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UVM Fruit Blog

Grape canopy management

Posted: July 11th, 2019 by fruit

By Terence Bradshaw

High Summer is here, and this period from after July 4 through early August is the perfect time to apply some canopy management to the vineyard. By thinning and positioning shoots; removing unwanted clusters; and cleaning up trunks, we can significantly increase penetration of sunlight into the canopy and especially into the fruiting zone. This will make for measurably better juice and wine quality, improved winter hardiness, and less disease pressure.

There are a number of practices that should be performed, but the most important is shoot positioning (also known as “combing”). This practice includes separating each shoot from its neighbor and directing the growth into the vertical plane: usually down, for high-wire cordon vines, or up for those on a low wire, vertical shoot positioning system. Once shoots are pointed in the right direction, it’s easy to see where runty secondary or tertiary shoots are in the canopy, and where smaller clusters that are behind in development compared to the main crop are- those can both be removed.

(Retired) Iowa State Extension Specialist Mike White presents a good overview of the concepts and practices behind canopy management in his February 8, 2012 newsletter found here.

There’s a video of some UVM staff doing some (silent) canopy management here.

Ohio State Extension has a nice video here.

While I have you, it’s worth mentioning that we’re not out of the woods as far as disease management is concerned. It has been a difficult year so far with all of the rain, and the frequency of it, to maintain fungicide coverage but I have been seeing mostly clean fruit and foliage in vineyards which have maintained an appropriate spray schedule of 4-5 well-selected and –timed fungicides since prebloom. At this point, phomopsis is pretty much done, and black rot will soon be winding down. Powdery and downy mildews (PM?DM) should be the main focus for disease management, as well as botrytis a few weeks down the road. If this wet weather continues, I would recommend a specific botrytis material such as Flint, Rovral, Vangard, Endura, or Pristine before bunch closure (the point where berries size up to the point where spray material cannot penetrate the cluster to protect fruit from infection). As always, check your Pest Management guide (New York & Pennsylvania or New England guides) and the label, rotate fungicide classes to reduce resistance likelihood, and follow all safety precautions when spraying. Organic disease management spray options include copper (DM, a little PM), sulfur (PM), stylet oil (PM, do not spray before or after a sulfur spray), and possibly some of the biologicals but I don’t know enough about them in regards to their performance against these late-season diseases.

Next week would be a good time to scout clusters for grape berry moth (GBM) webbing which could suggest a need to treat for that insect pest. The threshold for treating this generation is 6% of clusters showing damage, which appears as small bits of webbing in between berries up inside the cluster. GBM is the primary insect pest of established vineyards in Vermont, and if it is the only pest insect need to manage, then some very specific materials with low potential for non-target effects may be used, including lepidopteran-specific materials like Bt, Intrepid, Delegate, or Altacor (the latter has some activity against Japanese beetle). Bt (DiPel and others) and Entrust would be effective materials against GBM for organic growers- the former affects only lepidoptera, while the latter would have some activity against Japanese beetle and some other insects as well.

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.

Vineyard management at bloom

Posted: June 30th, 2019 by fruit

By Terence Bradshaw

Many vineyards are in bloom across Vermont, and inflorescence looks good and bodes well for a promising year. As I’ve been saying all along, be sure to maintain spray coverage for the next couple of weeks; to remove any diseased tissue as you find it; and to do your best to maintain an open canopy (more on that in a minute). All of the main diseases, including downy mildew, should be active now, so fungicide choice should cover all of the bases. That likely means applying a mix of materials that have multiple modes of action, like mancozeb (watch the 66-day preharvest interval) or captan and a strobilurin (Flint, Abound) or DMI (Rally, Elite, etc.). There are some good premix materials available that cover two modes of action, like Inspire Super and Pristine, but even they could use some protectant activity from mancozeb or captan to improve efficacy and reduce resistance development. The New England Small Fruit Management Guide has a good table that outlines the efficacy of the main fungicide materials available to growers. For organic growers, a rotation of sulfur and copper is pretty common now, but be sure to watch for signs of phytotoxicity. Coverage maintained for the next few weeks will pay off by allowing you to relax a bit for the second half of the summer.

Wild grape bloom occurred on June 19 in South Burlington, which sets the clock for grape berry moth management. The first overwintering generation is rarely significant enough to warrant a management spray except in vineyards that have had extreme damage in previous years. Each generation requires about 820 degree days (base 47°F, or DDb47°F) to complete, and the first generation typically emerges around the time of wild grape bloom. So if we use June 9 as our ‘biofix’ and track DDb47°F, we can estimate the best time to treat for the more damaging later generations.

