Immediate prebloom in grapes

By Terence Bradshaw

Grape bloom is looming in many Vermont vineyards, and this is a critical time for disease and vine management. As we mention in our initial IPM strategy for winegrapes, all of the major diseases save for late-season fruit rots are sensitive to management right now. That means that fungicide applications should be made, using a material or materials with broad range of coverage against powdery mildew (PM), downy mildew (DM), black rot (BR), anthracnose (Ant), and that last bit of phomopsis (Ph) for the season. Generally, this means a combination of materials, including a protectant (mancozeb, most effective against Ph, BR, PM, or captan (Ph, DM)) plus a systemic or more narrow-spectrum material. Those may include Vivando / Quintec (PM only); a DMI material like myclobutanil or tebuconazole ((BR, PM); or a strobilurin (BR, PM, also excellent against botrytis so save until later in the season in July if you have issues with that disease). I’ll mention other materials with excellent efficacy against DM and botrytis later when those diseases are of greater relative concern.

For organic growers, be sure to maintain your copper and/or sulfur sprays, watch for phytotoxicity, and remove diseased leaves and clusters as soon as you see them. The good thing is that it has been relatively dry this season, so disease pressure should be manageable. That said, in this vulnerable period, spray coverage should be applied prior to expected wetting events.

Insect activity is usually pretty quiet at this time of the season. Keep an eye out for bloom on wild grapes, as that sets the clock for the degree day model used to time management of grape berry moth (GBM). We typically add BT (Dipel, Javelin, etc.) or another material specifically active against lepidopteran pests soon after bloom at the earliest, so there’s time before we consider managing for this pest. GBM isn’t always a problem in every Vermont vineyard, we’ll talk about scouting for that pest in an upcoming bulletin. While we’re on the subject of insects, I haven’t seen much / any grape tumid gallmaker (GTGM) at the Hort Farm vineyard this year, but it has been a somewhat unlikely yet injurious pest in local vineyards in the past couple of years. I do not want to get into recommending treatment for minor pests of likely little economic importance, but if yours is one of the handful of vineyards which as suffered from extensive damage in recent years, consider using Movento or Assail if you see the first stages of galling by overwintering midges as they are hatching out now. There are only a very few vineyards where I’m even suggesting treatment for this- if you don’t remember this pest and its’ damage, then don’t worry about it on your farm. For more information on GTGM check the link above or my previous bit on them here.

Horticulture: There are two good times to collect petiole samples to assess vine nutrient status, bloom and veraison. Generally, you should stick with whichever timing you have been using so that you may compare to past tests. Dr. Joe Fiola at University of Maryland has a good fact sheet on petiole sampling. We recommend the Cornell Nutrient Analysis Laboratory for petiole sampling, as they have extensive experience in providing nutrient recommendations for grapes. Should nutrient applications be needed, this is a good time to apply boron, magnesium, and nitrogen as they are needed during this period of rapid shoot and fruit growth.

Other activities that I don’t need to tell you about: shoot thinning can continue, but shoots aren’t lignified at the base enough to comb them, they’ll just break off. Keep the vineyard mowed to improve airflow, but a golf course mowing regime isn’t necessary unless that’s your aesthetic choice. Keep the in-row weeds down however you can, but most herbicides should be put away for now because of likelihood of vine damage.

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

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Early season vineyard management

By Terence Bradshaw

Grapes are moving fast in Vermont vineyards, with most cultivars in the UVM vineyard at about 3” shoot growth. Shoot thinning now will give best results before the vines waste energy on growth that you won’t keep. We typically aim for 4-6 well-spaced shoots per foot of canopy, selecting for the most healthy/vigorous and those with appropriate orientation for our downward training system (high-wire cordon).

Figure 1 Before shoot thinning

Figure 2 After shoot thinning

This is a typical time to start a spray program to manage disease. First, a warning- do not spray anything in the heat we are expecting tomorrow May 25. Application of many materials just prior to and most anything during heat over 85°F can cause phytotoxicity to vines. The primary disease of concern at this point is phomopsis, as rachis infection at this point in the season is may cause significant fruit loss at harvest. Anthracnose may also be active at this point , given the warm/hot weather. Most growers would do best to cover early this week with a contact fungicide like mancozeb or captan.

