Agronomist Notes

I’ve been busy helping clients with pre-harvest and canola swathing timing over the last ten days. Pre-harvest glyphosate in wheat is in full swing but we’re still a week away from any significant canola acres being cut. Many producers are choosing to desiccate their cereal crops this year as the threat of frost is very real. We had frost at the farm on two nights with a -10C for two hours, some saying even a -40C! Thankfully, the majority of my territory to date has missed any major frosts and yields are looking well above average.

In this week’s Beyond Agronomy News we’ll look at the truth about strobilurin fungicides and their effect on maturity. Next, we’ll briefly list some tips on swath timing, pre-harvest weed control and desiccation in canola. I’ll also give you the low down on how early you can swath wheat and what to look for. Last, we’ll look at the effects of frost during the late stages of crop development. Market news will conclude the issue.

Fungicides containing strobilurin delay maturity

There’s been a lot of debate about the use of fungicides containing strobilurin or “strobis” in cereals. The debate is whether strobi fungicides like Headline and Quilt delay maturity due to the stay green effect compared to products like Tilt or Folicur which don’t contain strobilurin. Aside from cost, producers have been reluctant to use strobi fungicides because the last thing they want to do is delay maturity in an already short growing season. Today, I’m going to lay all the speculation to rest with my observations from a side by side trial I have with Quilt which contains azoxystrobin versus no fungicide. 

The picture you see above is the variety CDC Go and was planted on the 14th of May. All agronomy on this field was the same except for one side had an application of Quilt at early heading and the other had no fungicide at all. You can see strong evidence of the stay green effect from Quilt on the plants on the left hand side where the leaves are still grass green and grain filling continues. The plants on the right with no fungicide treatment have already senesced and grain fill has finished.

The bottom picture shows a closer look at the flag leaves and kernels. Again, it’s obvious that the maturity in the Quilt treatment has been delayed. I would argue there is roughly a 15 to 20% difference in seed moisture content judging by the kernels. That could translate to a one week difference in maturity. There is no evidence suggesting a strobi fungicide changes the physiological maturity off the plant. The product is simply delaying natural death brought on by disease, moisture, fertility or any number of stresses plants experience each year.

Trials on corn in the US have found similar results to what you see here. In corn, the difference in maturity from strobi fungicides also depends on the variety. That’s something we haven’t looked at yet but plan to next year in wheat and barley. I’m not frightened by the delay in maturity because I know my clients are doing everything they can to boost maturity up front so we can afford a delay when it counts during grain filling. Remember, every day you can delay leaf senescence during grain filling you’re adding 1.6% per day towards wheat yield. Paying attention to seeding date, seeding rate, seeding depth, variety and fertility can give you back the maturity you thought you couldn’t afford to lose. SL

Don’t be in a rush to swath canola

• The best time to swath canola for both yield and quality is at the 50 to 60% seed colour change on the main stem.
• If you have a lot of acres to cover and need to start early then at minimum make sure green seeds are firm when rolled between the thumb and forefinger.
• Swathing prior to 15% to 20% seed colour change will likely reduce yield potential and could contribute to green seed issues under hot and/or dry conditions!
• Sun scald, frost or natural senescence can make the canopy look ripened but often the seeds inside remain green. Always examine the seeds within the pods on the main stem to gauge timing accurately.

Source: Canola Council of Canada

Glyphosate vs. desiccant for weed control in canola

• Glyphosate is not a desiccant and will not speed up seed maturity.
• Glyphosate for pre-harvest weed control in canola should be applied at 30% seed moisture which is about 30 to 40% seed colour change.  
• Apply glyphosate seven days before swathing for full translocation within the target weeds, generally Canada thistle and quackgrass.
• If desiccation is required to manage uneven maturity in glyphosate tolerant crops, Reglone can be applied but will only provide top-growth dry down.
• Spray Reglone when 70% of the pods are yellow and the seeds are browny/bluish and pliable. Harvest 4 to 7 days after spraying.

Source: Canola Council of Canada

How early can I swath wheat without effecting yield or quality?

