Agronomy & Extension – Special Crops Archives - Page 3 of 4

Head Rot Identification in Sunflowers & Harvest Management

mca2022dev on September 8, 2022

Rhizopus Head Rot

Rhizopus rarely occurs in Manitoba and is more of a southerly disease, however it is possible to see it here after severe storms and hail, followed by very high heat. Identifying factors that separate Rhizopus from other head rots are gray mycelia with very small black structures.

Rhizopus begins as a typical “water-soaked” dark spot on the back of a sunflower head that grows into a larger watery, soft rot and then dries and turns darker brown. Eventually, heads dry down, though this occurs prematurely in comparison to healthy plants, and infected tissue shreds, exposing gray threadlike strands of mycelial growth.

Key points:

Enters head via wound caused by hail, most commonly
Water-soaked lesion on backs of sunflower head
Gray mycelial growth inside the diseased head, which can later present itself on the face of the sunflower head
Tiny black spots, about the size of a pinhead
100% yield loss potential due to dropped heads

Figure 1: Dry and skeletonized head (Bob Harveson, University of Nebraska)

Figure 2: Coarse, dirty white to gray, threadlike fungal growth of Rhizopus spp. in sunflower head (Bob Harveson, University of Nebraska)

Sclerotinia Head Rot

Sclerotinia is very common in Manitoba and in several grain crops, which makes crop rotation the best management practice for this prevalent disease. A recommendation for sunflowers is to only include it in rotation when other sclerotinia host crops have not been grown on that field for 4-7 years. Chemical control is used frequently, however due to the small window for application, coverage is difficult to rely on.

Sclerotinia presence can first be found in the field by identifying cup-shaped apothecia growing on the soil surface, which produce ascospores. Symptoms in the field include the typical tan-coloured lesions on the back of sunflower heads that may be soft to the touch. As the infection spreads, the head becomes pliable and easily torn open to reveal black sclerotia bodies amongst white mycelia. Fronts of sunflower heads may have white mycelial growth, or mould, visible between the seeds. Eventually, heads will likely shred and disintegrate leaving frayed vascular elements that appear broom-like.

Key points:

Cup-shaped apothecia on the soil
Water-soaked lesions on backs of sunflower head
Black sclerotia bodies inside sunflower head following disease progression
White mycelial growth between and on seeds
Shredding sunflower head, resembling a straw broom

Figure 3: Sclerotinia Head Rot on Sunflower

Figure 4: Sclerotinia Head Rot Symptoms in Sunflower

Figure 5: Sclerotinia Disease Cycle, American Phytopathological Society

HARVEST MANAGEMENT IN DISEASED SUNFLOWERS

Yield loss from sclerotinia head rot in sunflowers is a result of empty seeds, rather than poor quality. In fact, it is not uncommon to find large sclerotia bodies being harvested along with seed and degrading quality in that manner.

Due to the overall degradation of disease plants, not just from sclerotinia, it is a good practice to harvest infected fields first. The diseased areas should dry down more rapidly than healthy plants and standability isn’t reliable, whether that is a result of a stalk rot or head rot. The physical breaking of stalks or dropping of heads leads directly to yield loss due to the inability to pick up the grain with a header.

Article written by Morgan Cott, Agronomy Extension Specialist – Special Crops with Manitoba Crop Alliance

Late Season Planting

mca2022dev on June 3, 2022

The reality of seeding or planting any crop into June is that yield penalties will occur. This could be due to reduced bushel weight, small seed size, and low quality grain as a result of early fall frost or poor environmental conditions leading up to maturity.

Planting corn or sunflowers beyond May 30^th is still a possibility in 2022, but hybrid selection is of utmost importance, since we have already missed out on 250 crop heat units or more, depending on location. Sunflowers require 115 – 130 days to mature in Manitoba, with the varieties we currently have available. So, a sunflower crop that is planted on June 1^st, will mature by September 24^th, at the earliest.

Sunflowers are a great option in a wet year, if you can get them planted. They are one of the top water-users that we grow in Manitoba, only behind corn and roughly tied with soybeans. They are very well adapted to dry growing seasons as well because they will search much further for water sources than other crops.

