Crop Report – June 9, 2021

Figure 1. PLH feeding causes yellowing of leaf tips, called “hopperburn”, shown here in a new seeding of alfalfa. Photo credit: J. Lindeboom.

Corn Nitrogen Status

Nitrogen mineralization is favoured by warm soil temperatures with adequate soil moisture and aeration. Excess moisture can slow mineralization or increase the potential for losses through denitrification (especially under warm conditions) or leaching.

Spring of 2021 progressed similar to 2020. Sunshine and little rainfall resulted in great soil conditions through April and May. A period of cold temperatures dominated for a 1-2-week period early May, which was followed by seasonal to above seasonal temperatures. Variability in temperatures brought into question how N mineralization may be affected in 2021.

OMAFRA leads an annual Pre-Sidedress Nitrogen Test (PSNT) survey to gauge year-to-year levels across Ontario. From May 31 to June 2, 93 samples were collected across Ontario from a range of previous crops, soil textures and geographies. A V3-V4 stage is typically targeted for PSNT sampling but given the start of sidedressing and warm temperatures in the forecast, the survey was slightly ahead of schedule with most corn ranging V1-V3. Where corn fields without preplant N could not be found, soybean or processing vegetable fields were sampled if rotations were representative of grain corn (following wheat or soybeans).

The average PSNT value for the 2021 survey was 13 ppm. This is similar to 2020 (14 ppm) and slightly above the long-term average of 12 ppm (2011-2020) suggesting similar to slightly higher than normal mineralization by sidedress stage in 2021. For historical reference, these levels compare most to years 2012, 2018 and 2020. More information can be found at www.fieldcropnews.com. Optimal nitrogen (N) rates for corn are a function of both soil N supply and yield. Consider both when determining N rate requirements in 2021. PSNT survey results are a general indication of soil N status across Ontario, not a substitute for sampling your own farm.

Alfalfa Weevil and Potato Leafhopper

Alfalfa weevil and potato leafhopper (PLH) are being reported at extremely high levels in many fields.  Hot dry conditions have made it more favourable for these pests than their natural enemies (especially entomopathogenic fungi). Scout fields to determine if cutting is possible or if an insecticide application is necessary if thresholds are reached. Consider fields at threshold if both pests are present but populations are slightly below threshold for either pest.

Monitoring recently cut fields is extremely important as well, as infestations can overwhelm the young regrowth. Dry bean growers should also keep watch of their newly emerging dry bean plants for PLH as seed treatments will only protect the plants for a few weeks after planting.

Alfalfa weevil larvae initially feed within the leaf buds and then move to the tips of the plant. Pinholes are the first signs of damage but can quickly progress to skeletonized leaves. Heavily damaged fields will look greyish white from a distance. Heavy feeding not only impacts yield but also reduces feed quality. Fields at greater risk of alfalfa weevil include those seeded last year, pure alfalfa stands, and areas of the field with south facing slopes.

Potato leafhopper arrived recently on storm fronts from the US in heavy numbers.  Most vulnerable are new seedlings and young regrowth but all stands need to be monitored frequently (twice a week at least). PLH nymphs and adults suck out plant sap while injecting a toxin into the plant that interferes with transportation of nutrients in the leaves and stem.  The result is the characteristic “hopperburn”, which starts as a wedge-shaped “V” yellowish pattern at the leaf tips (Figure 1.). By the time hopperburn is noticed, yield and quality have been compromised. The taller the alfalfa, the more leafhoppers can be tolerated before control is necessary. Though PLH-resistant varieties of alfalfa are available, new seedings are still vulnerable, as the glandular hairs are not fully expressed the first year.  Use the conventional thresholds below for first year seedings of these resistant varieties.

Figure 1. PLH feeding causes yellowing of leaf tips, called “hopperburn”, shown here in a new seeding of alfalfa. Photo credit: J. Lindeboom.
Figure 1. PLH feeding causes yellowing of leaf tips, called “hopperburn”, shown here in a new seeding of alfalfa. Photo credit: J. Lindeboom.

 

 

 

 

 

 

 

 

 

 

 

Action thresholds for both alfalfa weevil and PLH depend on the height of the plant. More information can be found at www.fieldcropnews.com. PLH is also a pest of dry beans, but insecticide seed treatments on dry beans will offer protection through the first few weeks of dry bean growth.

Weather Data

Location Year Weekly May 31 – June 6 Accumulated
Highest Temp (°C) Lowest Temp (°C) Rain (mm) Rain (mm) April 1st GDD 0C April 1st  GDD 5C April 1st CHU May 1st
Harrow 2021 30 7 22 124 846 530 604
2020 30 11 3 159 726 422 595
2019 25 7 43 287 775 448 557
Ridgetown 2021 29 5 18 115 786 478 574
2020 31 6 14 139 669 380 564
2019 25 5 12 226 696 381 482
London 2021 30 6 14 120 782 480 553
2020 28 6 3 146 639 352 517
2019 24 5 18 243 645 345 468
Brantford 2021 32 4 15 115 760 455 537
2020 29 5 6 123 626 345 497
2019 24 4 23 245 637 340 459
Welland 2021 29 4 11 82 758 450 523
2020 27 8 6 137 652 364 519
2019 24 6 16 208 675 367 479
Elora 2021 31 3 10 94 689 394 478
2020 29 4 4 99 570 308 454
2019 23 2 22 244 555 272 393
Mount Forest 2021 30 4 7 99 698 406 495
2020 28 5 2 109 562 313 465
2019 23 4   129 537 263 380
Peterborough 2021 31 0 9 90 687 380 480
2020 28 4 5 102 584 309 483
2019 24 2 16 239 573 280 401
Kingston 2021 28 4 12 94 705 399 466
2020 26 3 15 148 635 342 504
2019 20 6 30 251 624 320 422
Kemptville 2021 31 3 19 98 788 476 547
2020 29 2 13 124 600 317 484
2019 23 2 12 189 583 291 396
Earlton 2021 32 7 14 80 655 369 454
2020 25 4 8 107 432 232 388
2019 21 2 6 184 355 137 254
Sudbury 2021 31 7 1 96 663 377 458
2020 25 4 11 113 480 256 414
2019 20 3 1 183 366 143 240
Thunder Bay 2021 32 3 8 179 533 261 390
2020 30 4 4 49 435 227 395
2019 26 -2 32 139 362 131 257
Fort Frances 2021 36 2 1 114 587 308 482
2020 29 7 4 59 500 269 443
2019 25 -2 13 109 418 173 304
Report compiled by OMAFRA using Environment Canada data. Data quality is verified but accuracy is not guaranteed. Report supplied for general information purposes only. An expanded report is available at www.fieldcropnews.com.