University of Vermont

By Terence Bradshaw

Despite my sheepish warning in my last post, it appears that we are in a high risk period for fire blight infection in Champlain Valley and other warmer orchard sites with open blossoms this week. The charts below were generated using a best guess date for the start of bloom and the “fire blight occurred in your neighborhood last year” setting in NEWA. High risk indicates a need for treatment if wetting occurred (and in most sites it did or will), extreme risk indicates that streptomycin application is required to prevent infection. Of course this assumes that you have a local population of the infective bacteria Erwinia amylovera in or near your orchard, and that you have open susceptible blossoms. Adjusting the model to “no fire blight in your neighborhood last year” drops all sites down one category (I.e., from “Extreme” to “High”, or “High” to “Caution”), so adjustment based on historical disease occurrence may be appropriate. Application of strep, especially to highly susceptible cultivars, is recommended at this time for site with high or especially extreme risk. Strep will protect blossoms for 24 hours before and after application, so an immediate spray will cover for yesterday’s and tomorrow’s wetting events. Organic growers may apply Serenade or Double Nickel to reduce fire blight infection, although neither is as effective as strep, which was removed from the approved list of organically-acceptable materials in 2014.

This is also a good time to consider Apogee application to reduce vegetative shoot growth, which could be excessive in this potentially low-crop year. Apogee has no effect on blossom blight, but is effective in reducing the severity of shoot blight symptoms. Dr. Nikki Rothwell recently presented a good summary of use of Apogee in orchards in Michigan which is appropriate for Vermont growers as well.

By Terence Bradshaw

Bloom status in Vermont orchards is all over the map. Of course, cooler high elevation and inland sites are generally going into full bloom now while Champlain and Connecticut Valley sites are at petal fall (PF). Honeycrisp (in the Champlain Valley anyway) are lagging behind most other cultivars worse than usual: at the UVM orchard, we just started to see some king blooms yesterday while neighboring Mac and Empire are at full bloom and starting to think about PF. So this information may be more timely for some than others, but we’ll all need to be thinking about some complicated orchard management items in the coming week.

Disease: rain today, more on Tuesday may trigger an apple scab infection period, keep covered. Many Addison County orchards had enough rain and wetness from last Thursday’s (May 19) rain to trigger what was probably the biggest infection of the season. Depending on models, what you input for green tip date, and your trust in the weather forecasting/measuring systems used by NEWA and other sites, we are at about 85-95% apple scab ascospore maturity (with a wide range of deviation). Keep covered against rains for the next 7-10 days anyway. Fire blight infection is still a possibility in orchards with a history of the disease and open blossoms (even those stragglers blossoms, which I’m seeing a lot of). I discussed this last week, but keep protection against fire blight (strep, Serenade only if organic and you have no other option) on within 24 hours of rain or other wetting events in blocks with high-risk cultivars and/or any history of the disease. I don’t think this fire blight season will be a big one for two reasons: one, most orchards will be in full petal fall by the time the risk gets too high, and two, we didn’t have much fire blight at all around last year so inoculum is relatively low. Still, if I had a block of Honeycrisp, Gala, or late-blooming cider varieties I would consider treating. In fact, I’m spraying the UVM farm tomorrow morning and will be including strep In the tank since we have had a history of FB in one block with Gala, Cortland, and Mutsu and adjacent to a block with tall spindle Honeycrisp that I wouldn’t want to lose to save a little extra effort.

