Grower Services - Degree Days

Year 2013 Growing Degree Days (using a base temperature of 50°F):

Update through May 27th, 2013:

• Bangor: 93 GDD
• Calais/St. Stephen: 77.4 GDD
• Lewiston-Auburn: 114 GDD
• Bar Harbor: 43 GDD

Update through May 19th, 2013:

• Bangor: 78.5 GDD
• Calais/St. Stephen: 63.4 GDD
• Lewiston-Auburn: 83.3 GDD
• Bar Harbor: 32 GDD

Update through May 13th, 2013:

• Bangor: 65 GDD
• Calais/St. Stephen: 59.4 GDD
• Lewiston-Auburn: 64 GDD
• Bar Harbor: 32 GDD

Target Numbers:
Cranberry Tipworm eggs first appearing: ~225 GDD (but crop stage is a more accurate predictor, I feel; eggs generally appear as soon as tiny new shoots begin to arise from the runners, and are deposited almost exclusively on the tips of the new shoots)
Black-headed Fireworm larvae first hatching: ~252 degree days GDD

Year 2012 (using a base temperature of 50°F):

Update through May 29th, 2012:

• Bangor: 285 degree days (tipworm target reached ~May 24th) (fireworm target reached ~May 26th)
• Houlton: 178 degree days
• Lewiston-Auburn:  283 degree days (tipworm target reached on May 24th and new cranberry shoots were present at that time as well) (fireworm target reached on May 26th)
• Bar Harbor: 174 degree days

Update through May 6th, 2012: [Even this late into the season] Bangor is now at only 85 degree days, Houlton is only at 50, Lewiston-Auburn is at 102, and Bar Harbor–for a coastal comparison–is only at 36 degree days, incredibly!

Update through April 9th, 2012: Unchanged since March 26th! Bangor still at 44 degree days, Houlton still at 24, and Lewiston-Auburn is still at 56.

Update through March 26th, 2012: Bangor is now at 44 degree days, Houlton is unchanged at 24, and Lewiston-Auburn is at 56.

Update through March 22nd, 2012: Bangor is now at 41 degree days, Houlton is at 24, and Lewiston-Auburn is at 48.

March 21, 2012: We are starting to accumulate degree days with these really warm (if not HOT) days we are experiencing.  Bangor has picked up 15 through yesterday, Houlton 10, and Lewiston-Auburn is out in front with 18.  Despite the impressive heat of these last several days, we still have a lot of degree days to go before we should be seeing tipworm or fireworm on the cranberry beds.

Year 2011 degree-day monitoring was done at five sites: Troy, Etna, Aurora, Deblois and Columbia Falls. [Monitoring start date was April 15th, and a base temperature of 50°F was used]

Results (when did tipworm eggs first show up?):

• Troy (Tipworm eggs started May 26th): 229.5 degree days – this is very consistent with the ‘average’ number  previously determined (228 degree days) from past degree day work at Troy from 2007 – 2009, though that number represented the start of tipworm fly emergence as opposed to the start of egg-laying.  It makes sense, though, that in some years, those two tipworm processes might occur within a short time frame of one another.  If the cranberry uprights are at an appropriate stage when the flies first start to emerge (which may well have been the case this year), it makes sense that egg-laying would begin just a few days later because individual flies only live for about 3 days. As soon as they emerge, they have just one thing on their collective minds — to mate and lay eggs.
• Etna (if using the same time period as Troy): 193 degree days – I do not know when tipworm eggs began in Etna because I usually don’t get any tipworm in my small plot (I think it is too small for them to become established). But, I like monitoring in my plot for comparison purposes and to be able to get easy snapshots of accumulations so that I can have an idea of how quickly things might be moving everywhere else. It is also useful because it tends to be pretty similar to the site in Troy (just 20 minutes away).
• Aurora (Tipworm eggs started May 30th): 224.5 degree days [two loggers used (one on each end of the bed) and averaged together; this result is very close to the same number found for Troy this year (229.5), and in fact, one of the loggers registered 229.6 degree days, which is virtually identical to Troy -- the other one registered 219.5 degree days]
• Columbia Falls (Tipworm eggs started June 1st): 196 degree days [two loggers used (one each on two different beds) and averaged together -- individual logger totals were 200 and 192.5]
• Deblois (Tipworm eggs started May 31st): 222 degree days [two loggers used (one each on two different beds) and averaged together -- individual logger totals were 216.6 and 227.4]
• Conclusions? Much, much more agreement compared to last year, for the values across all of the sites.  But this year’s results leave me feeling even more convinced that Columbia Falls is a colder location than the others, and the tipworm there (and by logical conclusion the tipworm everywhere)–just as I thought after last year’s findings–apparently are much more driven by plant stage than they are temperatures.  The fact that ‘that’ would be true for any location signals to me that the start of tipworm egg-laying is definitely driven more by plant stage than it is by temperature. Otherwise, it would have taken more time before the tipworm eggs first appeared in Columbia Falls!  But, nevertheless, it is surprising just how similar the value was this year amongst the other three locations where (and when) tipworm eggs first appeared: Troy, Aurora and Deblois (229.5, 224.5 and 222, respectively). Those numbers are remarkably consistent with one another!

As of May 12th, 2011:
It is too soon to give you a report from this year’s loggers, but I can tell you that online data for Bangor shows an accumulation of only 50 degree days (using a base temperature of 50°F) from April 15th – May 11th.  So, even though we are well into the month of May, we’ve nevertheless not had many degree days thus far, even if you are in a warmer region of the state.