This is made easy by the Network for Environment and Weather Applications (NEWA) system, which I coordinate for Vermont. The network includes twelve on-site weather stations (all located at orchards) and six airports, and imports data in near real-time for use in pest models. It is free to use, and growers can locate the site nearest them and develop a best-guess of phomopsis, black rot, and downy mildew infection periods as well as a sense of the grape berry moth generational development.

Plant tissue sampling is one of the best ways to plan fertility management in your vineyard, and now is one of the important times for collecting samples. Petiole samples may be collected at bloom or veraison, and comparisons between years or blocks should be based on the same time of collection. The benefit of a bloom sampling is that it gives you time to make corrections, if needed, during the present growing season.

Samples should be collected separately for each cultivar or block. In each sample, a random collection of 75-100 petioles should be collected from throughout the planting. Petioles should be collected from the most recent fully expanded leaf on the shoot, not across from the fruit cluster as is collected for a bloom sample. Just remove the whole leaf and snip the petiole (the leaf ‘stem’ off with your pruners. Gently wash each sample in water with a drop of dish detergent, then rinse fully and place in an open-top paper bag to dry. The closest analytical lab for grape petiole analysis that also provides pretty comprehensive management recommendations is the . There is a great section in Appendix A of the Wine Grape Production Guide for Eastern North America (which every grower should have a copy of on the bookshelf, ready to grab with short reach) which helps to guide fertilizer application rates based on soil and petiole samples. If you have a copy of those to send to me, I’d be happy to help you with the numbers as well.

Finally, I have two events to mention. First is a reminder of the July 9 Canopy Management Workshop we will hold at Ellison Estate Vineyard in Grand Isle. Please preregister here to attend.

The second is a UVM Horticulture Research & Education Center Research Open House that we will hold at the farm in South Burlington on August 6. Researchers with projects across the farm and working in multiple disciplines will showcase our work. I will host a tour of the research vineyard, and will have a pre-harvest management workshop at which we will discuss bird protection, late-season canopy and crop management, and preharvest sampling procedures to optimized juice quality at harvest. Watch for details on that event in the next week or so, but plan on it happening in the later afternoon around 3:00.

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 maggot fly traps

Posted: June 29th, 2019 by fruit

By Terence Bradshaw

The time has come to hang apple maggot fly (AMF) traps in Vermont orchards. Last year, we saw higher populations state-wide, for which I don’t really have a good explanation. These are some of the easiest pests to manage using an IPM strategy, so there’s really no excuse. The idea is to assess the population in the orchard before applying prophylactic sprays. By using red sticky traps, you can time treatments for best effectiveness, and maybe even skip treatments if the populations are low enough. Traps are red plastic balls that you coat with Tanglefoot adhesive. Kits including traps and adhesive are available from Gemplers and Great Lakes IPM.

Traps should be hung at least four per 10-acre block, preferably at the orchard perimeter and especially near sources of the insect, like wild or unmanaged apples. Placement in the tree should be about head-height, and surrounding foliage should be trimmed away- this trap is largely visual, and you should be able to see it from 10-20 yards away. The traps may be baited with an apple essence lure that improves their attractiveness dramatically. For monitoring to time sprays, unbaited traps that catch one fly per block (as an average of all the traps in the block) would warrant treatment; the lure makes them much more attractive such that you can wait until an average of five flies per trap are caught before treating. For most growers, the main insecticide used against AMF is Assail, Imidan also works but it has a long reentry interval and tends to leave visible residue on fruit. For organic growers, Surround works well, but its use in midsummer may increase European red mites, and it can be hard to remove at harvest; spinosad (Entrust) works pretty well too. First AMF treatment is still a few weeks off, most likely

It is summer lepidoptera season, and treatment should be on everyone’s minds, especially for codling moth (CM) and obliquebanded leafroller (OBLR). CM are active and eggs hatching or soon to hatch across the state, so growers who have caught CM in their traps or who often have issues with this pest (that’s most everyone) should apply something effective against them soon. Very specific materials like insect growth regulators (Intrepid, Rimon) or granulosis virus (Madex, Cyd-X) can be used that are very safe to non-target insects. One or two applications of a material should suffice for first generation. OBLR are just showing up in traps, and treatment should be timed at 360 degree days (base 43°F) after first catch. There is a NEWA model for this pest, and a material like Bt (Dipel, etc.) is effective (but not against CM).

