You’ve seen articles in past issues of Potato Grower about targeting the weed species in each field with the right combination of herbicides and not using the same combination on all fields even if different weed species are present in those fields. Crop competition with weeds not controlled season-long will result in the reduction of tuber quality and yield loss, which means profit loss from the field. The Tank-Mix Partner (TMP) Choice Charts in this article can help concoct the best brew for return on your investment.
Herbicides labeled for use in potatoes in the U.S. and Canada are in the first column of the TMP Choice Charts. Not all trade names for herbicides are provided in these charts due to space limitations. Trade names specific to Canada are noted. Pre-plant and pre-emergence burndown herbicides and vine-kill products are not included.
Five weed species critical for control in many potato production areas—hairy nightshade, redroot pigweed, common lambsquarters, kochia and green foxtail—and levels of control provided against each by each herbicide are shown in the first chart. Charts with different weeds can be created to reflect the possible spectrums in your fields.
The second TMP Choice Chart shows the control levels for a possible mixture of hairy nightshade, common lambsquarters and green foxtail present in a field of interest.
Herbicides shown in similar colors are in the same herbicide mechanism-of-action classification group. Tank-mix herbicides with different mechanisms of action (MOA) should be used in order to attain broad-spectrum weed control and prevent or delay the development of herbicide-resistant weed populations.
Control levels in the charts are as follows:
- G, Good = 90 to 100 percent control;
- F, Fair = 80 to 89 percent;
- S, Suppress = approximately 50 percent;
- PN, Poor to None = 0 to 30 percent; and
- N, None = 0 percent
The best-case scenario would be to have a tank mix with 90 to 100 percent (G) control of all weeds present, but this might not be possible. Of course, the next-best would be to have at least one herbicide with 90 to 100 percent matched up with a herbicide that can provide 80 to 89 percent (F) control.
Herbicide resistance management during the potato crop year should also be a goal. Choose tank-mix partners with different MOAs that have overlapping control of all weed species present—a species is controlled 90 to 100 percent with at least two different herbicide MOAs. Depending on the situation, one of the herbicides could have 80 to 89 percent control. If it is not possible to have more than one MOA controlling the same weed during the potato season, choosing herbicides with different MOAs in rotation crops is important.
The third TMP Choice Chart shows a two-way mixture for the example scenario of hairy nightshade, common lambsquarters and green foxtail in a field of interest.
The weed control goal in this scenario can be reached with Outlook + Linex/Lorox applied pre-emergence (after hilling and incorporated with sprinkler irrigation or rainfall):
- Hairy nightshade is controlled season-long 90 to 100 by Outlook and 80 to 89 percent by Linex/Lorox.
- Common lambsquarters is controlled 90 to 100 percent by Linex/Lorox.
- Green foxtail is controlled 90 to 100 percent by both herbicides.
It should be noted, of course, that more than one tank mixture can target the three weeds in the example scenarioj, as shown in the TMP Choice Chart.
University of Idaho research has shown that two-way tank mixtures of Matrix, Chateau, Eptam, Outlook, Reflex or sulfentrazone applied pre-emergence will improve season-long hairy nightshade control compared with any of these herbicides applied alone, especially in heavily infested fields.
The same weed management approach will not work for all fields because the number of weed species can vary greatly from one field to another, even if they are in close proximity. Use TMP Choice Charts to create a customized herbicide tank mixture that will target the specific weed species in a field of interest.
Tank mixtures can be designed for pre-emergence only, pre- plus post-emergence, or post-emergence only application timings, depending on a specific field’s needs. Even though a targeted tank mix could cost more in terms of time and money, returns on investment could outweigh the cost: weeds competing with crops reduce yields and profit, and add to the weed seed bank in the soil, resulting in higher weed densities and higher costs for weed control in the future.
Happy tank-mixing!
Pamela J.S. Hutchinson is a potato cropping systems weed scientist based at the University of Idaho’s Aberdeen Research & Extension Center. She can be reached at phutch@uidaho.edu.