VT Grape IPM: Diseases showing up in area vineyards

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. This season did start out cool, with just enough wet to cause some infections. 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 dry, cool weather (not counting this hot stretch we’re having this weekend) in June, black rot infection periods have been few, but 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 managemt 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.

That should be enough 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, UVM Extension, USDA NIFA E-IPM Program, and USDA Risk Management Agency.

UVM Extension helps individuals and communities put research-based knowledge to work. 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.

VT Apple IPM- Apple maggot fly traps should be prepared and hung

Assuming that you have dealt with codling moth, we’re in a calm spot between insects but it is time to hang your apple maggot fly (AMF) traps. 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. Remember to rotate your insecticide chemistries to avoid resistance development in pest populations. Resistance isn’t a huge issue with apple maggot fly that has one generation per year, but codling moth and other lepidopteran pests are still about and subjecting successive generations of them to the same class of materials can induce resistance. 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.

Think about including calcium in all of your foliar sprays until harvest, and on Honeycrisp and other large-fruited varieties, you may want to make some specific trips just to get more Ca on. Also, if you see any fire blight, please let me know as I have colleagues at Cornell and Connecticut Agricultural Experiment Station who are looking to sequence samples to test for streptomycin resistance.

VT Apple IPM Codling moth management due any time

At the UVM Horticulture Research and Education Center, we caught our first codling moth in our pheromone traps on Thursday, May 26. Using that day as a biofix, we start accumulating degree days (base 50°), or rather let NEWA accumulate them, and plan to apply a treatment at egg hatch. Most literature references 220 DD as the beginning of egg hatch, but the NEWA model suggests treatment just a bit later at 250 DD for most materials to improve efficacy and ensure that more larvae contact treated materials or surfaces. A second application would be applied 10-14 days after that to cover the entire generation. In order to reduce the likelihood of CM evolving resistance to specific spray materials, be sure to rotate materials so that no two successive generations receive the same class of material. There are a number of materials effective against CM, compared to the old days when organophosphates and pyrethroids were the first and often only materials to come off the shelf. Heather Faubert published a nice summary of materials effective against codling moth here a couple of years ago. Avoid using ovicides (materials targeted at eggs rather than larvae) like Rimon or Esteem at this time, as those should have been applied around 100 DD for best effectiveness. For resistance management, check the IRAC code on your material and be sure to rotate codes so that no two generations see the same material. This includes applications made against other pests, i.e., if you apply a neonicotinoid (IRAC 4A) against apple maggot in a few weeks, that also counts in your resistance considerations for CM. Since many growers rely on a neonic application for summer management of apple maggot, I suggest not using one now.

However, there’s more to the story. We have been trapping CM in some orchards in northwest Vermont and have seen widely variable catch numbers. At HREC, we have only caught that one moth, which indicates a low population in a pheromone-baited trap; at another orchard, over 40 moths have been caught. Unlike for some other pests, there is no “spray when you see X caught insects” threshold for codling moth. The rule of thumb is that captures over five to ten moths in a week suggests a high population that warrants two treatments per generation. However, a low population, as observed at HREC, may be treated with a single application at around 360 DD, or sometime next week.

This tailoring of spray application to the specific life stage of the pest, based on empirical scouting and use of accurate weather and pest models, is an excellent example of how modern IPM, using a combination of scouting, weather data, accurate models, and modern pesticide chemistries are combined to dramatically reduce environmental impact of apple pest management and likely save the grower a few dollars, too. If you’re not trapping but rather rely on the default ‘first catch’ date in NEWA or a general calendar-based timing, I do not recommend a single treatment for the first generation, you should default to two. Advanced IPM requires a thorough knowledge of your orchard and pest systems, you can’t just wing it, cut your sprays, and assume that you’ll get the best effectiveness.

Other things to think about: Nitrogen fertilizers should be wrapping up in the next week or so. All sprays should include a calcium product, and on bitter pit-prone varieties, you may want to consider making specific calcium sprays every 10-14 days until harvest. Keep an eye out for fire blight- we saw our first strikes this year on inoculated trees in one of Dr. Kerik Cox’s trials at HREC. Thinning should be done now- if you need a little more in high-value varieties hand thinning is the way to go. Scab should be done for most orchards aside from the cooler upland ones, so you could take a break in the Champlain and Connecticut valleys if you’re scab-free at this point and plan on next fungicide in a couple of weeks when the summer diseases ramp up.

