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IPM Message for Cranberry Growers: May 12, 2023

May 12, 2023

Sweeping this past week has yielded high numbers of cranberry weevil and green spanworm, sometimes in numbers over threshold. Various colors of (springtails) colembolas (red, yellow, and black) have also been picked up. BHF larvae are likely out there, but they are very hard to see. Other larvae of concern that you may see in your net include cutworms such as blossomworm, gyspy moth, and spanworms. Cutworms have 4 pairs of legs in the rear while spanworms have one pair.  The action threshold for cutworms is 4.5 larvae per sweep set; it’s 18 for spanworms. Anne and Marty are hosting a “Bug Workshop” on Tuesday May 16 from 730-930 am in the Entomology Lab (Rm 106 in the Lab Building).

Chlorothalonil sprays for upright dieback control are timed for when the bud has broken dormancy and new growth has begun. For most varieties and locations, this will be this coming week. We are planning our spray for Monday night. The first spray for Fairy Ring control is also timed for budbreak. A combination spray of Indar and Abound is recommended. Please see the Chart Book for details (p13 for URD and p22 for Fairy Ring).

Kerb Use Approved for Dodder Control as Emergency Exemption for 2023 in MA. You must have dodder on your bog to use Kerb under this Specific Exemption. Scout NOW to find seedlings and apply once seedlings are found. One grower reported having seen dodder seedlings on May 11. Search in the canopy and/or in areas where you off-load your fruit and trash. These are the best places to find dodder seedlings.

A maximum of 2 PRE-emergence applications per acre can be made per season. A single application can be made at the rate of 2.5 to 5 pt/A, not to exceed 5 pt/A. Alternatively, two applications can be made at 2.5 pt/A, not to exceed a total of 5 pt/A. Although the herbicide should be watered in (0.1-0.2 inches of irrigation or rainfall), do not apply just prior to a major rain or lengthy frost protection event. Drop the water level in your ditches prior to application. Keep the planks in the flumes and plug all leaks prior to applications. If you can hold water on the bog after the application, please hold for 24-72 hours. Avoid all off-target application by using half-heads or screens as needed. Handler restrictions will likely apply. Contact your handler PRIOR to using Kerb!!

You must wait at least 20 days between applications. A 75-day pre-harvest interval must be observed. The REI is 24 hr. The exemption expires June 30, 2023. MDAR requires that all applications are reported to them by November 30, 2023. Labels (available now) and MDAR reporting forms (coming soon) will be available at all ag retailers, at the Cranberry Station, and on the Cranberry Station web site.

Kerb is Zone II-restricted. If you are in a Zone II, please call Hilary at the Station to determine if you qualify for a letter. You cannot apply Kerb in a Zone II without a qualifying letter.

Late Water Bogs. For those of you holding water on inland bogs, the water should come off by May 15. Coastal Plymouth County bogs should have the flood removed around May 20 and Cape bogs should pull water in late May. Remember that the frost tolerance will be 29.5 F as soon as the flood is removed, no matter what the buds look like. Casoron can be applied for dodder control after the flood is removed but wait for the bog to drain before applying. You still need to scout your LW bogs for early spring insects, even though you will likely be able to omit the early insecticides. Cutworms and spanworms can still be found on LW bogs. Cranberry weevil is NOT impacted by LW and may need management depending on what numbers you pick up. Nitrogen needs for the vines are usually less on LW bogs, so you can usually skip your first N application and/or reduce the fruit set dose. It is best to wait at least 2 weeks after flood removal and add small amounts and monitor the progress of growth. Generally, no fertilizer is need before bloom, but go out and look.

Please see the May 5th IPM message if you have seen Japanese Knotweed on or around your farm; I listed control options.

If you are trying new or different spray mixtures, please do a jar test first. For more info: Be sure to feel the jar after mixing. It should stay at room temperature; heating or cooling indicates a chemical reaction is happening and this is not good.