The following tables are taken directly from a NDSU Extension article, “Replanting or Late Planting Crops”: https://www.ndsu.edu/agriculture/ag-hub/publications/replanting-or-late-planting-crops. Note that the majority of North Dakota accumulates several more crop heat units than Manitoba, even at our most southern locations, but these tables do depict a good indication of what a farmer is looking at for yield loss when planting into June.

https://www.ndsu.edu/agriculture/ag-hub/publications/replanting-or-late-planting-crops

The data provided here is very cautious and simply states that anything grown after May has very little chance of being economical, which isn’t completely true, but it does encourage the fact that a farmer does have to be wary of what is being seeded after that point. The risks involved are obvious and great care must be taken in order to get any late seeded or planted crop to germinate as quickly as possible and off to a healthy start. It is not unheard of to have a crop emerge within just a few short days of planting when soils are warm and have good moisture, and the quicker that crop gets growing, the more water it will start using. Take great care in placing seed accurately in the soil, control weeds and fertilize accordingly to mitigate any early season stresses.

Corn Ear Drop

mca2022dev on September 27, 2021

Drought conditions affect a corn crop in many different ways throughout the growing season. Silking and pollination stages are very sensitive to hot, dry conditions. Not only does the lack of rain and extreme temperature cause silks to dry up, poor pollination, and aborted kernels, but these conditions can also interfere with ear shank development.

In drought stress situations, the grain will “steal” carbohydrates from the rest of the plant, including the ear shank, in order to fill and improve quality. As result, the ear shank may become weak and eventually be unable to hang onto the ear as it becomes heavier. Another possible culprit for weakened ear shanks is in a year with rapid drydown in late summer. The cells that connect the ear shank to the ear dry too quickly and become brittle and unable to hold that ear tightly anymore. A disturbance to the corn plant, eg. a silager or combine header, can shake the ear from the plant which results in a complete yield loss for that plant.

Stalk diseases are not common in a drought year, however they are still possible. Stalk rots, such as Fusarium, will weaken the corn stalk and also the ear shank, potentially causing ear drop. Insects like European corn borer will also burrow throughout a corn plant, like in the stalk, ear shank and even the ear, which will weaken those areas of the plant.

This is generally not an issue related to genetics and it would be extremely rare to have a hybrid registered that showed such a glaring default. Ear drop won’t be something that occurs in every field, even if conditions were the same all season long. This will be an effect of planting date, conditions at planting, silking date of the given field and other agronomic factors. In other words, not preventable and simply, bad luck.

To mitigate some yield loss at harvest, combine (or silage) affected fields before any others. When harvesting grain corn, raise header just below cob height and reduce both ground and header speed. When silaging corn, it would be ideal to also raise the header, though that is not going to be popular advice to give a grower. Instead, slow ground speed to the point that you see greatest ear retention.

If there was evidence of stalk rots or insect damage, consider using hybrids with appropriate traits in the future.

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Several dropped ears in silage field. Photo credit: Madison Leonard, Clearview Consumers Co-op Ltd., Steinbach, Manitoba.

Article written by Morgan Cott, Agronomy Extension Specialist – Special Crops with Manitoba Crop Alliance.

Estimating Yield and Physiological Maturity

mca2022dev on September 2, 2021

Producers and agronomists should be assessing each grain corn field now for yield estimates. Pollination is long since complete and we have an excellent idea of how many kernels have been pollinated.

The following is taken from Dr. R.L. (Bob) Nielsen on estimating corn grain yield prior to harvest. Dr. Nielsen has some excellent articles on corn production that are worth looking into. (www.agry.purdue.edu/ext/corn/news/timeless/YldEstMethod.html)

At each estimation site, measure off a length of a single row equal to 1/1000th acre. For 30-inch (2.5 feet) rows, this equals 17.4 linear feet.
TIP: For other row spacings, divide 43,560 by the row spacing (in feet) and then divide that result by 1000 (e.g., [43,560 / 2.5] / 1000 = 17.4 ft).

Figure 1. Row length required to measure 1/1000^th acre in various row widths – Ontario Grain Farmer (ontariograinfarmer.ca/2017/06/01/cropside-corn-stand-checkup/)

Count and record the number of ears on the plants in the 1/1000th acre of row that you deem to be harvestable.
TIP: Do not count dropped ears or those on severely lodged plants unless you are confident that the combine header will be able to retrieve them.
For every 5th ear in the sample row, record the number of complete kernel rows per ear and average number of kernels per row. Then multiply each ear’s row number by its number of kernels per row to calculate the total number of kernels for each ear.
TIPS: Do not sample nubbins or obviously odd ears, unless they fairly represent the sample area. If row number changes from butt to tip (e.g., pinched ears due to stress), estimate an average row number for the ear. Don’t count the extreme butt or tip kernels, but rather begin and end where you perceive there are complete “rings” of kernels around the cob. Do not count aborted kernels. If kernel numbers per row are uneven among the rows of an ear, estimate an average value for kernel number per row.
Calculate the average number of kernels per ear by summing the values for all the sampled ears and dividing by the number of ears.
EXAMPLE: For five sample ears with 480, 500, 450, 600, and 525 kernels per ear, the average number of kernels per ear would equal:
(480 + 500 + 450 + 600 + 525) divided by 5 = 511
Estimate the yield for each site by multiplying the ear number (Step 2) by the average number of kernels per ear (Step 4) and then dividing that result by a kernel weight “fudge factor”. Unless your seed company can provide some insight into kernel weight values for their hybrids, I suggest simply performing separate calculations using “fudge factor” kernel weight values equal to 75, 85, and 95. This range of values probably represents that most commonly experienced in the central Corn Belt.

