVENTATIVELY…meaning apply it now even if you don’t have the disease outbreak. But if you’ve never had the yard die out from the disease, you may be one of the lucky ones. Even better for disease control is to add a second product, propiconazole. It too is available at the big box stores.

      I hope this helps!



      • Also I neglected to mention the weather relationship. Hot, humid weather is when brown patch hits. When we’re miserable, turf is miserable! Dew points above 70 and night temps above 70 are significant contributors to disease. When patch hits my yard, it’s in the area with full sun, on slope facing west. Talk about stress!


    • Marty, sorry I didn’t fully answer your question about the weather and the rain. There are different diseases that like cool, wet weather. Brown patch shows up like clockwork in June, with heat and humidity, even without rain. Wet grass through the night helps the disease spread. Even without rainfall, our summer humidity is usually high enough to have a dew in the morning–that’s enough moisture to help the disease spread. In full disclosure, I don’t use fungicides on my lawn. I just do everything else as good as I can, and reseed in September, if I need to. For those wanting to prevent brown patch, start NOW! There is a professional product called Headway G (a granule). A 30 lb bag covers 10,000 sq ft as a preventative fungicide, but only 5,000 sq ft as a curative product. If you don’t know where to get this, you can buy azoxystrobin at Home Depot and you can buy a second product with propiconazole. I would apply azoxystrobin ASAP, and 2 weeks later the propiconazole, and two weeks later repeat the azoxystrobin. So, every 2 weeks you’re applying a fungicide. You can usually stop in early September. Fungicides are very expensive! That’s why I use my money on new seed, but I hire out my aeration! Good luck. Write back if you want.



      • Hi Trav, Marty again. Thank you a ton for all the info and reiteration. I have followed all suggestions and I believe it IS making a noticeable difference. Azoxystrobin. New blade and , sharpened the old one to have as a second. Always have mowed high in hot weather and always have watered in early am👍🏻. Again, thx for taking the time. Great info!! Happy gardening


      • Marty, keep up the good work! I’d like you to rotate some propiconazole into the fungicide mix, every now and then. Do this to broaden the spectrum of the diseases controlled and delay the onset of resistance. You could alternate azoxystrobin and propiconazole for the same price, essentially. Thanks for your note.


  3. Trav,
    What are your thoughts on a routine for a spring overseeding of a lawn and a pre emergent application? I overseeded (fescue) in the fall and I never see the fall growth like I want and over the winter I get concerned that I won’t see my bare spots fill in like I expect in the spring. I’m always tempted to reseed in the spring but my experience has shown that it is necessary to apply a PE soon after the last frost. I understand that the use of PEs affect grass seeds as well as weeds. What would you think of an application of grass seeds followed by an application of a PE? I assume there needs to be a certain amount of time to allow the new seedlings to sprout and become strong enough to withstand whatever the PE would do to hinder their growth. How much would a spring reseeding allow the new grass to outcompete potential weeds for nutrients in my lawn? I guess my questions are how long are PE effective (I use them regularly every spring and still have some weeds appear in summer & I know you advocate for a 2nd application) and when is it ok to apply a PE to a reseeded lawn?

    PS. I’d love to see a post about moss, its effect on a lawn and causes/treatments



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