Insects: pretty quiet, but the extended bloom and many orchards with no protection may add up to a lot of damage while we’re waiting for all petals to fall to get in with an insecticide. Eric Boire is setting some traps around the Champlain Valley this year and reporting back to me; to date, he’s been clean on codling moth (CM), European apple sawfly (EAS), oriental fruit moth, and oblique banded leafroller in the few orchards he’s been able to deploy traps and check them. We’ll be checking traps tomorrow so my data is a week old, but we have been catching EAS and red banded leafroller in our orchard, some of which of course includes an unsprayed block. If I were spraying tomorrow, I would add a Bt product into the tank to give some protection against lepidopteran larvae (remember, Bt only works against lep larvae, not flying adults) until we can get a full petal fall insecticide on. The warm temperatures of the last couple and next few days will drive plum curculio (PC) into orchards, so a full-orchard insecticide once all of the bees and flowers are gone will be warranted. Organic growers can start applying Surround any time now to get the base coat built up before PC start to oviposit. Remember that Surround and Bt have relatively little effect on codling moth, which is likely only starting its flight now and thus has no larvae in the orchards to worry about. I mention this because a targeted CM spray will likely be needed in orchards with a history of that pest in a few weeks, we’ll discuss that as it comes closer.

Thinning: The $64,000 question this week, and likely worth a lot more than that. The reports I’m getting are that not only are the blossom stages all over the place, but blossom quality has been extremely variable too. Many of us have seen freeze damage likely from that April 5 snap, haggard-looking blooms, missing king blossoms, and ragged spur leaves. I’ve heard one report of open flowers with what appears to be no pollen in them. Many trees were likely stressed by an overabundance of crop last year, those trees and many others may be short on critical nutrients, although you should be applying foliar zinc, boron, and nitrogen and nitrogen, potassium, and whatever else is called for to the soil to keep things in good shape. The good part is that we have had some great bee flying days, although early blooming sites and cultivars were a little cloudy during king bloom but I think weather on May 14 was conducive for good flight.

With all that being said, here’s my take on things. Fruit set is likely to be all over the place, and given that, I would avoid a petal fall thinner on all but the healthiest looking trees (bloom-wise) and even then might think twice. Most thinners are likely to be more active, relatively speaking, than usual this year. The spur and early shoot leaves developed under cool, cloudy weather and thus likely have thin cuticles. Upcoming warm and at least partly cloudy days will increase carbohydrate deficit in trees which enhances thinning activity. And the generally weak-looking buds are likely to produce less set fruit. NEWA has a carbohydrate thinning model calculator component that, in most years, may help growers guide thinning decisions. However, I and most regional Extension professionals am suggesting that it not be relied on to make your final thinning decisions this year given the poor state of bloom and tree condition.

I’m going to be careful on specific recommendations except to say that multiple applications of mild thinners may be best this year. Look at the orchard in the first few days after petal fall. If you have time, tag some clusters and measure fruitlet growth with a micrometer and track the growth of those fruitlets after thinner application; fruit that stop growing in diameter a few days after application will likely thin off. When fruit approach 5-6 mm in size, a mild thinner application such as carbaryl, Maxcel/Exilis, or Amid-Thin (any one of those applied alone) may be your best bet. Another look at 10-12 mm may suggest that another application is needed, but I would be hesitant to apply a big shot all at once now. The 2015 New England Tree Fruit Management Guide has a good synopsis of thing options in Chapter 11, but keep in mind that any options this year should be on the conservative side. That said, no action may lead to overset of fruit, so don’t be afraid to do something in blocks that look healthy and have reasonable fruit set.

By Terence Bradshaw

Orchards in the Champlain Valley are largely in full bloom now, although Honeycrisp appear to be holding out for a couple of days as usual. I’ve heard reports of good bee flight last Saturday, but cool cloudy weather slowed things the last few days. I did see great bee activity in the UVM orchards this morning though, and the next several days look like good bee days as well, so we should get a decent pollination season out of this. Cooler inland orchards should see bud development pick up with the coming weather, and I expect bloom in Washington and Orange counties to be in full swing by the end of the weekend. Feel free send me reports from your corners of the state.

I’ll get to pest management in a minute, suffice to say that things are a little quiet. Bigger considerations are horticultural: get your fertilizers on, water (especially new trees), and knock down dandelions and other flowering plants in the orchard to concentrate bees in the trees where you want/need them.

