The time has come (and I’m actually a little late on this notice, so this shouldn’t be delayed) to hang apple maggot fly (AMF) traps in Vermont orchards. 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. We have some available from our program as well, if you want to swing by South Burlington. If you want to come by for traps, please email me and we’ll be sure to have some ready.

AMF 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. (Video here: Vermont Apple IPM: Hanging apple maggot fly traps.) 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. When using traps to monitor AMF populations 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 monitoring and treatment should be on everyone’s minds. It’s past treatment time for first generation codling moth in most orchards, the next best time to treat is after second generation flight next month. OBLR have been showing up in traps for a couple of weeks 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). Other good materials targeted at this lepidopteran pest include Intrepid, Rimon, Delegate, and Belt.

I have seen one pretty bad case of European red mites already, and hot, dry weather is also conducive to mite flare-ups. A weekly or, if the numbers indicate, bi-weekly scouting will help to indicate if there are high enough mite numbers to consider treatment. Information on monitoring: https://netreefruit.org/apples/insects/mites. Mites should be treated based on the following thresholds: in July, 5 mites per leaf the threshold for treatment; in August, trees are more tolerant of feeding so treatment should only be applied if there are over 7.5 mites per leaf.

Diseases: keep checking on your scab, if you have none (I mean none), then it’s okay to relax. That said, 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. I am also seeing more leaf spot diseases (here’s a great article on the different leaf spots you may encounter) this year that may warrant continued coverage to reduce potential defoliation and/or spread to fruit rots. Recommendations from our colleagues at Cornell suggest including a FRAC group 3, 7, or 11 fungicide with your captan cover to reduce incidence of these diseases. Keep in mind that one inch of rain washes off half of your coverage, after two inches, it’s gone.

It’s time to wrap up any ground-applied nitrogen fertilizers, but potassium and magnesium fertilizers can be applied any time in summer. It’s also a good idea to keep up your regular foliar calcium sprays, especially on bitter pit-prone cultivars like Honeycrisp and Cortland.

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Terence Bradshaw (he/him)
Associate Professor, Specialty Crops

Chair, Dept of Agriculture, Landscape, and Environment
(formerly Plant and Soil Science)
College of Agriculture and Life Sciences

University of Vermont
117/210 – Jeffords Hall | 63 Carrigan Dr
Burlington, VT 05405

(802) 922-2591 | tbradsha
https://go.uvm.edu/alebradshaw

UVM Commercial Horticulture | UVM Fruit Blog
Horticulture Research and Education Center
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The main management items that should be on the minds of growers right now are disease management, groundcover management, disease management, and maybe some insect management. Canopy management probably needs to wait a little bit.

We have been seeing some symptoms of Phomopsis, a little black rot, and some downy mildew in the vineyards we have been checking in the Champlain Valley, not to mention the unsprayed vines on my deck arbor in central Vermont. The good thing about Phomopsis, assuming that you identify it correctly, is that there are no secondary infections during the growing season. Next year’s infections are caused by overwintering inoculum on canes and rachises from this year’s infections, but the disease does not continue to spread for this season. That means that Phomopsis-infected leaves may not need to be removed to prevent spread this year, but infected canes and wood needs to be removed and preferably burned before next season. Phomopsis is a greater problem issue in years with cool, wet springs like we experienced this year. Vineyards, especially if managed with organic practices, should have all diseased wood cut out by the beginning of vine growth. When in doubt, prune it out. Infections on rachises which occurred this past month may not be visible until veraison, so keep your eyes out.

With the relatively cool, wet weather this month, we have had numerous black rot infection periods—if vines were not protected or high inoculum was present, we should be seeing lesions now. Black rot does have a secondary infection cycle, where conidial spores may be produced in active lesions, leading to continued infection throughout the summer. Black rot lesions are brown, often circular but with irregular margins, and may have a purplish halo at their margin. The key diagnostic is the presence of small black fruiting bodies, pycnidia, in the center of the lesion. These leaves should be regularly removed and destroyed any time you are passing through the vineyard, especially if you are using organic practices.

Downy mildew is just starting to rear its head. This disease is a little different than the others in that it’s caused by an oomycete, rather than a fungus. Consider it something like a cross between a fungus and a bacteria (I am oversimplifying, but the analogy works for me) in that it requires water to move, reproduces rapidly in warm weather, and forms lesions on leaves from which spores for the next cycle are borne. Downy mildew management picks up around now, as the summer heat, and especially warm rains, pop up. For organic growers, copper rotated with LifeGard may be a best option for management of this disease. For non-organic growers, captan, Revus, Ranman, and the Phosphorous acid fungicides (e.g., Phostrol, Rampart) are very effective. A great symopsis of downy mildew management is included in Dr. Katie Gold’s 2022 Grape Disease Control article (go to page 9).

