One of the biggest challenges that corn fertility planning faces is with nitrogen (N) (see image at top). The right rate of N is dependent on so many other factors that it remains one of the hardest to predict in any given year. Too much N leads to higher chance of losses to the environment, and too little N prevents a crop from maximizing yield, economic return, or both. One of the most difficult aspects of N rate planning is accounting for the plant available nitrogen that is mineralized in the soil and is accessible to the crop through the growing season.

Water-extractable mineral nitrogen (WEMN) testing has shown to be a strong indicator of the soil’s ability to provide plant available nitrogen to a corn crop in Ontario, according to a recently published study.

Research completed by Stoeckli et al., and funded by the Grain Farmers of Ontario, indicates that Ontario corn producers may soon have a more reliable tool for N fertilizer rate recommendations ahead of planting.

Currently, corn growers have a few tools at their disposal for N fertilizer recommendations, including the Pre-Plant Nitrate Test (PPNT), Pre-Sidedress Nitrate Test (PSNT), and the Ontario Corn N Calculator, among others. The PPNT and PSNT involve nitrate testing of the soil, and can improve accuracy of N recommendations, but can be limited by variables like early season rainfall or timing and method of testing in-field. PPNT and PSNT recommendations are also calibrated to a fertilization system that has not yet received broadcast N fertilizer and doesn’t have organic sources of N such as manure or legumes in the previous year. When used in situations that don’t meet these criteria, it’s very difficult to identify where the soil test nitrate value is coming from, making it difficult to adjust N fertilization rates. 

The study evaluated different methods of measuring nitrogen and carbon portions of the soil in lab-based testing. Soil cores were taken to a 30cm (12”) depth consistent with standard N sampling procedures. Researchers compared the soil test results from the lab to yield and Maximum Economic Rate of Nitrogen (MERN) to identify correlation. The study was conducted on 13 different sites over 2 years within Ontario corn fields with a history of synthetic N fertilizer use, with most sites being part of OMAFRA’s corn response trials.

Water-extractable mineral nitrogen is the readily available form of N in the soil solution. WEMN testing is performed in the laboratory using room-temperature water, as the name suggests, instead of a Potassium Chloride (KCl) solution that is used in PPNT and PSNT tests. Among the lab-based testing done on these sites, WEMN showed the strongest correlation with yield and MERN, outperforming tests looking at the organic-N portion of the soil. 

Soil texture has a great impact in the availability of nitrogen in the soil. Heavier clay soils were found to have lower N availability to the corn crop in season, when compared to coarser textured soils. Soil texture leads to differences in N loss pathways as well, where fine-textured clay soils are less prone to leach nitrogen, but more likely to have denitrification occur in wet conditions.

However, WEMN tests showed consistent results across soil types, leading researchers to conclude that this testing should be suitable for use throughout the highly variable soils across Ontario. Since the research focused on fields receiving synthetic N fertilizer, fields receiving a high amount of their plant nutrition from organic sources like manure may not follow the same trend with WEMN testing. Nevertheless, for farmers without livestock, this testing could be a game-changer in the future.

Part of the reason for uncertainty with pre-plant N recommendations is because of nitrogen’s relationship with water. Nitrogen moves into the plants as nitrate or ammonium in a solution with water in the soil. In very dry conditions, if the plant can’t access water, it won’t be able to utilize the N, no matter how much is in the soil.

The next step for this research should involve a multi-year study looking at the relationship between WEMN and N fertilizer recommendations, with more field sites to achieve proper calibration throughout Ontario soils. Still, this gives hope that Ontario agriculture may soon have a more reliable way of generating corn N recommendations on an individual field level.

With an ever-increasing focus on reducing nutrient losses from the field, as well as reducing greenhouse gas emissions from our fertilizers, fine-tuning N recommendations for corn using WEMN tests could optimize N rates for the growing crop and reduce the risk of adverse environmental effects. This includes limiting the amount of residual Nitrate-N left in the soil after corn harvest, which would improve Nitrogen Use Efficiency.

At the same time, an improved N fertilizer calculation could increase yield and profitability, especially in times of volatile input costs and grain markets. Better determination of N fertilization rates helps improve the sustainability of Ontario’s corn production. As the research continues, Ontario’s farmers can hope to put together one more piece of the nitrogen fertility puzzle in the coming years.