I do not, however, advise placing much faith in using degree days for the timing of one’s first cranberry tipworm insecticide, in light of last year’s findings (the degree days did not match up very well from site to site relative to when tipworm eggs and larvae began to appear), but it may be wise/helpful to include another year’s worth of findings to see if the numbers still do not correlate well (so that is my thinking for this year).  But for tipworm management, instead of relying on degree days for one’s signal, I strongly recommend going by ‘plant stage’ for the best predictor of tipworm egg-laying and the start of larval presence.  As soon as brand new shoots begin to sprout up from the runners, that is the time to expect tipworm activity to be starting as well — the larvae cannot survive without active growth occurring, i.e. without new and growing shoots to feed upon, and I have never found tipworm eggs prior to that particular stage of plant growth.  The actual tipworm flies emerge over an extended period of time (evidence suggests), and any mating and egg-formation taking place before the cranberry plants are in the ‘new-shoot phase’ thereby is in vain (from the fly’s perspective).  But, with flies emerging at all different times, the flies who emerge at the ‘right’ time are rewarded by virtue of having new tips upon which to lay their eggs.  I am not really sure what happens to any eggs formed from the ‘early-season’ flies…if they deposit them on blueberry plants, don’t deposit them anywhere, or what?  It seems unlikely that they would choose to hold their eggs and die without laying them somewhere — remember, individual flies only live for 2 to 3 days — so I am inclined to think that they probably deposit them on some other host plant, such as blueberry, given the fact that I do not find them on cranberry until the vines are sending up new shoots.

Monitoring for Year 2010 degree day accumulations began at three sites on March 17th. This was much earlier than each of the past three years’ start dates, which weren’t until early April [The 'start date' in cranberry is the date when the bed is first free, for the most part, of either ice, snow or water].

d

* = 1 male tipworm fly found (female tipworm flies were found on May 13^th in Deblois and the degree day total at that time was only 168.7) – So they appeared earlier than expected; target number was 228 based on my findings from 3 years of monitoring their emergence at a site in Troy; begs the question, ‘How reliable is degree days at predicting tipworm fly emergence?’ – it seems that the number of degree days needed is far too variable from year to year to place much faith in it.

** = tipworm eggs & larvae found (in the tips of brand new shoots – brand new shoots were everywhere in the beds, rising up from the runners)

▲ = tipworm eggs & larvae found on tips from Troy (near Etna), on May 21^st [But degree days through May 21^st in Etna were only at 183.5 and given how close Troy and Etna are in distance, you would expect the degree days to be similar, meaning the number of degree days in Troy would also be expected to be somewhere around 183.5 when the tipworm eggs and larvae were found, but 183.5 is a fair amount less (i.e. sooner) than the ‘fly’ target of 228, when the first flies would be expected, say nothing about eggs and larvae]

♦ = No tipworm found (not even flies); Plants did not have new shoots yet; they were still in the bud-break stage (even though the degree days were very high—well past the value when the tipworm should have been present).

Conclusions: My current thinking is that the stage of the cranberry vines themselves, rather than degree days, is a more reliable indicator to use for predicting the start of tipworm flies and especially for predicting the start of tipworm eggs and 1^st-instar larvae.  Regardless of how many degree days have accumulated at a given site, if there are no brand new tips present on a bed, I have not been able to find any tipworm eggs or larvae.  The one thing that sites ‘do’ consistently have in common with regards to tipworm is that the tipworm doesn’t start until there are brand new shoots present, independent of what the degree days are indicating at that location.  Thus, I think it must be true that the fly emergence occurs over an extended period of time (3 weeks or more), and any tipworm flies that emerge what to us may seem ‘early’—before the cranberry sites have any new shoots on them—are apparently doing one of three possible things: they are either not mating (since eggs and larvae are not being found during that time), or they are mating and holding onto their eggs (i.e. ‘waiting’—though they can’t wait long since they only live for a few days anyway), or else they are mating and laying their eggs on something other than cranberries (wild blueberries, most likely) in the absence of any new cranberry shoots [this 3^rd possibility is the one that seems most likely to me], and the offspring from those ‘other’ plants (blueberry or otherwise) turn into new flies that are then poised to move into the cranberry beds as soon as they have new shoots present.

From degree day work at a tipworm site from 2007 – 2009, the number of degree days needed for the start of tipworm fly emergence ‘seemed’ to be somewhere at or close to 228, using a base temperature of 50°F and using temperatures from the surface of the cranberry bed, where the tipworm flies emerge (as opposed to air temperatures away from the ground). Data from 2010 calls into question, however, the reliability of the 228 number, or the reliability of using any degree day estimate when it comes to managing Cranberry Tipworm — the current recommendation is to go by one’s crop stage instead (as soon as new shoots appear, tipworm eggs and larvae are soon to follow).

For the first generation of blackheaded fireworm larvae, again using a base of 50°F, and measuring soil temperature at the cranberry bed surface, the number of degree days (found in Maine) is roughly 252 (represents an average from the years 2007 – 2009 at the same location that was monitored for tipworm).

Cranberry questions? Contact Charles Armstrong, Cranberry Professional. University of Maine Cooperative Extension || Pest Management Office || 491 College Avenue || Orono, ME 04473-1295 || Tel: 207.581.2967 [email: charles.armstrong@maine.edu]