University of Vermont

By Terence Bradshaw

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

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

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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.

By Terence Bradshaw

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

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

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

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

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

· Carbaryl

By Terence Bradshaw

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

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

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

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

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

The label is the legal document for the product use.

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

label.

The UVM Tree Fruit and Viticulture Program is supported by the

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

Grant, and USDA Risk Management Agency Funds.

By Terence Bradshaw

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

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

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

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

The label is the legal document for the product use.

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

label.

The UVM Tree Fruit and Viticulture Program is supported by the

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

Grant, and USDA Risk Management Agency Funds.

By Terence Bradshaw

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

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

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

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

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

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

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

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

The label is the legal document for the product use.

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

label.

The UVM Tree Fruit and Viticulture Program is supported by the

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

Grant, and USDA Risk Management Agency Funds.

By Terence Bradshaw

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

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

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

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

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

The label is the legal document for the product use.

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

label.

The UVM Tree Fruit and Viticulture Program is supported by the

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

Grant, and USDA Risk Management Agency Funds.

By Terence Bradshaw

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

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

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

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

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

The label is the legal document for the product use.

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

label.

The UVM Tree Fruit and Viticulture Program is supported by the

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

Grant, and USDA Risk Management Agency Funds.