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, UVM Extension, USDA NIFA E-IPM Program, and USDA Risk Management Agency.

UVM Extension helps individuals and communities put research-based knowledge to work. 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.

Vermont Grape IPM: Peak Disease Management

We seem to be in a Goldilocks sweet spot in regards to moisture- just enough for the vines, not too wet to get work done. That can let some folks get complacent, but as vines are entering the immediate prebloom period, we are at peak disease pressure with all of the major diseases active to one degree or another. Every vineyard should be covered with the full suite of disease management products this week. That means mancozeb or captan plus a DMI, SDHI, or strobilurin (group 3, 7, or 11, respectively) material for non-organic vineyards; and sulfur plus copper (watch for incompatibilities on certain varieties, page 9 here) on organic vineyards. This would also be a good time to add biologicals, since we’re at ‘all hands on deck’ right now. Some materials, like Lifegard and Howler, are systemic acquired resistance promoters and need to go on a few days prior to infection. Others, like Serenade and Double Nickel, are biological extracts but can be mixed with other materials. Either way, these applications should be made a before infection, so spraying in the next day or two is a good idea.

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, UVM Extension, USDA NIFA E-IPM Program, and USDA Risk Management Agency.

UVM Extension helps individuals and communities put research-based knowledge to work. 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.

Calibrating Airblast Sprayers, June 29 or 30

Forwarding this great opportunity to the Vermont grower community. This would be appropriate for apple, grape, and other berry (e.g., bramble, blueberry, etc.) growers.-TB

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Wednesday, June 29

3:00 pm – 5:00 pm

Whitecliff Vineyard, 331 Mckinstry Rd, Gardiner, NY 12525.

OR

Thursday, June 30

3:00 pm – 5:00 pm

Rulf’s Orchard, 531 Bear Swamp Road, Peru, NY 12972

George Hamilton, University of New Hampshire Extension Field Specialist Emeritus, will demonstrate the importance of and best techniques to calibrate air blast sprayers. Proper calibration will ensure effective, efficient, economical and legal spraying. Inadequate spray coverage is usually the cause of poor spray efficacy and additional spray applications. Overuse of some sprays results in unhealthy residues and can lead to fines.

Calibration should be done several times each season, or when you incorporate any new equipment or repairs – from the tractor to the nozzle. Join us for a refresher or send new employees for training. This workshop is open for any grower that relies on an airblast sprayer to deliver plant protectants to fruit or vegetable crops.

$20 per farm—Pre-registration is Required

(Please list each person attending so that we have a proper count…space is limited)

2.0 DEC credits available in 10, 1A, 22, and 23

Register Here: https://bit.ly/calibratingairblastsprayers

Agenda

3:00 pm – Welcome and Introductions

3:10 pm – Why are you Spraying and Benefits of Calibrating

3:20 pm – Calibration Factors Affecting Application Rate

3:35 pm – Pre-Calibration

3:45 pm – Sprayer Maintenance

4:00 pm – Calibration Notes

4:10 pm – Calibration Demonstration (water sensitive paper deployment exercise included)

4:30 pm – How to evaluate success – Understand deposition

4:55 pm – Q&A

5:00 pm – Adjourn

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CCE ENYCHP | enych.cce.cornell.edu
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Vermont Apple IPM

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 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.

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 1/2 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 1. Plum 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.

Codling moth have now been trapped in many 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. Retired Cornell entomologist Dr. Art Agnello offers the following specific recommendations for CM management the June 10, 2019 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…Products with insect growth regulator activity, such as Rimon, Intrepid or Esteem, would also be suitable options 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 (note: I like to avoid pyrethroid use in orchards if possible sonce they can substantially disrupt beneficial insect populations- TB). 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…This 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 nearly done with primary apple scab season. That doesn’t mean that scab management is done, you should keep covered for at least one more good infection period. Inland/cooler sites likely have inoculum left through next week, so you’ll have at least two sweeks more of fungicide coverage before backing off. Scout your orchard regularly for scab, especially in the tops of the trees, ends of rows where nozzles may have turned off, or on susceptible varieties. f 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.

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 few weeks to give trees time to harden off for winter. Potassium fertilizers can go on any time now.

