Q&A: Everything you need to know about Marengo

Steve Larson is a greenhouse and nursery crop specialist with Envu. He’s been in the industry for more than 45 years. We asked him why growers should consider using pre-emergence herbicides like Marengo.

What makes Marengo a unique herbicide?

It’s a single molecule. A lot of the broader spectrum products in the market tend to be combination products that have two active ingredients. Marengo is a single active ingredient, Indaziflam, with a broad spectrum of activity on both grassy and broadleaf weeds. But the real game changer with Marengo, or specifically the active ingredient, indaziflam, is its longevity.

We have two formulations. We have a liquid formulation which is principally used for outdoor nursery stock, field-grown. It also is used as a bed treatment for container-grown nursery stock — the graveled areas underneath plants. They spray the liquid products, which are a little cheaper in cost and use cost per acre as opposed to the granular. The granular product is principally used over the top of container-grown shrubs, vines, smaller trees.

Do more nurseries prefer the liquid or granular formulation of Marengo?

We sell roughly 60% liquid versus 40% granular. The subtle difference is that the granular product when put out at its highest use rate delivers a lower active ingredient load than the liquid when it’s put out at its highest use rate. In other words, the liquid is more concentrated. Consequently, it just lasts longer.

How quickly does Marengo start working once applied?

One of the things that we recommend growers to do — in fact, it’s on the label — is that after an application is made, whether you spray it or spread it, both require about ¼ to ½ inch of rainfall or irrigation to activate the product. And at that moment, it’s ready to go. If you spread it as a granule, it can sit for up to 21 days with no problem before it gets irrigated. But it’s not going to give you effective control until you do that initial treatment with water.

How long does it last in most situations?

It depends on rate. The longevity will vary a bit based on environmental conditions, mainly temperature. But you can get four months of control, as much as five in cooler areas, with the max rate of the granular product.

The high rate of the liquid product is 18.5 fluid ounces, which is a little over a pint of product per acre. However, that treatment will last eight months in terms of active herbicide. That gives you an idea of how much more active we’re putting out in the highest rate of the liquid — about 2.5 times more than goes out with the high rate of granular.

How can using Marengo save growers money?

Envu funded research with Dr. Hannah Mathers, retired professor and extension specialist at The Ohio State University, who has a consulting business (Mathers Environmental Science Services, LLC).

We asked Dr. Mathers to scour the data that exists in the marketplace and piece together the overall value of using pre-emergent herbicides in a nursery. We found with the use of pre-emergent herbicides in a rotation, along with periodic hand-pulling every other week, you could save 70% over the grower that doesn’t employ any pre-emergence herbicides. All of that savings is made up in one category: labor. Reliable, affordable labor is the no. 1 issue in our industry. Pre-emergence herbicides like Marengo can free up labor dollars to be employed elsewhere in the nursery, whether it’s loading trucks, pruning trees, spacing plants or potting.

We also compared Marengo to other competitive pre-emergent herbicides. While it might cost more than some other products, it lasts so much longer that what you lose in that upfront cost you gain in longevity. The take home message is don’t be confused by that upfront package cost. Take a look at how it works for you and how long it works for you and calculate the value of that in terms of labor savings.

What are some effective rotation partners for Marengo?

I would never want to diminish the importance of chemistry stewardship, whether it’s an insecticide, fungicide or herbicide. Rotation, rotation, rotation: we preach it all the time.

Take a look at your region. What weeds are important in your area? It’s different in South Florida than it is in Maine or the Pacific Northwest.

Weeds have a regionality to them but also a seasonality. Marengo is great on a wide range of late-winter, early-spring weeds like oxalis, as an example. Another weed that is prevalent in nurseries in the summer months is spurge. FreeHand is a product that has an active ingredient of dimethenamid-P, which is just outstanding on spurge. In the cooler times of year, there’s a weed called bittercress that is a scourge for most of the U.S. We recommend BroadStar, with the active ingredient Flumioxazin, in the fall.

Marengo in the spring, FreeHand in the summer and BroadStar in the fall is a rotation we recommend a lot to growers because it seems to work in a lot of different regions. And they all have different modes of action.

For more: www.us.envu.com/ornamentals