– Click here to read the August 3 field crop report at the Field Crop News website.

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It seems as though our seasons are becoming more and more variable each year, with bigger temperature swings and dramatic changes in precipitation. With more time between rain events, crops need to be efficient in water conservation and usage.

A research report published in 2015 titled “Increasing Crop Diversity Mitigates Weather Variations and Improves Yield Stability”, demonstrates that more diverse crop rotations beyond corn and soybeans is a key factor in yield increases. Reducing and adjusting tillage is also shown to have a significant effect on yield. As part of Dr. Bill Deen’s research team at the University of Guelph, Amelie Gaudin and colleagues studied thirty-one years of weather data from the University of Guelph, Elora Research Station. Both crop rotations and tillage data were evaluated for corn yield advantages, corn and soybean yield stability and any other potential benefits.

Their findings showed moving from a 2 crop (corn-soybean rotation) to a 3-crop rotation (adding wheat to corn-soybean rotation) increased the following average soybean yields by 13 per cent. The 5-year average for Ontario soybeans is 49 bu/ac. The more crops in a rotation, and the more times the complex rotation repeated, the better the long-term effects.

Corn and soybeans displayed different yield reactions to the various methods of mitigating stresses. While corn appeared to favour crop rotation and diversity, adjusting tillage practices had little effect on yield and stress tolerance. However, soybeans preferred changes in tillage programs over rotation diversification. Less tillage on soybean ground resulted in more consistent crop stress mitigation than conventional tillage. Tillage and crop diversity had a greater positive effect on crop response to heat and drought than they did for wet and cold periods. These practices offered some yield stabilization for wet and cold periods (or entire seasons), but it was lesser than the effects noted during drought stresses.

More recent research published in 2020, confirmed the earlier results. Sites across Canada and the United States saw an average yield increase of 28.1 per cent across all conditions when crop rotations were more diverse (Long-Term Evidence Shows that Crop-Rotation Diversification Increases Agricultural Resilience to Adverse Growing Conditions in North America). They also saw a large reduction in yield losses on drought years. Sites used both synthetic nitrogen and organic nitrogen, and varied tillage systems between no till, reduced till and conventional tillage.

Adding small grain cereals, forage legumes and other niche crops can add some costs and can complicate management practices, but does it have a place on your operation? The more complex the rotation, and the more diverse the tillage practices, the higher the potential to reduce crop stresses. Add in the potential benefits for weed, pest and disease control, and the value may soon dramatically outweigh the cost for your farming operation.

– Click here to read the July 6 field crop report at the Field Crop News website.

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Alfalfa in western and southwestern Ontario suffered a great deal of die out this winter. Farmers had to make quick plans to address this issue. Alternatively, alfalfa and winter wheat in eastern Ontario weathered the winter better than normal and producers there are pleased with these crops. Frequent rains in the east, northwest, and Algoma district are challenging dry hay harvest.

The early spring wet period kept most out of the fields in late April and early May. While the rainfall rates were for the most part not excessive, we didn’t get typical spring sunny warm days to dry out the soil and the frequent small showers continued to slow down the drying process. As well in many places’ soils were still saturated into spring from the excessively wet fall of 2021. These factors led to a condensed planting window for our major row crops. Eastern Ontario especially received more than average rainfall making for additional unwanted stress. The pressure at edible bean planting time had diminished but farmers were finding some dry soil conditions they had to contend with. This added extra pressure to the retail input suppliers and farmers to keep ground preparation going, planters rolling, and sprayers struggling to keep up.

In general, the soil conditions have been excellent for seeding this spring when we finally got to them, we are now seeing evidence of compaction in areas created by starting in the fields when the soils were not quite” fit”. In many places soils were dry in the top ½” but saturated below. Working this ground too early leads to smearing and can cause problems with and following planting. With large planters and equipment, the number of acres that can be covered in short order means a “too early start” can impact a lot of acres. Additionally, the wet period was followed by a dry period and some producers over worked ground which made finding moisture at planting depth problematic. Those on heavy clay soils across various regions of the province had significant struggles in planting in a timely way into fit soils (see photo at top).

This past week with the heat, “pineapple” corn and rolled soybean leaves have been seen in both lighter and heavier soils. Moisture is needed to keep the good potential for yield on track. With the heat and where soil moisture is adequate, we are entering the elongation phase of corn growth leading to mid to late July tasselling depending on location. In soybeans, much of the crop is starting to flower. The heat has brought on rapid colour change in winter wheat as it heads toward grain fill and maturity.

