GRAPE DISEASE CONTROL 2018, Part 1

Bryan Hed, Department of Plant Pathology and Environmental Microbiology, Penn State Extension

As the new grape growing season commences, this is a good time to revisit some of the fungicide updates that were discussed at grower meetings earlier this year. While these materials are available to growers in most states, some of them have not yet cleared the extra hurdles required for legal use in New York, and in those instances, I make specific mention of that. I hope this blog will be useful for growers in the 2018 season.

FUNGICIDE CHANGES, NEWS, & REVIEWS

First, Aprovia/Aprovia Top. The active ingredient in Aprovia is solatenol (benzovindiflupyr), and while it does not represent a new chemical class for us grape growers (succinate dehydrogenase inhibitor or SDHI) it is a new and improved chemistry. The SDHI fungicides belong to FRAC Group 7, which also includes chemistries in products like Endura and Pristine (boscalid) and Luna Experience (fluopyram). Aprovia was available for use in most states last year but has now been labeled for use in New York as well. As a solo product, Aprovia is very effective for the control of powdery mildew as trials in NY over several years have shown. Trials at Penn State over the past couple of seasons have also revealed some efficacy on black rot, but I would consider it more in line with “suppression” of this disease and I cannot recommend it for black rot control, especially on susceptible varieties. Also, it should not be relied on for significant control of Botrytis, unlike other SDHIs. The label also lists control of Phomopsis and anthracnose, but I have not seen any real proof of that. Penn State has tested this product over two years on Concord, to examine it for any potential crop injury issues to that variety. in comparison to Revus Top, a standard spray program, and an untreated check, there were was no injury to Concord grape from Aprovia, while, as expected, Revus Top caused severe damage to leaves developing at the time of application.

Aprovia Top, on the other hand, is a mixture of two active ingredients: i) solatenol, the active ingredient in Aprovia and ii) difenoconazole, a DMI fungicide with very good to excellent activity against powdery mildew, black rot, and anthracnose. Aprovia Top is also labeled for control of Phomopsis, but again, local experience and published results of trials with Phomopsis is lacking. The label rate for Aprovia Top is 8.5 to 13.5 fl oz/A; 13.5 fl oz of Aprovia Top provides about the same amount of solatenol as 10.5 fl oz of Aprovia; it also provides about the same amount of difenoconazole as 18 fl oz of Inspire Super, but falls a little short of that found in 7 fl oz of Revus Top. Aprovia and Aprovia Top have a 12 hr REI and a 21-day PHI. As with all the products containing difenoconazole, Aprovia Top should not be applied to Concord grape and other varieties on which difenoconazole injury has been reported. This includes Brianna, Canadice, Concord Seedless, Frontenac (minor), Glenora, Noiret (minor), Skujinsh 675, St. Croix (minor), and Thomcord.

Intuity. The active ingredient in Intuity is mandestrobin, and if that sort of sounds familiar, it’s because this is another strobilurin fungicide (FRAC group 11).  Intuity offers protectant and antisporulant activity against Botrytis, for which it is exclusively recommended, though it will provide suppression of powdery mildew, at least where strobilurin resistance has not yet developed. In limited NY and PA trials, Intuity has provided good to fair control of Botrytis equivalent to current standards like Elevate, Vangard, Scala, and Switch. The label rate is 6 fl. oz/A with a maximum number of three applications (two is recommended) and 18 fl oz per season. Do not make sequential applications; rotate with non-FRAC 11 materials (Elevate, Endura, Fracture, Inspire super, Rovral, Scala, Switch, Vangard) and allow at least 20 days between Intuity applications. Intuity is at risk for resistance development by the Botrytis fungus and it is essential that its use is limited to rotations with other, unrelated Botrytis fungicides both within and between seasons to reduce the development of resistance.  Intuity is rainfast within 2 hours of application, has an REI of 12 hours and PHI of 10 days. Do not use Intuity on V. labrusca, V. labruscahybrids or other non-viniferahybrids. Avoid mixing with organosilicone surfactants. Intuity has not yet been cleared for use in New York.

Presidio. Presidio has been with us for about 10 years now and is used for downy mildew control, for which it has been very effective. Unfortunately, Valent has pulled the grape use from the Presidio label and any new product will not be legal for use on grapes this year. However, grape growers will be able to legally use up old stock of Presidio with the grape use pattern on the label.

