R1 Soybeans Starting - Aphid Recommendations Kick In

Earlier planted soybeans are starting to flower (R1- Beginning Bloom) which means we are starting to cross into the more normal timeframe for soybean aphid activity. And we are confident with the threshold recommendations set for this time period. Regular weekly scouting should start now and continue until the plants are well into the R6 (Full Seed) stage, that is when the seeds in the top pods of the plant fill the seed cavity.

Scouting Results so Far

Our weekly scouting efforts indicate that aphids are now present in many fields in Ontario, but are still quite low in number. This however could change quickly, as winged aphids could move in from other regions or from the few heavily infested fields already present in Ontario at any time. We are noticing a high percentage of winged aphids at the 3 or 4 sites that started out with very heavy populations right away. And there is a storm front coming that could pick them up and carry aphids this way or out to eastern Ontario and Quebec. Typically these mid summer winged aphids select fields that have been planted later, giving their offspring younger plants to suck on. But I think this year has already proven to me that aphids can bend the rules so I'm not going to count on that norm. The aphids do not like this high of heat though and do not reproduce as quickly but with the pending change in weather and temps, they may start to reproduce more quickly soon after.

Fields still of most concern continue to be those fields planted around May 5th. In some of these fields, aphids have reached threshold and required spraying. Unfortunately, these fields may in fact require a second spray because of the absence of natural enemies now after the first spray. However, in other early planted fields, natural enemies have brought the aphid population from near threshold to nearly zero again, demonstrating the importance of scouting and determining if management is indeed necessary.

Soybean Aphid Recommendations for 2007

1. Scout each field every 7-10 days from now until early September or until the crop is well into the R6 stage of soybeans. Scout fields more frequently (every 3-4 days) as aphid populations approach the threshold. Look at 20-30 random plants across the field. Avoid field edges.
   
   
2. Estimate the average number of aphids per plant in that field. A minimum of two field visits is required to confirm that aphid populations are increasing.
   
   
3. Take action if aphid populations are actively increasing above 250 aphids per plant on 80% of the plants from the R1 up to and including the R5 stage of soybeans. If aphid populations are not actively increasing above the threshold, this is an indication that natural enemies are keeping up with the aphid population.
   
   
4. More aphids per plant are needed once soybeans are in the R6 stage. Beyond the R6 stage, economic return from any insecticide application is not likely.

What to Use and How to Spray it

This is what everyone wants to know. My response is that it depends on the field and the conditions that year as to which product works better. I still recommend Matador over dimethoate. In years of dry conditions when the crop was stressed, Matador outperformed dimethoate. I suspect this is partly due to the plants being so stressed from lack of rain, they were not able to move the systemic product (dimethoate) through the plant well enough to see any benefit to using it. It is still not a product that the US researchers recommend. I have already witnessed a dimethoate product fail to control the aphids this year and those sites will require another spray this week. Matador was in the same trial and does not require a second spray. However, Matador is heat sensitive so you must only use it in temperatures lower than 27 degrees C and because it is only works on contact, it can be challenged when the canopy is tall and dense and the aphids are lower on the plant. It is in this scenario that I have in a few instances witnessed dimethoate working better, perhaps because the plants are able to move the chemistry somewhat systemically compared to Matador which is strictly relying on contact. But Matador has recently been registered to include a higher rate to be used in these challenging situations. That is, when the canopy is dense and the spray needs to get deep down to reach a higher than threshold number of aphids. The lower rate that you are accustomed to still works well when the canopy is not as high and dense and especially when the aphids are not just on the lowest leaves of the plant. So far, the aphids are still on the newest trifoliates at the top, which makes them much easier to hit.

Regardless of what product you use, the most important aspect is spray coverage. You might as well use soap if you are not going to set up your sprayers correctly to deliver the product in the best way possible to kill the aphids. Helmut Spieser recommends that to spray for aphids you want a MEDIUM spray quality to get adequate coverage on the plant surface to control the aphids. Therefore you need to do the following:

1. calculate the size of nozzle required based on GPA, travel speed and nozzle spacing
2. select nozzle type to produce a MEDIUM spray quality
3. if pump limitations don't allow sufficient pressure to produce a MEDIUM spray - choose a different nozzle type
4. calibrate your sprayer
5. operate boom at proper nozzle-to-target distance, typically 20" or 50 cm

Where Can You Go For More Information?

• USDA PIPE -United States Department of Agriculture - Pest Information and Platform for Extension and Education
• OSG - Ontario Soybean Growers
• OMAFRA CropLine at: 1-888-449-0937

Thanks for all of you who have already called in to see about getting a copy of the Canadian Soybean Aphid Scouting Cards and Threshold Postcards. They are free for everyone and will be shipped out from the printers to OMAFRA offices early next week (July 3rd). Feel free to stop by at one of our locations to pick up your copy.

Figure 1 and 2. Introducing the "Soybean Aphid Scouting Card" and "Soybean Aphid Threshold Postcard"

Related Links

• OSDA -PIPE (United States Department of Agriculture-Pest Information Platform for Extension and Eduction)

• OSG (Ontario Soybean Growers)

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