Capt. Tom, i'm having the same problem and not sure how to treat it now.
Roger

I too am having the same problem. Glad to know I'm not alone. I would appreciate any help.

Thanks
Tony
Jackson, NJ

I suggested overseeding in this thread because it's something you really should do if you never have or haven't in a few years. Herbicides to control crabgrass will prevent overseeding. If you want to control crabgrass now, Ortho and Bayer Advanced have products labeled for crabgrass.

Bestlawn

I have used the Ortho crabgrass killer with pretty good results.

However, the idea of puting down the preemergent in June was to avoid the problem I am now having. Would the June application of Halts prevent germination in September (3 or 4 months later)?

Capt Tom

The pre-emergents are a useful product, but they have their limitations. First, they have a window of opportunity. That might or might not be the 'useful life' listed on the label. That depends, obviously, on the conditions under which the product was put down.

So let's assume you spray, and it's supposed to be good for three months. It might even stretch to four, but you can't count on it.

Well, poa annua germinates in the fall. Those seeds become viable in the fall, winter over, and sprout in the spring.

Crabgrass germinates in late spring, AND LATER.

One would think that one could simply overdose the lawn, and spray every thirty days for twelve months, and that would do it. It might, by the way. I've been sorely tempted. But size of lawn, and expense, have kept me from it.

Other than that, you've got the concept of re-seeding. The pre-emergents aren't a WEED (with a W) killer, they are a SEED (with an S) killer. The theory of a pre emergent is that 'no seed will germinate'. That's how you stop the cycle of poa, or crabgrass, continuing to grow from seeds from prior crops. But that means that grass seed won't germinate either, doesn't it? If your lawn is primarily Kentucky Bluegrass, that's less of a problem, as you can, with fertilization, get the existing plants to spread out, and fill in bare or thin spots. That's not possible with the ryes, and fescues. They don't spread much, if at all.

Striking some sort of balance, between the need to re-seed, and putting down pre-emergent, is more art than science. Sometimes you get lucky. Sometimes you don't. But that really is the nub of the problem.

But needing to put down multiple applications of pre emergent, over the course of a year, is fairly common. Having to do it for a two year or three year period, is fairly common. You've got to break that cycle of weeds-to-seeds-back-to-weeds-again. And it ain't easy.

Captaintom, by your question, I assume your only application was the June one. Because crabgrass begins germinating in early spring, usually March, you need that early spring pre-m. Because it continues germinating into early summer, you needed that late spring application (June). Now understand this. Crabgrass does not germinate in September, August, or July. The crabgrass plants you see during these months are the ones that were able to germinate earlier and are now matured.

Provided all of you did apply pre-m and applied it timely, you should not be so inundated with crabgrass. That you are complaining of seeing so much, I can only think of two reasons that may be. One is your own spreading effort, in that you didn't get the coverage you thought you did. The other is that it is not crabgrass you are looking at but something else entirely.

Correction.....

Because it continues germinating into early summer, you needed that late spring application (June).

That might actually be May rather than waiting until June.

Crabgrass is going to die out in frost, but just before that is when it flowers and leaves seeds behind. It is those seeds that germinate the following spring. If you're not planning to overseed this fall, then an herbicide for crabgrass will be a good idea now to prevent flowering/seeding. You still want pre-m next spring though. But I still don't know for certain that you have such a crabgrass problem right now if you applied pre-m in spring. Pictures will help us.

In short, yes, you can reapply preemergent later in the season. In southern climates, many people do this since it is warm for considerably more than the 3-4 months most products last. They also sell preemergents that last for longer periods of time, but you probably won't find them at home depot.

In northern climates, one application is usually enough as long as you don't apply it until the forsythia are in full bloom. If you jump the gun, it fades out sooner and you get more weeds. If you have a lot of major washout thunderstorms though, all bets are off.

Thanks for the comments.

In fact, I did apply Halts just when the Forsythia bloomed. All was fine until roughly two weeks ago and there was an explosion of crabgrass.

I am fighting the crabgrass now by handpicking and using a herbicide. I thought that for next year a second application in May or early June might be helpful. I will be overseeding this September so it is too late to try it this year.

Capt Tom