Early season grape vine canopy management

By: Suzanne Slack, Ph.D.

Early season grape vine canopy management is essential for producing high-quality grapes and ensuring a successful harvest. Proper management practices can help to promote healthy vine growth, increase yields, and improve fruit quality. In this article, we will discuss some of the key management practices that grape growers should consider during the early stages of the growing season with special emphasis on disease control.

Fertilization

Fertilization is essential for promoting healthy vine growth and optimal fruit production. The timing and amount of fertilizer applied depend on the specific soil conditions and nutrient requirements of the grapevines. Generally, fertilization should be done early in the season before bud break to provide the vines with the necessary nutrients to support early growth. However, if that window is missed it is not too late! Grape petiole samples are typically collected at either full bloom or 70- 100 days after bloom. Petiole samples should be collected annually or every other year to gauge the need for or response to applied fertilizer. The general recommendation for best results is to collect at full bloom, when approximately two thirds of the flower caps have dropped.

Pest and disease management

Pest and disease management are critical for preventing damage to grapevines and reducing the risk of crop loss. Early season management practices should focus on preventing pests and diseases from becoming established in the vineyard. This can include monitoring the vines for signs of pest or disease damage, removing infected plant material, and applying preventative treatments. Begin fungicide applications at 1–3-inch new shoot growth; repeat at 7-10 day intervals or according to label instructions and environmental conditions

Downy and Powdery Mildew

Powdery mildew is a fungal disease that is prevalent in cool and humid growing conditions. The disease presents as a powdery white coating on the leaves and fruit of the grapevine. If left untreated, powdery mildew can reduce grape yield and quality. Primary infections of powdery mildew can occur during grape bud break to pre-bloom. Adding a FRAC 3 fungicide (Cevya, Mettle, Procure, Rally, Tebuzol) in the third or fourth spray during this time improves control of powdery mildew and black rot.

Downy mildew is a fungal disease that affects grapevines during periods of high humidity and rainfall. The disease presents as yellow or brown spots on the leaves and shoots of the grapevine. Downy mildew can reduce grape yield and quality if left untreated. The downy and powdery mildew pathogens are especially prone to fungicide resistance. Avoid back-to-back applications of any one systemic fungicide class and fungicides in FRAC group 7 or 11 during this period.

Botrytis cinerea

Botrytis cinerea, also known as grey mold, is a fungal disease that affects grapevines during periods of high humidity and moisture. The disease presents as grey or brown mold on the grapes and can reduce grape yield and quality. While not recommended to target directly until bloom in cold hardy hybrids, any period of prolonged warm, wet days should be followed up with a systemic fungicide.

Black rot and Phomopsis cane and leaf spot

Black rot and Phomopsis cane and leaf spot are fungal diseases that affect grapevines during warm, wet, and humid conditions. Black rot presents as black spots on the leaves and fruit of the grapevine. Phomopsis cane and leaf spot presents as brown or black spots on the leaves and shoots of the grapevine. Both diseases reduce grape yield and quality if left untreated. Pre-bloom applications for these diseases are covered in the regular cover spray program; see notes about phytotoxicity.

Phytotoxicity alert

Inspire Super, Quadris Top, and Revus Top all contain the active ingredient difenoconazole. All fungicides with difenoconazole labeled for grapes have the following precaution: “On V. labrusca, V. labrusca hybrids, and other non-vinifera hybrids where sensitivity is not known, the use of Inspire Super, Quadris Top, or Revus Top by itself or in tank mixes with materials that may increase uptake (adjuvants, foliar fertilizers) may result in leaf burning or other phytotoxic effects.” 

Revus Top cannot be used on Concord, Concord Seedless, and Thomcord grapes.

Flint 50WG should not be applied to Concord or other American type grapes, as injury may occur.

Luna Experience is labeled for wine grapes only and should not be used on Concord grapes. 

Pristine should not be applied to Concord or other American-type grapes, as injury may occur.

For more information and specific fungicide recommendations please see the Midwest Fruit Pest Management Guide 2023 to 2024 edition section on Grapes.  https://ag.purdue.edu/department/hla/extension/_docs/id-465.pdf

Insecticides

Insecticides should be used sparingly to control insect pests. Please see the Midwest fruit pest management guide for specific insecticide recommendations. Whatever using insecticides, special attention is needed for the PHI of these products even with wine grapes.