We will be hosting a series of webinars for cold climate grape growers during the winter months. The first two webinars in this series are taking place in December, and will cover pest management and spray programs.

• Tuesday, Dec. 10, from 12:00-12:30pm: Revisit and Improve Your Vineyard Spray Program
• Tuesday, Dec. 17, from 12:00-12:30pm: Developing Your Vineyard Weed Management Plan

Click here to sign up

Having a spray program that effectively and sustainably targets the diseases, weeds, and insects present in the vineyard, is an important skill for all grape growers regardless of experience level or vineyard size. An effective pest management program leads to higher yields, higher quality fruit, and more satisfied winemakers.

Even seasoned grape growers should be re-evaluating their spray program every year and making improvements to it. December is a great time to do that, so that you can order products for 2020 before the spring rush.

We will discuss how to decide which products to spray based on the pest species in your vineyard, when to spray them, and how to use a variety of resources to develop or improve a current spray program. 

Click here to sign up for the webinars

Registration is free, but we need you to register so that we can send you the login information.

This webinar series is funded by a grant by the North Central Sustainable Agriculture Research and Education program.

Bill Hutchison¹, Eric Burkness¹, Lu Yin² & Matt Clark³

¹Dept. of Entomology, Extension IPM Program, ²Graduate Student, Dept. of Horticultural Science, & ³Dept. of Horticultural Science & UMN Extension, University of Minnesota

The foliar form of Grape Phylloxera (GP) is quite common throughout Minnesota and most eastern grape growing regions of the U.S. Although we have experienced a late spring so far this year, the first grape leaves for most hybrids have started to appear; this is a good time to begin monitoring for the “yellow crawler” stage of GP, as the crawlers hatch from their “mother” galls (including a female with several eggs, Fig. 1).

Grape Phylloxera Life Cycle

In brief, the GP life cycle is quite complex, with galls formed on both root and foliar portions of the vine. However, given the genetic background of the cold-hardy grape hybrids in the Midwest region, the primary potential for damage is the presence of foliar galls formed by GP. Much of this information is taken from a recent publication by one of our graduate students in Horticultural Science, Lu Yin (Yin et al. 2019; see full citation below).

Figure 1: Mature grape phylloxera female and eggs (indicated by red arrow) and crawler (blue arrow) on a young grape leaf (Hannah Burrack, NC State).

Following the hatch of overwintered eggs (on trunk of vine), typically in early May (though later this year), the first-generation nymphs, or “crawlers” move to the grape shoots to feed on 1st to 3rd expanding terminal leaves. The leaf forms a gall around each crawler; at this time the crawlers will form less than 5 galls/leaf.  During May-June, each crawler matures within the gall (Fig. 1) and will produce 100-300 yellow, oblong eggs.  The subsequent emergence of young 2nd generation crawlers (Fig. 1) will begin, and crawlers will move out from the “mother gall”, to establish new galls on new leaves during the summer months (Fig. 2 and 3). 

Figure 2: Fig. 2. Early pin-sized galls (open), and mature foliar galls (closed), Grape Phylloxera, MN (Lu Yin, Univ. of Minnesota).

Figure 3: Mature foliar galls formed by Grape Phylloxera crawlers (E. Burkness, Univ. of Minnesota).

Scouting and Management

The crawlers that hatch from the mother eggs, are the most critical generation for timing a 1st insecticide application, early summer. These crawlers will walk up the plants to 5-6th open leaves, and generate 40-50 galls per leaf, common on susceptible varieties. Three or more generations can occur in MN depending on the year, with additional galls being formed throughout summer.

For timing, growers can use a degree-day (DD) or “heat unit” model to track the initial infestation rates of crawlers. Degree-days for GP are calculated from the bio-fix date (time at which 1st leaves unfurl) by the following: DD = Average daily temperature – 43F, and accumulate DDs each day. The 2nd generation crawler emergence period occurs at 500-800 DDs; in MN we recommend to start scouting at 450 DDs, and twice weekly when possible.