Organic growers are in for a bit more work. The standard fungicides, copper and sulfur, have only fair efficacy against this disease at best, and in a couple of weeks when black rot becomes the next disease of concern, those materials will have even less efficacy against that disease. The first line of defense in an organic vineyard is a strict sanitation program. This includes removing all mummies still in the canopy (not dropping on the ground, but actually removing them from the vineyard) as well as any obviously diseased wood. Phomopsis and anthracnose both overwinter largely on infected wood in the canopy, and removing this wood during dormant pruning or now is essential to reducing disease pressure. Stubs left at the ends of spurs should now be removed since you can see where this year’s shoot growth will resume (at the developing shoot)- these stubs will die and may become infected with phomopsis this season (or were last season) .

Figure 3 Removing stubs at end of retained spurs.

It is worth noting that both copper and sulfur (including lime sulfur) can cause phytotoxicity on certain cultivars. Dr. Patty McManus summarized her research on copper and sulfur sensitivity in cold-hardy grapes in the 2/8/16 Northern Grapes newsletter, and I’ll summarize it to say that Brianna should receive no copper; and Frontenac (all types), LaCrescent, Leon Millot, Marechal Foch, Marquette, and St. Croix should receive no more than 2-3 copper sprays per season. Dr. McManus also suggests no copper or at most a limited trial on Louise Swenson, as it has similar parentage as Brianna which showed substantial phytotoxicity to that material. Save limited applications of copper for later in the season when black rot and downy mildew become bigger concerns. Sulfur sensitivity was observed on several cultivars, and its use (including lime sulfur) is discouraged on Foch, Millot, Brianna, and Louise Swenson; with limited (2-3) applications suggested on LaCrescent and St. Croix.

So, if you have removed all diseased wood and are ready to cover your vineyard for protection against phomopsis and anthracnose, the best choices is likely lime sulfur applied at two quarts per acre in sufficient water (25-30 gallons should do it) to wet the canopy. Lime sulfur is hot stuff: caustic, corrosive, and noxious. Use appropriate personal protective equipment and spray in cooler weather to reduce phytotoxicity. Powdered sulfur may also be a good choice, I would suggest 3-5 pounds per acre at this stage.

Finally, a word of warning:
Starting Saturday May 26 and for two weeks I’ll be away on a USAID assignment helping some farmers in Lebanon (the country) to set up cider operations to improve the profitability of their orchards. Some of these sites are pretty remote, and as such, I expect I’ll be out of contact for a bit. By the time I return, all vines should be shoot thinned, another fungicide or two applied (and we’ll be well into black rot season by then), and weeds controlled by whatever method you choose to use. Here are links to some past postings that are relevant to this time of the season and should give some advice on management as we enter the bloom period:
http://blog.uvm.edu/fruit/2017/06/06/vineyard-management-approaching-bloom/
http://blog.uvm.edu/fruit/2016/06/03/vineyard-disease-management-june-3/
http://blog.uvm.edu/fruit/2015/05/28/prebloom-disease-management-and-frost-prevention/

Best of luck and I’ll drink a glass or two of Lebanese wine for you all,

Terry

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

The label is the legal document for the product use.

Disregard any information in this message if it is in conflict with the

label.

The UVM Tree Fruit and Viticulture Program is supported by the

University of Vermont Agriculture Experiment Station, a USDA NIFA E-IPM

Grant, and USDA Risk Management Agency Funds.

Fire blight risk on Friday

By Terence Bradshaw

This is just a quick word of warning that the heat, peaking on Friday, will allow for buildup of the fire blight bacteria to infective levels in orchards where the pathogen is present. While most or many apples and especially pears are past petal fall, any that are still in bloom should be treated with streptomycin (or Serenade / Double Nickel if organic) any time between now and early Saturday.