With the condensed spring season, a significant acreage of intended T3 fungicide was not applied or applied late. Fusarium is showing up in fields in the southwest that are well advanced. Farmers should scout their fields to determine the level of fusarium damage and plan to harvest accordingly to ensure quality of the best portion of the crop.

Winds this spring never seemed to let up making the spraying job that much harder. Everyone needs to consider the risks of spraying under windy conditions which can lead to off target drift and injury to other crops/plants and reduces the efficacy of the products at their intended targets.

Weed control has been a struggle and it is important to scout fields as we enter summer. Are there weed escapes that need attention before we run out of time to address them? Are there weeds coming because of the weather conditions or maybe herbicide resistance? Its important to identify that now so you can prepare plans to address any resistance through your weed control choices in the coming fall and spring. Resistance should be checked by collecting seed of some of the escapes and submitting them according to the information at a Plant Agriculture page at the University of Guelph Plant Agriculture website.

If you are going to retreat weed escapes it is important to gather plants/seeds according to the instructions at the URL link above before treatment. Live plants that can set seed are needed to test for herbicide resistance. Resistance testing is important since many species are showing multi mode of action resistance. Not knowing the extent of resistance inhibits your ability to plan the best weed control program in future. A lot of time and dollars are invested in the 2022 crops currently growing. It is vitally important to preserve that yield potential by scouting those fields and addressing problems that can be fixed before we run out of management options available to the 2022 crop.

– Click here to read the June 29 field crop report at the Field Crop News website.

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Thrip infestations have been spotted in a few corn fields again this year. Typically, not a pest of concern, thrips have become an annual problem for some corn, soybean and spring cereal fields in Ontario. These tiny cigar shaped insects feed on the underside of the leaves, leaving scars along the veins of the leaf. When young plants are stressed from lack of rain or a nutrient deficiency, thrips may thrive, moving beyond the lower leaves, causing feeding injury up to the newest leaves. No thresholds are available as typically the plants can grow ahead of the infestations. Control may only be warranted if infested fields continue to be significantly moisture stressed with no rain forecasted, and there are several thrips per leaf throughout the plant, but especially if causing injury on the newest leaves.

Potential upcoming pest issues

Two-spotted spider mite (TSSM) populations in Ontario soybeans and dry beans are becoming tolerant to dimethoate (Lagon® or Cygon®). Despite last year’s field season not being ideal for TSSM, samples were collected in ten fields in southwestern Ontario that had reached threshold. Populations from these sites were found to be resistant to dimethoate. In a hot dry year, we expect to see significant problems in soybean and dry beans. Through a collaborative research project with Western University, AAFC – London and OMAFRA, we hope to understand the distribution and extent of this resistance. Currently, dimethoate is the only active ingredient registered for spider mites in soybeans and dry beans, so this finding is very concerning. It also increases our need to test these populations to find what possible alternative products are still effective and can be registered to replace dimethoate. If you find any spider mite populations in soybeans or dry beans before an application is made (preferable), or after a dimethoate application that was not successful at controlling the population, please contact Tracey Baute (tracey.baute@ontario.ca). Samples will be taken back to Western University for testing. Fields with a history of spider mite problems or fields close to greenhouse operations are of special interest, since they could influence which products they have been previously exposed to.

Corn rootworm (CRW) populations could be heavy again this year, as Bt resistant populations continue to spread and new counties are identified with problem fields. Hot, dry conditions are ideal for adult activity which is expected to start over these next few weeks. In continuous corn fields with repeated use of Bt rootworm hybrids, monitor for beetles in July and August. Those fields that had heavy adult pressure last year will have experienced abundant egg laying in late summer. The larvae that hatched from those overwintered eggs are happy to find corn roots planted in those same fields again this year. Look for signs of lodging and goosenecking to dig the roots to determine the extent of the root feeding. Contact your seed provider or Tracey Baute, OMAFRA if unexpected damage in Bt rootworm hybrids is found.  

