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Soybean Aphid Activity In Ontario
Everyone is asking what soybean aphids are up to this year. So far, we are finding very low levels of aphids in fields ranging from Windsor to Ottawa. It is very normal to find small pockets with plants having 10-1000 aphids on a few plants in spots while just feet away, other plants having no aphids on them at all. This is how aphid colonies start up in fields. The winged mother stops at a plant to give birth to a few babies before going off to find another plant and repeating the process. The baby nymphs left behind grow up as wingless adults and continue to build the colony up from what their original winged mother started. This process of "bulking up the colony" takes place for a couple of weeks before the colonies get crowded enough to start producing more winged versions that can help spread the population out to other fields and other plants. It is usually shortly after that "spreading period" or migration that we start to see aphids on every plant in the field. If weather conditions and predator levels allow, it is then when there is the potential for aphids to reach threshold levels. If it wasn't for the predators, parasites and pathogens that help control the aphids, we would see colonies build up more easily and reach thresholds earlier in the season. The good news is that we are seeing a lot of predators in the fields. Not just the ladybugs which seem to always get all of the attention but minute pirate bugs, lacewings and syrphid fly larvae are showing up too. We have even found aphid mummies (carcasses of aphids that were killed by a parasitoid) which is the earliest we've seen them here so far! But the war has not been won by the natural enemies just yet. As we have learned, temperatures play a role in this too. As temperatures become more "pleasant" again, we will need to be very diligent and watch over our infested fields. Soybean aphids love pleasant summer days when it is not too hot. If conditions favour them over their natural enemies, populations could build quickly. Again, the threshold is "250 aphids per plant with increasing populations on 80% of the plants" up to the R5 stage of soybeans. Following this threshold ensures that a sprayer gets into the field in time, before the populations reach damaging levels. Pulling the trigger before reaching the threshold is not necessary and could cause more problems because of the harm to the natural enemies. I have provided a "Steps for Managing Soybean Aphids" for this CropPest volumn to help you determine if and when you need to manage your aphids. And should soybean rust find its way into Ontario this year, tankmixing
both the fungicides for rust and insecticides for soybean aphids is
not recommended unless thresholds for BOTH pests are reached at the
very same time. Studies have shown that tankmixing to save time can
cause the aphid populations to rebound when thresholds have not yet
been reached. REMEMBER, you want to see aphid populations on the increase,
above 250 per plant. If they are lower than that or hovering around
250 per plant, this means that the natural enemies are still gorging
on aphids and fighting the battle for you. Give them a chance..you
might be surprised at what they can do. | Top of Page | I For more information:Toll Free: 1-877-424-1300 Local: (519) 826-4047 E-mail: ag.info.omafra@ontario.ca |
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