Regarding insecticidal control, the two most common options used in MN have been Danitol (pyrethroid) and Movento (systemic).  To minimize the risk of resistance, these can be alternated (via different modes of action). In most years, only one spray for GP is necessary, or a maximum of 2 sprays.

With Movento, on recent on-farm trials, we have found that one application is often sufficient. After the first spray, check again for any additional gall formation instead of assuming an automatic 2nd spray is needed. As with other crops, sprays should ideally be applied during the evening hours to minimize the risk of direct contact, and mortality to bees and pollinators. Prior to any insecticide use, the label should be reviewed carefully to follow all application safety and use requirements. For more information, review the 2019 Fruit Pest Management Guide (cited below). Finally, in recent years, for some MN vineyards, we have noticed that once GP has been controlled (1 or 2 sprays), it may take up to 2 additional years for the pest population to re-establish, at least at high levels. Bottom-line: to monitor vineyards each spring/summer to verify low or high infestations via the presence of early galls.

More Information

For more information on insecticide options for managing GP, see the 2019-2020 Midwest Fruit Pest Management Guide, at: https://ag.purdue.edu/hla/Hort/Documents/ID-465.pdf

For more information on the history and biology of grape Phylloxera in the U.S., click here for the open access article by Lu Yin et al. (2019), https://academic.oup.com/jipm/article/10/1/16/5490144

For additional Fruit Insect IPM updates, see: www.fruitedge.umn.edu

Recent rains have caused berry splitting for grape growers around Minnesota, leading to spotted wing Drosophila infestations. Insecticide applications are warranted to prevent damaging affects on wine quality, and must be done at least one day prior to harvest.

With the wine grape harvest upon us, and a recent increase in Spotted Wing Drosophilla (SWD) counts, via our weekly trapping network, growers should be aware of the potential contamination of juice or wine, if berries are exposed to SWD just prior to harvest.  The concern with late-season SWD in grapes is two-fold, including a) the potential for direct contamination of fruit/juice via egg-lay and larval infestations, and b) the surface exposure of adults and/or larvae contributing to increased levels of volatile acidity (VA) at either the juice stage or during fermentation --- which is responsible for a vinegar taint to the wine. 

Regarding the risk of direct berry infestation, our 2017 research, via a graduate student (Dominique Ebbenga), we found that with intact (non-damaged) berries, the vast majority of MN grown varieties were resistant to egg-lay. Among 34 varieties tested, only 2 commercial varieties (Swenson red, Vanessa) experienced egg-lay and larval infections. However, the complication this year with recent heavy rainfall, is that excess splitting is underway with several varieties, and splitting allows SWD to easily lay eggs and generate larval infestations.

Regarding concerns with VA, Ebbenga's research found statistically significant, and higher levels of VA in Frontenac, Marquette and La Crescent juice, following exposure to 20 SWD adults (vs zero adults) for 10-14 days prior to harvest. For more information on VA, and how this contributes to a vinegar taint, see the enclosed fact sheet from Penn State. This study is being repeated this year, and will be extended to assess VA levels in wine as well. 

In brief, in preparation for this year's harvest, if growers are in an area where trap catches, or adult numbers are high, or have their own traps to confirm, and one or more varieties are splitting, an insecticide application prior to harvest is warranted. Unfortunately, there are few options available with a short pre-harvest interval (PHI). Mustang Maxx is the primary pyrethroid product to consider, with a 1-day PHI and 12 hr re-entry interval; this is a Restricted Use Pesticide (RUP), and the label should be reviewed. In other words, growers must wait at least one day after applying Mustang Maxx before harvesting.

For recent SWD counts at selected TC-metro locations, see: https://www.fruitedge.umn.edu/swdtrap

Click here for additional SWD management information and labelled insecticides via our UMN guide.