Fall Frost Threats

We are getting to that point where the first frost of the fall could come up any day, but just because the temperatures dipped doesn’t mean that your crop is a write off. There are a number of factors that come into play from crop type to length below freezing.

 Quick explanation on what a freeze event does to a plant; When freezing occurs in the plant it causes the cells to expand causing them to burst or rupture.

The first factor that comes into play is the humidity. Cooler air will hold less water than warmer air. When temperatures drop to below where the relative humidity (RH) reaches 100% (dew point), the air becomes oversaturated and condensation occurs. When water changes from liquid to ice it will give off heat. As the dew on the plant is begins to freeze it gives off heat which can help keep the plant tissue above freezing point. So as water is freezing on the outer parts of the plant, the temperatures remain at about  0  degrees C until all the dew has froze. At this point there is no longer protection for the plant which is when we run into the issue of time below freezing and how it can affect the plant. If it begins to warm up right after this point, damage should be minimal, if temperatures continue to drop or stay around that point then there is potential for damage to occur.

The next thing to take into account is that the liquid within plants does not necessarily have the same freezing point as water. There are sugars, proteins, and a number of other solutes occuring in the plant. These other substances within the plant can take the freezing point anywhere from 2 to even 5 degrees (or more) lower than it would be without them. This shows us that a healthier plant which may have a higher degree brix (sugar) or higher protein content etc may in fact also be hardier than a less healthy, diseased plant.

Temperatures and stress leading up to the frost event can also be a driving factor in how much damage you will see from a frost. If temperatures have been cooler leading up you may see a tougher plant that is less susceptible to light frosts. Other stresses can also cause plants to shake things up a bit with hormones and photosynthate distribution etc. that allow a plant to tolerate lower temperatures, as we all know plants are very efficient at adapting to stress. The speed at which temperatures drop can be a factor as well, the faster they drop bigger the concern for damage.

Moisture content of the crop is another big concern, if your crop is still sitting at 50% moisture then it is a much higher risk than a crop sitting 30% moisture (close to swathing stage in other words).

Each crop has a different susceptibility, much like seedling frost tolerances vary by crop.

Canola:

Canola is susceptible at a temperature of about -2 to -3 if it is sitting at a higher moisture content like I commented on above. Frost damaged canola dries down very rapidly locking in green seed count. If you have a canola crop ready to swath you may escape damage and if you have a canola crop that is below 25% moisture you should be relatively safe from damage. To avoid losses from a frost in canola you can swath prior to a frost event, ideally 48-72 hours to escape damage. This can be effective even at 0% seed colour change to avoid some of the damages. The other comment I have on canola is even a light frost of -1 degree C can have an impact on the enzyme that helps clear chlorophyll which may also cause green seed to get locked in. Remember to inspect fields after a frost, ideally 48-72 hours to look for frost damage. If it is a severe frost and you see significant damage, swathing immediately is recommended.

Cereals:

Again moisture content comes into play with cereals, if at a milk stage they are more susceptible to frost than a soft dough stage. For example a slight dip below 0 at milk stage may cause losses (shrivelled seed), but at soft or later dough stages they can tolerate upwards of -5 degrees. Cereals that have gotten a frost can be significantly impacted when it comes to germination, so be weary about using frost damaged kernels as seed. Cereals may take a week or so before you can truly evaluate damage. Wheat tends to be slightly more tolerant to fall frosts than barley.

Obviously, there are other crops, but I’m going to leave it there. If you have any questions about anything or on other crops feel free to ask.

 

Source: Sask Ag

 

Pre Harvest Glyphosate and Desiccation

Lentils are the main crop that will get hit with Reglone (diquat) and I will touch on them first. Ideally the staging is so that the lowest third of the plant pods are rattling and the seed itself is hard and doesn’t split, the middle third of the plant will be hard and not juicy, but will split nicely into 2 halves and the top third will be full size, but immature. This is also the proper stage for glyphosate timing. The MRL of glyphosate did get increased to 10PPM (same as peas) this year so you are able to use glyphosate if you wish. Be aware glyphosate is NOT a desiccant. It will kill the plants, but it does very little to increase dry down like Reglone will. A glyphosate app still means you could have 10-14 days or more till the proper harvest timing, where as 4-7 days (can be 10) is typical time from Reglone app to harvest.

Peas proper staging for Reglone/Glyphoate is the bottom third of the pods will have seeds detached and rattling with the pods being translucent and shrunken, middle third will have shrunken and leathery pods and will split when squeezed, upper third will just be starting to turn. Again, glyphosate is not a desiccant and will only speed up harvest by a few days or so vs. no glyphosate.

When it comes to using Heat (saflufenacil) from BASF there is no MRL set and I would suggest to avoid using it if you can to save yourselves from having to deal with a buyer denying your lentil crop. If you do decide to use Heat be aware that it will not be as effective as Reglone, atleast not in my experience. You also must use an increased rate as opposed to the 10.4g/ac (80ac/jug). You should use atleast 14g/ac and ideally use upwards of 20grams per acre (40ac/jug) to see better results.

Aim (Carfentrazone) from Nufarm is also registered as a desiccant. You have to increase the rate significantly to get the results you want. In my experience it is a product that will still get the job done if you decide to go this way.

For wheat and barley(not malt) timing of glyphosate, you are looking at close to the same time as swathing. The wheat and barley will be at 30-35% moisture, or hard dough stage. A finger nail imprint will remain on the seed. You can get away with maybe 2-3 days before a typical swath timing would be, but remember if you go in to early with glyphosate the seeds will appear shrunken and it will have a similar appearance to frost damage. In wheat you may also look at the peduncle which is the stem located just below the head, and it will have turned from green to a brown colour.

Remember glyphosate is much better on perennials so if you have a field with lots of quackgrass, Canada thistle etc. then using glyphosate is your best route to go. Not going to be effective to tank mix them, but if you want to get the best of both worlds then using glyphosate first and then hitting with Reglone 3 days later is probably your best bet to get dry down and good perennial weed control.

Some notes on Reglone:

-Reglone prefers water pH of <7

-Ideally use 15-20 gallons of water per acre, the more the better.

-Doubling up on surfactant can be very effective to ensure chemical penetration into the plant.

-Be sure to increase PSI to above 50

-I have heard mixed comments on nozzles, Twin TurboJet seem to be a good option though.

-LI700 is a surfactant that helps get the chemical into the plant as well as lower pH, seen good results with it. Rate is 0.1% v/v, 0.2 if you want to double the rate. Note: Syngenta wants 0.25% v/v to support this adjuvant use.

-If you are using an AgSurf product for example then it is reccomended to double it.

-Reglone is a contact that reacts off UV light so spraying in the evening allowing the chemical to get into the plant is a very effective route to go. This means it is fully soaked into the plant for the next morning/day. You may get some slight local systemicity vs. straight contact as well if sprayed at night due to it soaking in a bit better within the leaves.

-Very rainfast, 15 minutes.

-Reglone prefers hot temperatures so if you can time it so that you spray in the evening and the next day is HOT, it will be more effective.

-Reglone is a group 22, this can be an effective chemical to change up herbicide groups in your rotation.

-The rate is 0.7-0.8L/ac typically, heard of guys going 1L/ac. My main tip with the rate is don’t assume that since you are going the high rate you can cut the water volume, in my experience going the lower rate with higher water volume is MUCH better than going high rate with a low water volume.

It has been a while since my last blog post, hopefully I shook the rust off and wrote one that some get atleast a little bit of info from.

If you have any questions or comments feel free to ask.

Sources: Syngenta Canada