Storms, insects, and disease – Oh My! We are about halfway through the season, and 2024 is proving to be an interesting year. I discuss this and more in this week’s vineyard scouting. 

Phenology 

At the West Madison Agricultural Research Station (WMARS) in Madison, WI, vines average around E-L* stage 31 (Berries pea-size) for Frontenac and E-L* stage 33 (Berries still hard and green) for Brianna. 

The minimum air temperature recorded at NEWA weather station at WMARS for the early morning of July 3rd was 65.6°F. 

Pests

Last week, a fungicide (Revus Top** at 7 fl oz/acre) and insecticide (Assail 30 SG** at 5 oz/acre ) application went out on Monday, June 24th at WMARS. Our goal for the fungicide was to protect the rachis of the cluster before the berries enlarged too much and were touching, which would inhibit proper fungicide penetration. The tank mix of insecticide was decided to target phylloxera as galling had been noted. The application was completed around noon with an unpredicted shower coming through Verona around 7pm. We anticipate another fungicide application next week. 

The high humidity and rainfall over the last several weeks has made conditions optimal for aerial root development. I primarily saw this in Petite Pearl, but other vines can develop them as well. While it might look like your vines have been attacked by some alien pest, don’t fret! It’s normal and not a major issue for vines.

Phomopsis and Anthracnose foliar infections were continually observed this week. Likewise, Phylloxera galling was still present. A reminder that you can review phylloxera management in this article. Downy mildew was noted in WMARS table grapes, primarily on Reliance, but nothing was observed in the wine grapes. Conditions have been ideal for disease development, so be sure you are checking your clusters for potential infections. Our first Japanese beetles of the season were noted! Damage is not noticeable yet, but I am keeping an eye on progression. Just as a reminder, cold-climate grape vines are very durable and can take up to 25% damage before action might be required. 

At WMARS and other commercial vineyards, Rupestris speckle has been observed in Frontenac vines. This is a unique phenomenon in cold-climate grapes, specifically those with Vitis rupestris in the parentage. This is purely cosmetic and not a threat to your vines. This is my third season in WI vineyards, and this is by far the worst year for the condition that I’ve observed. Typically, the condition is present when vines are stressed. Some vineyards experiencing the condition tested their petioles with results showing no nutritional issue. As you test your petioles for the season, this can also help determine if what you are seeing is Rupetris or nutritional. 

Key tips to know if you are seeing Rupestris vs Disease:

1. Old leaves vs New Leaves: Rupestris will be seen primarily on older leaves. 
2. Shoots vs Leaves: Vines with Rupetris will have clean shoots whereas fungal diseases attack all green tissue, so you are likely to see foliar AND stem infections when a disease is present. 
3. Foliar Appearance: Black rot lesions are tan with a dark margin. Phomopsis infections are characterized by a black dot with a yellow halo. Rupetris can cause freckle-like spots and reddening, which is not typically observed with fungal pathogens. 
4. Varieties: Not all varieties are noted to be affected by Rupetris speckle. Look at your other varieties to see if you are seeing the same pattern. 

**The mention of a product is not an endorsement. Reference the Midwest Pest Management Guide for fungicide efficacy and additional information. 

Growing Degree Day (GDD) Accumulations

Below displays the GDD accumulations from April 1 through July 3 for the past three seasons. This data is collected using the NEWA website. You can visit their “About degree days” page to learn more about the concept of degree days as well as the formulas utilized for calculations. 

Growing degree day accumulation as of July 3, 2024 (April 1 start date; base 50°F BE*) at the WMARS. 

Location	2024	2023	2022
WMARS	1103	1142	1047
PARS	716	807	699

*BE = Baskerville-Emin calculation method

Accumulation of growing degree days (GDD) as of July 3 (Starting April 1) at WMARS and PARS for 2022, 2023, and 2024.

This article was posted in Grapes and tagged aerial roots, Amaya Atucha, Christelle Guédot, Courtney C Meeks, gdd, grape phenology, Grapes, growing degree day accumulations, Growing Degree Days, Leslie Holland, PARS, phenology, Rupestris, vineyard, vineyard scouting, WMARS.