FLINT Extra. A new formulation of an older material, FLINT Extra is a liquid (500SC) formulation that replaces Flint 50WG. The use rate of the new product is the same (in terms of active ingredient) as the old product. In other words, 2 fl oz of FLINT Extra 500SC = 2 oz Flint 50WG. But the new product is labeled to increase the application of active ingredient per acre. For example, for powdery mildew, the new product label lists a 3-3.5 fl oz rate as opposed to the 1.5-2 oz rate on the old product label. This represents a doubling of the amount of active ingredient for powdery mildew control by the new product. For Botrytis, the old 3 oz rate is now 3.8 fl oz, and for black rot, the old 2 oz rate is now almost doubled on the new label to 3.5-3.8 fl oz. Well, what does this mean then in practical terms for grape growers in the northeast? It could mean better disease control with the new product. However, if you already have powdery mildew resistance to the strobilurins in your vineyard, then increasing the amount of active ingredient probably won’t boost efficacy against that disease, and relying on the new formulation for powdery mildew control is risky. The same goes for Botrytis control, as strobilurin resistance among Botrytis isolates becomes more common. For black rot, it could represent improved control of that disease. However, I thought the 2 oz black rot rate for the old material was pretty effective already, and to my knowledge, there have been no cases of black rot resistance to the strobilurins (though I’m not aware anyone has been looking for it). And yes, it is registered for use in New York.

That’s what new. This next section borrows from Wayne Wilcox’ fungicide updates from last year. I have updated that information with new information from some of our research trials as well.

Fracture. According to Wayne’s insights last year, “Fracture is a product whose active ingredient is a fragment of a naturally occurring plant protein, and which has been registered for use on grapes for a couple of years. It has a 4-hr REI and a 1-day PHI, and the residue of its active ingredient is exempt from tolerance by the US-EPA (i. e., it is considered safe enough to humans that there is no limit on the allowable residue level in/on food products)”. We’ve now tested it for powdery mildew control over two years in Concord and Chambourcin and consider its activity against that disease to be modest. New York trial results appear similar. Trial results for bunch rot control I think are a bit more promising; we got fair to good control of bunch rot on Vignoles with this product last year (as good as a standard Botrytis fungicide program), and we’re looking forward to testing it again for that purpose this season. New York trials with Fracture have also shown control of Botrytis as good as standard materials, as well as some activity against sour rot. Fracture is expensive but may appeal to growers looking to reduce reliance on synthetic fungicides for bunch rot control, especially if used in combination with strict sanitation and cultural controls like leaf removal. We’re hoping to look at Fracture again this season, in combination with pre-bloom mechanized leaf removal, for integrated bunch rot control on Vignoles.

Polyoxin D zinc salt. Polyoxin D zinc salt (PZS) is a relatively new fungicide active ingredient with very low mammalian toxicity that has been classified by the U.S. Environmental Protection Agency (USEPA) as a “biochemical-like” pesticide. It degrades rapidly in the environment with a soil half-life of 2-3 days. Production of PZS occurs through a fermentation process using the soil bacterium Streptomyces cacaoi var. asoensis. The active ingredient inhibits chitin synthase, an enzyme essential for the production of chitin, an important component of fungal cell walls. The product is being sold as Tovano and OSO5%SC and is marketed through Certis USA. Over the past two seasons, our results with OSO on Concord and Chambourcin grapes have shown good to modest efficacy against powdery mildew, but no practical level of activity against black rot. For powdery mildew efficacy on fruit, OSO, at the 13 fl oz rate, was equal to or better than BadgeX2 (fixed copper), and equal to a standard rotational program of Quintec/Vivando/Toledo. As with most of the biopesticide type fungicides, cost per application is generally going to be higher than that of the standard synthetic fungicides.

