What is in this article?:
- New glyphosate-resistant pigweed hybrid found in Mississippi.
- From pastures to row crops.
- How did it happen? What are the implications?
A SPINY AMARANTH/Palmer hybrid discovered in a Mississippi cotton field. Notice the flower head with male flowers between zero and 3 inches and fuzzier female flowers between 3 and 5 inches.
Your predictions? The possibilities of where this could go?
Molin: “With the formation of the hybrid, it can survive in farmers’ fields. It’s doubtful that regular spiny amaranth would be there.
“Also consider that one male Palmer plant in the middle of a field is incapable of producing seed. A single plant of this spiny hybrid is perfectly capable of producing seed. The prognosis is not good — this could turn out to be a problem just like Palmer.”
You’ve been at this since 2011?
Molin: “Yes, it takes time. You have to get the suspect plants, get seed, grow it out in the greenhouse and proceed through the testing.
“We’ve been back to the field a second time and collected plants this year. We found several that were resistant. So, we know this is a year-to-year problem. How quickly that problem will expand, we don’t know.
“Part of the issue with this is the seed are very small. It’s easy to move the seed from field to field on farm vehicles.
“One of the things we’re now doing is collecting seed from neighboring fields to see if the resistance and hybridization has spread. We don’t have that information, yet but at least in the one field population the resistance is being propagated.”
Has the population in that field gone up? Remained steady?
Molin: “We haven’t seen it during the cropping year so we’re still unsure of what’s exactly going on.
“The next phase of this from the field aspect is to collect soil samples this spring to be tested for the presence of the hybrid spiny. In the summer, we’ll return to the field and see what plants are up and how the grower is handling them.
“One of the things we noticed last fall was a lot of spiny at the entrances of other fields. We collected some of that and it’s in the process of being tested. The research into this is in the early stages and it’s fortunate it was caught fairly early.”
As researchers, the hybridization probably didn’t surprise you, right?
Molin: “There have been several studies — mostly with other Amaranthus weeds like waterhemp — showing hybridization under controlled lab or greenhouse conditions. Those studies show that ALS-chemistry resistance can be transferred from species to species.
“However, we didn’t expect that the resistance would transfer from Palmer to spiny. We didn’t know it would then move into an agronomic field. That was certainly a surprise.”
On the threat of resistant waterhemp…
Nandula: “Historically, Palmer amaranth is a dry-area weed while waterhemp prefers more swampy conditions. Waterhemp used to be limited to the Midwest. But because of the changing crop rotations pushed by commodity prices and custom harvesting equipment moving so much around the country, these weeds have spread all over the place. These weeds are being found in regions where they’ve never been seen before.
“One waterhemp population found in Illinois is resistant to four different herbicide families. When you have gene transfers, imagine pollen carrying resistance to four herbicide chemistries producing a brand-new hybrid. The results of these gene transfers really complicate weed management.”
Currently, the spiny hybrid is only resistant to glyphosate?
Molin: “We only tested for glyphosate. We’re most interested in glyphosate-resistance at this time. We’re preparing to see if there’s also resistance to Staple. However, if the Palmer transfers resistance to ALS chemistries — a big ‘if’ — that would be a problem in cotton with Staple. In soybeans, though, that resistance would mean a whole host of products would be removed from a grower’s control options.
“In 2013, the field with this resistant hybrid was converted from cotton to soybeans. So, there was obviously a change in the herbicides used. That’s another reason to check for more resistance.”