Don’t ignore powdery mildew or anthracnose. The former is fairly easy to manage but easy to get away. If you see it, consider application of stylet oil or sulfur, but not both as they are a very phytotoxic mix. Same with oil and captan- keep those two at least 7-10 days apart in the vineyard.

Managing groundcover now is an important (potentially) non-chemical IPM tool to manage disease. Tall groundcover shades lower leaves and increases humidity in the canopy, which enhances the conditions for disease formation. If you do not have a clean strip (herbicide, cultivated, or mulched) under the vines, be sure to mow, including the strip between vines that the regular alley mower misses.

Some growers may be seeing grape tumid gallmaker, but for most, I don’t recommend management. For those who have it bad, Movento is a good non-organic material.

The UVM Tree Fruit and Viticulture Program is supported by the University of Vermont Agriculture Experiment Station, UVM Extension, USDA NIFA E-IPM Program, and USDA Risk Management Agency.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the United States Department of Agriculture. University of Vermont Extension, Burlington, Vermont. University of Vermont Extension, and U.S. Department of Agriculture, cooperating, offer education and employment to everyone without regard to race, color, national origin, gender, religion, age, disability, political beliefs, sexual orientation, and marital or familial status.

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.

We have a video up on YouTube this week if folks want to see what’s going on in our orchard. -TB

We are settling into summer mode in Vermont orchards. For most of us, the weekly disease management treadmill is behind us, as all overwintering apple scab ascospores have long been released, so as long as we covered our orchards well and have no scab in the orchard, it will not spread for the season and we can check that one off the list. If you do have apple scab, and you should do a thorough scouting to see if you do, then you’ll need to keep a consistent 10-14 day coverage of protectant fungicide to prevent conidial infections from spreading. Some rust and powdery mildew have popped up here and there but are largely under control from sprays applied around the bloom and postbloom window. Diseases to keep an eye on include sooty blotch / flyspeck and the various summer rots; captan does a pretty good job on those and I like to add in a single-site material like a group 3, 7, or 11 in late June or early July if weather has been hot and humid to add some activity against the rots.

Plum curculio ovipositioning should be wrapped or soon wrapping up in all orchards but those I the coolest sites, as that pest is only active for 308 degree days base 50F after petal fall, so no more applications need be made for them. We are well-into scouting and management season—last week I mentioned that we were well-timed for a spray to target codling moth based on our first trap capture on 5/20 (an application was timed for 200 DDb50F after that), and we may make a second application in 10-14 days if trap captures remain at 5 or more moths per week.

We have just started catching obliquebanded leaf roller in baited pheromone traps. Many growers have been asking about other moths in their baited OBLR traps, as there are many other pests that can be attracted to them, particularly redbanded leafroller. We don’t tend to manage specifically for the latter pest, as managing for OBLR typically takes care of RBLR as well and the trapping and degree day model for OBLR is more accurate than for OBLR. For orchards with a history or consistent catches of OBLR, the first spray for managing them may be timed at 350 DDb43F after the first catch (and there’s a NEWA model for that). Finally, on the insect front, you may want to start scouting for mites, especially in historically problematic blocks or if you have backed off prebloom oil applications. Page 14 of this archived section of the 2015 New England Tree Fruit Management Guide has a good description of the protocols for mite sampling.

It’s getting late to be applying nitrogen fertilizers, so plan on wrapping those up soon. It’s not a bad idea to have calcium in every foliar spray this time of year.

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Terence Bradshaw (he/him)
Associate Professor, Specialty Crops

Chair, Dept of Agriculture, Landscape, and Environment
(formerly Plant and Soil Science)
College of Agriculture and Life Sciences

University of Vermont
117/210 – Jeffords Hall | 63 Carrigan Dr
Burlington, VT 05405

(802) 922-2591 | tbradsha
https://go.uvm.edu/alebradshaw

UVM Commercial Horticulture | UVM Fruit Blog
Horticulture Research and Education Center
Message me on Teams

UVM’s Our Common Ground Values:
Respect | Integrity | Innovation | Openness | Justice | Responsibility

UVM is subject to the Vermont Public Records Act and communications to and from this email address, including attachments, are subject to disclosure unless exempted under the Act or otherwise applicable law.

We caught our first codling moth in pheromone-baited Traps on May 20th, which set our biofix date for the degree day model used to track egg hatch and larval development. As of today we have reached the threshold for treatment in South Burlington, and will be treating our orchards tomorrow morning. It is important for growers to ascertain their biofix date for their own operation, so that they may specifically target this particularly damaging test. If you do not have traps in your orchard, you may assume somewhere around May 20th if in the northern Champlain Valley, and probably a week to 10 days after that if in a cooler inland or upland site. Warmer sights in the southern Champlain Valley or southern Vermont may need to advance that, but it is always best to maintain your own traps. This biofix date may be used in the NEWA codling moth model. Treatments for the first generation with most insecticides are best applied at 220 degree days base 50°F after the biofix date.

