Agronomy Update – August 7th

Good morning everyone,

I’m a little later in the week getting this report out to you this week.  Morgan and I were out in fields on Monday and Tuesday checking on a number of trials and visiting with some growers.  Then the last two days we had our AIM Working Group meetings, which is a good opportunity to hear from growers and industry partners on what’s happening on-farm and what sort of projects we need to be addressing through the Agronomy Initiative.  As always, feedback if welcomed and encouraged.

I don’t really need to tell any of you how dry it is.  The rains from last week were much needed, but not everyone was fortunate to receive a decent amount and that moisture has long been used up by the plants in most areas.  East Prince and West/Central Queens are the driest parts of the Island, with the south shore particularly missing significant amounts during the thundershowers last week.

Here is some weather data that Morgan has compiled to illustrate where we’re at on rainfall and growing degree days (GDD).

Table 1: Accumulative Rainfall for 2020 Growing Season

  Rainfall (mm)  
Location May June July 2020 Totals Historical Average
East Point 49 23 86 158 278
Charlottetown 63 30 51 144 266
Summerside 59 17 38 114 260
Elmsdale 65 15 58 138 261

Table 2: Accumulative GDD for 2020 Growing Season

Growing Degree Days (GDD >5oC)  
Location May June July Totals Historical
East Point 133 332 407 872 780
Charlottetown 137 339 465 941 850
Summerside 138 340 472 950 843
Elmsdale 141 354 439 934 830


Table 3: July 2020 growing degree days (GDD) and rainfall amounts (mm)

Location GDD (>5oC) Rainfall (mm)
Elmsdale 439 58
Miscouche 472 38
Malpeque 470 57
Augustine Cove 452 41
Charlottetown 465 51
Alliston 450 70
South Lake/Elmira 407  86

 As you can see…we’re about 100 GDD ahead of average (and about 200 ahead of last year), but we’ve had less than half of the usual precipitation in some areas so far this growing season.

Until this week, potato fields were holding on well.  However, the combination of continued dry weather and some windy days has had a detrimental impact on the look of the tops in a lot of fields.  Some fields that look decent from the road have noticeable yellowing of the bottom leaves when you get looking at the plants.

As we are ahead on degree days and behind on precipitation, it makes sense that we are also ahead on Early Dying/Verticillium wilt.  Starting to see some typical Verticillium wilt symptoms in several fields this week.  Here is a photo from Tuesday that shows typical Verticillium wilt on Russet Burbanks, with chlorosis/necrosis on one side of the petiole more than the other.

While there isn’t much to be done when Verticillium wilt starts to appear in your crop, it is important to record where you are seeing significant symptoms and mark those fields for future Verticillium and nematode testing.  As well, it’s worth sending any “suspect” disease symptoms in to the pathology lab to identify if there are any other diseases that are contributing to early dying in your field (ie. black dot, brown spot, early blight, etc).

Spore Trapping Update:

Here are the spore trapping results for early blight (Alternaria solani) and grey mold (Bortrytis cinerea) for this week.  Note that no late blight spores have been collected in PEI this season.  Late blight spores have also not been reported in NB or Maine either this season so far.  The hot, dry weather this week is generally not conducive to late blight infection.

Table 4:  Spore Trapping Results for Monday, Aug 3rd and Wednesday, August 5th:

Community Mon, Aug 3
Early Blight
# of spores
Wed, Aug 5
Early Blight
# of spores
Mon, Aug 3
Grey Mold
# of spores
Wed, Aug 5
Grey Mold
# of spores
Elmsdale 240 27 347 27
O’Leary 9 0 160 129
Wellington 124 0 462 18
Summerside 187 27 4 13
Kinkora 93 27 293 18
Meadowbank 36 9 213 40
New Glasgow/Rustico 258 18 40 53
Oyster Bed/Winsloe 36 9 13 0
Souris 9 0 973 169
Elmira 0 4 5956 244
Dundas 9 4 1067 5000
Stratford 18 4 13 13
Average 85 11 795 477

As you can see, early blight spore number have decreased from Monday to Wednesday significantly.  Grey mold spores have also decreased substantially (outside of one location that increased to skew the averages a bit).  I have seen some foliar symptoms of both early blight and brown spot (Alternaria alternata) this week, but not in huge quantities.  I’ve also been seeing blackleg symptoms in a couple of fields, particularly irrigated fields.

Fingers crossed that we get some unexpected rainfall in the near future to help relieve some of this moisture stress.  I am still encouraged by what I’ve seen in terms of the number of tubers per plant in most varieties.  If we can catch up on rain, there is still the opportunity for a decent crop….but you all need some help from Mother Nature on that.