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The Cropwalker - Volume 3 Issue 22

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Crop Conditions

Soil moisture is variable with some soils becoming dry while others have good moisture, and some are still wet. Winter wheat Fusarium spraying is in full swing in higher heat unit areas to heads still in the boot in lower CHU areas. Products of choice for FHB are Caramba, Miravis Ace or Prosaro. Current weather conditions are conducive to the start of fusarium. Review of FHB timing. Once 75% of heads are emerged is day 0. The next 3 days, day +1 to day +3 are the optimum days to spray for FHB control. Prosaro or Caramba can be sprayed from day +1 to day +5. Miravis Ace can be sprayed from day 0 to day + 5. Corn is advancing quickly. Earliest is at 6th-7th leaf stage. Probably putting out 2 leaves a week. Between this week and next week, majority of the corn in Ontario will be at the maximum stage for herbicide applications. Only a handful of products safe to apply in the 6-8 leaf stage.  Soybeans are at 1-3rd trifoliate and loving the heat. Be extra careful spraying dicamba products Forages first cut continues. Yields have improved on fields that received rain last week. New seedings are at or nearly at 3-4th trifoliate. Spraying 2,4-DB at this time especially under hot conditions can damage new alfalfa. Weed control Pre emerge herbicides seem to be holding well. But this is a critical time for weed escapes. All fields both corn and soybeans must be checked now for escapes. If no annual weeds, use this as an opportunity to set back perennials.


Corn – Leaf Staging

Last week we had posted a chart on corn staging. The popular method for Ontario crop staging for crop protection products is the leaf over method. When looking research documents or US publications that use the Vegetative Staging i.e. “V4”, what they are referring to is leaf collars (blue arrow). The plant in the photo below has 4 leaf collars, or is at V4. Notice that the there are two additional leaves, one out of the whorl, but without a collar, and one in the whorl just emerging.

Picture 1 - Corn Staging

Question My alfalfa is at the 4-5 trifoliate. Is it still ok to spray with 2,4-DB (Embutox/Cobutox)?

Answer No. Young alfalfa plants cannot metabolize 2,4-DB. Once plants get to the 4-5th trifoliate they can and it converts in to the amine form of 2,4-D. Spraying at this stage will set the alfalfa back. Better to live with the weeds and cut early to control them.

Rolling Emerged Soybeans

There is a slight benefit to rolling soybeans after they have emerged. It does punch stones down to make harvesting easier and will punch down corn cobs which can be an issue with IP soybeans Replicated work by Horst Bohner Soybean Specialist with OMAFRA has determined that it is most crop safe between the 1st and 2nd trifoliate. Excess stem breakage occurs at the 3rd trifoliate. Does it add additional yield? Maybe 1-2 bu/ac compared to rolling at planting, provided the timing and conditions are right.

The caveats to making rolling emerged soybeans work are; 1) crop must be at least at the unifoliate stage, preferably at 1st trifoliate, 2) top soil should be dry, 3) less or no stem breakage occurs when rolled on days with full sun in the mid-afternoon (plants are flaccid), 4) use a smooth roller.

Winter Wheat – T3 Application

Prognosis is for high Fusarium levels in wheat this year. A FHB fungicide application can reduce DON levels by 50%. A fungicide application at this time can increase yield by 7 bu/ac if 100 lbs/ac N was applied and 10 bu/ac, if 135 lbs./ac N was applied. (Source: SMART Wheat Trials) It is OK to spray fungicides during hot weather. However, if temperature gets above 30  C consider spraying in the evening. If you add an insecticide or foliar fertilizer you could increase probability of leaf damage if weather is hot. As one CCA who works with a fungicide manufacturer said “Don’t miss the flower timing due to hot temperatures. If possible, spray later in the day. Our only concern is when temperature gets above 30  C.

Fusarium Head Blight Timing Scale

Days prior to 0 (-1, -2) indicate the head is still in the boot/stem.

Day 0 75% heads fully emerged

Day 1 – First flowers visible.

Day 2 Anthers visible in middle of head

Day 5 Pollination complete.

See our last issue focused exclusively on FHB products, timing, expected response, water volumes and spray tips at; http://newsletter.fieldwalker.ca/issues/the-cropwalker-wheat-management-edition-fhb-254177

Proper Timing of T3 Fungicide Application in Wheat Improves Coverage

I had made a comment to a client late last week that the wheat head needed to clear the flag leaf collar prior to spraying, partially for coverage, but also for it to physiologically initiate flowering. Ryan Benjamins captured a great photo of what wheat looks like when it is within in the proper window, vs too early.

Which Leaves in Wheat Contribute the Most Yield?

Between the ear (head), flag leaf and leaf “2”, almost 50% of the leaf surface comes from these top 2 areas of the plant. Photo from UK Agriculture and Horticulture Development Board – Wheat Growth Guide.

Picture 2 - Wheat Leaf Area

Insect alert

Cereal leaf beetles are active in traditional areas. Black cutworm US have been catching lots of moths. Check traditional areas. They are attracted to grassy areas. Armyworm US numbers had about average number of moths. Their crop of choice is winter wheat. They may start in a downed area of the field. Typically, damage is leaf feeding. Most fields will have the odd army worm. If you find an area just watch it. Wet weather favors build up of a disease that kills them.

