Frost, tar spot, and soybean harvest – fall has begun.
Frost this past weekend caught many of us off guard. The forecast given last week was for a cooler weekend, with a warmer, and drier week ahead. We didn’t realize cooler meant frost! That’s how the weather works, it sometimes sneaks up on you when you are not looking. I guess, with no wind, clear skies, and dew point below 4° C it can lead to a frost event. But that doesn’t explain why it was more injurious than normal?
Tar spot on corn is presumed now to be in the province of Ontario. Samples were collected early this week that resembled tar spot and are currently at the lab for confirmation.
Soybean harvest has started strong this week with seed moistures dropping rapidly as we are in a dry and warm period during harvest.
Frost
The forecast for Friday night, September 18, was for a low of 6° C,, but we awoke with 4° C to 1° C on the thermometer depending on who you talk too and when they woke up. The Environment Canada website recorded -0.2° C for our local weather station and most around the province ranged from 3.3° C in Windsor to -3.3° C in Peterborough.
What happened? Well frost occurs when water vapour in the air forms as ice on a surface. As the surface looses heat energy over the night to the cooler air, the cool surface in turns takes heat out of the water vapour causing the water vapour to form an ice crystal on the surface. The surface could be the ground or the crops top surface, or the roof of buildings. Our temperature measurements are officially taken at 1.5 metres from the ground, so colder air will settle below what we have measured, a recorded -0.2° C temperature Saturday morning may mean that the air below the thermometer was much colder. Also, many farmers may have thermometers by the kitchen window. The house will continue to radiate heat through the night and the air temperature beside the house is not the same as just above the ground. So, it’s colder than your think at the surface of the crop.
But still, why so much damage? I’ve had 0° C before and no damage. Maybe the air was more still this time, or there was more moisture in the air that created greater ice crystals, and maybe the bright sun on Saturday morning reflecting on the ice crystals intensified the solar radiation on the leaf surface (magnifying glass effect) creating damage to the leaf. At least in the southwest the corn leaves look like sun scorch damage, while further north the leaves had that dark green/grayish water soak look to them like the leaf cells were frozen.
Corn
The Ontario corn crop is rapidly trying to finish the last little bit of kernel fill as the frost events have started the plant shut down. As the plants will be limited to any more sugar production, the plants will need to rely on translocating the current sugars from the leaves and stalk to help finish the kernel starch pack. We can expect that the lack of sugar in the stalk will weaken the stalk strength when we get further into the fall. Keeping an eye on stalk deterioration will be important as you pick which fields to harvest first or which ones to leave for later.
The frosted corn will also have a fast moisture dry down in the whole plant as silage producers are rushing to finish harvest before the plant becomes too dry. In turn, with dry weather conditions, good grain drying will also occur as no moisture will be taken up by the plant as its shutting down.
Tar spot was identified in Ontario for the first time on September 21, 2020 in Chatham-Kent and Lambton counties. Samples from Ridgetown have been confirmed in the lab that it is tar spot and the Lambton samples are in the lab waiting confirmation. Since tar spot has been a fungal disease in the U.S. midwest since 2015, it was all but a matter of time until it the spores would blow into Ontario and infect some of our corn crop. The appearance late this fall at a very low level will not cause any yield or economic harm today. But it does pose the threat for future years since the spore are now here and will over winter in the residue. The disease pressure will build in the future under ideal growing conditions of cool and moist weather. Early infection causes the greatest yield damage and will be another disease we will have to keep an eye on while doing our route scouting in the spring and summer. The good news is we have had several years of learning with the infection in the U.S. Midwest and through the cooperative work Albert Tenuta (OMAFRA) has done with the Crop Protection Network https://cropprotectionnetwork.org/ with funding from Grain Farmers of Ontario, we are prepared to have BMP’s and potential fungicide solutions that can help manage this disease and prevent the major yield losses many U.S. growers faced in the first years of the outbreak state side.
Soybeans
Harvest has begun across the province. With the dry weather this past week and a half, farmers have experienced rapid drying of soybeans and moistures have fallen from ideal to way too low in a matter of hours. Reports have come in that harvesting at 13.5% (ideal) one day and by the third day fields are down to 8%. It seems simple to just harvest on the day soybeans are ideal, but unfortunately there is not enough hours in the day or machines available to do that. Usually when the seed first dries during dry weather, there is the concern that plant stems may still be wet/green which makes for hard cutting and wrapping of the plants on the header reel. When the plant is dead and dry, than the soybeans are too dry under these low humidity conditions. Usually a rain before harvest just before the plants mature will help ripen the plants and seed more uniformly and keep soybeans at the right moisture. Harvesting soybeans when the seed is too dry brings up the concerns that the seed can crack, pods at the head shatter, and field losses occur. More importantly, seed is traded at 13%, and shipping seed at 8% is giving slightly more than 5% of the volume away, or at $12 per bushel it’s like only getting $11.40 per bushel. The processing of dry soybeans is also more difficult and in the case of seed soybeans, seed treatment applied to the seed can be sucked into the seed and can reduce the germination of the seed. Its all bad at that low of moisture. Rain is forecasted for early next week and for those fields way to dry, it maybe an opportunity for them to gain some moisture and allow farmers to harvest soybeans at a better moisture level.
Cereals
Winter wheat is starting to be planted right behind the soybean harvest this fall. If planting much earlier than your optimum planting date, backing off on the population is advised as good plant growth and tillering can be expected with the warmer fall that is predicted. If planting at ideal dates, population should be at normal populations and later planting dates will require higher populations in order to compensate for less plant growth and fewer tillers. Planting populations range from 1.2 million to 1.8 million seeds per acre depending on planting time, soil type, and management. Always check your seed source and adjust population depending on the tested germination. If planting by pounds per acre, as that’s how the drill is set up, make sure to check seed size and adjust how many pounds you are seeding. Based on variety and environment where the seed was grown, seed lots can vary up to 3,000 seeds per pound. If seeding 103 pounds to the acre this could mean close to 400,000 seeds per acre difference. Which in turn could mean a too thin stand or a way too thick stand that may get more disease and be more lodge prone. Adjust the planter based on what you are seeding.