Apple scab continues to be quiet. Several sites in the NEWA system were reporting an expected infection period for today, but I’m just not seeing it with the sporadic rain in the forecast and good drying weather. That said, ascospore maturity is very high right now, so any wetting will release a lot of spores with high potential for infection. That assumes that you see rain and subsequent leaf wetness in your orchard. At the temperatures we’re seeing/expecting around the state, you’ll only need 6-7 hours of wetness to trigger an infection period. Sunday looks like our next chance for sustained wetting and significant rain, and even then the chance is not very high (30% listed for most parts of the state). Calm conditions in the next couple of days will facilitate spray applications. Here’s my advice: if you get any significant wetting in the orchard this afternoon and/or tonight, get out tomorrow or soon thereafter with an effective kick-back fungicide, tank-mixed (of course) with a protectant to give some protection against possible infection on Sunday. NO insecticides in this spray- even though some orchards have likely seen a bit of petal fall, I’d take a bet that there is still bee activity (including native bees) in your orchards. If you can hold off for a day or two and have concerns about fire blight because you have susceptible cultivars or had it in the orchard last year, read on.

Conditions for fire blight infection will be increasing as temperatures do over the next couple of days. At this moment, forecast data is not getting pulled into NEWA as I can see it (and a tech support email has been sent), but our own running of the Maryblyt model and my quick NEWA check earlier today suggest high to very high potential for infection if rains come on Sunday. Actual risk in your orchard depends on the same factors I discussed last week: open flowers, a wetting event, warm temperatures, and inoculum present. If you had NO fire blight last year or for several years, this may not be a big issue. But if you have susceptible cultivars and any history of fire blight, this may be one event you want to protect against (assuming you are in bloom). In that case, I would hold off spraying until Saturday, and apply your fungicide along with a full rate of streptomycin with the appropriate surfactant. I would avoid Captan if this is the route you choose to take since phytoxicity may occur when mixed with surfactants. Nothing else in this spray- no growth regulators (Apogee, petal fall thinners), no nutrients, and no insecticides. Petal fall sprays would start next week.

Organic growers should consider applying protective sulfur and avoiding liquid lime sulfur at this stage, since fruit set may be questionable given the early season freeze damage and we’re not sure about what level of thinning may be required. If you have open blossoms and suspect fire blight may be an issue, Serenade and good monitoring may be your best bet. It wouldn’t be bad to start applying Surround to build up a coating for plum curculio season at this point, that can be mixed into this spray and shouldn’t affect pollination.

We’ll talk about petal fall next week after assessing what’s out there to consider thinning. Again, feel free to send me reports from your orchards.

-Terry

By Terence Bradshaw

A quick note on apple scab: we are likely entering an infection period for the disease starting today through Sunday. If you aren’t covered with a protectant, either get one on between rainshowers or come in with an appropriate kick-back material as soon as possible after the rains stop.

As we enter the bloom period in most Vermont orchards, thoughts naturally turn to potential fire blight infections. This bacterial disease has been on the rise in the state in the past decade or so, and blossom infection is driven by four necessary components: 1) open blooms through which bacteria can enter the plant; 2) wetting events during bloom to move bacteria into susceptible tissues; 3) sufficient heat (daily average over 60°F) during an infection event to permit bacterial reproduction in susceptible tissues; and 4) sufficient levels of bacteria present going into bloom. The first condition is met just by having open blossoms in the orchard, remember that early or late blooming cultivars can extend the window. The second is likely to be met with occasional rains expected today through the weekend. The question remains about whether the other conditions will be met. Forecast temperatures look like sufficient heat will be present today and tomorrow for infection to occur in at least some orchards, particularly in southern Vermont. However, cooler temperatures starting Sunday, May 15 will reduce any risk of infection, at least as far as the near-term forecast is concerned.