The Regional Corn Rootworm Trap Network will continue in 2022 and we are looking for more trap participants in Ontario. Trap supplies are free to growers and crop consultants, thanks to funding from the Grain Farmers of Ontario (GFO) and the Agricultural Biotechnology Stewardship Technical Committee (ABSTC). Monitoring sticky traps weekly during adult activity helps us gain insight as to whether it is a good rootworm year and alerts us to regions and fields where rootworm activity may need further scouting and monitoring for potential resistance issues. It is also improving our understanding of where both northern and western CRW populations are in Ontario and across North America. Trap sites in continuous corn with a history of repeated use of Bt rootworm hybrids are preferred trap sites. If you are interested in getting free trap supplies in Ontario, please contact Tracey Baute (tracey.baute@ontario.ca) so we can get traps to you before July when trapping will start.

– Click here to read the June 22 field crop report at the Field Crop News website.

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Cereals

Herbicide applications are underway in spring cereals and reports indicate these crops are looking good across the province, including the northeast. Seeding deadlines were extended until June 5th in Northwestern Ontario to support producers dealing with record-breaking rainfall. However, continued wet conditions meant that most seeding of cereals had not been completed by June 5th.

Cereal leaf beetle is not being observed in high numbers yet this season, even in areas where pressure has been high in recent years. Little to no disease has been reported to date in winter wheat, aside from some cases of powdery mildew that has been linked to susceptible varieties. Fungicide applications for prevention of fusarium head blight are either complete or planned for this week when the weather cooperates. Some producers have reported that they do not observe pollen on the heads, making it difficult to determine the ideal fungicide application stage. Wheat anthers may not extrude pollen but if heads are fully exposed the window for fungicide application is open, provided it has not entered the preharvest interval – check the fungicide label for the preharvest interval. Wheat planted in November is heading now.

Soybeans

The spring has been relatively normal in terms of soybean seeding and progress. While unplanted fields have been noted in some areas, soybean growth stages range from emerging to 2nd trifoliate stage. Populations look low in some fields, and this may be because of poorer performance of drills on heavier soils compared to row unit planters. Some no-till fields look thin and a few replants have occurred. Soybeans can perform well with thinner stands, and it is commonly reported that no-till soybeans look tough early in the season but yield similar to tilled fields. Cool nighttime temperatures and crusted soil may contribute to slow or reduced emergence. Rolling before rain can increase the risk of crusting. Rolling at V1 (first trifoliate) during the heat of the day with a smooth roller is recommended and does not significantly damage plants or reduce stands compared to other timings.

Some wireworm and seedcorn maggot have been observed but overall reports of these pests are low. Bean leaf beetle have been noted in early emerging soybean fields, and typically these fields are second year soybeans or adjacent to alfalfa fields. During soybean seedling stages (VC-V2) the threshold is 16 adult beetles per 30 cm of row, although control is also warranted if they are clipping stems. Black cutworm has also been reported in some soybean fields which is uncommon, and there is no specific threshold established. Monitor the level of stem clipping and plant populations and consider controlling cutworm where stands are being affected, the larva are still small (under 2.5 cm) and seed for replanting is not available. Bt traits should control cutworm, but ingestion of the toxin requires they feed on a plant and therefore clip off a stem. Within two weeks they should no longer be an issue.

Corn

Corn growth progress looks good and stands are generally healthy. Growth stages range from V2 to V5. Some producers have noted purpling of leaves on corn seedlings. In many cases this is related to genetics and is not a major concern. Where it is related to genetics, purpling may be present on the first 4 to 5 leaves and occurs after a few bright, sunny days followed by cool nights. It is a result of anthocyanin pigment formation. With warm weather the corn will outgrow this quickly, but the purpling may remain if growth is slow due to cool temperatures. If purpling is uneven across the field and continues beyond the 6-leaf stage, there may be a phosphorous deficiency. Deficiency will be most visible on the oldest leaves and may result in stunted growth. Soil tests will aid in diagnosing phosphorous deficiency.

Dry beans

Dry bean planting is ongoing, and soil conditions have been good. Adzuki beans, which are often planted earlier than other market classes, have emerged in many fields. Some white and black beans have emerged, but most bean fields were planted within the past week. Cranberry beans are typically planted last because they mature faster than other beans. Early June is the ideal planting window, when soil conditions and temperatures allow, but planting will continue to mid-month. Later plantings often result in issues with late harvest. It is expected that acreage of dry bean in Ontario will be lower this year than in the past 5 years.