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

The label is the legal document for the product use.

Disregard any information in this message if it is in conflict with the

label.

The UVM Tree Fruit and Viticulture Program is supported by the

University of Vermont Agriculture Experiment Station, a USDA NIFA E-IPM

Grant, and USDA Risk Management Agency Funds.

Apple management week of May 20

By Terence Bradshaw

While it’s beautiful out now on Sunday evening, we certainly saw a significant apple scab infection period over the past 24-36 hours in every orchard across the state. If you weren’t protected with good coverage of a full-rate protectant fungicide going into this, then you’d best cover up ASAP. A material with good post-infection activity like a QoI, DMI, of SDHI material should go on within the next day or (at the latest) two. If you were not covered with a mancozeb or other EBDC fungicide, one of the DMIs like Procure, Rally, Rubigan, or of course the workhorse Inspire Super will help to manage cedar apple and other rusts, which are active right now.

With the cool weather, blossom fire blight is a non-issue. Insecticides need to stay in the shed until petal fall, but there are a number of them on the horizon that will require management as soon as possible. I’ve seen very high catches of European apple sawfly in a couple of orchards, and those should be managed right at petal fall to avoid significant damage to developing fruitlets. Trapping is really necessary to determine the need to get in early vs. waiting for timing to manage first codling moth hatch. On that note, we’re seeing codling moth in most orchards. The first flying adults aren’t to worry about, but tying their first catch in pheromone traps allows for accurate model tracking to time management against first-generation larvae. I caught CM in Washington and Orange counties on May 17, and expect to use that date for the biofix in the upland regions. In Bennington county, moths were flying solid week earlier. Management against codling moth should start between 100 and 200 degree days (base 50°F) after first catch, which should be sometime next week in many areas and orchards.

Overall, bloom looks good to great- I’m not seeing or hearing of much in the way of low bloom density, and some varieties are being reported with snowball bloom. Pollination conditions were very good overall, so expect to thin this year. It’s tough to make a specific thinning recommendation without seeing your specific orchard and knowing all factors. However, consider that a) bloom was good; b) pollination weather was good; c) no frost was experienced; and d) weather has been fairly stress-free (sunny, cool, just enough rain) so tree carbohydrates are plentiful. Chemical thinners tend to work based on competition among fruitlets, so these condition make thinning more difficult, and thus an aggressive tactic may be pursued. I recommend multiple passes of a moderate rate of thinners, starting at petal fall. Of course, keep an eye on things between sprays. Tagging specific fruitlet clusters and tracking fruitlet growth with a set of calipers will give you a sense of whether certain fruit will abscise, as fruitlets stop growing a few days before signs of abscission (yellowing stems, open sepals) are apparent. Keep thinning until you’re down to single fruit per spur, spaced six inches apart on the limb.

Dr. Duane Green from UMASS has a good list of general recommendations for using thinner materials at petal fall:

If you did not apply a bloom spray, make certain that you do apply one at PF. In some instances, application at both times may be appropriate.

· Carbaryl

Apple scab and fire blight management

By Terence Bradshaw

Apple scab- this one is simple, we likely have an infection period coming on Saturday that will likely release another quarter or so of the season’s entire ascospore load. Every orchard needs to be covered for this event. Overnight tonight through Saturday morning looks like good spray weather. This is a good time to apply a protectant plus a second material that has activity against powdery mildew rusts, like a DMI, QoI, or SDHI. Organic growers are mostly limited to sulfur (which is excellent on powdery mildew), although I have heard anecdotal reports that Regalia may have some effect on rust.

Fire blight- Many growers are concerned about this, but I still suggest cautious optimism should rule. Remember the four factors I referenced already that are needed for blossom blight infection to occur: bloom, wetting, heat before wetting (simplified as Epiphytic Infection Potential, EIP), and heat during the infection event. We have the first two in virtually every orchard in the state. However, we’re lacking the last two in most orchards in the state. EIP generally need to reach 100 before we consider the population infective, and we’re below that value in every orchard that I’m monitoring.