The final condition required for infection to occur is a sufficient population of Erwinia amylovera bacteria present in the orchard. Bacteria are present in orchards in differing amounts, and may be present in wild trees surrounding the orchard. The Cougar Blight model used by NEWA to predict infection allows for multiple settings, including “no fire blight occurred in your neighborhood last year”, “fire blight occurred in your neighborhood last year”, and “fire blight is now active in your neighborhood”. Those settings can substantially affect infection predictions, so please adjust the model as appropriate for your orchard. Despite dire warnings of a fire blight apocalypse in 2015 due to the hot weather leading up to and during bloom, dry conditions and growers application of antibiotics prevented much infection at all in the state. Still, if you had fire blight last year or even in recent (2-3) years, consider moving the slider up into the more conservative class if using the NEWA model.

Models require entry of a date for first bloom. This is not your full bloom date, nor is it applicable only to McIntosh. Accumulation of heat units to assess the epiphytic infection potential (a measurement of the potential population level of infective bacteria) is somewhat complicated, but suffice to say that calculations begin within a certain window of bloom and end when all blossoms are gone so earlier bloom date entries may increase EIP substantially. The point of the model is to run given the best conditions and data you have in your orchard and to use that information to make a sound decision. Being too conservative in the model may overestimate potential for infection (and the reverse is true as well).

That said, for most locations in the Champlain and Connecticut Valleys, fire blight infection risk is high for today and tomorrow, and treatment may be appropriate for susceptible cultivars (Cortland, Paulared, Mutsu, Gala, Honeycrisp especially) that are in bloom if you had fire blight anywhere in your orchard last year. Risk drops for all sites to a ‘caution’ level if “no fire blight in your neighborhood last year” is selected. Treatment must be applied within 24 hours of infection (before or after) but only protects blossoms that were open during application. Typically, streptomycin is the best material to use and there is no known resistance to that material in Vermont. Organic growers may no longer use streptomycin and should use a biological like Serenade, possibly coupled with low-rate copper but fruit russeting may occur. Full label rates should be used, and with streptomycin, a wetting agent also included.

Take-home message: At this point I don’t consider fire blight to be a significant risk unless you had the disease in your orchard last year and you have susceptible cultivars in your orchard blooming now. Remember, if you don’t have open blossoms, then you don’t have any risk of the (blossom blight phase of) the disease.

By Terence Bradshaw

I traveled around the Champlain Valley a bit today and saw apples well into the pink bud stage (and one open blossom), with a few caveats. Damage from the cold snap in early April is becoming more evident, which coupled with generally weaker trees going into the weather after the heavy 2015 crop may result in uneven and reduced bloom in many orchards. I observed many blossom clusters with damaged or missing king blossoms, missing side blossoms, and quite a few generally weak and lagging clusters. Orchards in Addison County are at pink, and I saw one with hives already in the orchard. In the northern Champlain Valley, buds are a couple of days behind at advanced tight cluster, but a warm day or two will advance things rapidly. Here are my thoughts on some management items to keep in mind:

Apple scab does not look like a concern until at least the end of the week, and the rains over this past weekend did not trigger an infection period in most central and northern Vermont orchards based on NEWA data, but southern Vermont orchards appear to have had an infection event. Keep an eye on the weather and apply coverage before the next rain events during this peak period of ascospore maturity and release, but you can find other things to do until later in the week at least.

However, insect management at pink may be important in some orchards. I observed sporadic damage from tarnished plant bug and redbanded leafroller today, and have heard reports of some green fruit worm active in some orchards. The upcoming weather looks warm but not hot, and bloom may be extended so a pink insecticide targeted at those pests if observed in your orchard while scouting may be warranted. Growers in the southern Champlain Valley have likely missed the boat if an insecticide gas not yet been applied since bloom is right around the corner; in the northern Valley, tomorrow May 10 looks like a good day weather-wise to get a spray on if desired. Remember, if you have blooms and/or active bees in the orchard, insecticides must be kept on the shelf for the time being.

This is a good time to focus on in-row weed management, either via herbicides or cultivation. Similarly, nitrogen fertilizers should be going on now, both to the soil and foliar if the latter is desired especially to give cold-damaged buds a bit of a boost. Remember to follow Dr. Wes Autio’s 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.