Forages

First cut forages were harvested in the past week. Grasses were ahead of alfalfa for maturity. Yields in the southwest were disappointing in some fields where there was more winter damage than first expected. Some fields were repurposed to silage corn or soybeans depending on feed inventories. Alfalfa weevils are present in many fields. Growers are taking advantage of good weather conditions to apply manure to harvested forage fields.

– Click here to read the June 8 field crop report at the Field Crop News website.

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Winter wheat

Fields that went into last winter in good shape, with uniform emergence and stands, continue to look good this spring. However, uneven, “spotty” stands that have been more commonly found on wet, heavy clay soils have struggled and some of those fields have been terminated. Applied nitrogen varies from region to region, but significant progress has been made over the last week. Estimates range from 30 to 75 per cent of acreage having received an application of nitrogen. The most advanced wheat fields have approached first node (Zadoks 30). Once nitrogen has been applied, the focus will shift to weed and disease management.

Although winter annual weeds are already present, the emergence of annual weeds has just begun and as soil temperatures increase, species like common ragweed will emerge. When applying herbicides, it is important to pay attention to air temperatures, as adverse conditions can increase the risk of crop injury. Avoid making applications if large fluctuations in temperature (>10 C) are forecasted and/or the nighttime temperatures are predicted to dip below 5 C the day before and after you intend to make the application.

Weed control principles in field crops

Making sure that crops emerge in a weed-free environment ensures that any yield losses from weed competition are minimized. For example, recent research by Dr. Peter Sikkema (University of Guelph, Ridgetown Campus) has demonstrated significant economic losses from delayed weed control.

Herbicide resistance – Waterhemp

Waterhemp populations resistant to group 27 herbicides (e.g. Callisto) have been confirmed in 7 Ontario Counties (Chatham-Kent, Elgin, Essex, Lambton, Middlesex, Northumberland, The United Counties of Stormont, Dundas and Glengarry). This means that populations of waterhemp exist that are resistant to 5 different herbicide modes of action. Fortunately, many soil applied herbicides still provide effective early season control of this weed. An ongoing “integrated weed management” study conducted by the University of Guelph (Ridgetown Campus) has demonstrated that the best approach to managing waterhemp and minimizing its production and dispersal of weed requires the following approach:

1. Plant a diverse crop rotation.
2. Establish competitive cover crops after harvest, mow or clip if necessary to reduce seed production of any emerged weeds.
3. Use effective soil applied herbicides with multiple modes of action.
4. Plan on a second herbicide application to control later emerging seedlings.

Further resources on waterhemp identification and management:

• Field Crop News (search “waterhemp”)
• Ontario Crop Protection Hub (‘weed control’ search)

– To read the full field crop report for April 27, visit the Field Crop News website.

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Cereals

Some areas of the province are seeing high powdery mildew pressure in certain susceptible winter wheat varieties. Management decisions should be based on the severity and on protecting the flag leaf. If the disease slows down with warm, dry weather and doesn’t move up the canopy, intervention can wait. If growing a susceptible variety and the disease is getting close to the flag leaf, growers should consider a fungicide application before T3. Susceptibility ratings for specific varieties can be found on the “head-to-head” page from the Ontario Cereal Crops Committee. Powdery mildew symptoms on the flag leaf (1 per cent of the leaf) and the second leaf (3–5 per cent of the leaf) require immediate attention, especially if prolonged wet, humid weather is forecast.

As flag leaf emerges in winter wheat across the province, the crop is approximately 250-275 GDD from pollination and T3 fungicide timing. Application should be targeted for day 3 (three days after 75 per cent of heads in the field have fully emerged.

Cold temperatures kept sprayers out of action in some areas of the province. Those still considering herbicide applications should keep an eye out for flag leaf emergence. If flag leaves are present, it is best to skip the spray in order to avoid injury to the flag leaf and significant yield loss that can accompany it.

Spring cereal growth was slowed during the cool early weeks of May, and so may still be in the critical weed-free period (up to third leaf, GS13). Annuals are emerging and should be controlled.

Cereal leaf beetle (CLB) is showing up in some winter wheat fields. As spring cereals emerge, CLB adults and larvae will move to these fields and scouting is recommended. Recent observations are indicating that CLB are particularly fond of oats. Control is warranted if an average of 3 larvae per tiller are found before boot stage. One CLB adult or larvae per stem warrants control after boot but prior to heading. If significant feeding is taking place on the flag leaf in the early heading stages, control may be warranted. Natural enemies are highly effective at controlling this pest. For the safety of these natural enemies, chemical control is not recommended unless pest population exceeds the action threshold. The Cereal Leaf Beetle Survey is being conducted again this year and agronomists are invited to participate.