Mites are a no-show statewide. Keep scouting leaves, as their populations can grow very quickly, especially as the weather heats up.

Diseases: keep checking on your scab, if you have none (I mean none), then it’s okay to relax. The summer diseases sooty blotch and flyspeck are of concern now, but they require 270 hours of leaf wetness for lesions to form, so fungicide coverage between that period should be maintained. Keep in mind that one inch of rain washes off half of your coverage, after two inches, it’s gone.

Enjoy the holiday this week and remember that trees shouldn’t be sprayed when it’s over 80-85, and application of sulfur, captan, and other potentially phytotoxic materials should be avoided when hot weather is in the forecast for the next couple of days.

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.

July 9 UVM Grape Canopy Management Workshop

Posted: June 19th, 2019 by fruit

By Terence Bradshaw

Summer canopy management is one of the most important tasks for producing high-quality winegrapes, especially in cool/cold regions where ripening can be impacted by low heat unit accumulation. The tasks taken to open and manage canopies aren’t necessarily intuitive, and are often overlooked by beginning fruit growers.

Join the UVM Fruit Program on Tuesday, July 9, 2019 for a hands-on workshop on managing canopies in cold-climate hybrid grape vineyards. The workshop will run 9 AM – Noon at Ellison Estate Vineyard 69 East Shore North Grand Isle, VT 05458 United States. There is no fee for this workshop, but please pre-register by completing this very short survey.

https://survey.uvm.edu/index.php/187557?lang=en

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.

Grape pest management, June 19

Posted: June 19th, 2019 by fruit

By Terence Bradshaw

June 19, 2019

It’s always impressive to me how fast grapevines can go from zero to full foliage in a matter of a couple of weeks. Vines at the UVM Horticulture Research & Education Center are generally at 16-24” shoot growth. We’re not quite at “Immediate Pre-Bloom” stage, but not far off, either. Now is a critical time for disease 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. It’s been a wet spring, although a bit drier since grape budbreak that earlier in the year. I expect diseases will be pretty significant problems for growers this year, so stay alert.

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.

We are seeing a bit of grape tumid gall (GTGM) in the UVM vineyard this year. This is an infrequent pest that causes visually striking but (usually) relatively insignificant damage to the vines, and management practices are not recommended against them. However, serious cases can affect fruit clusters, especially in La Crescent and Marquette, so any signs of them in clusters may warrant treatment. I discussed this pest in a post on June 8, 2017:

This insect is similar to phylloxera in that the larvae feeds on leaf tissue which responds by forming a protective gall around it. GTGM is different in that it also affects rachises and fruit, and when the galls become fully engorged, can look pretty dramatic.

Figure 1. Grape tumid gall on a fruit cluster in midsummer. UVM vineyard, 2009.

GTGM is an midge insect (small fly) that lays eggs on grapevines. Flies are ephemeral and only live a day or so; management should not be targeted at adults. Hatching larvae burrow into vine tissue and are thus protected from contact insecticides. In most vineyards, GTGM is considered a minor pest or even a curiosity as the galls can be quite drastic-looking. That said, I have been hearing reports of high levels of GTGM in vineyard this year, and some of these vineyards reported them last year under different management, so I suspect that certain vineyards have increasing and potentially problematic populations.

Figure 2. GTGM on Marquette, UVM vineyard, 2010..

Vineyards should be scouted before assuming you have a problem with this pest. There is no threshold established, as most growers tolerate low levels of damage. However, I have heard reports of 50% or more leaves affected in some vineyards, and I can’t imagine how that wouldn’t negatively affect vine productivity.

Figure 3. GTGM on inflorescence. UVM vineyard, 2011.

Sanitation is an important method of reducing GTGM populations and may be enough in low-pressure situations. Galls can be crushed if seen on leaves, or severely affected leaves removed and destroyed. In organic vineyards, as always, this should be the first line of defense since spray options are minimal. If the extent of damage is beyond physical removal, an application of Movento is the best (only) recommended option I can find. Movento is a systemic insecticide with a unique mode of action and is listed as posing low risk to wildlife, and as non-toxic to fish and birds. It is best used at first sign of galls, practically speaking, as scouting for hatching larvae (which hatch from microscopic eggs) is difficult under normal field conditions.

GTGM may be distinguished from phylloxera by the gall surface, which is smooth compared to phylloxera which is bumpy or warty. Movento is effective against phylloxera as well as GTGM and has a long residual control period, so may be a good material if either or both of those pests are common in your vineyard.

