Early season management of grape diseases and insect pests – Facts for Fancy Fruit

Early season management of grape diseases and insect pests

Grapes are in the early stages of growth across the state, from bud break to 4 to 6 inch shoots. Significant frost and freeze damage occurred in central and southern areas so that will set growth back a couple of weeks as the secondary buds break. With a reduced number of primary shoots, protection of all the secondary shoots will be critical to assure a full, balanced crop. And now that the temperatures are warmer there is an increased risk of damage from climbing cutworms and flea beetles. Growers should scout their planting regularly and be ready to make an insecticide application if more than 10% of the buds are showing damage. There are a number of options, depending on which insect pest is present, or both. IRAC 3A products such as Baythroid or Danitol are effective on both pests. Carbaryl, or Sevin, is also effective on both.

This early stage of growth is also the most important time to maintain “preventative” control of the major grape diseases such as Phomopsis, black rot, powdery and downy mildew. Phomopsis is of special concern. If left unchecked, the early shoot infections will spread to cluster stems and developing berries. The organism then remains latent in those lesions during most of the season and cannot be controlled with additional fungicide applications. As fruit maturity begins the fungus becomes active and damages berries or cluster stems, causing a soft, brown berry rot. Secondary spoilage organisms usually become involved at that time, resulting in very poor fruit quality. Losses can be 50% or higher and overall fruit quality is greatly diminished. Many of the popular varieties grown in Indiana such as Traminette, Seyval, Chardonel, La Crescent, and Marquette are highly susceptible to Phomopsis. So prevention of the early season infections is critical.

Control of Phomopsis is relatively easy with captan or mancozeb. Mancozeb is the preferred fungicide because it is broad-spectrum and also controls black rot and downy mildew. Captan is weak on black rot. It is important to understand that captan and mancozeb are protectant fungicides and must be on the plant before any infection periods occur. So they must be applied before the next rain event and reapplied after a major rain event. Fungicide applications are needed on a 7 day interval through bloom. This is usually about four spray, but may need to be more if rainy weather persists. When vines reach the “immediate pre-bloom” stage, addition of a demethylation inhibiting (DMI) fungicides in the FRAC 3 group greatly improves black rot control and provides powdery mildew control. Rally, Tebustar, Procure, and Mettle are common FRAC 3 fungicides. This group is systemic, thus very rainfast. There are a number of other options available, but this simple approach (mancozeb plus a FRAC 3) has been very effective in our trials. This tank mix should be applied through the post bloom stage. One note; since mancozeb has a long pre-harvest interval (66 days), growers may need to substitute a different protectant in the post bloom sprays, especially on early ripening varieties. Captan or Ziram are effective. Another option to to alternate or switch to one of the strobilurin FRAC 11 fungicides like Sovran, Flint or Abound, or with one of the pre-mix products that contain FRAC 3, 7, or 11 ingredients in the bloom time sprays. Pristine, Quadris Top, Revus Top and Luna Experience are examples of pre-mix products.  A “Suggested Grape Spray Schedule” is available on my web site, along with the full spray program in the 2019-2020 Midwest Fruit Pest Management Guide. Find both at: https://ag.purdue.edu/hla/fruitveg/Pages/Grapes.aspx





Share This Article
It is the policy of the Purdue University that all persons have equal opportunity and access to its educational programs, services, activities, and facilities without regard to race, religion, color, sex, age, national origin or ancestry, marital status, parental status, sexual orientation, disability or status as a veteran. Purdue is an Affirmative Action Institution. This material may be available in alternative formats. 1-888-EXT-INFO Disclaimer: Reference to products in this publication is not intended to be an endorsement to the exclusion of others which may have similar uses. Any person using products listed in this publication assumes full responsibility for their use in accordance with current directions of the manufacturer.