Summer diseases control

Hi Fruit Grower,

Apple orchards are looking good! I’m happy to say that very little fire blight has been found in Rhode Island orchards this year.

We are still a few weeks away from when apple maggot fly damages apples. Usually an insecticide is needed around the third week in July.

Save the date of July 21st for the Massachusetts Fruit Growers Summer Meeting. More information about the meeting later.

The following is a review of controlling summer diseases written by Dave Rosenberger, retire pathologist at Cornell’s Hudson Valley Lab. Also, Orchard Radar has models for when to reapply fungicides depending on what fungicides you use. See these models at http://web.uri.edu/ipm/ under Orchard Radar on the left hand side.

Controlling Summer Diseases on Apples – A Brief Reminder

Dave Rosenberger, Anna Wallis, and Dan Donahue

Current recommendations for control of sooty blotch & fly speck (SBFS) and fruit fungal decays:

Fungicide recommendations have not changed much in recent years.  A quick summary is provided below:

  • Topsin M + Captan: Standard treatment for SBFS and summer fruit rots, but late-season applications of Topsin M are not acceptable for some markets, and the Topsin M label limits applications to a total of 64 oz/A/year. Most growers are finding that Topsin M must be applied at 12-16 oz/A for good results, so that means that this combination can be used no more than 4 or 5 times per year.
  • Captan plus a labeled phosphite fungicide: This combination is just as effective as Topsin + Captan against SBFS, but the phosphites have little or no activity against black rot. Thus, with this combination control of black rot and other summer fruit rots is dependent on the rate of Captan that is applied.
    Inspire Super + Captan: Inspire Super is very effective against SBFS, but like the phosphites, it is less effective than Topsin or strobilurin fungicides for controlling fruit rots. Using Inspire Super during summer may also contribute for selection pressure for DMI-resistant apple scab if primary scab was not completely controlled, although that assumption remains unproven.·         Flint + Captan, Pristine + Captan, and Merivon + Captan all provide nearly equivalent control of both SBFS and summer fruit rots. The latter two have better long-term residual activity than Flint and are therefore preferred for the last spray in August or September when a long residual is needed to cover the gap until harvest. All of these combinations include strobilurin fungicides (FRAC group 11) and have label limitations on the total number of applications per season and/or the number of sequential applications that are allowed.

    ·         Fontelis does not have much activity against SBFS and is not recommended during summer.

    Captan applied alone can be effective if applied at higher rates (4 to 5 lb/A of Captan 80W) and at no more than 14-day intervals.  However, mixing captan with one of the fungicides mentioned above generally provides better results.