Resistance Roundtable: Interview with Les Glasgow, Ph.D., Caydee Savinelli, Ph.D., and Allison Tally, Ph.D.

Proactive, diverse strategies are essential when it comes to effectively managing resistance.

From left to right: Allison Tally, Caydee Savinelli and Les Glasgow
(From left to right) Allison Tally, Ph.D., technical product lead, fungicides, Syngenta, Caydee Savinelli, Ph.D., pollinator and IPM stewardship lead, Syngenta, Les Glasgow, Ph.D., technical product lead, herbicides, Syngenta.
Why is resistance a real concern and resistance management a real need?

Les Glasgow, Ph.D., technical product lead, herbicides, Syngenta: Over the last 10 years, we’ve seen a significant increase in the incidence of herbicide-resistant weeds. This trend was confirmed in a 2012 grower survey*, which estimated that glyphosate-resistant weeds infested 61.2 million acres. Of the growers interviewed, 49 percent reported glyphosate-resistant weeds on their farms, representing a staggering 51 percent increase over the previous year.

If we do not respond proactively to this serious threat, there will be significant changes in agriculture. Growers will lose the tools they have as more herbicide modes of action become compromised across a wider range of weed species. As a result, the use of tillage - with its associated negative environmental impact - will likely increase. The development may reverse the conservation tillage and no-tillage gains made in the last 20 years, resulting in increased erosion and contamination of surface water with soil and nutrients. Weed management will become less diverse, less efficient and less effective. We will see an increase in management costs coupled with a reduction in productivity and profitability. If this scenario comes to pass, a decrease in land values will be inevitable, and reduced economic stability in the production of key agricultural commodities - such as corn, soybeans, cotton and cereals - could lead to increased bankruptcy in farming communities. At the same time, significant increases in food and fuel prices will hit consumers.

Caydee Savinelli, Ph.D., pollinator and IPM stewardship lead, Syngenta: Insecticide resistance can greatly diminish the value of products in the marketplace. It can lead to an increase in the number and frequency of applications to control insects at the same level as in the past. With the onset of insecticide resistance, product nonperformance complaints go up and grower confidence goes down. Resistance management strategies and tactics that delay or minimize resistance development are important aspects of product stewardship and critical for the long-term maintenance of crop protection technologies. For effective resistance management, the practices used must help delay resistance development, while also being practically oriented and cost-effective so that growers will adopt them.

Allison Tally, Ph.D., technical product lead, fungicides, Syngenta: We’ve all heard about staph-resistant bacteria in hospitals and warnings not to use antibiotics when they aren’t needed to help prevent resistance. Microorganisms can reproduce quickly and mutate, developing resistance to the medicines that can help us. Plant diseases can also become resistant to “plant medicines,” rendering them either totally or partially ineffective. At Syngenta, when we develop a new fungicide, we also study the potential resistance risk. When a pesticide has multiple modes of action - that is, it attacks several different sites in the pest - it is less likely to become resistant than those that target a single site.

Why should resistance management be top of mind, even for growers who are not currently experiencing a problem?

Glasgow: While awareness of herbicide resistance is high among growers, many do not see it as a problem on their own farms. It is someone else who has the issue, so the response is, “Why should I change my low cost, convenient weed-management tactics and spend more on inputs?” They do not realize how soon their neighbor’s problem will become their own through pollen or seed movement. In many cases, the resistant weeds are already present on the farm but not detected until it is too late. Weeds, such as Palmer amaranth or waterhemp, can produce up to 1 million seeds from a single plant. It doesn’t take long to cover a field with resistant weeds that can compete severely with the crop.

Savinelli: All growers need to make best use of the available tools to control insects. This requires them to consider their options and not use the same insecticide over and over again. Even if they aren’t currently experiencing resistance in their fields, the threat is there; they, therefore, should use insecticides judiciously.

