University of Vermont

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.

By Terence Bradshaw

Apple buds are rapidly expanding into tight cluster bud stage in most of Vermont, which sets the calendar close to ‘normal’ after the cool, slow start to the season. Apple scab infection periods have been somewhat scarce, depending on when you started you clock for ascospore maturity (green tip, minus any confidence you have in slow maturation of a low inoculum population because your orchard was clean last year). We potentially had an infection period April 27-May 1 right at green tip with low ascospore maturity and little tissue open; some had an infection period May 3-4, and others may be waiting for the first one that could occur today and into tomorrow. You should be covered with a protectant going into this event, and if you aren’t or question your coverage, plan on applying a material with kick-back activity like one of the Lunas, Merivon, Inspire Super, or even one of the older strobilurins or DMI fungicides (if they still work against your local population) this morning or early tomorrow.

Once we get through today’s rains (and the likely overnight wetting event), the warm, sunny weather this week is going to push disease management to the side for a spell but will push bud phenology and insect activity along. Growers who use them should already have traps deployed for tarnished plant bug (TPB) and European apple sawfly (EAS), which are attracted to blossoms (thus the use of white sticky cards to catch them in the canopy). Compare cumulative mean catch per block to our monitoring chart to determine the need to treat.

That said, there are important considerations to make when determining the need for prebloom insecticides. At the time the accepted thresholds were established, the majority of Vermont’s apples were sold to wholesale markets with little tolerance for cosmetic blemishes like TPB or a low infestation of EAS may cause. However, increased direct-marketing of apples today may increase consumer tolerance for those ‘ugly’ fruit, so really consider your own tolerance for damage before applying a broad-spectrum material. Then again, I’ve seen EAS infestations that looked worse than an unmanaged codling moth outbreak and where the larvae feed into the core, causing fruit abscission instead of just cosmetic injury. If you’ve had a history of EAS and show a high population on traps, that one may be worth treating. However, if bloom is short, a petal fall application may be preferable.

I am making all of these caveats because of the concern for impacts of spraying on wild and managed pollinators. Dr. Rufus Isaacs at Michigan state University recently posted a good summary of consideration in reducing risk of pesticide impact on pollinators, which I summarize here but you can follow the link to read in full:

· Use integrated pest management (IPM) to reduce the need for sprays.

· Avoid pesticide sprays during crop bloom.

· Apply pesticides after sunset or before sunrise, or when air temperature is below 50°F.

· Select the least toxic pesticides and formulations when possible.

· Reduce drift onto areas outside crop fields.

· Remove flowering weeds from crops.

· Provide bee-friendly habitat away from crops.

· Develop and implement a pollination contract with your beekeeper.

That last one should remind everyone that it’s time to get our bees lined up if you’re planning to rent hives. My old mentor Lorraine Berkett used to have us make bets on when the first McIntosh blossom would open in South Burlington. This year, I’m guessing May 11.

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

Last week, apple buds in the traditional growing regions in the Champlain and Connecticut Valleys and Bennington County moved into the green tip stage which triggers the beginning of primary infection season for apple scab. Many weren’t ready to protect from infection during the rainy window of Wednesday through now, and in orchards with little scab last year and where little tissue is out, you’re probably fine if you missed getting some fungicide protection on. It’s looking like this rain will wring itself out sometime tomorrow Monday April 30 and we’ll have a dry slot during Tuesday (with low winds, too) and Wednesday to get covered. Wednesday we’re expecting temperatures in the upper 70s, which means that buds will open pretty rapidly. Then, more rains are expected later in the week. All along the way, apple scab ascospores are maturing and will be ready for the next wetting event to infect this rapidly expanding tissue.

Growers at green tip or beyond as of now should get covered with a protectant fungicide early this week ahead of the rains. Copper should not be used at full field rates (4-12 pounds per acre, depending on the product) after the half-inch green bud stage, so if your buds are pushing fast and/ or/ you’ve already applied copper this season, put it away. But many orchards can probably get by with it applied Monday through Tuesday. Otherwise, a protectant fungicide like mancozeb or sulfur (latter if organic) should be used ahead of the rains. If you had substantial scab last year and missed coverage prior to this current wetting event, and you had significant green tissue showing by Friday April 27, you may want to add an anilinopyrimidine fungicide like Scala or Vangard (FRAC class 9) to this mix, but know that any infection that started late last week is too advanced for the fungicide to work really well against when applied five days later. Therefore, I recommend that tactic in only the highest inoculum orchards, the AP fungicide would have best been used no later than Friday or Saturday. I do not recommend the use of lime sulfur to burn out an infection I this low-risk scenario- it just isn’t worth it. But really, if you missed this last one, know that the risk is relatively low and you’d be best to put your efforts into protecting against the next ones.

Oil can be applied at any time now, either alone or in your fungicide (but not with or within ~~7 days of a captan or sulfur application) to help manage mites and scale. If applying with your fungicide, know that oil needs to be applied in as dilute a spray as possible to fully soak overwintering insects and eggs, so your calibration needs to be adjusted so as to not over apply fungicide at the same time. Oil rate of 2% by volume is fine now, but should be decreased by 1/2% for each advance in bud stage until; tight cluster, after which it shouldn’t be used save for summer rescue applications.

For orchards in the cooler upland regions where buds are still closed, this is a great time to get copper on your trees. It’s also a great time for everyone to flail mow or apply urea to leaf litter to aid in decomposition which will reduce scab inoculum.

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 hope everyone’s ‘second winter’ is going well. While we’ve had some pretty good cold snaps this week, I don’t expect that the warm spell in February significantly reduced apple bud hardiness. Time will tell, however, if I’m right, but keep up with your pruning because spring will be here before we know it.

I am posting a link to a program sponsored by IPM Institute of North America and University of Wisconsin Eco-Fruit Project, “Apple Talk”: https://ipminstitute.org/projects/specialty-crop-grower-services/appletalk/. The IPM Institute operates on a subscription system, and Apple Talk registration is $150 for the year. This weekly conference call covers numerous aspects of apple pest and crop management in an interactive environment. I was a subscriber and occasional contributor about ten years ago and the quality of material was very good. I recommend it as a means to get a sense of what other growers are facing during the growing season. However, keep in mind that the program is based in the upper Midwest, and conditions there may not always translate to those in our region.

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.