Some fields are showing deficiencies in sulfur (S) and manganese (Mn), and remedial applications should be considered. Deficiencies in S are most common in low organic matter and coarse soils, while Mn deficiency is often found in high pH and dry soils. For S deficiency, optimum application rates are 10-15 lb/ac of actual sulfur as ammonium thiosulfate or ammonium sulfate. Foliar applications are recommended for Mn, with optimum rates provided from 8 kg/ha (7 lb/acre) manganese sulfate in 200 L (53 gal) of water. Use a “spreader-sticker” in the spray. Fields with manure applied might still show S deficiency as low temperatures (first half of May) result in slower mineralization of organic S. The same conditions control the rate of transformation (oxidation) of elemental S to plant-available sulfate.

Soil insects in corn and soybeans

With warmer soil temps, grubs and wireworms have been very active at the soil surface. Any early planted seeds that have been slow to emerge could be at risk of feeding injury. Recent temperatures have helped to push the crop out of the ground, though dry conditions can also slow this and give these pests more time to feed on roots and seedlings.

Corn

The corn crop will be mostly planted by the fourth week of May. During emergence, evaluating the uniformity of emergence and development can be used to assess planter performance. If late emergence or variability is observed in the row, try to determine the cause(s) – planting depth, residue interference, seedbed quality and seed-soil contact can influence emergence. Any issues should be noted and addressed next season with equipment or operation changes where appropriate. As plants progress to V3 and nodal roots take over, stand variability may be caused by compaction or smearing in the seed trench limiting root access to moisture.

Corn will be in the critical weed-free period between V3 and V10. Although lack of rain for activating pre-emergence herbicides will reduce their effectiveness, research has shown these products will still provide some control and are still useful for decreasing weed pressure and the burden on post-emergence weed control.

Growing degree days are advancing much faster than this time last year. Black cutworm traps at Ridgetown captured 9 moths on April 12. 8 moths’ or more is the biofix date when we start to calculate GDDbase10.4C for black cutworm development. Prediction models estimate that corn cutting is a risk once approximately 156 to 184 GDD10.4C have accumulated. Based on forecasted temperatures, cutting won’t take place for at least another two weeks. Corn is most vulnerable to cutworm cutting prior to V5 stage.

Soybeans

As soybean planting continues, concerns about soil moisture deepen in some areas. Soybeans should be planted ½” into moisture, with the ideal depth being 1 ½”. Moisture is the more important factor, however, and trials have shown that soybeans can be planted as deep as 2 ½”. While deep-planted seed takes longer to emerge, warm temperatures in the forecast should accelerate germination and emergence. Deep planting is generally less risky in lighter-textured soils, with seedbed quality becoming more important as clay content rises.

Excessive tillage has contributed to moisture concerns in some fields by causing excessive evaporation before seed could be planted. In an average year it would also increase the risk of crusting, though pounding rains are generally not anticipated in the forecast and temperatures should be conducive to rapid emergence.

Land rolling can help to reduce evaporation, in addition to facilitating soybean harvest. While rolling is typically done soon after planting, field trials in Ontario have shown that soybeans can be rolled after emergence. Unifoliate up to second trifoliate stages are safest, especially in the afternoon when the heat of the day makes soybean stems more pliable and likely to recover. Avoid early stages and anything past second trifoliate, when risk of excessive plant injury and stand reduction are highest.

Rolling carries risks for soil quality. When rolling soil with low residue cover, soil aggregates can be destroyed more than necessary, resulting in increased risk of crusting, re-consolidation (i.e. compaction), and decreased infiltration leading to runoff and erosion.

Forages

Early first cuts have started. This is earlier than the typical May long weekend timing, which may be due to tight inventories. Yield will be lower from early cuts while quality will be high, but in some cases, this is a necessary trade-off.