VT Grape IPM

Vine growth is flushing out rapidly in Vermont vineyards, with many vines at or approaching 5-8” shoot growth. We are entering a critical window of disease management when anthracnose, black rot, Phomopsis, and powdery mildew can all be active. There isn’t a lot of rain in the forecast, but showers mid-week may cause enough wetting to initiate infections. Vineyards should be covered with your fungicide(s) of choice this week.

This is also a great time to apply any ground-applied fertilizers, as this period of rapid shoot growth is when plants need nutrients the most. Nitrogen need in Vermont vineyards is relatively low (but not non-existent), but most vineyards need some potassium and often magnesium. Please base your fertility applications on soil and foliar analyses (more on that next week) or visual symptoms, especially for magnesium.

Vermont Vineyard IPM

Grapevines at the UVM Horticulture Research & Education Center are showing up to three to five inches of shoot growth, depending on variety. We are beginning to enter a critical time for disease management- all growers should plan on starting your spray program this week or soon thereafter (for inland growers with less growth). I pretty-well listed the strategies to take last week, so I’ll allow folks to look there.

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 wrote a good summary of shoot thinning available here. I suggest reading it on the deck this holiday coming 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.

As a reminder, all of my older IPM bulletins are archived on the UVM Fruit Blog.

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, UVM Extension, USDA NIFA E-IPM Program, and USDA Risk Management Agency.

UVM Extension helps individuals and communities put research-based knowledge to work. 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.

VT Apple IPM: (early?) petal fall on apples

Apple scab is still a concern in Vermont orchards. However, as heat gas continued to accumulate and relatively regular showers have provided for spore release from leaf litter, the supply of inoculum available to infect orchards, assuming you have prevented infection during these wetting events, is dwindling. The NEWA model in some sites shows up to 99% spore discharge by the end of this week, but like all models, we need to be careful as reality on the ground may be off by as much as 10%, which can be enough top cause infection. Bottom line- don’t let your guard down on scab yet, but this does look like an early-ending scab season. Stay covered and we’ll revisit next week.

Normally when we think of a cool / downright cold spell after a warm stretch conducive to fire blight, we consider the risk to decline with the temperatures. However, all of the usual fire blight models predict continued risk to blooming trees today and into this week. As there are fewer blossoms out there in many orchards (although inland/upland orchards may be in full bloom still), it may be easy to think that we’re out of the woods. However, I would consider treating high value blocks of young trees of fire blight-susceptible varieties, at a minimum (cider varieties, Gala, Mutsu, Cortland, Paulared, Northern Spy, Fuji, Macoun, etc). Word on the street has it that the streptomycin supply is low to unavailable. I’d suggest treating what you can with what you have, consider Apogee / Kudos even at half-rate to reduce shoot blight, and paying close attention to strikes as they show (and cutting them out aggressively).

Many folks are seeing the beginnings of petal fall and are considering an insecticide or thinning treatment containing carbaryl. Please reconsider that if you have any bloom, including in groundcover, in the orchard. I can’t in good conscience (nor legally, in keeping with the insecticide labels) recommend both treating blossoms with streptomycin while also applying an insecticide in a thinning program. So if you have blossoms but want to thin, I’d recommend NAA (Refine) or 6-BA (Maxcel) alone without carbaryl. This looks like a decent week for thinning.

Spray conditions look best tonight (Monday May 23) though Wednesday.

Vermont Apple IPM: Petal fall considerations

Orchards around the state are either in bloom (inland) or at/approaching petal fall (Champlain / Connecticut Valleys). This is always a tricky time for management, and growers may need to be ready to apply different treatments to different parts of the farm. Here’s my quick rundown:

Insects: Generally, there are still too many flowers out there- both apple blossoms and dandelions on the orchard floor to be spraying without impacting pollinators. In few cases is a pink insecticide spray needed, in my opinion, especially in retail-oriented orchards. Keep an eye on traps, and if you haven’t hung any yet, at least get your codling moth traps up to determine your biofix date. Point being: be ready to treat after bloom (and mow those groundcover flowers first), but don’t get knee-jerk. Wait and see, for now.

Diseases: Fire blight risk decreased this week with the onset of cooler weather, but is shooting right back up with this weekend’s expected heat. There are a lot of flowers still out there, even on petal fall-adjacent cultivars. Apple scab is primed with very high ascospore maturity. Any decent wetting event is likely to cause an infection, so keep covered with a protectant fungicide and use a single-site SDHI, Strobilurin, DMI, or combination material if you have any questions about coverage going into a wetting period.