More information on GTGM may be found in this Cornell fact sheet: https://ecommons.cornell.edu/bitstream/handle/1813/43134/tumid-gallmaker-FS-NYSIPM.pdf?sequence=1&isAllowed=y

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.

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.

Petal fall and then some (sometimes quite a bit more)…

Posted: June 14th, 2019 by fruit

By Terence Bradshaw

Orchards in the highest elevation and coolest areas are at or just past petal fall, so all the advice I’ve had for other growers applies there as well now. All orchards should have started or, more likely, completed chemical thinning by now. Fabulous thinning weather occurred last week and those who applied the usual materials should see the effects by now. If a little more ‘nudge’ is needed to break up clusters, carbaryl , 6-BA 9 (Maxcel, etc.), and NAA (Refine, etc.) will still work so long as the fruit you’re thinning are under 15 mm diameter. If you have a lot of larger fruit, up to 20 mm, then Ethephon + carbaryl can help in a pinch, but be careful, as that mixture is relatively unpredictable. Wes Autio and Win Cowgill have a factsheet on such rescue thinning for more information.

Regular readers may have noted that I (almost) took a week off from updates- I also took a week off from spraying. Where petal fall insecticides were applied against plum curculio (PC) and European apple sawfly, you’re probably good until another is needed for PC due to rain washoff or codling moth rears its head. As for the former, PC is only ‘programmed’ to lay eggs and cause fruit damage for about 308 degree days (base 50) after McIntosh petal fall, and we’re only about 1/3 there at the UVM Hort Farm. It would be wise to check for PC damage to fruitlets and consider reapplication at the first sign of fresh damage.

Figure 1Plum curculio damage on a developing fruitlet. This damage is about a week old, note the dried surface and lack of sap. Fresh stings after an insecticide has been applied indicate potential need to reapply.

As for the latter pest, codling moth have now been trapped in most scouted orchards in the state. To best manage the first generation of this pest, calculate degree days (base 50°F) from the date of first capture in pheromone traps. Most materials should be applied at 200 degree days after catch, which should be in the next week or so. Cornell entomologist Dr. Art Agnello offers the following specific recommendations for CM management in the latest Scaffolds newsletter: “The best products for controlling both CM and OFM in apples and stone fruits are those in IRAC Group 28 (containing a diamide; i.e., Altacor, Exirel, Minecto Pro, Voliam Flexi or Besiege) or IRAC Group 5 (mainly spinetoram, Delegate; spinosad, formulated as Entrust, is an organically approved option). Two applications from either of these groups on a 10–14-day interval would be recommended starting at 220 DD50 from biofix; we’re already beyond this point in Highland and Geneva, but sites in WNY range from 81-247 DD50, depending on proximity to the lake (refer to “Model Building” numbers in this issue). Products with insect growth regulator activity, such as Rimon, Intrepid or Esteem, would also be suitable options this week in apple sites at the lower end of these values. Other products with activity against internal leps include the neonic Assail, the biological Grandevo (also organically approved) and, in orchards where resistance has not developed to the newer pyrethroids, also Baythroid, Danitol, Endigo, and Leverage. Most older broad-spectrum materials like Imidan, Lannate, and the older pyrethroids, which were formerly more effective, are generally not as good choices because of insecticide resistance issues…Now would also be an appropriate time for an application of a granulosis virus product in pome and stone fruits such as Cyd-X, Madex, Virosoft CP4 or Carpovirusine (apples and pears only), in addition to the larvicides discussed above. These are biological insecticides, which must be ingested to initiate the infection, after which the virus replicates inside the larva until it is killed; this releases more virus particles into the orchard. This is a very useful approach for long-term population reduction, particularly when used in at least 2 applications per generation. Madex, and now Virosoft CP4 (see “Chem News” in this issue) contain an isolate that is also effective against OFM.”

As for diseases, all sites should be done with primary apple scab season. That doesn’t mean that scab management is done, just that there are no overwintering spores left in leaf litter. If you have NO scab, you’re done managing this disease for the year. However, I suspect that many orchards missed an infection period or had spotty coverage, and that there is a good bit of scab out there. If you have scab, plan on maintaining some level of preventative fungicide (Captan is about all you have, sulfur if organic) for the next month or so until fruit and foliage become resistant. Do not use single-site fungicides like DMIs, strobilurins, or SDHIs (FRAC codes 3,7, 9,11) on active lesions to reduce development of fungicide resistance.