Other things to keep in mind during this part of the year:

• Honeycrisp trees could receive low-level (2-4 oz per acre) NAA applications for the next four weeks to improve return bloom.
• Keep an eye on the results of any thinning treatments and consider one final application if inadequate numbers of fruit have thinned off. Most orchards are reaching the end of the window for most effective thinning.
• All cultivars, and especially Honeycrisp, will benefit from regular applications of foliar calcium now through mid summer.
• We are nearing the end of the window when soil applied nitrogen fertilizers should be applied.
• Apple scab should be largely finished with its overwintering spores so preventative management of that disease should be done in near every Vermont orchard. It is very important to carefully scout orchards for any scab that may have broken through spray applications before secession of fungicide applications. If fresh scab is found, growers should maintain regular preventative fungicide applications for at least another month.

The UVM Tree Fruit and Viticulture Program is supported by the University of Vermont Agriculture Experiment Station, UVM Extension, USDA NIFA E-IPM Program, and USDA Risk Management Agency.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the United States Department of Agriculture. University of Vermont Extension, Burlington, Vermont. University of Vermont Extension, and U.S. Department of Agriculture, cooperating, offer education and employment to everyone without regard to race, color, national origin, gender, religion, age, disability, political beliefs, sexual orientation, and marital or familial status.

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.

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.

Terence Bradshaw
University of Vermont
Sent via Mobile

Apple scab ascospore maturity models for essentially every weather station in the state indicates that we are at the end of the primary scab infection season. That means spores that could cause apple scab have matured and either has or likely will release after the next good wetting event. However, growers should maintain protective fungicide coverage on all trees for the next 1 to 2 weeks and should inspect their orchard carefully to ensure that infections have not occurred before backing off from coverage for the season. This is a good time to use group 7 or 11 fungicides to also provide protection against powdery mildew and apple rusts.

The warm weather we are expecting this week could cause fire blight infections in susceptible varieties with lingering blossoms such as newly planted trees. Consider protection if your orchard is in that situation. This is also a good time to maintain a program of 3-4 sprays of prohexdione-calcium (e.g., Kudos, Apogee) at 6 oz per acre or 2-3 oz per acre with Actigard at 2 oz per acre to stiffen up cell walls in developing shoots to reduce shoot blight susceptibility.

Plum curculio is active in orchards. If full block insecticide coverage was applied at petal fall, only border row sprays may be warranted until you have reached 308 degree days base 50F after petal fall, after which the insect is no longer actively laying eggs and causing fruit damage.

Codling moth are slow to take flight around the region. Growers should check pheromone baited traps daily and set the biofix for the management model as the first date of trap capture. The NEWA model will calculate accumulated degree days (base 50F) after sustained flight to predict egg hatch, most insecticides should be applied 100-200 DD later to be most effective. We don’t expect that to occur until next week, anyway.

The big management activity for this week should focus on thinning applications. The warm weather we are expecting today through Friday coupled with low wind conditions mean that thinners will be particularly active this week. In most orchards that I have seen in the state that were not affected by the April 20 freeze, I am recommending an aggressive thinning strategy this year to prevent a large crop of small fruit and subsequent biennual conditions next year and the years following. The weather conditions in the next few days are especially conducive to using the 6-BA thinning materials, which are especially useful on small fruited cultivars such as Empire, Macoun, and Gala. Larger fruited cultivars may benefit from NAA applications. Either of those would be enhanced with the inclusion of 1 pint of carbaryl per 100 gallons. This is the most important window for you to manage this year’s crop, so take advantage of it.

Terence Bradshaw (he/him)

Associate Professor, Specialty Crops

Chair, Dept of Agriculture, Landscape, and Environment
(formerly Plant and Soil Science)
College of Agriculture and Life Sciences

University of Vermont
117/210 – Jeffords Hall | 63 Carrigan Dr
Burlington, VT 05405

(802) 922-2591 | tbradsha
https://go.uvm.edu/alebradshaw

UVM Commercial Horticulture | UVM Fruit Blog
Horticulture Research and Education Center
Message me on Teams

UVM’s Our Common Ground Values:
Respect | Integrity | Innovation | Openness | Justice | Responsibility

UVM is subject to the Vermont Public Records Act and communications to and from this email address, including attachments, are subject to disclosure unless exempted under the Act or otherwise applicable law.