With some very late wheat crops in the country I bet some producers are wondering how early they can swath to help avoid the frost. Did you know that hard red spring wheat can be swathed up to 45% seed moisture content can still have good bushel weight and make the No.1 CWRS grade? To help you identify 45% seed moisture content (mid-dough stage where it can be easily crushed between finger and thumb) have a look at the picture here. I went out on Monday with the portable combine and moisture tester and looked for various seed moisture content to give my own eyes a better understanding of what high seed moisture content looks like in wheat.

If you have a sprout tolerant variety like AC Harvest then I wouldn’t be afraid to swath it early knowing it will lay on the ground for a while and not lose a grade. If you’re still two to three weeks away from harvest then swathing early might be the best option. I hope these pictures help you like they did me! Special thanks to Hilton Farms for lending me their Simple Sampler portable combine and to Gerry Berreth for lending a hand and his moisture tester for this project. SL

What to expect from frost damage this late in the growing season

Article adapted from SAFRR

With recent frosts and risks of frosts in my territory I’ve been asked how much damage we can expect with our late maturing crops. It’s a difficult question to answer because the extent of damage depends on the temperature, length of exposure, humidity levels and the speed to which the freezing temperature was reached. For example, even if the air temperature drops to 0oC the crop itself can be 4 or 5 degrees cooler because the plants loose heat faster than the surrounding air temperatures.

First we must understand plant cells to understand the effects of frost. Plant cells contain not only water but also many substances such as proteins, sugars, amino acids and other solutes that can lower the freezing temperature and protect the cells against intracellular ice formation (similar to antifreeze in your car). What this means is that even though water freezes at 0oC a plant cell may need temperatures down to -4oC or lower before the cells will freeze and damage occurs. Different parts of the plant, different stages of development of the plant, and different types of plants can have varying levels of these ‘antifreeze’ compounds that result in a range of susceptibility to frost. Environmental conditions such as drought, cold temperatures, heat, etc., can also influence the levels of these compounds, and thus affect the tolerance to freezing temperatures. Frost damage occurs as moisture within the plant crystallizes and expands. This causes cells to rupture and fluid to leak out thus, the watery appearance of plant tissue or seed after a damaging frost.

Effect of Moisture:

Cold air can hold less water than warm air. As temperatures drop overnight to below where the relative humidity reaches 100% (dew point), the air becomes oversaturated and condensation occurs. If this occurs close to the earth’s surface, fog or dew forms. When water changes state from liquid to solid (ice) it gives off heat. So as the dew on the plant is exposed to freezing temperatures and undergoes the process of freezing, it gives off heat which can help keep the plant tissue above freezing. While water continues to freeze on the outside of the plant (extracellularly) it remains at 0oC until all the water is in the frozen state. Once this occurs the temperature can then drop and there is no longer heat to protect the plant. As one can see it is the duration of the frost can be critical.

Flax: Immature seeds of flax can be killed by temperatures from 0 to -4oC depending on the length of exposure. Research trials by Agriculture and AgriFood Canada looked at frost tolerance of crops. Flax was found to show considerable damage to immature flax bolls when temperatures reached -3 to -5oC (for one hour) while stems required -6 to -7oC. after flax seed reaches the dough stage it is more resistant to frost.

Cereals: Typically wheat is more tolerant than barley, and barley is more tolerant than oat to fall frost. Cereal plants exposed to frost at the late dough stage sustain less injury than plants exposed at the early dough stage. In the milk stage temperatures below 0oC can result in shriveled kernels. After mid-dough stage, temperatures down to -4oC can result in bran frost, kernel shrinkage and possibly a reduction in germination.

Lab experiments have shown that wheat, barley and oats show little yield reduction at the late dough stage when exposed to -8oC for one hour. However, germination was reduced in the barley and oat. At the early dough stage the crop yields were affected by one hour at -6oC and all had reduced germination

Research with AAFC has shown that hard red spring wheat swathed at up to 45% moisture (mid-dough stage where it can be easily crushed between finger and thumb) can have good bushel weight and make the No.1 CWRS grade. Drying conditions will influence the quality obtained as wet weather could cause mildew and heating damage.

