Crop Report – September 21, 2022

The left side of this picture was planted less than 1 inch deep into dry soil resulting in delayed emergence. The right side was planted 2 inches deep into moisture.

When does a killing frost no longer damage soybean seed?

Late planted fields or double cropped soybeans may still be green in late September or October. A killing frost will not significantly harm seed quality once the field is at the R7 (beginning maturity) growth stage. R7 is reached when 50% or more of the plants in a field have a pod that has matured and turned brown or tan. Most leaves and pods will have turned yellow by this stage. When looking at seeds inside the pod, R7 occurs when the pod wall interior membrane is no longer attached to the seeds. When opening the pod this white membrane stays attached to the pod wall not the seed. See Figure 1. This indicates the seeds are physiologically mature and safe from frost injury. The pod membrane status is a visible indicator that soybean seed has reached physiological maturity (maximum dry matter achieved). This stage is equivalent to “black layer” in corn.

Figure 1. Physiological maturity is reached when the white pod membrane is no longer tightly attached to the seed.
Figure 1. Physiological maturity is reached when the white pod membrane is no longer tightly attached to the seed.

Purple Seed Stain

The amount of purple seed stain is increasing in some parts of southwestern Ontario. It can be a challenge for IP growers and fields grown for seed production. This fungal disease is seed-borne, so subsequent crops will be infected from diseased seed. The inoculum also overwinters in soybean residue so it’s more prevalent in fields with a poor crop rotation. Severely discoloured seed will have lower oil and protein content, but the main problem resulting from this disease are the purple stains left on the seed. See Figure 2. Planting clean seed that is treated with a fungicide will greatly reduce the problem in subsequent crops. There are also varieties with greater tolerance, so proper variety selection can be important in the management of purple seed stain.

Figure 2. Purple Seed Stain causes a distinctive purpling of soybean seed and will result in downgrading at harvest.
Figure 2. Purple Seed Stain causes a distinctive purpling of soybean seed and will result in downgrading at harvest.

Phomopsis Seed Decay

Phomopsis seed decay is the most widespread seed quality issue in Ontario, especially if harvest is delayed. Symptoms include seed that is cracked, shriveled, lightweight, and has a chalky white appearance. See Figure 3. This disease is favoured by warm, wet, and humid weather during the pod-fill and maturity stages.

Figure 3. Seeds infected with Phomopsis seed decay have a chalky mouldy appearance and a shriveled seed coat. This seed has lower oil content and viability.

Uneven Maturity at Harvest Time

A field that has many green patches or individual green plants can delay harvest. Sometimes the cause is obvious, such as late emerging plants. See Figure 4. This is a difficult problem to address, but planter units that place the seed at a more consistent depth will have more even emergence. Some growers report they can start harvest a few days earlier when using a planter compared to a drill because the crop matures more evenly.

Figure 4. The left side of this picture was planted less than 1 inch deep into dry soil resulting in delayed emergence. The right side was planted 2 inches deep into moisture.
Figure 4. The left side of this picture was planted less than 1 inch deep into dry soil resulting in delayed emergence. The right side was planted 2 inches deep into moisture.

When individual plants remain green, it’s usually a result of having fewer pods or pods with no seed. These abnormal pods are called parthenocarpic (seedless). Drought, herbicide drift, viruses, or in many cases a genetic mutation will cause plants to have little seed and remain green. When seedless pods are present, something has adversely affected normal pollen development. Stems and even leaves stay green because the plant has produced more carbohydrates than the number of seeds on that plant demands. This results in excess photosynthate in the fall so dry down is delayed.

If the whole plant has seedless pods from top to bottom, that usually means there was a genetic mutation in that plant (or in a previous generation that expressed itself this year). Those plants will show up as the odd plant here and there, but make up only a small percentage of the overall crop. This mutation is more prevalent in certain varieties and may only be evident in dry years. 

If there are specific areas in a field that remain green, that often means an environmental factor was the cause, not a genetic mutation. Herbicide drift or drought may have impacted normal development, resulting in fewer pods per plant. Insect feeding and viral infection may also cause plants to remain green. In those cases, field edges are more impacted. Fields with low levels of P and K will not mature as quickly or evenly as fields with good fertility. This difference in senescence in the fall is also due to a lack of pods and seeds per plant in the low fertility areas. Fields with uneven maturity at harvest should be soil tested to see if additional fertilizer is needed in future years.

Weather DataSeptember 11 – 18, 2022

LocationYearHighest Temp (°C)Lowest Temp (°C)Rain (mm)Rain (mm) April 1stGDD 0C April 1stGDD 5C April 1stCHU May 1st
Harrow202227.210.625.1412305222293467
202130.713.16.5462308522483393
10 YR Avg. (2011-20)23.310.88.7509300821563424
Ridgetown202227.89.98.0285290020853220
202128.99.613.5454291720893199
10 YR Avg. (2011-20)23.18.68.2462283619883187
London202227.26.515.2333282520153136
202127.28.423.8406288620623147
10 YR Avg. (2011-20)22.69.48.7485280819643162
Brantford202227.36.223.3311283320173075
202128.59.247.7408285720333082
Welland202225.57.415.3380288520603223
202127.710.580.1449287320443150
10 YR Avg. (2011-20)22.99.315.1432282719823190
Elora202226.53.72.7256260518012827
202127.17.123.2363264418282858
10 YR Avg. (2011-20)21.56.610.2480253717072821
Mount Forest202225.34.55.0379259617992870
202127.38.229.2483264418322873
10 YR Avg. (2011-20)21.27.68.9490252717042845
Peterborough202224.11.818.6342259717792818
202126.34.914.0363264318172827
10 YR Avg. (2011-20)22.15.313.2430256717352813
Kemptville202224.66.032.3489276019233039
202125.87.319.8333283420023030
10 YR Avg. (2011-20)22.47.416.7483269818693011
Earlton202220.63.460.1412233315642568
202125.04.711.5531244216352572
10 YR Avg. (2011-20)20.65.422.1435220014540
Sudbury202222.60.027.9347239416172695
202125.06.211.7451248716822667
10 YR Avg. (2011-20)21.37.112.6457236015912680
Thunder Bay202223.60.778.9556213013892326
202123.61.929.1305233415422479
10 YR Avg. (2011-20)19.84.716.1422211713582283
Fort Frances202225.62.146.7622221714782491
202122.7-0.513.1278240116032569
10 YR Avg. (2011-20)19.84.614.5421224214652420
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.