Friday, July 22, 2016

Part 5 ----> Just the facts: A review of the biology and economics behind insecticide recommendations

prepared by:
  • University of Minnesota: Bruce Potter, Robert Koch & Phillip Glogoza
  • Iowa State University: Erin Hodgson
  • Purdue University: Christian Krupke
  • Penn State University: John Tooker
  • Michigan State University: Chris DiFonzo
  • Ohio State University: Andrew Michel & Kelley Tilmon 
  • North Dakota State University: Travis Prochaska & Janet Knodel 
  • University of Nebraska: Robert Wright & Thomas E. Hunt 
  • University of Wisconsin: Bryan Jensen 
  • University of Illinois: Kelley Estes & Joseph Spencer 

Biology helps determine the profitability of crop production on your farm – Ignoring biology is expensive


None of what we have presented here is new, or groundbreaking information. However, all of what we have presented here is based on science that has been vetted and implemented over thousands of acres for more than a decade. Economic injury levels take commodity prices, labor and control costs into account. Fortunately, the biological components of an EIL are not sensitive to commodity or input prices. The insects on your farm do not eat faster or more when crop prices are high or insecticide costs are low; nor is your crop more sensitive to insect damage (remember the damage boundary). Yield loss occurs at the same level of pest population, regardless of market prices of commodities. It makes no sense to treat if there is no reasonable likelihood of damage.

Science is best when it does not sit still. New research on pest and crop biology and on new management tools may change EIL’s and associated ET’s over time. However, since the adoption of the 250 aphid/plant economic threshold, additional research has only confirmed the results of the original multi-state biological and economic research.

While some may view an insecticide costing "only a couple of dollars" as inexpensive when compared to other production inputs, it is still an added cost for no added benefit. These inputs add up with each acre applied. Farmers often find the "free" application costs when insecticides are tank-mixed with herbicides or other pesticides have unintended negative consequences - poor control from poor timing or application techniques of one or more products. Using an ET, based on sound, peer-reviewed research will help you apply your crop input dollars where they are most likely to produce a positive return on your investment and minimize the chances of creating other problems for yourself.

Using fear or faulty economic logic is tried and true as a very effective sales tool. It’s always prudent to be a skeptical consumer and consider the messenger when you evaluate information - a conflict of interest can arise if a profit motive underpins recommendations made without facts behind them. Be very wary of ETs that are based on "feel," eyewitness accounts, or other anecdotes that are not supported by hard scientific data. ETs that are radically different from those recommended by agricultural research universities are another red flag.

Hopefully, this article has provided you with information that will help you sort through the information clutter on TV, radio, print media and especially the internet. A list of research references is included in the complete article (http://z.umn.edu/soybeanaphidfacts) for those who would like to read and learn of some of the research supporting our soybean aphid management guidelines and economic threshold recommendations. Contact Extension for the most up-to-date and state-specific recommendations.



This is the 5th and final installment in a series on soybean aphid management and insecticide recommendations.  Previous installments covered how recommendations are created, how aphids hurt yield, the economics and biology of aphid insecticide recommendations, costs associated with early treatment and how to know if you have a soybean aphid problem.  A link to the complete document is provided in this installment or at (http://z.umn.edu/soybeanaphidfacts) .




Thursday, July 21, 2016

Part 4 ----> Just the facts: A review of the biology and economics behind insecticide recommendations

Costs of treating soybean aphids too early

While some newer insecticides target a narrower range of insects, most insecticide applications are not specific. They will kill beneficial insects (lady beetles, parasitic wasps, etc.) as well as pests, later allowing soybean aphid populations to rebound in fields without those beneficial insects to slow them down. By using the ET, natural enemies will have a chance to suppress the aphid population and possibly prevent it from reaching economically damaging levels. After application, insecticide residues will kill insects for a short time, but insecticide activity invariably declines over time (generally, this is considered a good thing). With most insecticides registered for soybean aphid control (such as pyrethroids), soybean foliage emerging after treatment is not protected. Insecticides that are absorbed and translocated within soybean plants typically move upward only a leaf or two and eventually leave unprotected foliage, especially when applied early in the season. 

Applying treatments early can result in a false sense of security and a reduced reliance on scouting. If a re-infestation is not detected before reaching the EIL, yield may be reduced. If detected, the cost of additional insecticide applications are incurred. Early treatment can reduce or eliminate the cost efficiencies of a single, well timed threshold-based treatment. Finally, unnecessary insecticide applications do nothing positive for a short-term return on investment. Importantly, long-term returns can be reduced if insecticide resistance becomes fixed in the soybean aphid population. This has happened many, many times in the history of pest management. We know that managing pesticide resistant pests is seldom "cheap and easy" (for example, consider the problems with herbicide resistant weed control).

Wednesday, July 20, 2016

Part 3 ----> Just the facts: A review of the biology and economics behind insecticide recommendations

Economics of soybean aphid infestations: Math and biology matter


Figure 1. Relationship of insect population and crop yield
 (Modified from Pedigo et al. 1986).

The lowest level of aphid infestation that has been shown to cause yield loss in soybean is several thousand aphid-days. This value, referred to as the damage boundary, is a biological relationship between the insect, crop, and environment, and is independent of crop and input costs. Below the damage boundary, no damage can be measured. Therefore, management efforts directed at treating aphid levels well below the damage boundary cannot provide a return on investment.


The economic injury level (EIL) is the point at which the yield loss from insect damage is equal to the cost of a management action, such as an insecticide application. Insecticide applications made to pest populations that have not reached this point, and are unlikely to reach it, would not provide any return. To more readily apply this yield-loss relationship to field scouting and aphid management, a value in terms of aphids per plant was calculated as the threshold to apply an insecticide to threatening populations.

Tuesday, July 19, 2016

Part 2 ----> Just the facts: A review of the biology and economics behind soybean aphid insecticide recommendations

How can soybean aphids reduce soybean yield?

The soybean aphid feeds on the phloem fluids (sometimes referred to as "sap") by inserting piercing-sucking mouthparts directly into the phloem vessels that carry products of photosynthesis from the leaves to other parts of the plant. Prior to feeding, aphids "taste" the sap to determine if the plant is a suitable host species and if the quality is acceptable. Once they settle and begin feeding, the injury from soybean aphid infestations can reduce plant growth, pod number, seed number, seed weight and seed oil concentration (2, 24). Early and prolonged aphid infestations can affect all yield components, while later infestations tend to only reduce seed size (2). In addition, soybean aphids decrease photosynthesis rates of soybean plants (11).

Direct yield loss from soybean aphid feeding does not occur when the first (or five or ten) aphids begin feeding. Today’s soybean varieties are equipped to handle minor challenges, including a few aphids. Yield loss from soybean aphid is related to how many soybean aphids are present and for how long the aphids are present and feeding. The amount of aphid population pressure over time is calculated as aphid-days. Simply put, this is the average number of aphids on a plant multiplied by the number of days they are present. A single soybean aphid on a plant for 10 days is equal to 10 aphid-days, 200 aphids on a plant for 20 days is equal to 4,000 aphid-days, and so on. This aphid-day concept proved to be a good indicator of how soybean yield responded to aphid populations (23).