I think you can get this information locally from the nearest county extension office. I don’t know how much you know or don’t know about the subject, but I found this explanation helpful and maybe somebody else will too:
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That article is a good illustration of why more people don’t use degree days
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The info was very interesting and I would like to understand it better, but I don’t believe it works in my area.
I’m at slightly less than 300 Degree Days around the “pink” stage and the WSU model is for oil at around 375 DD.
Can someone help me with these questions?
Are degree days and maturity states of apple trees like greentip or pink more or less universal between geographic region in terms of degree days?
Anybody spray a light concentration of oil around pink or 375 DD?
I think you can spray a heavy concentration just before bud break- somebody please correct me if they know better.
I think it should work for any area: if the weather in your location is warmer/cooler than elsewhere you’ll accumulate degree days at a faster/slower rate. If you’re at 300 degree days now and your average temperature is 50 F then you’d be at 350 degree days in just one day- unless I misunderstand the model, which is all too possible. So you’d spray heavy oil very soon. And then, only three days later, you’d apply the cover spray of granulovirus. At this point you’re still maintaining organic control. You could also use spinosad and still be organic, and possibly pretty successful. Or you could forgo organics at this point and start using the convention control of your choice.
Now let me be very clear: I have not depended on this approach- my dormant oil applications have been haphazard, and I mistimed my spinosad spray last year and lost my meager crop of apples. So I’m only giving you my understanding for the sake of discussion. I’m counting on others to weigh in.
I believe that apples universally reach full bloom at about 175 DD °F and that codling moths’ first flight (biofix) is about that time. Egg hatch begins around 425 DD °F (biofix + 250 DD °F), which is the traditional timing for first codling moth treatment. What the above article recommends is an early treatment at 375 DD °F to kill eggs before hatching. The author(s) suggest horticultural oil.
Here is a similar recommendation for an early treatment at 275 DD °F with Rimon followed by a delayed treatment at 525 DD °F with any number of other chemicals:
The delayed larvicidal treatment is possible because the early ovicide treatment kills eggs that would have hatched in the period starting at 250 DD °F [from biofix]. Another nice feature of this program is that the delayed application of the larvicide is a more efficient timing than the standard first cover timing of 250 DD °F. Only a small portion of the first generation egg hatch occurs between 250-350 DD °F, ca 15 percent, while more than 50 percent of the hatch occurs over a two to three week period beginning at 350 DD °F. The combined strategy also shortens the period of time that larval control is necessary, presenting an opportunity to reduce the number of sprays needed to achieve control.
- Wise, John, et al. “First Generation Codling Moth Management.” 18 May 2010. Michigan State University Extension. 14 Apr. 2018 <http://msue.anr.msu.edu/news/first_generation_codling_moth_management>.
I should say that I have only ever used the traditional timing with Sevin.
You may be mistaken about your current cumulative DDs. You can check your current cumulative DDs at an airport near you. Please see my previous post.
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How hard? Please see @blueberrythrill, I think I understand that the above statement is in error. After reading @CRhode’s web page I believe that I should have compensated for the threshold temperature, and I’m still reading to understand that.
That page he links above is really excellent and I recommend it.
Do you know which version of Degree Days I should be looking at? The model I’m looking at uses Base 50BE by default.
I’m almost to 300 DD based on info from my local airport from the Cornell NEWA site and I have not reached pink. NEWA - Weather Station Details
I spray oil with copper at max rates around 1/4 inch green but I wonder if I need another dose of oil at a lower rate around TC to pink. So far CM has not been a problem
It appears the base temp depends on the specific crop/pest in focus, which happens to be 50F for codling moth. So that should work, I guess. I wonder about the variation in cycles at different locations.
Wow! Looking at airports from Greenboro, NC, to Raleigh-Durham, to Burlington, it seems like you’re three-weeks ahead of the 30-year average, sitting at 280 DD °F. You should have passed full bloom a month ago, so something ain’t right.
The problem has to do with the fact that the computation for base 50 and the number for base 50 BE are very different. I don’t understand why but Cornell says;
"Currently, in all the NEWA apple disease and apple insect phenology models that utilize DD accumulations, the BE formula is being used. Drs. Cox and Agnello have chosen to use BE DDs because of their higher precision. Furthermore, BE DDs have been used in the entomology field observations in Geneva, NY, for the past 25 years or more.
When I choose base50 rather than the default base 50BE, my degree days fall to about 159 which matches what you described with full bloom at around 175 DD.
I believe BE stands for Baskerville and Emin who first published the technique for modeling diurnal temps with a sine wave. This is the standard calculation for codling moth. I’ll have to do a little more digging. I believe the figure of 175 DD °F at full bloom does refer to the B&E calculation.
The BE model is more useful than the standard for spring growth. In the standard model, if you had a 65F day and a 30F night, it wouldn’t count as any DDs–but clearly that day pushed the plant closer to bud break (or in this case, allowed the moth to travel/mate/etc.). The BE model, instead of simple averaging, fits the temps to a sine curve.
I wonder if there’s any relationship between growing degree days and heating degree days
There must be, but I don’t know what it is. It may be a very simple correlative thing.
Cooling degree days is the conventional max-min calculation:
TAvg=(TMax+TMin)/2.0
DD=TAvg−TThreshold
Growing degree days is a little more complicated:
D2=2∗TThreshold−(TMax+TMin)
Theta=arctan(D2/sqrt((TMax−TMin)∗(TMax−TMin)−D2∗D2))
GDD=(1/2π)∗((TMax−TMin)∗cos(Θ)−D2∗(π/2−Θ))
Uh … yes it is, isn’t it!
D2=2∗TThreshold−(TMax+TMin)
Theta=arctan(D2/sqrt((TMax−TMin)∗(TMax−TMin)−D2∗D2))
GDD=(1/2π)∗((TMax−TMin)∗cos(Θ)−D2∗(π/2−Θ))
M
Of course if TMin>TThreshold, then GDD=DD, and you skip the trigonometry, which is simple enough but only good during warm weather.
But I’m surprised that GDD accumulates so much before bud-break in the South. I’ll have to look into this.
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[cringe]
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