There have been some reports of fire blight showing up from the marginal infection periods that occurred May 20, 23, or 26. Keep your eyes out, especially in blocks that have had a history of the disease or on susceptible cultivars like Gala and Paulared, and cut strikes out as you see them.

If using nitrogen fertilizers in your orchard, plan on wrapping up applications in the next week or two to give trees time to harden off for winter. Potassium fertilizers can go on any time 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.

Expect insect activity to pick up later this week

Posted: June 5th, 2019 by fruit

By Terence Bradshaw

Finally, it looks like we’ll be entering an extended stretch of warm, sunny weather starting Thursday and especially Friday and lasting through the weekend. In South Burlington, we’re expecting temperatures just near 80°F by Sunday. That is great weather to drive plum curculio and European apple sawfly activity, so I suggest treating against those pests Tomorrow or Friday. I’ll be going out Friday morning when the wind is looking more favorable for spray application. But remember, if you’re one of those high elevation sites with petals and bees still present, you need to wait.

All for 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.

Orchard management at petal fall (and then some)

Posted: June 2nd, 2019 by fruit

By Terence Bradshaw

This week I’ll just say, “more of the same…” Apple scab primary ascospore season is done or nearly done in Vermont orchards. Check carefully for apple scab in your orchards before stopping fungicide coverage. Lesions can take two weeks to appear, so you may not see the latest infections for a bit. By now, growers who have been using more than three pounds per acre of mancozeb should put that away for the season, captan will be the protectant fungicide of choice. Sulfur should be the standard in organic orchards, although lime sulfur may be appropriate, especially if there are active lesions that need to be burned out and you want some thinning activity. Remember, lime sulfur is extremely caustic and corrosive to metal, to take care of yourself and your equipment if you use it.

Keep an eye out for fire blight strikes as you walk your orchards. We were generally on the ‘no conditions for infection’ side of the line in most orchards, but there is a chance that some got through, especially in warmer sites with a history of the disease where streptomycin was not applied. Prune out strikes as you find them.

Insects: still quiet. Codling moth has shown up in some sites, which means a targeted application of an effective product 250 degree days (base 50 °F) after the biofix of the first date caught in a pheromone trap. In the meantime, where you have 100% petal fall and no bees in the orchard, an insecticide application targeted at plum curculio and (if present) European apple sawfly may be warranted. Dogwood borer are rearing their heads more and more. If you have them (check burr knots on trunks, especially young trees on M9 or M26 rootstock), consider a coarse, soaking trunk spray. Best bet now is probably Assail; the old standby Lorsban (chlorpyrifos) is no longer registered for use in Vermont, and for good reason. Organic growers may consider Pyganic, and probably several applications.

Thinning: weather isn’t looking very good for 6-BA thinners like Maxcel until later this week. If planning to use those materials on smaller-fruited cultivars like Empire and Fuji, wait a bit. NAA thinners should be effective, but plan on using higher rates given the cool weather. Keep an eye on developing fruit following thinner applications, fruit will be susceptible to hormone sprays up to 17 mm diameter, after which we need to take more drastic and unreliable measures.

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.

Grape disease management and shoot thinning

Posted: June 2nd, 2019 by fruit

By Terence Bradshaw

I’m probably a tad late on getting this out for some growers. The growing season continues to be cool and wet, and grapevines at the UVM Horticulture Research & Education Center are showing about four to five inches of shoot growth. We are beginning to enter a critical time for disease management. Growers should consider applying a protective fungicide soon that has activity against phomopsis in particular, although anthracnose and, to a lesser degree, black rot may be active, especially in high inoculum vineyards. 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. 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) .

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. Save those for later 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.

Organic growers should absolutely begin application of something at this stage in combination with keeping up sanitation of all dead or infected wood , rachises, and other grapevine debris- sulfur, one of the bicarbonate materials (e.g., Armicarb, Kaligreen, etc.), or a biofungicide like Serenade, Sonata, Regalia, or Double Nickel may be used, although there is little good efficacy data on that last class of materials.

I mentioned sanitation- now is a good time to get out and clean up the ‘nubs’ left at the ends of spurs after pruning that will die out and serve as reservoirs for phomopsis and other diseases. While you’re at it, this is an especially good time to thin shoots. Cold hardy grapes trained to a high-wire trellis and in good health can support about six shoots per foot of canopy; select the best developing shoots and break off the others now while they are easily breakable with your fingers. Maria Smith and Dr. Michela Centinari at Penn State recently wrote a good summary of shoot thinning available here. I suggest reading it on the deck this holiday weekend with a nice glass of wine, and getting out in the vineyard next week to set this year’s crop on the right track.