Many growers have asked about my thoughts on thinning in this complicated year. My advice now (and of course there isn’t anything to do until petal fall at least, I definitely don’t recommend a blossom thinner this year given the low bud count and/or damaged blossoms we’re seeing) is to sit tight and observe: look at your blooms as they open; at bee activity during bloom; and at the weather after pollination windows (you want temperatures >60°F and sun to get optimum fertilization of pollinated flowers). Besides the relatively weak and/or variable bloom in many orchards, most spur leaves have emerged under cool, cloudy weather, and therefore will have thin cuticles and will make trees more susceptible to thinning. Every orchard is different, given the block history, cultivar, tree age, and general health/stress level of trees, and growers should be thinking about thinning needs in their orchards over the next week or so and be prepared to thin cautiously this season.

As always, please refer to the 2015 New England Tree Fruit Management Guide (plus the 2016 updates) for specific spray material selection and always follow the label.

By Terence Bradshaw

As I mentioned Monday, we are in the middle of an extended apple scab infection period this week and trees will require sustained protection to protect against the disease. Our situation is not as bad as in the Hudson Valley, which Dave Rosenberger detailed in a blog post last night, where two inches of rain have fallen since the weekend with another inch expected the remainder of this week. However, trees are expanding leaf tissue every day, and the rain that we have seen (around 3/4”) has removed some residue from previously applied sprays. It would be prudent to apply another fungicide any time this week, and consider applying a material with kick back properties in the tank mix. I agree with Dave’s caution about using captan in tank mixes which contain any materials with adjuvant to reduce potential for leaf burn because leaves which have opened in this cool, cloudy weather have thin cuticle tissue and may be susceptible to phytotoxicity.

At the Hort Farm in South Burlington we are at tight cluster on most cultivars. Any time now would be a good time to apply foliar zinc, boron, and nitrogen. Wes Autio from UMASS has published a good fact sheet on prebloom foliar nutrients here. Soil applied nitrogen and boron applications may also be applied at any time now.

Insect activity should be picking up in orchards soon. Many orchards choose to apply a pink insecticide prophylactically to manage tarnished plant bug and European apple sawfly, but those pests are best managed based on trap capture data. White sticky traps hung three per ten-acre block at knee height for TPB and head height for EAS may be monitored to assess whether populations are above economic action thresholds. Traps may be ordered from Great Lakes IPM or Gemplers and should be hung as soon as possible if they are not up yet. Thresholds for scouted insects may be found here. For TPB, five captured bugs per trap (eight for retail orchards with higher damage tolerance) is the economic threshold for an insecticide spray at pink. At the Hort Farm, only one bug was seen on Monday May 2 on four traps located in an unsprayed orchard, with none observed in managed blocks. Cool weather this week is expected to keep activity low for the time being. EAS are typically managed at petal fall, and threshold for management is nine per trap averaged over all traps in the block for blocks that received a prebloom insecticide or five per trap for those where no spray was applied at that time.

Codling moth is an increasing pest in Vermont orchards and are best managed using degree day models to time insecticide sprays. CM are monitored using wing traps available from the sources listed above. Traps should be hung at pink and monitored daily to record the first moth capture. This biofix date may then be entered into NEWA or used in your own degree day calculations to time management sprays later in the season against this pest. Debbie Breth from Cornell Lake Ontario Fruit Program has a good fact sheet on codling moth and other internal lepidopteran management here: http://www.fruit.cornell.edu/lof/ipm/pdfs/codling_moth.pdf.

Some growers may be interested in using mating disruption (MD) against codling moth this year. We have been deploying MD for several years on an experimental basis at UVM since we had significant damage a number of years ago in the organic orchards, and feel that it has been relatively successful. MD is expensive, however, works best in large contiguous blocks, and should be deployed orchard-wide to be most effective. There is some question about registration status of MD products in Vermont, Eric Boire at Crop Production Services ((802)759-2022) would be a good contact to explore this option further.