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Southeast WI | Not exactly sure what you are asking. Here's what I use. I go with the threshold of 250 per 80% of plants that is meant to give you 7 days to treat as aphid numbers, on average, double in about 6 days from that level and 600 per plant is the EIL. I find this pretty accurate and when we get levels in that 50-100 range I get back to those fields every 3 days to see where they are going. I consult on a 40 mile radius of home so you can imagine how onerous scouting gets. Aphids are the single most difficult pest because our predictive ability is way too low for comfort. You have to look all the time.
Also lower levels of aphids over a long period of time can be detrimental to yield, although i dont think there is a very good database documenting that. Do you have that info in Iowa? There is also a very low level of confidence in what to do with aphids at R6 and beyond. We are seeing them come in later and later each year as opposed to showing up at treatable levels July 1. When we had to spray that early we almost always were back 2 weeks later since all the predators were destroyed too. That is why even now we have to be careful with knee-jerk "spray at 50 per plant" levels. I know the Hefty Boys rec even less than that and i would like to see the database they are working with to get to those conclusions. Let me know if this answered your question. | |
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aphids- spray or wait??
