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To Spray or Not to Spray the Aphids

A lot of calls are coming in this week from growers and reps who have fields that are hovering around the 250 aphids per plant range. With the poor weather and wheat harvest some are anxious to make the call if they need to spray. In fact, there are some rumours out there that some are spraying before the field reaches 250 aphids per plant. I stongly DISCOURAGE this as I have witnessed many times that this does not save you a spray or your time but in fact increases the chances that you will need to spray again in the next 10 days or so because of the natural enemies that were making an effort were instead killed off, leaving the aphids that survived to live well and prosper.

The best way to increase your chances of only having to spray once is to spray well within the threshold, when you have been able to assess that the aphids are definetly on the increase past 250 per plant.

Figure 1. Heavy Aphid Populations

Here are my best recommendations for the current situation:

1. In regions where the fields are quite dry and the crop is appearing stressed, plan to spray just above 250 aphids per plant, after you have confidently determined that the aphid population is actually on the increase. This indicates that the natural enemies are not keeping up and are no longer valuable enough for you to save.
2. In regions where there have been some timely rains and the crop is not stressed, plan to spray when the aphids start to reach around 400-500 aphids per plant. The economic injury level (when the cost of spray is equal to the cost of control) is around 600-700 aphids per plant. In a healthy crop you can be a bit more patient and wait to see if the natural enemies kick it in gear and lower the aphid population. But experience has shown me that once you start to crack the 400-500 aphids per plant mark, there is less of a chance that there will be enough natural enemies and time for them to keep the aphids from reaching the economic injury level.

And keep an eye out for SPIDERMITES, especially in the regions that have not had these rains. Wheat harvest is starting and spidermites will be moving into soybean fields. Timely rains help manage them but not every field has had these rains.

Please let us all know if you are starting to see spidermite injury in your area!