Thinning: It’s looking like a heavy bloom year, so aggressive thinning is probably going to be called for. Plan on, at a minimum, a petal fall application, followed up by another at 7-14 mm fruit size. Successful thinning depends on many factors, I’ll highlight them more in light of upcoming weather in a few days. Be sure to adjust materials based on the NEWA Apple Carbohydrate Deficit Model. I’m also including Dr. Duane Greene’s advice from a recent UMASS Healthy Fruit Newsletter here.

“Bloom and Petal Fall Thinning

Duane Greene

Flower development has been erratic and proceeding in fits and spurts. However, it does appear that development in many orchards is approaching or will be at full bloom this week. The bloom and petal fall stages are excellent times to start your chemical thinning.

Bloom and Petal Fall

Bloom is a time when orchardists frequently do not choose to thin. The bloom period has not yet occurred so there is uncertainty about how favorable it will be for bees to fly. Also, the potential for frost still exists. However, it should be noted that the sooner you can start the thinning process, the better chance you have of influencing and encouraging return bloom. There are several options available to use at bloom.

Petal fall is a thinner time of application that most orchardists choose. The pollination period is known and there is a reduced chance of frost. If a bloom thinning spray was not applied a petal fall application of a thinner becomes very important.

With one exception (Carbaryl) the same hormone thinners can be used at either bloom or petal fall. When selecting a thinner(s) it should be emphasized that thinners are not as potent when used at bloom as when they are applied at the traditional 7-14 mm stage. A rough rule-of-thumb is that thinners applied at bloom and petal fall are about 50% less effective at thinning as they are if they were applied at the 7-14 mm stage.

Naphthaleneacetic Acid (NAA)

NAA has been used by growers for over 75 years. There is some comfort in using a compound that has passed the test of time. I routinely suggest application of NAA at 10 to 12 ppm. I have never over-thinned a tree using these rates. Lower rates will be less effective. NAA at 10 to 12 ppm could be applied to a broad spectrum of cultivars.

Naphthaleneacetamide (Amid-Thin)

This is a thinner that has garnered increased interest from growers recently. Amid-Thin is a weaker thinner than NAA and it rarely, if ever, over-thins. It has a reputation for being a reasonably consistent thinner. The label allows application of up to 8 oz/100 gal. I do not recommend using a rate any lower than 8 oz/100 gal. (Ed. note: Amid-Thin W is not currently registered in Rhode Island.)

Ethephon

Ethephon may be used as an early thinner. The recommended rate is 300 ppm or 1 pt/100 gal. Some have applied it at a rate as high as 400 ppm with good results. It may not be as consistent as other thinners but it remains a viable option. Since it produces ethylene it may also be useful to enhance return bloom.

Carbaryl

Historically, this has been the most popular thinner in New England. Unfortunately, it is very toxic to bees so it can not be used until the bees are removed from the orchard at petal fall.* Carbaryl is unusual as a thinner in that its effectiveness is concentration independent. It is routinely used at 1 pt to 1 qt/100 gal. Carbaryl is an excellent choice to combine with either NAA or Amid-Thin at petal fall to enhance thinning activity. I like the addition of carbarly with Amid-Thin to enhance the thinning activity of Amid-Thin.

Petal fall is a somewhat nebulous term. I consider it to be a period of time between the time petals fall from the flowers and when the receptacle starts to grow. Early in this period the receptacle is not growing, or growing very slowly, so there is little carbohydrate demand exerted by the fruit. Consequently, I generally do not pay much attention to the carbohydrate model during this period of time. However, when fruit grow to 5-6 mm then the carbohydrate model plays an important role in making thinning decisions.

Bloom and petal fall thinner applications are an important component in a comprehensive thinning program. This opportunity to help regulate crop load should not be missed. The real danger in bloom and petal fall thinning is not over-thinning but not thinning enough!”

Here’s what I’m putting on the orchard this morning: mancozeb @ 4 lb/acre (last application before switching to captan); Inspire Super (difenconazole / DMI) @ 12 oz/acre; Harbour (streptomycin) @ 1 lb/acre; Refine 3.5 WSG (NAA, thinner) @ 6 oz/acre / 15 ppm @ 100 gallons water/acre).