For orchards that have susceptible cultivars or a history of the dis, I get it- a streptomycin spray is a cheap insurance against this potentially devastating disease. But take this note- I have strep in the shed at the UVM orchard, I have aa block with Gala, Cortland, and Mutsu that gets fire blight fairly commonly, I’m spraying a scab fungicide tomorrow anyway, and I’m not applying strep. The heat just isn’t there for a Saturday infection, and every model is in agreement.

For those that wish to go ahead and treat because the cost of application is much lower than that of an infection occurring because I or the weather forecast is wrong, take heart in knowing that a) use of prophylactic streptomycin at labeled rates against blossom blight has never been implicated in the development of resistance to the antibiotic by the pathogen, and b) based on pretty extensive literature, there is extremely low likelihood of the use of streptomycin as a foliar-applied spray in orchards affecting resistance in human pathogens. If using strep, it should be applied at full rate with a nonionic surfactant, and applied on a full-row basis. Attention may be paid to the most susceptible cultivars and areas with a history of the disease. Again, I don’t see this event as serious enough to warrant attention to the whole orchard, so if you want to focus on spot-treating, that should be fine.

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

The label is the legal document for the product use.

Disregard any information in this message if it is in conflict with the

label.

The UVM Tree Fruit and Viticulture Program is supported by the

University of Vermont Agriculture Experiment Station, a USDA NIFA E-IPM

Grant, and USDA Risk Management Agency Funds.

Early season vineyard management

By Terence Bradshaw

Buds have broken in Vermont vineyards and many vines are at 1-3” short growth. This brings up a few pest management considerations for your vineyards. Most cold-climate cultivars will not need disease protection until 5-8” of shoot growth, but any vineyards with heavy disease pressure last year may wish to begin earlier, especially if inoculum reduction through thorough removal of diseased wood and mummy berries and/or dormant application of lime sulfur was not performed. I still recommend our fact sheet, An Initial Integrated Pest Management (IPM) Strategy for New Cold Climate Winegrape Growers as the best resource to boil the decisions down to a simple ‘prescription’, with the caveat that since it was written some new pest management materials have been released and inoculum may have increased in your vineyards which could lead to increased disease pressure. Growers should have an up-to-date copy of the New York and Pennsylvania Pest Management Guidelines for Grapes as a reference for specific materials, their efficacy, and use considerations. Remember however that the guidelines are written largely for vinifera and less disease-resistant hybrids, so the specific spray programs recommended may be overkill in Vermont vineyards.

The warm weather in the past few days may have increased emergence of grape flea beetle or cutworms. Grapes are susceptible through about the one inch shoot growth stage, so vines will eventually outgrow the threat. However, cooler temperatures over the weekend may hold the vines at this susceptible stage long enough for damage to increase to unacceptable levels. A scouting of your vineyard for feeding on swelling buds or developing shoots may be warranted. If damage is evident on more than 2% of buds, an insecticide treatment may be warranted. But if shoots expand rapidly over the weekend, don’t worry about this pest. More information may be found here.

Since buds at ground level have begun to emerge, applications of systemic herbicides should either be halted or very carefully controlled to prohibit contact with green tissue. Now is an appropriate time for cultivation in vineyards to manage weeds. It’s also a good time to keep water on newly planted or young vines. With soil warming and growth beginning, nitrogen fertilizer applications, if needed based on foliar analyses or observed low vigor last year, may also be made now.

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

The label is the legal document for the product use.

Disregard any information in this message if it is in conflict with the

label.

The UVM Tree Fruit and Viticulture Program is supported by the

University of Vermont Agriculture Experiment Station, a USDA NIFA E-IPM

Grant, and USDA Risk Management Agency Funds.

Apple scab infection period

By Terence Bradshaw

Okay, today was wet. Without question this was a substantial apple scab infection period. Fire blight- I’m still on the fence an lean towards ‘not a problem’ unless you had a substantial amount last year and have susceptible cultivars. NEWA estimates across the state suggest that 12-30% of the entire season’s apple ascospores were discharged today. What does that mean?

