Drop Arms: A Valuable Addition
Table 1 – Leaf Coverage
Table 2 – Stem Coverage
Obsolete Pesticide Collection

Drop Arms: A Valuable Addition

Jason Deveau and Sean Westerveld, OMAFRA

Good disease control depends on an effective product, good timing and achieving good coverage of all above ground plant surfaces. Coverage can be defined as having a droplet density between 50 and 70 distinct droplets per square centimetre and this is especially important for those fungicides that are not systemic. This includes all of the fungicides used for Alternaria and Botrytis control. Stem coverage is essential for these two diseases because of the potential for stem infections to kill the entire top. Later in the season, stem infection by Alternaria or Botrytis does not necessarily damage the top but can produce inoculum for further leaf infections within the year or in the following growing season. Due to the dense canopy in older ginseng gardens it can be difficult to get spray to penetrate for good stem and lower leaf coverage. 

For certain products (eg. Bravo), water volumes are not specified on the label or a range of volumes can be used. For these products in the past, an OMAFRA field trial found that high-volume (dilute) applications using hollow-cone nozzles on a horizontal boom and drop arms with hollow-cone nozzles behind the sprayer wheels were required to optimize coverage. Since then, many growers have begun using Arag disc-core style nozzles from Italy on the booms at lower volumes and often without drop arms.

With the kind assistance of a local grower, we performed a spray coverage trial on a 3-yr old garden to determine three things:

1. Do lower volumes provide adequate coverage of leaves and stems?      
2. Do drop-arms equipped with hollow-cone nozzles make a difference in sub-canopy coverage?      
3. Given the expense of the disc-cores ($75.00-$120.00 each), can the cheaper dual-flatfan nozzles (~$10.00 each) spraying medium droplets provide similar coverage?

Data from this trial is still being analyzed, and so this summary will focus on the second of these objectives. Further information will be available in an updated OMAFRA Factsheet on sprayer technology for ginseng in the near future. 

An average water volume was used for this experiment that is within the label rates for certain Alternaria and Botrytis fungicides. Be sure to follow the water volumes registered on the label for every fungicide. Consult the product labels for the appropriate water volumes. More than 300 water-sensitive cards were placed through the canopy of a three-year old ginseng crop. Cards were placed face-up in the upper canopy, face-up and face-down in the inner-canopy and wrapped around the stem at ground level and at just below the prongs. These cards were then analyzed for per cent coverage using an optical scanner and Image analysis software.

The results clearly demonstrate the advantages of using drop arms to improve inner canopy leaf coverage, particularly on the under-leaf surface (Table 1). Stem coverage was greatly improved by drop arms, particularly at ground-level (Table 2).

Table 1 – Leaf Coverage

Condition	Upper Canopy	Inner Canopy
	Leaf Upper Surface (% Coverage)	Leaf Upper Surface (% Coverage)	Leaf Lower Surface (% Coverage)
1,000 L/ha – flat fans and drop arms	48.8%	37.9%	41.6%
1,000 L/ha – flat fans and no drop arms	81.9%	9.3%	0.5%
1,400 L/ha – flat fans and drop arms	69.4%	24.6%	35.1%
1,400 L/ha – flat fans and no drop arms	81.2%	12.5%	0.1%
1,100 L/ha – disc-cores and no drop arms	64.1%	62.4%	13.7%

Table 2 – Stem Coverage

Condition	Stem Near Prongs (% Coverage)	Stem Near Ground (% Coverage)
1,000 L/ha – flat fans and drop arms	16.6%	31.2%
1,000 L/ha – flat fans and no drop arms	5.2%	1.5%
1,400 L/ha – flat fans and drop arms	21.2%	36.0%
1,400 L/ha – flat fans and no drop arms	13.7%	2.4%
1,100 L/ha – disc-cores and no drop arms	21.0%	19.8%

Overall, the disc-cores improved inner canopy coverage (stems and leaves) compared to flat fans, but the drop arms did a much better job of coverage under the leaves and on the stems at ground level.

A boom equipped with disc-cores and drop arms would combine the strengths of both approaches, and should provide better overall coverage then either system alone. Water volume should be increased to compensate for the additional volume sprayed by the drop arms, if such an increase is permitted on the label. For those labels with specified water volumes, the label water volumes should be sufficient to accommodate the use of drop arms.

In this study, drop arms behind the wheels of the sprayer were able to span most, if not all, of the adjacent bed. However, for those plantings with more than 3 beds between the posts, it may be worth installing drop arms over each alley, not just behind the wheels. Because this may cause damage to an overgrown canopy, the boom should be fitted with a fender (similar to those in front of the wheels) to part the canopy at each alley. Keep in mind that these results apply to a fully grown 3-yr canopy and would likely be different for younger or frost damaged canopies.

Questions about pesticide application technology for ginseng can be directed to Jason Deveau, OMAFRA’s Application Technology Specialist at 519-426-8934; E-mail jason.deveau@ontario.ca

Obsolete Pesticide Collection

The Ontario CleanFarms program for the safe and environmentally responsible collection of obsolete pesticides, livestock medicine and used sharps is being held Oct. 20-22, 2009. It is free!
Collection Locations:

Ailsa Craig: Hensall District Co-operative
Courtland: Cargill AgHorizons
Jordan Station: Vineland Growers’ Co-op
Vienna: Max Underhills Farm Supply Ltd.
Kitchener: FS Partners Distribution Centre

For more information contact the Agricultural Information Contact Centre at 1-877-424-1300.

Questions about ginseng can be directed to Sean Westerveld, OMAFRA’s Ginseng and Medicinal Herbs Specialist at 519-426-4323; E-mail: sean.westerveld@ontario.ca.