Figure 2. Grain corn yield estimate formula – Iowa State University (crops.extension.iastate.edu/cropnews/2017/08/estimating-corn-yields-using-yield-components)

Example: Let’s say you counted 30 harvestable ears at the first thousandth-acre sampling site. Let’s also assume that the average number of kernels per ear, based on sampling every 5th ear in the sampling row, was 511. Using “fudge factor” values of 75, 85, and 95; the estimated range in yield for that sampled site would (30 x 511) divided by 75 = 204, or divided by 85 = 180, or divided by 95 = 161 bushels per acre.

Repeat the procedure throughout field as many times as you deem representative. Tally and average the results separately for each “fudge factor” used for the calculations.

Remember that this year we have very uneven uniformity in most corn fields, which will influence the accuracy of any yield estimation technique. The less uniform the field, the greater the number of samples that should be taken to estimate yield for the field.

Figure 3: Measurements for each reproductive stage of corn development and how a killing frost would affect yield at that stage.

In early September, we tend to estimate when the corn will reach physiological maturity even more than we estimate yield in each field. In recent years, Manitoba has been getting early to mid-September killing frosts, so the chart above has been a very well-used reference. If you need help determining stage of corn, visit Grain Fill Stages in Corn (Purdue University), or a simple Google search for countless resources on how to properly identify milk line or physiological maturity (black layer).

Article written by Morgan Cott, Agronomy Extension Specialist (Special Crops) with Manitoba Crop Alliance

Effects of Drought Stress on Corn

mca2022dev on July 13, 2021

In recent years, we have dealt with drought stress in corn a lot. Most frequently, it has been overcome by timely rains and not had an impact province-wide. 2021 doesn’t appear to be letting up on the crop completely and reproductive stages of corn are just around the corner. Some sheltered areas along tree rows and yards are even beginning to tassel.

So, what happens to the plant when there isn’t enough moisture? Most visibly, corn leaves begin to curl and make the plant resemble pineapple leaves or onion greens. This occurs because the leaves are protecting themselves from excessive moisture loss or transpiration. Believe it or not, the more readily a plant curls its leaves up, the more beneficial it is to that plant. This year it is hard to determine with absolute positivity whether those plants are protecting themselves, or really in dire straits for moisture availability. There is no question, though; leaf rolling is a response to moisture deficits and it is widespread. This transpiration increases as leaf area increases and it is the mechanism that water moves from the soil, through the plant and into the atmosphere. If leaf rolling is resulting from true drought stress and occurs for 12+ hours a day, grain yield is likely to decrease, even prior to reproductive staging.

Right now, mid-July 2021, the crop is at a detrimental stage for water requirements. The corn is a little behind “normal” as a result of the lack of moisture and high heat combination, so on a regular year the corn would likely be at tassel (VT) or silking (R1) stages. “Potential ear size is already determined by the time silks emerge from the ear shoots. In fact, potential kernel row number is set by the 12-leaf collar stage (about chest-high corn.) Potential kernel number per row is determined over a longer time period, from about the 12-leaf collar stage to about 1 week prior to silk emergence” (https://www.agry.purdue.edu/ext/corn/pubs/corn-07.htm).

We know that row number is heavily predetermined through genetics, but kernels per row is not and has a strong sensitivity to environmental stresses. Below is a table identifying the potential yield reduction from drought stresses (with 4 consecutive days of leaf wilting) throughout the growing season.

Severe drought stress has the greatest impact during silk elongation, which often results in poor pollination. Silks on the base of the ear begin to elongate first, followed by those from the center and then the tip of the ear. So, when plant water is in low supply, the silks elongate slowly and may not even elongate beyond the husk. If the silk isn’t outside the husk during pollen shed, it will not pollinate those potential kernels. During these conditions, silks that do emerge have an increased chance of desiccating quickly, making them unable to receive pollen.