If you went in to this rain event with a full, as in 6 lb/acre of mancozeb or 5 lb/acre captan applied in the past five days, you’re probably good. Any less than that, and you should really consider coming in in the next 48 hours with a material with post-infection activity, like one of the DMIs, QOIs, or SDHIs. If those look like alphabet soup to you, check your New England Tree Fruit Management Guide for some more clarity. Organic growers should get more sulfur on, and if coverage was questionable, this is a time when lime sulfur may be called for to burn out germinating spores before infection gets too ahead of things.

For those with stone fruit, this was also likely a major brown rot infection period, so trees should be covered with a suitable material in the DMI or QOI classes within this same time window.

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

The label is the legal document for the product use.

Disregard any information in this message if it is in conflict with the

label.

The UVM Tree Fruit and Viticulture Program is supported by the

University of Vermont Agriculture Experiment Station, a USDA NIFA E-IPM

Grant, and USDA Risk Management Agency Funds.

Fire blight concerns 5/15/2018

By Terence Bradshaw

I’ve had a number of people ask my thoughts on fire blight infection potential with today’s rains. I’ve looked at a couple of models, and generally, they hover around the point of calling or not calling an infection. Let’s look at the conditions required for infection:

1. Bloom. If you’re inland or upland and don’t have any open blossoms, then stop reading now. You don’t have any blossom blight risk during this wetting event.

2. Wetting. I think everywhere in the state will receive at least some wetting today that could contribute to infection.

3. Heat during and after the wetting event. This is marginal, but if there’s a high enough bacterial load, then infection could occur.

4. Build-up of sufficient population of the pathogen to trigger infection. This is known as the Epiphytic Infection Potential (EIP) and requires a) an overwintering or introduced pathogen source and b) heat prior to the infection that allows for that bacteria to multiply. This is the part that has been generally just below threshold.

Remember that models are only as good as the information that goes into them. Both the eastern (Maryblyt) and western (Cougarblyt, used by NEWA) models allow for some adjustment based on the level of fire blight that has been in your neighborhood this year and the past two. For orchards with no fire blight in the area last year, EIP does not reach infective threshold in Vermont orchards. But, if you had fire blight in your orchard recently, and have susceptible cultivars (Paulared, Gala, Macoun, Cortland), then a streptomycin spray may be warranted. Remember that strep works 24 hours in either direction, before or after an infection event, and it must contact an open blossom to protect it. There’s potential for another infection event on Thursday that looks to also be marginal, but carry slightly than today’s.

For organic growers, streptomycin is no longer allowed by NOP standards. Some materials that may be effective include lime sulfur, which burns flower tissues so will only help a blossom that is already pollinated; low-rate copper materials like Cueva and Badge, which may russet fruit; and biologicals like Double Nickel or Serenade. None of those are as effective as streptomycin but each may be better than not treating at all in an infection situation.

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

The label is the legal document for the product use.

Disregard any information in this message if it is in conflict with the

label.

The UVM Tree Fruit and Viticulture Program is supported by the

University of Vermont Agriculture Experiment Station, a USDA NIFA E-IPM

Grant, and USDA Risk Management Agency Funds.

Apple management: Bloom for most

By Terence Bradshaw

There are several key points to consider in managing apple crops this week: the lack of rain, and bloom. The dry weather has reduced scab infection pressure, but has also put developing ascospores into a brief ‘hibernation’ period. Trust that the next significant wetting period will release a large proportion of the season’s ascospores, and remember that many orchards had a fair amount of scab last year. So, during this dry spell, don’t worry too much, but be sure to be fully covered with a fungicide prior to the next significant rain. That might be Tuesday in southern Vermont, or as late as Friday in northern. During bloom, know that captan has been shown to negatively affect pollen germination, and DMI fungicides (FRAC code 3) like Rally, Inspire Super, etc. may negatively impact pollinators, so avoid those if possible.