LifeGard. LifeGard is another biopesticide approved for use on grapes in all states. It has provided really good results for the control of downy mildew in New York trials. Our past two years of testing in PA were a bust due to very dry conditions and little to no downy mildew up here in Erie County, PA. However, maybe we’ll get a good test of this product this year. LifeGard works by triggering a plants’ natural defense mechanisms against pathogens so the product may perform best after the vine has been ‘primed’ by an initial spray a few days before it is challenged with the pathogen. The label states that “initial triggering of plant defense response occurs within minutes of application, but 3-5 days are required to attain maximum level of protection”. This may be the reason our greenhouse inoculation trials with LifeGard were largely unsuccessful; we applied the pathogen just a few hours after application of the material instead of allowing ample time for the vine’s natural defense mechanisms to build up. Grapevines do not generally tend to respond to efforts to induce resistance, but the results from New York trials are encouraging and testing should continue.

There are several products also worth mentioning that have recently been made available to New York (and hence all) grape growers. Here is a brief recap of those materials.

• Luna Experience: a combination product consisting of two unrelated active ingredients, tebuconazole, (a very familiar sterol-inhibitor (FRAC 3)) and fluopyram, a newer SDHI (FRAC 7). Luna Experience is labeled for powdery mildew control at 6.0–8.6 fl oz/A, and for Botrytis and black rot control at 8.0 – 8.6 fl oz/A. Trials in New York have obtained excellent control of powdery mildew with the 6 fl oz rate. For Botrytis, New York trials suggest the 6 fl oz rate works well from bloom through bunch closure but the 8 fl oz rate would be best by veraison or later, especially if there is any pressure. The higher rate is also recommended for black rot control for the first few weeks after bloom when berries are most susceptible. The fluopyram provides most of the powdery mildew control and all of the Botrytis control, while the tebuconazole provides most of the black rot activity. For resistance management, limit the number of applications of FRAC 7 materials (SDHIs) to two per season.
• Zampro: We tested Zampro a number of years ago and found it to be an excellent material for downy mildew control. More extensive New York trials have gotten similar results. Though it has been approved for use in New York, it still cannot be used on Long Island. Zampro is another combination product of dimethomorph (FRAC 40, same as mandipropamid in Revus) and a new chemistry, ametoctradin.
• Rhyme: The active ingredient in Rhyme is flutriafol (sterol inhibitor, FRAC 3) and extensive powdery mildew trials in New York have shown more consistent results at the 5 fl oz rate rather than the 4 fl oz rate: Rhyme was a little better than Rally (myclobutanil) and tebuconazole, about equal to Mettle (tetraconazole), but not as good as difenoconazole (the newer, more potent sterol inhibitor in Revus Top, Inspire Super, Quadris Top). It received a registration a couple years ago and is also available for use in New York as well (except for Long Island). Rhyme has excellent activity against black rot.
• Topguard EQ: A combination product of flutriafol (just discussed above) and azoxystrobin (the ai in Abound). Obviously, this can’t be used in Erie County, PA, but is available to New York grape growers (except Long Island). The azoxystrobin picks up downy mildew (and Phomopsis?) that the flutriafol won’t, unless of course there is a significant presence of strobilurin resistant isolates of the downy mildew pathogen in your vineyard. For powdery mildew, the azoxystrobin adds a second mode of action against that disease, unless (once again) there is a significant presence of strobilurin resistant isolates of the powdery mildew pathogen in your vineyard. So, if you’re farming grapes in areas where sterol inhibitors and strobilurins have been used for many years and downy/powdery mildew resistance is suspected/likely or known, this product may not provide adequate control of these two important diseases, especially on highly susceptible wine varieties. What this product will definitely control is black rot: the azoxystrobin has excellent protective activity and flutriafol has excellent post-infection activity against this disease.

And finally, what’s new in the pipeline?

Miravis Prime. Miravis Prime is a product with two active ingredients: a new SDHI called adepidyn (FRAC 7) and an older, unrelated active ingredient known as fludioxonil (FRAC 12). This product is not yet registered for use on grapes, but federal registration may occur later this year, which will make it available for growers in most states (New York will probably have to wait at least another year). Our tests with Miravis Prime have shown good to excellent activity on powdery mildew, Botrytis, and black rot. Adepidyn (Miravis) provided excellent control of black rot in our 2015 and 2016 trials on Concord and Niagara fruit. The fludioxonil component in Miravis Prime is an older Botrytis fungicide, (introduced about 25 years ago) that is also found in a registered product called Switch (for Botrytis control in grapes). Having two active ingredients for Botrytis control makes this product effective at controlling Botrytis bunch rot disease in wine grapes.

Part 2 of this blog post will be published next Friday, May 18, 2018.