Blog: Agronomy & Extension

In alternate years, the National Sunflower Association performs a sunflower survey in six states (ND, SD, MN, CO, KS and NE). The survey looks at several agronomic pests and pressures and the potential yield impacts in the given year. In 2023, Manitoba Crop Alliance (MCA) participated in the survey with the help of Ahmed Abdelmagid, research scientist for oilseed crops pathology at Agriculture and Agri-Food Canada’s (AAFC) Morden Research and Development Centre. Nine sunflower fields were surveyed in Manitoba, reflecting the approximately 85,000 total sunflower acres in 2023.

This project serves two purposes:

1. Identifying factors that affected yield in the given year and which may be of increasing importance in the future, and
2. Identifying potential research priorities.

Factors that were looked at specifically during the survey were the following:

• Yield components – plant population, head diameter, seed size, % good seed, % centre seed set, bird damage
• Agronomic information – crop type, row width, tillage practices
• Weed Assessment
• Diseases
• Insect & bird damage

Fields were visited in mid- to late-September, once R9 was reached and each was surveyed at two different sites within the field. Of the nine Manitoba locations, six were oilseed production fields and the remaining three were confections, and all locations were distributed throughout southern Manitoba from Eastman to Westman areas.

The initial process in each sampling location was to do a plant count followed by another count including only “harvestable” plants (this would not include very small heads, heads with no seed, lodged plants). These harvestable plants were used in yield estimation against all the factors that lay ahead. Head diameter was measured in inches on five plants per location and centre seed set was measured (diameter of seed not set in the centre of each head). Next, seed samples were taken from three heads and stored in a paper bag to send for testing, but not before determining percentage good seed (% filled seed) and seed size.

A general assessment of the field was made at each sample location for yield limiting factors (birds, disease, insects, weeds, drought, uneven plant growth, hail, herbicide damage, lodging and plant spacing within the row) and the top two limiting factors were ranked. The most common limiting factor across the nine surveyed fields was disease (five fields) and the remaining four fields had greatest limiting factor being birds, drought, lodging or weed pressure. It was rare to find a second limiting factor in these fields, which had a positive impact on yield due to less pressure on the crop.

Bird damage was estimated in the percentage of seeds lost. Five fields had bird damage at the time of surveying, ranging from 0.5 – 4.5 per cent seed loss. Surveying is typically done around the same time blackbirds tend to begin feeding on sunflowers and one of these surveyed fields had a significant increase in bird damage by harvest.

Insect presence measurements accounted for sunflower midge, sunflower seed maggot, sunflower bud moth and long-horned beetle damage (not found in Manitoba). 25 heads at each field site were examined for the above insect damage, aside from long-horned beetle, which required stalk splitting to identify the larvae presence.

“Corn roots will not grow into dry soils.” – Dr. Joe Lauer, professor of plant and agroecosystems sciences, University of Wisconsin-Madison (retired)

When Manitoba experiences a dry cycle, a major concern is the ability of our crops to endure very dry and crusting soils. Spring drought is particularly concerning for crop germination and emergence. Without moisture, germination simply will not occur. With limited moisture, germination may begin and become halted if/when moisture runs out, resulting in an unproductive seed(ling).

According to Joel Ransom, North Dakota State University small grains & corn extension agronomist, “For most soils, 0.5 inches of rain (sandy soils require slightly less) is needed in order for moisture to move to a two-inch depth (the seed zone) in dry soils. Poor seed-soil contact can restrict the corn seed from extracting enough moisture from the soil to germinate. Crop residues that touch the seed can similarly impede the movement of water to the seed. Occasionally, fertilizers placed with the seed inhibit germination due to their salt effect being more pronounced in dry soils¹.”

Of course, soil moisture is not just required for germination. It is required for all vegetative and reproductive growth. Nodal root development is occurring as the growing seedling reaches V1 staging and this requires ample moisture in the top two inches of soil. This new root development will be the primary means by which the plant acquires water and nutrients by the V3 stage¹, so successful nodal roots are critical for further development. If soil is to remain dry around the crown (where nodal roots develop, about 0.75 inches below soil surface) for extended periods during early vegetative growth, these nodal roots will not develop. As corn plants grow larger, they become too heavy without the support of this root system and will flop over. This is where the terms floppy or rootless corn syndrome come from and these have frequently been found in areas of higher compaction or shallow seeding in recent years but will be a common symptom of dry growing seasons.

Figure 1: First set of nodal roots developing on a V1 Corn Seedling. Photo: Dr. Bob Neilsen, Purdue University.

Weather conditions in the entire month of May are impossible to predict. It is extremely rare to have so little soil moisture that the crop is unable to germinate or that the crop runs out of moisture during early development. It is rare that this should occur and to the best of our knowledge, it has not happened in Manitoba on a large scale.

Should a crop failure occur in spring due to dry conditions and young seedlings die off via dehydration, a replanting scenario may be considered. Stand reduction does have to be very significant to justify replanting corn simply because of the delayed planting date. Manitoba Agricultural Services Corporation (MASC) historical data shows that there is an estimated yield loss of 5% per week delay in spring planting.

Figure 2: Average relative yield reported to MASC during each sowing week for the selected crops grown in Manitoba for the period of 2010-2019.

Replanting corn is a very expensive decision and most often is not economical unless stand loss is over 16,000 plants per acre. Even in that scenario, the farmer may still be looking at too significant a loss to make it worthwhile. Replanting grain corn should only ever be considered after careful economic analysis of costs against any potential gain².

For more information on growing corn on the Prairies, see Corn Production Resources on our website.

References

1. Ransom, Joel. “Dry Soils and Poor Corn Emergence.” NDSU Crop & Pest Report, NDSU, 1 June 2017, https://www.ndsu.edu/agriculture/ag-hub/ag-topics/crop-production/crop-pest-report.
2. Manitoba Agriculture, Corn Seed Bed Preparation. https://www.manitoba.ca/agriculture/crops/crop-management/grain-corn/corn-seed-bed-preparation.html