There is no gain made in worrying about what may happen over the next few weeks. What is promising is that corn has an amazing ability to recover from drought stress when it does receive rain. It is very unlikely that no pollination will occur whatsoever, but if dry conditions persist, it is likely that grain will not fill to its full potential. This is where rain events can really improve grain quality and the length of the crop’s life after it has been under severe stress.

Farming through a drought is something Manitobans haven’t had to do in decades and it is a steep learning curve. The best thing you can do is choose wisely where to put crop inputs and where not to. Producers are all under a great deal of stress this year, but we are all here to provide each other with the support we need. This year is teaching us a great deal about what crops and what fields handle a lack of moisture the best, in the same way that we learned about excess moisture tolerance in past years.

With that being said… time to go fishing??

Assessing Plant Stands

mca2022dev on June 22, 2021

Seeding rate for sunflowers depends on sunflower type. Oil-type sunflower populations range from 20,000 – 22,000 plants per acre (0.6 plants per ft²) but confection-type sunflowers should not exceed 18,000 plants per acre (0.4 plants per ft²) to ensure large seed size.

The easiest method to measure plant stand per acre is by doing the following:

1. Determine row width and using the table below, identify the correct distance to measure 1/1,000th acre.

2. Using a measuring tape, lay out the appropriate length for 1/1,000th acre.

3. Count all plants in the length laid out. When there are doubles, consider only counting one of the plants, since only one is likely to be productive.

4. Document plants counted.

5. Repeat steps 2-4 ten times.

6. Average all plant counts to determine and approximate final plant stand.

Another simple way to assess plant stand is to use the table below, developed by Manitoba Agriculture and Resource Development:

Seed Density as a Function of Row Spacing

In years when establishing a healthy and robust sunflower crop seems impossible due to various growing conditions, it is a very difficult decision on whether to terminate or keep a crop. Above are just a couple of ways to accurately determine how many plants are viable, which will help to estimate yield potential and all the costs required to bring sunflowers to maturity.

There is no documented data on the lowest plant population a producer can grow and still make a profit. Good record keeping and market knowledge will help someone in this situation make an educated assessment on whether the crop will be profitable or not.

Growth Stage and Herbicide Application

mca2022dev on June 7, 2021

Herbicide applications are well-underway in corn, including tank-mixes. Fields should always be scouted before any herbicide application for weeds present, precise crop staging and environmental conditions that could have an affect on efficacy.

Applying a herbicide at early growth stages provides greater crop safety, in most cases. The corn plant has a smaller surface area to be in contact with the herbicide, which means a smaller risk of damage. Herbicides with active ingredients like 2,4-D or dicamba can need to be applied to the crop as early as possible for this reason: the larger the crop, the greater the plant surface area and the greater the risk to the crop. It is very important to refer to all herbicide labels and contact appropriate companies with any questions prior to applications.

Refer to Manitoba Crop Alliance’s Vegetative Growth Stage ID factsheet for staging tips.

Also available is a Quick Herbicide Reference Guide for current pre-emergent and post-emergent herbicides on the market in Manitoba.

Post-emergent herbicide application tips: (for full list, visit https://www.dekalbasgrowdeltap…)

ALWAYS READ AND FOLLOW LABEL DIRECTIONS.
Corn under stress may not have the ability to metabolize some herbicides quickly enough to avoid crop injury. Weeds under stress may not may not accept the herbicide to its full capacity.
Spray additives can increase the rate of herbicide uptake by the crop.
Herbicide residues from previous applications may remain in the spray tank causing contamination.
Post-emergent herbicide injury symptoms can include leaf chlorosis or necrosis, onion leafing, internode stacking, rat tailing, ear pinching, ear bottlenecking, brace root malformation, and green snap.

Reference: https://www.dekalbasgrowdeltap…

Flax: Emergence and Frost

mca2022dev on May 26, 2021

Frost Impact on Flax

Flax plants just emerging (cotyledon stage) are the most susceptible to early spring frost, but can withstand temperatures down to approximately -3° Celsius. After the seedlings have passed the two leaf stage and are hardened by exposure, they can withstand temperatures as low as -8°C for a short time, without significant damage (https://flaxcouncil.ca/growing…).

Flax is generally at the first whorl stage right now, so a hard frost can have significant damage on the crop. It is important to follow the typical frost scouting techniques and wait 3-5 days to see whether frost has impacted the crop or not.

Emergence Monitoring (posted by SaskFlax: https://www.saskflax.com/quadr…)

One way to work towards optimizing flax performance on your farm is to determine the plant population and calculate emergence rate. Relating these numbers back to the seeding rate used, the environmental conditions and other factors at seeding can help determine management practices for the growing season and adjustments that can be made next year.