Picture 3 - Armyworm Leaf Feeding

Cereal Leaf Beetle

Are showing up. Threshold is 1 adult or larva per stem after boot stage. Adults have a bright red head. Larva are slug like critters. If you walk through a field and your jeans are covered with small black stains (larvae feces) them it is an indication to check closely. The eggs are a golden brown colour.

Picture 4 - Cereal Leaf Beetle Larva

Trivapro vs. Miravis Ace – The tale of two SDHI fungicides.

In speaking with Leanne Freitag of Syngenta, the Trivapro’s SDHI, Solatenol, is a leaf disease specialist, while Miravis Ace’ SDHI, ADEPIDYN, is a fusarium specialist. Both SDHI’s are expected to last as long as a strobilurin. One reason to consider using fungicides with these actives is to minimize fungicide resistance, as many products on the market currently rely on only two fungicide groups (FRAC-3 and FRAC 11).  SDHI is FRAC 7.

Physiological Fleck of Wheat

In my notes the earliest I have as seeing this problem was 2002. It is caused by UV sunlight. The plants were sun burnt. It sort of looks like a disease. But it is general through the field. It occurs as much or more on the top leaves as the bottom leaves. According to Peter Johnson of Real Agriculture varieties with a blue tinge to the leaf tend to exhibit it more. From his experience there is very little leaf loss due to sun burn. If you are not sure what you have put some leaves in a bag with a couple of drops of water and if it is a disease the flecks with develop a visible disease of either mycelium growth or black pepper like specks.

Picture 5 - Physiological Fleck - Source: Deb Campbell
Picture 6 - Physiological Fleck
Picture 7 - Physiological Fleck

Cleansweep Tips

Missed your pre-emerge application on non-gmo or IP soybeans? This is a common issue on years like this, but don’t miss your Cleansweep window as well! Label states up to 21 days after planting. Don’t wait 3 weeks. Target 10-15 days after planting for your first application. Ideally the annual grasses will be 1-3 leaf, with the broadleaves at the cotyledon to 2 leaf stage. Use 20 gallons of water, flat fan spray tips, and do not forget to add the 0.8 L/ac of 28% UAN. Do not add any additional Pursuit, it will not improve upon what’s already in the co-pack. A second cleanup application (in-crop) maybe required depending on weed spectrum and resistance.

Permit for nutsedge control in corn

You can apply Permit (halosulfuron) to corn for control of emerged nutsedge. Typically, nutsedge is not through the whole field and you can spot spray areas. Permit is a group 2 herbicide that does control a number of broadleaf weeds. It is registered on several crops other than corn. Permit is a bit expensive to apply to the entire field since it needs other actives to be a complete corn herbicide (i.e. to control grasses). In research trials the year after application Permit plots had about 25% the number of nutlets as the Primextra or glyphosate treated plots. Field experience backs up the fact that with Permit, there is less nutsedge the next year. Gowan usually recommends the 19 gr/ac rate. This rate will also provide residual control of weeds such as; Common Ragweed, Lamb’s Quarters, Pigweed and Velvetleaf. It is not registered on soybeans, if sprayed on soybeans, you will have to replant another crop

Figure 1 - Tuber Counts Following Year
Figure 2 - Visual Control Year of Application

Why poor corn emergence? Was there a difference among hybrids?

Well the cold soil was the main culprit. Corn hybrid companies test hybrids for emergence under cold conditions. The issue was that we have never had this cold of soil before. So, the companies could not rate hybrids for emergence under conditions this cold. There is definitely a difference among hybrids. Some best-selling hybrids have lower than expected final stands on some fields. I started to make a list of hybrids with poor emergence. I sent this list to a group of agronomists and they had fields with these hybrids where there were no emergence issues. They said that the problems were compacted soils and or manured soils. In many fields there is obvious insect damage. Probably seed corn maggot but may also be wire worm damage. This year the seed was in the ground longer, so the insects had longer to feed on the kernel. It appears that corn planted May4-6th was hit hardest.

Adjusting nitrogen rates for lower populations

There are a lot of fields with lower populations in parts of the fields. The chart below is our potential yield estimate based on various final populations. Part of the range in yield estimate is because of nitrogen rate. Looking at the chart consider using the highest estimate as the percentage of total nitrogen to use. Consider using your full intended rate on populations of 27,000 plus. At 20-24,000 consider using 90-95% of intended use rate.

Figure 3 - Corn Yield Potential by Population

Sun burn corn leaves

The high levels of UV last week also caused sun burn on some corn leaves. The leaves will appear white. Typically, the burn is on the top leaves. If not noticed for a few days the new leaves will be green and sunburnt leaves below have a whitish colour.

Picture 8 - Sunburn on Corn Leaves

Hail damage

Last weekend there was hail. Young corn and soybean plants typically outgrow this damage when it occurs early in the season. Some believe applying a fungicide helps. I have not seen any trials to support this. If wheat has a lot of leaf shredding it can affect yield.

