The new Pulse Spray to Swath Interval Calculator helps take the challenge out of timing your desiccant (diquat) or pre‐harvest herbicide (glyphosate) application in faba beans this fall.
The Spray to Swath Interval is the minimum number of days that must pass between product application and cutting your crop by swathing or straight‐cutting. On farm chemical labels, you’ll see it referred to as the Pre‐Harvest Interval or PHI. Cutting before this interval has lapsed can leave unacceptable residues on harvested seed. There are also Spray to Swath Interval Calculators available for peas, lentils, dry beans and chickpeas available at https://keepingitclean.ca/phi/spraytoswath/.
Spraying faba beans too early can decrease yield and seed size while spraying too late, especially after a frost, can greatly delay the dry down of the crop as well as have yield implications.
“We recommend desiccation in the Central Alberta area be no later than Sept. 10 because of the risk of frost,” said Pulse Research Scientist Robyne Bowness Davidson of Alberta Agriculture & Forestry. “You have to look at the crop. Look at the calendar and make a desiccation decision considering growth stage and environmental conditions. There can be frost any time after the middle of September in Central Alberta, so therefore you must make the call aiming for the highest yield potential found in the bottom of the plant and not wait for the green material at the top. If frost hits the crop, the green material at the top will go to absolute mush resulting in yield losses whereas the more mature pods will be fine. The ones that do have a bit of firmness, depending on moisture likely will turn black. The black ones will not be accepted into the human consumption market but will still be suitable for the feed market. If the seeds split into two halves when squeezed, it is an indication that moisture levels are below 40% and yield can be captured.”
Comparing the colour change of the hilum (the scar or crease on the seed) in the top pods and bottom pods on the main stem is helpful for proper timing. The seeds in the top pods of the plant should ideally be full size and the hilum should be similar in colour change to those seeds at the bottom pods. The hilum colour change in tannin variety faba beans, typically for food markets, is from a greenish colour to black. When top pod seeds and bottom pod seeds hilum colour is similar and changed to a black in colour, it indicates the top seeds have fully matured. It is more difficult to detect the change in hilum colour in low tannin varieties such as Snowbird. When the hilum on the bottom pod seeds and top of the plant pod seeds on the main stem have both changed from green to light tan in colour, this indicates the seeds have fully matured.
Ensuring the seeds at the top of the plant have matured fully will prevent reduced seed size and ensure that you achieve your full yield potential. Unfortunately, depending on the year and environmental conditions this may not be possible, especially if frost is in the forecast. In most cases, it is better to err on the later side than to spray too early. Diquat has a much faster dry down period and can work within five days while glyphosate works much slower (10‐14 days or longer until green weeds and stems begin to turn colour) and should be utilized to aid in perennial weed control.
Source: Alberta Pulse Growers