Keep an eye out for alfalfa weevil damage as some fields have reported activity. With lack of rain, plants might not advance quickly enough to avoid damage. If there is 40 per cent leaf-tip feeding, with 2 or 3 active weevils per stem, and there are more than 7–10 days to preferred harvest date, consider applying an insecticide. Natural enemies are generally highly effective at controlling this pest. For the safety of these natural enemies, chemical control should not be considered unless pest population exceeds the action threshold. Registered insecticides can be found in Chapter 3 of Publication 812.

It has been noted that in mixed stands grasses have outgrown legumes. If feed quality is important, these fields should be harvested when the grass is ready in order to maintain the protein content of the feed. Cereals are best harvested for baleage between flag leaf and boot stage.

Manure should be applied to forage as soon as it is harvested. Damage to regrowth is minimized when trampled less than 48 hours after harvest, though in a pinch it can wait up to five days.

The new ONForageNetwork.ca website is the online hub for forage, pasture and biomass crop production in the province. Here you can find information on seeding, growing, harvesting, storing, and marketing these crops. The network is a partnership between the Ontario Forage Council, the Ontario Hay & Forage Co-op, and the Ontario Biomass Producers Co-op.

Canola

Spring canola is being planted and should be in the ground by the end of May. Flea beetles have been active. The threshold for treatment is 25 per cent defoliation. (FCN)

Winter canola has begun flowering. Some fields are receiving preventative fungicides applications for white mould (Sclerotinia stem rot), though risk levels are low with current conditions. Cabbage seedpod weevil has also been spotted. For more information, see White Mould and Cabbage Seedpod Weevil Management in Canola.

Weeds

Dry weather such as we’re experiencing will cause weeds to grow shorter. This should be considered when timing herbicide applications – focus on growth stage rather than height.

Dry conditions have also resulted in reduced control from soil-applied pre-emergence herbicides. Scouting fields for escapes 14 to 21 days after pre-emergence application will provide a much better chance for dealing with them effectively with post-emergence weed control.

Bluegrass seems to be a growing concern in a number of fields. These grasses are challenging weeds, and these fields should be flagged and prioritized for fall management.

To read the full Ontario Field Crop Report for May 19, visit fieldcropnews.com.

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How do low pH knolls develop?

Low pH knolls can develop on undulating landscapes where surface soils formed from deposits of sand, such as where glacial meltwater deposited sand at the entrance to historical glacial lakes (Webber and Hoffman, 1967). Tillage, water, or wind erosion may have also removed topsoil from these knolls. Soils naturally acidify over time through rainfall, organic matter breakdown, and mineral weathering, and through applications of ammoniacal fertilizer. Sandy soils have less ability to buffer against these processes, resulting in lower pH.

A low pH case study

We visited a field in Kent County in May where a producer was struggling with crops establishing on some sandy knolls. There were questions as to why – soil pests? Nematodes? pH? Fertilizer injury? The first step in diagnosing emergence issues is to dig for clues. Most seeds appeared to have germinated, but many failed to emerge and seedlings appeared off colour with poor vigour. While the odd wireworm was found, most seedlings failing to emerge did not show obvious feeding damage. Un-emerged seedlings were also not showing clear, characteristics fertilizer burn symptoms such as blackened roots, missing or “nubbed” seedling roots or root tips.

With no obvious symptoms to explain stand loss, soil samples were collected from the poor establishment area on the knoll and from areas off the knoll where the corn stand was healthy. Two major differences jumped out – much lower pH and magnesium in the poor stand on the knoll compared to the healthy stand around the knolls.

To read the full article, “Getting to Know Your Knolls Part 2,” visit the Field Crop News website.

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Some wheat fields have two or more pests present at the same time. Cereal aphids or cereal leaf beetle (CLB) and armyworm larvae are active in some fields. Cereal aphids are more of a concern in a younger crop. It takes 12 to 15 aphids per stem prior to heading and 50 aphids per head once the crop has headed. More aphids are required to have the same impact on yield that armyworm or CLB can have. It only takes 1 CLB adult or larvae per plant prior to heading and 4-5 armyworm per square foot to impact yield. Focus on these later two pests, even if aphids are present to make a spray decision. Flag leaf feeding again is the ultimate decision maker.

Cabbage seedpod weevil have been observed in spring canola. They lay their eggs in developing pods during the early bloom stages. They are often more abundant at field edges. Scout using a sweep net in a few areas of the field. The action threshold is 25 – 40 weevil per 10 sweeps at 10 per cent to 20 per cent bloom.

What pests are next?

