By Dr. Jason S.T. Deveau, Application Technology Specialist, OMAFRA
Spray advice for ginseng has changed and evolved over the years in Southern Ontario.
Growers once used the Cassotti sprayer, which sprayed impressive volumes of water under high pressure over large areas. The ineffectiveness of this method was demonstrated in work performed by OMAFRA’s Paul Goodwin and Jan Schooley in 1998. The Casotti gave poor coverage deep in the canopy, with very little spray impinging under the leaves. At that time, Paul recommended growers use drop-arms equipped with hollow-cone nozzles to get under the canopy. It was also proposed that growers apply products in about 1,000 -1,400 L/ha of spray volume.
In 2009, Sean Westerveld and I worked with a local grower to see if coverage could be improved. Many growers are now using the Arag Microjets (see Figure 1) which did a good job of foliar coverage, and could penetrate the canopy to the stem, but still benefited greatly from the addition of Paul’s drop-arms. From this data, we made a case for about 1,000 L/ha of spray volume.
Figure 1. ARAG Microjet nozzle (pictured here with a smaller dual flat fan nozzle)
Note the 400 L/ha difference. The reason is that increasing the water volume beyond 1,000 L/ha increased coverage, but only a little bit. The volume of liquid that can be retained on a surface is limited, so once wetted, the surplus drips down on to the soil. Paul and Jan knew this, but encouraged the high volumes because product saturation into the soil might offer additional protection to the crown and root.
As an applicator, it is important to know when you want that run-off, and when you don’t. For example, run-off into the straw layer and the soil would be beneficial for Phytophthora, a disease that affects both tops and roots. On the other hand, there is minimal benefit to run-off of products that control only foliar diseases such as Alternaria and Botrytis. Using one volume throughout the season, across all product types and modes-of-action is not an efficient or effective way to spray.
What does good coverage look like? Here are three water-sensitive papers (see Figure 2), demonstrating: Left – Insufficient coverage, Middle – Ideal foliar and stem coverage, and Right – Excessive foliar and stem coverage, approaching run-off.
Figure 2 – Left – Insufficient coverage. Middle – Ideal foliar and stem coverage. Right – Excessive foliar and stem coverage.
When you are deciding what volume to use, keep these points in mind:
1) Lots of spray volume and/or big droplets will run off the leaves and stems of broadleaf plants.
2) ARAG Microjet or hollow cones should be spaced about 50 cm apart and spray at a height of 50 cm from tip-to-target.
3) Drop arms should be located in each alley, including behind the wheels, and aimed about 25 degrees higher than horizontal.
4) Old, worn nozzles can sputter, causing gaps in the pattern. An exaggerated version of this is nozzles operating at too low a pressure.
5) Use water-sensitive paper to see what coverage you are actually getting by stapling them to leaves, or wrapping them around stems, held with bobby pins.
If you are willing to make changes to your spray volume throughout the season, you should realize more effective and efficient spray applications. For more information, check out our factsheet:
