By: Dr. Jason S.T. Deveau, Application Technology Specialist

Alternaria is the biggest issue in ginseng gardens at this time, as is often the case this time of the year. Good control requires regular monitoring for the development of new lesions, timely application of a rotation of registered fungicides, and good coverage of leaf and stem surface with the fungicides. Here’s a reminder about how to achieve, and diagnose, good spray coverage.

Spray Volume:

You need to raise your spray volumes as the crop grows and fills to compensate for increased canopy density, and the difficulty of canopy penetration. However, using exceedingly high volumes will give a rate of diminishing return; higher than 1,000 L/ha is probably not worth it. If you’re trying to get spray to run down to the crown or into the straw, know your pest and read the label to confirm whether or not the product will actually do you any good down there. For example, there’s no point of drenching when spraying for Alternaria or Botrytis, but for root disease control high volumes may be required.

Nozzle Position:

Put away the Cassottis, and put drop arms on your booms. Place them in each alley, including behind the wheels, and aim them at least 25 degrees higher than horizontal. Use hollow cones down there so they have the best chance of spanning the entire raised bed and hitting all surfaces of stem and under-leaf. Still using Arag Microjets along your boom? Consider getting the cheaper and much easier-to-calibrate version without the mixing valve (see Figure 1). Perhaps better still, consider using conventional disc-core hollow cones instead.

Diagnosis:

Don’t just spray and pray. With many applications per season, that’s a lot of time, water and money. Know where your spray is going by placing water-sensitive papers in your crop. Clip them to flags and to the upper and lower sides of the leaves. Spray water and retrieve the cards. See where your spray is going, or not going, and make changes to your spray program until you see the coverage you need.

Figure 1 – The original ARAG Microjet is big, hard to clean, and the mixing valve can cause calibration errors up to 20%. The smaller, cheaper version has the same spray quality, but is easier to maintain and calibrate.

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 this factsheet: http://www.omafra.gov.on.ca/english/crops/facts/10-079.htm and be sure to visit www.sprayer101.ca for sprayer basics.