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Cool Season Preemergent Strategy |
The deadline for preemergent applications looms like an approaching freight train. This year it may seem all the more ominous considering the complications of new estimates to do, broadleaf weeds to control, bad weather to work around, and the knowledge that we have had some really bad crabgrass seasons of late. But it’s not all bad news. After all, problems drive sales, but you need a plan to take advantage of them and get it all done. Here are some considerations to help you plan for spring.
1.) What preemergent chemistry should I use?
There are certainly lots of choices and they all boil down to a compromise between cost, convenience, and efficacy. Here is my quick run down on the major products and some of their pros and cons.
Pendimethylin, (Pre-M®, Pendelum®) “Pendi” has been one of the most commonly used preemergents in turf. Low cost, rebates and reasonable efficacy have driven the popularity. Pendi is available in granular, fertilizer combinations, and tank spray formulations. While cost and versatility are advantages there are drawbacks. Pendimethylin is a root inhibitor and probably has more negative effect on turf roots than other preemergents used at label rates. Pendi is used in turf at about 1.5 lbs. per acre in most cases. It is not particularly long lived and can produce severe yellow/orange staining.
Trifluralin, benefin, (Treflan®, Balan®, Team®, Team Pro®) These molecules along with Pendi are dinitroanalynins (DNAs). They have that characteristic yellow / orange color, but they are not as prone to staining. For turf, combinations of Treflan and Balan called Team® and Team Pro® are most commonly used. Benefin is quick to set up and provides early efficacy while the trifluralin is longer acting and extends control. These are still some of the best cost effective preemergents on the market. Team is a traditional 2:1 ratio of balan to treflan and is usually applied at about 2.0 lbs of active per acre. Team Pro is a 1:1 ratio and is applied at 1.5 lbs. active per acre. The extra trifluralin boosts efficacy allowing for the lower rate. Both are widely available on fertilizer combination products and some straight granules. They are not available in a spray formulation.
Dithiopyr (Dimension®) Dimension is not in the dinitroaniline family and does not have yellow color or staining. Dimension is also less of a root inhibitor than the DNAs which can be particularly good after a fall overseed when there could still be immature seedlings in the stand. The other big news with Dimension is that there is early preemergent control of crabgrass extending the window of application. However, if you want to go out later and take advantage of this you must use the appropriate higher rate. Dimension is the most versatile preemergent in terms of late spring application and has excellent efficacy when applied evenly. The active does not move much though so skips in application can result in skips in coverage.
Prodiamine (Barricade® Cavelcade®) This is another DNA with the distinction of being the least soluble and therefore longest-lived. Prodiamine can last a very long time and some turf managers even use fall applications to prevent crabgrass in the following spring. The cost of prodiamine is lower this season due to patent expiration and the introduction of generics. Recent issues with late season breakthrough and new lower cost will likely prove a boost to this chemistry. Prodiamine is available in both granular and spray formulations and like the Team products is much less likely to stain than Pendi. Prodiamine does not have post emergent control, but due to it’s long residual you can extend your application window by starting earlier if weather will let you get on the lawns. One caution if you are seeding. Don’t underestimate the residual. Seeding failure from prodiamine is a common pitfall for those who do not take the label seriously.
Siduron (Tupersan®) This is a preemergent chemistry that is often overlooked. It is pricey, but siduron has one huge distinction, selective control of crabgrass while allowing cool season grasses to germinate. That’s right, you can seed and prevent crabgrass at the same time! In fact there are starter fertilizer Tupersan combinations. You need to know that the residual is short lived. Once your new seed is up and running a follow up application is in order. You could use more Tupersan, but I prefer Dimension as long as all of the seed is already germinated.
2.) What rate should I use?
The only official advice I will give here is “consult your local university and read the label”! The right rate is not rocket science, but there are too many permutations to cover them all. It’s never really very complicated until price enters into the equation. Here are some basic rules. First, cheat at your own risk. Too many times I have seen pros opt for low rates, or low formulation products when using fertilizer combinations, only to get very poor results because the active ingredient per acre is not enough to give good control. This is very common when we are lured into a false sense of security by one or two seasons of low crabgrass pressure. You might get away with it, and you might save some money, but don’t expect the manufacturer or the formulator to ride to the rescue if things go awry. Conversely be wary of fertilizer combinations with very high active ingredient loading. These products look good on paper because you can apply fewer bags per acre to get the target rate. This usually saves some money, but can your applicators get sufficient coverage at 2.5 or 3.0 lbs per 1,000 square feet?
Sample Herbicide Rates in Active Ingredient per Acre, Consult Label Before Use
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Chemistry
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High Rate
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Low Rage
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Split Application, Interval
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Pendimethalin
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2.0 Lbs ai/A
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1.5 Lbs ai/A
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1.0 – 1.5 Lbs ai/A, 4 weeks
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Team®
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3.0 Lbs ai/A
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1.5 Lbs ai/A
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1.5 Lbs ai/A, 8 – 10 weeks
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Team Pro®
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3.0 Lbs ai/A
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1.5 Lbs ai/A
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1.5 Lbs ai/A, 8 – 10 weeks
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Prodiamine
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1.0 Lbs ai/A
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0.65 Lbs ai/A
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0.35 Lbs ai/A, 60 – 90 days
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Dithiopyr
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0.25 Lbs ai/A
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0.13 Lbs ai/A
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0.13 Lbs ai/A, 6 – 8 weeks
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Siduron
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8.1 Lbs ai/A
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4.0 Lbs ai/A
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4.0 Lbs ai/A, 4 weeks
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3.) How should I apply my preemergent?
How you apply will be largely a function of your overall application strategy. If you are a liquid based company you might consider some granular applications for early season when cold weather can freeze lines or for windy days when drift might be an issue. If you are a granular based company you may find that some low volume liquid applications may be in order where it is difficult to operate a spreader. Around pools, courtyards, and so on. I think that granular combination products lend themselves to higher productivity while liquid applications offer superior versatility in rates and better ability to trim and edge. Avoid impervious surfaces with either so you don’t get complaints about stains. Established plants tolerate preemergents so overlap into shrub beds is not a problem. In fact these edges are prone to breakthrough so good rates along the edges are a must.
4.) When should I apply my preemergent?
There may be some debate about the exact temperature and duration, but for our purposes we can assume that Crabgrass germinates after several days of >55°F soil temperatures. When does this occur, there’s a difficult question? If you’re psychic skip the rest, otherwise read on. The dropping of Forsythia blooms is a good phonological indicator, a soil thermometer is even better, but these are not predictions they are measurements. Keep in mind that soil texture and exposure affect when this warm up occurs, so you will have hot spots, for example along paved surfaces. If you have a full production schedule you need to start as early as possible and assume you will run out of time. On the other hand, we have had cool wet springs recently so if you made early applications, and are using a single application program, you likely ran out of steam before the germination period was over. The answer if you want to remove some of the guesswork is split applications. This was very popular years ago and has fallen from favor. Maybe because split apps costs a little more, but more likely I think because of a shift to granular products. Until recently a second preemergent application was difficult because of the need to control broadleaf weeds and reduce callbacks during that late spring application window. Split applications make sense and new pre+postemergent granular combinations make the second application possible without forgoing one weed control for another.