Tally: A spray program may work great, as long as only a limited amount of the pest population is resistant. But over time, these can multiply and, all of sudden, there is no control. Rotating different modes of actions is an excellent way to keep the ones that may be resistant from increasing rapidly. It is a numbers game. Growers need to keep the pest population as low as possible.

What can growers and retailers do to fight resistance?

Glasgow: It’s important for growers and retailers to take a concerted, collaborative approach to manage herbicide resistance and preserve the tools that we currently possess. There are a number of important principles that Syngenta has supported for many years:

  • Do not rely solely on post-emergence-applied herbicides.
  • Start clean, utilizing tillage where appropriate or an effective burndown plus a pre-emergence-applied residual herbicide.
  • Always use a two-pass pre- and post-emergence system with herbicides at full rate and recommended adjuvants and proper application timing.
  • At each application, use multiple-mode-of-action herbicides with overlapping efficacy (activity on the same weed species with two or more different herbicide active ingredients).
  • Include diversified management programs, such as cover crops, mechanical weed control and rotation.
  • Do not allow weeds to go to seed and add to the seed bank; remove any escapes early by hand weeding, spraying a herbicide or cutting out patches.

Savinelli: Insecticide resistance management should be part of the integrated pest management of the insect. An understanding of the insect’s biology and population dynamics, as well as its economic threshold level on the crop, is essential. This will lead to better decisions on when to apply the insecticide and at what rate. The resistance management component is to not use the same insecticide for the control of multiple generations of the same pest in one crop. It is best to rotate insecticides with different modes of action.

Tally: Various cultural practices should be incorporated to help keep the pest populations to lower levels. If growers know that a disease is a routine problem, they know to use varieties that are resistant or more tolerant to that disease. Planting dates can help slow down the disease pressure. For example, if some diseases like warmer soils, then planting a little earlier when the fungus isn’t active can get the plant up and out of the ground where it may be less susceptible to the fungal attack. Another cultural practice is managing irrigation to avoid creating a good infection period. When season-long spray programs are needed, the grower and retailer should discuss a multipronged approach that uses different chemistries. Most chemicals now have a code that indicates their chemical class, so figuring out the rotation is easier than it used to be.

What support does Syngenta offer?

Glasgow: Since 2001, Syngenta has helped lead the fight against weed resistance, partnering with university and extension researchers to update growers on the latest management tactics. We also have a wide range of herbicides with different modes of action and use patterns that can fit almost any situation. In particular, we have led the way in developing premix products, such as Lexar® EZ and Lumax® EZ herbicides in corn, which ensure delivery of three effective herbicides with different modes of action. In soybeans, growers can apply Boundary® or Prefix® herbicides pre-emergence in a program with early post-emergence application of herbicides, such as Flexstar® or Liberty®, respectively. Since herbicide resistance management is a local and, in many situations, a field-specific issue, growers can contact their local Syngenta agronomist or sales representative to receive advice and a customized management program. In addition, Syngenta is a member of the Global and North American Herbicide Resistance Action Committee (HRAC) that has established the herbicide resistance management principles promoted widely in agriculture today.

Savinelli: Syngenta is a member of the Insecticide Resistance Action Committee (IRAC), both in the U.S. and internationally. We utilize the IRAC mode-of-action symbols on our product labels along with resistance management guidelines. As part of our technical training for the field sales force, we provide insecticide-resistance-management best practices and information. Our research facilities in Vero Beach, Fla., and Stein, Switzerland, also enable us to address field insecticide resistance. Additionally, we have a good working relationship with the university research and extension community in implementing resistance management guidelines and addressing emerging issues.

Tally: Syngenta offers several fungicides with different modes of actions that growers can rotate. We also have premixes, which provide a convenient way to apply two chemistries together. To slow resistance development, we recommend alternating different modes of action. In certain cases, we recommend that growers not use a product or use it only once per season because we know the level of control will not meet their expectations. The Fungicide Resistance Action Committee makes it easier to identify modes of action by providing guidelines for the various chemical classes. It would be nice if a red light turned on as soon as a problem started emerging in the field, but nature does not warn us when it comes to resistance.