| August 2007 - Soybean Aphid Update |
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Field
Notes:Soybean aphid update - numbers
exploding in some areas August 2nd, 2007 Robert Moloney, CCA-ON, Agronomist, FS PARTNERS I can't believe I'm still talking about soybean aphid at this time of year, but they are still a huge problem in some parts of the province.In some areas soybean aphid numbers really exploded over the last week. IF YOU DON'T HAVE SPRAYABLE NUMBERS OF APHIDS: make a note of the dates you checked the fields and the numbers of aphid you found. This may be important in areas with high soybean aphid pressure if you have crop insurance and need to prove that you followed proper agronomic practices (i.e. you did monitor aphid and didn't need to spray) and your crop insurance claim for low yields weren't related to aphid.This may not be an issue, but it's easier to cover yourself now than try to prove it later. NEEDING TO SPRAY:For whatever reason soybean aphid numbers are currently exploding exponentially. Normally we would be at or near a stage at which we don't worry about aphid.The threshold would say we need to worry about them from R1 (beginning of flowering) to R5 (seeds in upper pods 1/8" long).Most fields should be at or near this stage by now.Unfortunately this year, except in a few areas, we have been extremely dry. This is similar to conditions in Eastern Ontario 3 years ago where strip trials were getting yield responses to spraying through to the R6 stage (full seed stage - green seeds filling pods on top part of plant).If we get a timely rain we won't need to worry about aphids in these late stages, but if we continue with moisture stress it may pay to spray late. We had some growers tried late spraying a couple of years ago when aphids moved in late but we had really good growing conditions with no moisture stress and they did not get a yield response. WHAT TO SPRAY:I am completely against spraying Cygon/Lagon for early aphid sprays because they have been shown in research/field trials to have a much faster rebound of aphid numbers versus Matador. Most of our early (R1-R3) applications of Matador this year that were done properly (i.e. good coverage, not sprayed in the heat of the day) gave us 3 weeks to a month control before we had to go back in.Some of our more recent applications have had challenges getting coverage due to canopy size, and due to the current obviously favourable conditions that are resulting in all aphid numbers spiking, the small percentage of aphids not killed with these applications are reproducing vigourously. This is resulting in a very rapid rebound in numbers.No product is going to give 100% control even under perfect conditions. At this point in the year my recommendation changes and I would go to spraying Cygon/Lagon.We are late enough that I'm not as worried if we get a bounce back in 2 weeks rather than a month, and while Cygon is only upwardly systemic in the plant, it will move from one side of the leaf to the other which may allow you to get better kill. It is also not as sensitive to heat as Matador is.The potential downside of Cygon at this stage is if we don't get rain and the beans remain under stress we may need to keep the aphids off them longer than normal so we might actually need to worry about the bounce back. SPRAY VOLUME/DROPLETS: generally more water is better with either product (absolute minimum would be 20 gal/ac).You want to aim for a "medium" droplet size according to nozzle manufacturer recommendations for nozzle type/size and spray pressure (see Tee-Jet catalogue for example).Having a fine "fog" behind the sprayer isn't necessarily a good thing since most of these droplets will evaporate before they get down to the plant and therefore won't do any good. |
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