With this hot, dry weather, two spotted spider mites are the next major concern. As wheat starts to dry down for harvest, mites will be moving to other host crops. Plan to scout soybeans, dry beans, and even high value, younger corn fields for infestations over the next month. A recent Field Crop News article is available to help with scouting and management decisions.

Finally, soybean aphids are starting to pop up in a few fields. Hopefully some of the natural enemies present in cereal fields now will spread to soybeans to help provide control. The free Aphid Advisor app is available to help guide you on spray decisions once the soybeans reach the reproductive stages.

The format of the OMAFRA weekly weather report has changed. More locations have been added and assessment of growing degree days (GDD) for base 0 and 5 have been added to assist field and horticulture crop farmers. We have also changed from reporting the weekly values for the 30-year average to the values for the same week in 2019.  We are working toward an additional online report that will provide access to more weather stations, daily temperature and precipitation values and values for corresponding weeks based on the previous 2 seasons and the 5 and 10 year normal for those weeks and the seasonal accumulated values.

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Cereals

Most of the winter wheat crop looks excellent although the prolonged cool conditions have slowed growth. Some of the later planted winter wheat fields are struggling but people are wanting to keep these because of the current market pricing. Growth of annual weeds continues to be slow but is starting to get to the stage when herbicides should be applied. However, forecasted cold air temperatures (<5°C) can increase the potential for crop injury from herbicide applications and therefore will be delayed until air temperatures increased during the latter part of the week of May 11th.

There is more interest in plant growth regulators (PGR’s) this year. With the very good crop, producers are wanting to optimize it. When considering application of PGR’s, tank mixes with herbicides and fungicides during these cold conditions should be avoided. Timing of application relative to crop and pest growth stage is the most important consideration. Even if no PGR’s are planned, delaying the herbicide application until overnight temperature forecasts are warmer is recommended. Weeds will not grow rapidly under these cool conditions.

Disease pressure is low across the province with Septoria being the only disease reported in the lower part of the canopy in some fields. Scout to determine if a fungicide is warranted. In general, disease pressure is well below threshold for triggering application.

Spring cereals are all planted with increased acres across the province, especially oats. Cereals are taking 7-10 days to emerge under these temperatures, but seed was planted into “fit” soils and everything should be fine.

Corn

Corn planting has progressed steadily during the week of the May 4th and planting conditions have been excellent. While corn seed planted 3 weeks ago has not emerged, the ground is not overly wet, which is when the problems of slow germination are of concern. With relatively low temperatures predicted, it is fine that the corn has not yet emerged.

The rate of planting varies widely within and between areas. Some people are completely done and moved onto soybeans while others are just started or yet to start. On average we predict that around 50% of the corn has been planted across Ontario with higher levels in the west and far east compared to the mid-west and central regions. Areas with heavier soils continue to wait on field conditions to be suitable.

Where corn is still to be planted, ensure uniform seeding depth of 1.5 to 2.0 inches. Uniform depth is key to ensuring uniform emergence which provides excellent start to corn achieving its yield potential.

Soybeans

Soybeans, like other crops, do best when planted under ideal soil conditions and for the most part, the 2020 planting season has offered this. Some have expressed concern over the cold temperatures predicted for May 7-11. Once moved into May, the expectation is that temperatures will only improve so if soil conditions are good, growers should continue to plant. The recommendation is to plant 1.5 inch or deeper if you need to find moist soil. The emergence of soybeans planted this week will be a bit delayed, which under current soil conditions is fine and low temperatures should have passed by the time emergence occurs. The goal with any crop is uniform emergence of equally vigorous plants and the 2020 planting season is allowing that to occur so far.

Canola

Much of the spring canola in the traditional southern Ontario locales is completed. Seeding has started in northeastern Ontario. Seeding should be completed by May 15 for optimal potential and to avoid damage from swede midge during early growth stages.

Forages

Cool conditions have kept growth slow in hay fields and pastures. Flowering in grasses is linked to day length rather than heat, so this may reduce yield at first cut, especially for growers prioritizing quality. Scouting should focus on stem counts to assess alfalfa yield potential. Fifty-five or more stems per square foot (ft2) provides full yield potential; stands with fewer than 40 stems/ft2 have less than 70% yield potential and may need to be terminated after first cut. True armyworm scouting in grassy fields should start in the next couple of weeks where fields were green in April.

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