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.

Petal fall approaching for many; Bloom for others

Posted: May 27th, 2019 by fruit

By Terence Bradshaw

As has been the general case this year with the drawn-out, cool weather, we have bloom (and p-bloom) bud stages all over the place depending on elevation, proximity to the lake, cultivar, and latitude. For growers in upland sites just entering bloom, see my posts from the past couple of weeks that have been aimed at bloom-time management. Remember, no insecticides; mow flowering weeds in the groundcover to make your trees more attractive to bees; and watch for fire blight. Keeping an eye on that very weather-specific disease can be more difficult in upland areas where NEWA stations are less prevalent. However, a look at stations in East Dorset, East Montpelier, Morrisville, and Berlin (‘Montpelier’ airport) shows EIP (potential bacterial population) below infective level all week, although a warmer-than-expected Wednesday or Thursday may change that. Overall, I wouldn’t be too concerned about fire blight for those sites, but would keep an eye on things.

Growers in warmer areas, however, may need to be concerned. Shoreham was flagged as having had an infection event yesterday, and an application of streptomycin today (like, now) to open blossoms may be prudent, especially on susceptible cultivars. Remember that blossoms are pretty much done as far as disease susceptibility is concerned once the petals fall, or 80 degree days (base 40) after they open, or 3-5 days given the weather we’ve been having.

Apple scab is the main disease to stay concerned about statewide. This is proving to be a challenging year for the disease, with infection periods occurring every week since bud break and reports of numerous tractors stuck while spraying. The good news is that we’re on the tail end of the primary apple scab infection season when the overwintering spores resulting from last year’s infections on leaf litter are close to expended. If you manage to keep covered with fungicides during that window and all infections are prevented, then apple scab season ends when those spores are gone. However, any infection in the tree canopy will lead to development and release of conidial spores which creates a secondary phase of the disease. My point is, keep protected until you know that you are scab-free and the spores are all expended. Some stations (Bennington, Cornwall, Shoreham) called for the end of primary season last Thursday, many more are indication that we’re within 1-2% of the spore load left. For those orchards, I recommend maintaining a good coat of fungicide through this week, and likely next. Depending on the material you choose, this application will cover you against powdery mildew, rust, and moldy core which can be a problem in cool, wet bloom periods. In 7-10 days, get out and do a thorough assessment of foliage for scab lesions. Pick the worst-case spots- tops of trees, that corner of the orchard where you turn and can’t get good coverage on that one last tree, the shady spot where the trees stay wet longer. Only after you know you’re clean can you let your guard down.

Speaking of letting your guard down, many of us did on the insect front going into bloom because trap counts were low for most insects across the state. We’re now seeing high numbers of European apple sawfly on traps in many orchards, and I expect a petal fall spray will be warranted against them. Pay attention when making this spray- petal fall means that all blossoms are gone, your migratory bees are pulled out, and flowering weeds attractive to wild pollinators are mowed. There are a number of materials that are effective against EAS, and all are toxic to bees to one degree or another. For organic growers, now is the time to get a good, solid coat of Surround kaolin clay onto your trees to deter plum curculio. I always preferred to apply this base layer in two coats, one at ~50 lb Surround per acre followed by another 25 lb per acre to get a good build up going into petal fall and the beginning of the real incest management season.

Thinning. This is always tricky to give advice on, and the variable conditions across the state make the job even harder. Many orchards have a larger-than-normal potential crop, and pollination should have been sufficient given the handful of good ‘bee days’ where conditions were right for bee flight and fertilization. This is a good year to consider multiple ‘light coats’ of thinners. NAA + carbaryl are a typical mix to apply at petal fall on many cultivars. For smaller-fruited cultivars, 6-BA thinners may be used instead of NAA to increase cell division and final fruit size, but they need warm sunny weather to work best. NEWA has a good model (two of them, actually) for helping to determine the potential effectiveness of thinner applications based on weather before, during, and after application.

This is the most critical time to keep your eyes open out in the orchard. Stay alert for signs of fire blight and apple scab. Check traps daily for codling moths to help determine the biofix date that you’ll use for subsequent management decisions. Keep an eye on fruit clusters for signs of thinner activity (yellowing stems, sepals that don’t close up). Get you nitrogen and other nutrients on, multiple lighter coats are better in rainy years than one big one to minimize leaching and runoff. Watch for and enjoy the sunshine. This weather can’t last forever.

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.

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