With cereals frost damage first appears as soft watery kernels that ooze water upon squeezing. This is evident at the milk stage and early dough and can be seen within a couple days of the frost. With frost damage at these stages the kernels will shrink and become very light. At earlier stages, such as kernel development, the damage is harder to identify and may take longer to access. It may take up to 7 to 10 days to truly evaluate the damage. The developing kernels are halted in development and will become soft and start to shrink up. At later stages of development such as mid to late dough stages frost damage occurs in the form of bran frost and possibly some shrinkage. This is not evident until at least 7 to 10 days.

Canola & Mustard: With canola and mustard the flowers and pods freeze before the leaves. The leaves can tolerate -3.5 to -4.5oC while the flowers and developing pods can be affected by -2 to -3oC. Immature seed that contains 50 to 60% moisture can be severely damaged by -3 oC while those that are close to swathing stage (35% moisture) may escape damage. To escape most frost damage the moisture content should be at least 20% or lower. Frost at flowering will delay maturity but only causes minor reductions in yield by causing flower abortion. Flowers that are open are the most affected. Buds and already formed pods will continue to develop normally if not frozen. However, frost after flowering and during pod fill will cause significant yield reductions and possible down grading.

A fall frost may not injure the leaves but could have a significant effect on the yield and quality of the oils. Most of the damage occurs as a result of green seed at later stages of development which results in downgrading. Swathing at least 24 hours prior to a frost, and preferably 48 to 72 hours prior, can reduce the green seed count even at early stages such as 0 to 5 % color change (about two weeks from normal swathing stage). However, at the typical swathing stage (30-40% seed color turn) temperatures of -3oC for one hour will have no effect on chlorophyll content. As temperatures reach -7oC the chlorophyll content will be much greater. Swathing the crop 48 hours prior to -7oC will reduce the chlorophyll content compared to leaving the crop stand.

Once a frost has been received on canola or mustard it is important to assess the damage and extent of the damage. Swathing immediately can save the frozen seed (at later development stages) but may be too early for the undamaged seed. Delaying swathing can result in shattering so it is critical to make a proper assessment of the field and swath accordingly. Assessing the field (damaged vs. undamaged seed) is best done at 2 to 3 days after the frost or later. If there is no evidence of damage then leave it till the proper swathing stage. If the majority of the seed is damaged, then swath the crop immediately, as the whitened pods will start to shatter. SL

Source: http://www.agriculture.gov.sk.ca/Default.aspx?DN=0443309f-7978-42d5-ada9-5d1fc0900fe5

To evaluate whether there is frost damage in canola, look for the immature seeds to shrink and no longer be firm. They will become watery masses that look like pepper once they dry. The more mature kernels will remain hard but will retain the green color which causes quality reductions.

Pulses: During flowering are affected by -2 to -3oC while those in the podding stage are a bit more tolerant but will be damaged by -3 to -4 oC. During early pod fill a frost can cause discoloration and deformation of seeds. Frost damaged seeds will be water soaked and no longer firm as they start to ‘leak’. Heavily damaged pods will have a rubbery wilted appearance.

As pulses often mature from the bottom of the plant toward the top, frost injury may be much greater on plant tops. Seeds near the ground may have no frost damage and care should be taken to focus harvest efforts on these seeds.

Summary

Frost is very hard to predict in terms of damage potential in the crop as there are so many factors that affect the tolerance. In general -2 to -3oC frost over a period of at least an hour is expected to cause damage to crops, -1oC for an extended period such as 3 to 4 hours can also cause similar damage. Evaluating the damage is difficult and should be done approximately 24 to 48 hours after the frost for initial symptoms and up to a week to ten days for full extent of damage. A white appearance to the crop is a good early indicator of some frost damage. Heavily damaged crops will quickly show signs of frost injury including discoloration, darkening, water soaked appearance of fleshy tissue and pods. Slightly damaged pods or heads may show very little symptoms but the seeds within the heads may be damaged. Seed harvested from crops exposed to frost must be vigor tested prior to using the seed for next year’s crops.