Steps to determine actual plant population and emergence rate:

1. At 1.5 to 2 weeks after seeding, count the number of plants per square metre or foot in a few representative locations in the field and calculate the average. This number is the plant population. To maximize yield potential, the minimum desired population for flax is 300 plants/m2 (28 plants/ft²) and the maximum is 400 plants/m2 (37 plants/ft²).

Sunflower Frost Tolerance

mca2022dev on May 26, 2021

Frost Tolerance

Sunflowers are fairly frost tolerant up to the V4 or 4 leaf stage. The cotyledons just emerging are most frost tolerant, with risk of injury increasing as the plant adds leaves. If sunflowers become brown or black and the terminal bud is severely damaged, plants will not recover. Less severe frost damage may result in loss of apical dominance and plants will exhibit branching from axillary buds, resulting in multiple heads later in the season.

Tolerance to frost in sunflowers can be influenced by the hardening off process. If it is cool or cold for several days previous to the frost, seedlings may have better tolerance to lower temperatures. (https://www.gov.mb.ca/agricult…)

Plant Population

As the crop appears to be fully emerged in the late VE staging, it is a great time to do population counts to determine planting accuracy. Not all sunflower plants may have emerged at this stage, which makes timing appropriate. If the majority of the crop has emerged, a producer should be assessing what percent of the crop remains below the soil surface and why they are behind the rest of the crop. Dry soil, poor seed to soil contact, and consistent planting depth were all planting issues that have to be contended with in extremely dry planting conditions. Go out to the field and do some plant counts now to determine what may have gone wrong just a few weeks ago. Assessing a planting situation at harvest is not the time to learn from mistakes or environmental challenges.

To estimate plant population of emerged crop, determine the length of 1/1,000^th acre using the table below (http://corn.agronomy.wisc.edu/AA/A033.aspx). Measure that distance out and count how many plants have emerged. Record the number. Repeat this 10 times at random locations to get an estimated average of final plant population.

This is also the ideal time to be scouting for cutworms. John Gavloski, provincial entomologist with MARD, suggests scouting to make sure some cutworms are present before applying an insecticide. This time of year there can be a lot of natural enemies emerging. One John sometimes finds in high numbers early in the season is a small ground beetle called Bembidion, that can be very good at keeping levels of some other insects down. John warns that it would uneconomical to take out populations like these if the cutworm population was low. The take home message with early cutworm control is to always scout before applying an insecticide and avoid the proactive insecticide application.

Corn Emergence – Early Concerns

mca2022dev on May 25, 2021

SPRING FROST:

Late May consistently brings early frost concerns in all crops. Corn is quite tolerant of temperatures below freezing because the growing point remains below ground until V6 approaches, however, if air temperatures dip below -2^oC for more than a few hours, it is possible for the growing point to be damaged. See Is Corn Susceptible to Spring Frosts for temperature and scouting details following a spring frost event.

COLD BANDING:

Due to typical warming, followed by cooling spring temperatures as the corn crop was emerging, at VE and V1 staging it is possible to see cold banding on seedlings. As elongation occurs below the soil surface during warm conditions, a period of chilling can create a few growth issues. Most common is imbibitional chilling injury, which is the twisting or corkscrewing of corn mesocotyl as it is trying to emerge. This is when seed has imbibed (absorbed) the water required for germination and then the soil cools to temperatures below 10^oC for prolonged periods. Cold banding is when air temperatures drop to 5 – 10^oC and plants close to the soil surface get a yellow band across the leaf tissue. This is not cause for concern, but a common site at this time of year when temperatures bounce around.

PLANT POPULATION:

As the crop appears to be fully emerged in the late VE staging, it is a great time to do population counts to determine planting accuracy. Not all corn plants may have emerged at this stage, which makes timing appropriate. If the majority of the crop has emerged, a producer should be assessing what percent of the crop remains below the soil surface and why they are behind the rest of the crop. Dry soil, poor seed to soil contact, and consistent planting depth were all planting issues that have to be contended with in extremely dry planting conditions. Go out to the field and do some plant counts now to determine what may have gone wrong just a few weeks ago. Assessing a planting situation at harvest is not the time to learn from mistakes or environmental challenges.

WEED CONTROL:

The first in-crop herbicide applications can occur at VE in glyphosate-tolerant corn. Due to the dry conditions prior to May long weekend, weed emergence was slow. Following varying rainfalls, weeds will likely be germinating quickly now, so it will be important to stay ahead of weed pressure. See MCA’s Quick Herbicide Reference Guide to see what can be applied and when for certain weed spectrums. It is always recommended to refer to the herbicide label for complete information or Manitoba’s Guide to Field Crop Protection prior to all applications.