Mark VanGessel, Extension Weed Specialist; mjv@udel.edu
Prepackaged herbicides, those that contain multiple active ingredients in the same container, are a staple of the industry. It’s convenient to only have one container rather than 3 or 4. From a manufacturing standpoint the products can be formulated specifically to ensure multiple herbicides mix well and stay in solution.
There are a lot of issues with premixes. First is the right products. Let’s face it, no agrichemical company is blending a mixture for the Delmarva region. That means some of the products you may hear about do not fit our region because of our soil types, our crop rotations, or our weed spectrum. Or they contain active ingredients that are not bringing much in terms of weed control for use because we don’t have specific species. Some of these premixes may have as many as four different active ingredients, but in reality, you may only need two or three of them; and it stands to reason that there is a cost for each of those products, so you might be paying for something you don’t need.
One of the most common issues we face is that the ratio of the products may not be correct for our area. An incorrect ratio means that the individual herbicides are not applied at the correct rate. This often means we should be “spiking” a premix, adding additional herbicide to a prepackaged mixture to achieve the correct ratio.
A standard recommendation for clomazone (Command) and ethalfuralin (Curbit) for pumpkins and melons is 8 fl oz of Command and 40 to 48 fl oz of Curbit. Using 3pts of Strategy provides 8fl oz of Command but only 25 fl oz of Curbit. Using Strategy to achieve the correct rate of Curbit results in way too much Command. So, we recommend 3pts of Strategy but “spiking” an additional 14 fl oz of Curbit to get the total amount to 40 fl oz.
The hidden risk of these premixes delivering low rates of specific active ingredients is selecting for herbicide resistance. examine the label of these premixes and determine if each component is at the proper rate, meaning if you were using the product by itself what rate would you use. This can be a challenge to figure out, so we have tables in our weed management sections breaking down the individual herbicides and their use rates.
These tables can be found at:
Weed Control in Field Crops – Virginia Tech ENTO-566-E https://www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/456/456-016/ENTO-566-E.pdf
- This is a joint effort with Virginia Tech, Univ MD, Univ. of WV, Univ. DE, Rutgers Univ. and Penn State. This is the same information in the Penn State Publication, but this version is free
Weed Management for Vegetables – (Table E-6 in Mid-Atlantic Commercial Vegetable Production Recommendations)