Once orchards are in bloom, the only insects you should be thinking about managing are pollinators. Where orchards are still in the prebloom / pink bud stage, tarnished plant bug and European apple sawfly are the primary pests to manage, but should only be treated based on trap counts and an assessment of your damage threshold. Most orchards that aren’t shipping fruit to wholesale don’t need to manage those pests, and those that do usually know who you are.

The greater concern as we go into bloom is fire blight. That disease wasn’t especially prevalent in Vermont last year, so neighborhood inoculum is relatively low, but this warming trend going into bloom can rapidly advance bacterial populations where they do exist. Keep an eye on the NEWA fire blight model for you orchard or one near you and be ready with streptomycin if infection conditions are shown and you have open blossoms.

Finally, with rapidly developing leaf tissue and the activity around bloom, this is an important time to keep water and nutrients supplied to the trees. Irrigation should be run if available, and consider ground or foliar-applied fertilizers as needed based on your soil or foliar analyses.

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

The label is the legal document for the product use.

Disregard any information in this message if it is in conflict with the

label.

The UVM Tree Fruit and Viticulture Program is supported by the

University of Vermont Agriculture Experiment Station, a USDA NIFA E-IPM

Grant, and USDA Risk Management Agency Funds.

Thoughts on pest management at pink bud stage in Vermont orchards

By Terence Bradshaw

Many Vermont orchards hit the pink bud stage yesterday, which is an important time for crop management. The main concerns should be: apple scab, fire blight, and early season tree nutrition.

For apple scab, NEWA is predicting an infection period tonight and into Saturday, so orchards should be covered with a protectant fungicide. We’re in peak scab season now, so vigilance is suggested. While applying fungicide, it wouldn’t be a bad idea to apply the standard ‘blossom boost foliar nutrient mix of nitrogen, zinc, and boron. Rates are dependent on the products used, and are intended to boost blossom vigor as the trees enter the stressful bloom period Dr. Wes Autio’s (UMASS) recommendations for Prebloom Nutrient Applications for Apple Trees: 3 lbs/100 gallons (dilute equivalent) urea; 1 lb/100 gallon Solubor (or equivalent); and label rates of zinc chelate. Ground-applied or fertigated fertilizers can also start to go on any time now.

On to fire blight. Remember that the disease requires a number of factors to cause infection: sufficient buildup of the bacterial population (a function of heat in the days prior to infection, known as epiphytic infection potential (EIP)); open wounds (or open blooms); rain or heavy dew to move the bacteria into infection sites; and sufficient heat at the time of infection for disease to occur. First, most orchards in Vermont did not have a serious, or any, fire blight issue last year, so overall inoculum is likely low. If you’re one of the growers who had infection in 2016, maybe be a little more vigilant because there’s the likelihood that you have a few extra cankers in the orchard that were missed during pruning. The EIP clock starts at bloom, but sufficient heat (like yesterday’s) leading into it can increase populations. The infective EIP used in NEWA (or really, Cougarblight, which is the model NEWA uses) is 100, and orchards in the major parts of the state hovered around that number yesterday and today. However, note that the more conservative Maryblyt model showed lower EIP for South Burlington for yesterday and today, and an infection was considered unlikely.

That’s mainly because we don’t have a single open bloom in South Burlington, so the model doesn’t really apply. Where orchards have their earliest blooms (on Zestar or Gingergold maybe? What’s the bloom status in Windham and Bennington counties?) going into today’s wetting period, there is a chance of a fire blight infection period. However, the shift to cooler temperatures starting after tonight’s front passage will lower EIP and reduce likelihood of infection. I still like to keep some streptomycin on-hand during bloom, but my gut feeling is that, except in very specific circumstances of high likelihood of inoculum carryover from previous infections and open blossoms going into today’s rain, there is no need to treat at this time.

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

The label is the legal document for the product use.

Disregard any information in this message if it is in conflict with the

label.

The UVM Tree Fruit and Viticulture Program is supported by the

University of Vermont Agriculture Experiment Station, a USDA NIFA E-IPM

Grant, and USDA Risk Management Agency Funds.