Picture 9 - Hail Damage on Corn Leaves

Fertilizing forages after first cut

A good stand of forages can remove 50 lbs/ac phosphorous and 250 lbs /ac potassium. This is equixvalent to about 150 lbs/ac Map and 425 lbs/ac 0-0-60. So depending on how much you have already applied will determine how much you should apply now. A generic recommendation is 75 lbs/ac MAP and 200 lbs/ac 0-0-60. If you have not already applied sulfur consider adding 15 lbs/ac S now. This is also a good time to apply 1 lb/ac actual boron.

Apply Manure to Hay Fields

A 3-year forage stand removes about 900 lbs K20, which eventuallymust be replaced. Dairy manure is high in K, so forages are good place for manure in the summer months. There are added benefits to using manure, as your fertilizer source over commercial fertilizer on hay. University of Wisconsin research shows that spreading manure on hay ground increases both quality and yield by 5.6% and 10%, respectively. This combined equates to 12% more milk per acre on average. Apply 3,000-4,000-gal manure after cutting, but before regrowth begins, as tire traffic on new growth will reduce yield. This rate should give about 90 lbs K. It is not recommended to apply manure to hay that will be used for baleage, as it could cause improper fermentation.

Horsetail the Iceberg Weed

It is called this since only 10% is above ground. The other 90% is a massive root system that makes control difficult. It can grow in wetter and drier soils than most plants. It can grow in very high and very low pH soils. Tillage easily spreads roots. Horsetail, (snake grass, puzzlegrass) is the only living genus  in a family of vascular plants that reproduce by spores rather than seeds. Equisetum is a living fossil, as it is the only living genus of the entire class Equisetopsida, which for over one hundred million years was much more diverse and dominated the of late Palezoic forests. Some Equisetopsida were large trees reaching to 30 meters tall.

Picture 10 - Horsetail spread through tiling

Forms of N Loss - A Summary

Ross Mackenzie is a retired researcher and fertility extension specialist with Alberta Ag. He said it quite well on a number of factors of nitrogen loss, so I will use his words to describe the situations for the various forms of loss. All graphs in this article are from the IPNI's Nitrogen Notes series.

Figure 4 - Nitrogen Cycle


The losses from sandy soils are usually higher than from heavier textured soils and are greater at warmer temperatures versus low temperatures. Greatest volatile losses can occur where there is just enough moisture to put fertilizer into solution, but not enough to move it in to the soil, followed by hot, dry windy conditions.

Figure 5 - Urease activity by soil temperature
Figure 6 - Ammonia loss by fertilizer type


Lost in runoff waters and through runoff waters and through soil erosion. Major rain events with significant soil movement would be the risk at this point in the growing season.


Refers to the movement of nitrate nitrogen in the soil solution through and out of the root zone. Generally speaking, nitrate leaching is less of a concern in clay soils, where denitrification would be a bigger risk.

Figure 7 - Leaching potential by soil type


Refers to the conversion of plant available nitrogen to organic nitrogen by soil micro-organisms. Nitrogen is not lost but tied up temporarily and slowed release for crop use through mineralization. Immobilization of ammonium nitrogen is slight great than nitrate-nitrogen. High immobilization occurs in surface soil under minimum and zero-till management, reducing the amount of available nitrogen in these systems to crops in the early part of the growing season. Banding rather than broadcast incorporation, is an effective method to reduce nitrogen losses via immobilization.


This process results in the reduction of nitrate-nitrogen to nitrogenous gases such as nitrogen (N2) and nitrous oxide, which are lost to the atmosphere. Considerable nitrate-nitrogen may be lost by denitrification when soils are temporarily wet (early spring or after heavy rainfall). This is because the micro-organisms that convert nitrate to nitrogenous gas work optimally under high moisture or saturated soil conditions. Denitrification: NO3- ----> NO2- ----> N2O.  Areas that tend to be saturated for extended periods in the spring are the most prone to significant denitrification losses.

Figure 8 - Soil Moisture/Nitrogen Process Interactions
Figure 9 - Denitrification risk by Water filled pore space
Figure 10 - Soil/Water Matrix

Last Mystery Weed – Lamb’s Quarters

What has to be the most common weed in Ontario, Lamb’s Quarters is pretty much ubiquitous to field crop production. It was introduced from Europe as a salad green. Yield loss in corn and soybeans is estimated at 12-38% depending on level of infestation (1 to 5 per square meter). Most effective herbicides in corn are Group 27s (Acuron, Armezon, Callisto, Converge XT, Destra/Engarde, Halex, Impact, ShieldEx – note some have residual, some do not). In Soybeans, my preferred method is to use a group 14 pre-emerge (Authority, Valtera based products). Almost any cereal herbicide will take them out, provide group 2 resistance is not an issue. My preference is to control them early, as calcium deposits and or soil on leaves can reduce glyphosate efficacy, if trying to control post emerge.

Picture 11 - Mystery Weed for week of May 25 - Lamb's quarters