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.

 

 

2 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 🤔

    Like

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