University of Vermont

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.

By Terence Bradshaw

Rainfall beginning yesterday May 1 which will extend through today has caused an apple scab infection period is virtually all Vermont orchards. Rainfall amounts range in the 0.1 – 0.5 inch range, which would not be enough to wash off a well-applied fungicide spray made just before the wetting period. If there is any question about coverage for both the current infection period as well as the expected extension of it with more rain expected Tuesday night through Thursday, tonight and tomorrow May 3 are your best window to reapply. There are a lot of mature ascospores out there, don’t be lulled into thinking that you’re okay to slide on this one because we’re still early in the season. Best products would be a protectant (mancozebs, captan; sulfur for organics growers) plus I would consider a material with post-infection activity such as an SDHI or (if they still work in your orchard) DMI. Alternately, the post-infection material could be applied Friday after the infection period, but if you’re relying on that solely to cover newly emerged tissue with no fungicide residue or to make up for poor coverage from your last spray, you’ll be using the materials at the very edge of their efficacy and encouraging resistance development.

For organic growers, if a full application (10 lb/ acre) of sulfur was made prior to the rains, I would consider making another touch up application at 5-7 lb/acre to cover new growth and compensate for washoff. If you had poor or questionable coverage, lime sulfur may be used and will provide kick-back activity and protection through the end of the week’s rains, but it’s a material best used sparingly so plan to keep covered with sulfur for future infection events.

Foliar nutrients can start any time you have sufficient foliage to provide for uptake, I would recommend applying at tight or open cluster through pink. Zinc and boron are important minerals which will help trees recover from cold damage, and nitrogen is needed at this time of year when rapid growth taxes tree reserves. Refer to Mary Concklin’s quick summary here for more information: http://blog.uvm.edu/fruit/files/2016/04/Tree-Fruit-Foliar-Nutrient-Applications-and-Nutrients-PGRs-for-Frost-Freeze-Situations.pdf

Greetings.

The UVM Apple Program is seeking THREE volunteer orchard managers to participate in an Integrated Pest Management Assessment. Selected participants will receive personalized, one-on-one consultations to address their pest management needs. We will only be selecting three participants from interested respondents for this round of the program. This is a great opportunity to review your pest management practices and discover areas to improve IPM on your farm.

How this works:

1. You will complete a short online survey of yes/no questions based on an NRCS and UMASS instrument about your pest management practices.

2. Answers will be collected by the UVM Apple Program.

3. Specific practices will be assigned points based on their importance to an IPM system.

4. Total points scored will be used to determine your current IPM needs.

5. UVM Apple Program staff follow up with a consultation to assist with IPM implementation on your farm.

6. An follow-up assessment will be conducted after harvest to assess impacts of IPM educational efforts.

The assessment includes a series of research-based best management practices encompassing soil and nutrient management; cultural practices; pesticide application techniques, record-keeping, tactics for insect, disease, and weed management; and grower education.

By participating in this assessment, you will also be helping the UVM Apple Program to evaluate the usefulness of this tool for future IPM education and outreach efforts.

–> If interested, please contact Sarah Kingsley-Richards by May 6 at sarah.kingsley@uvm.edu.

By Terence Bradshaw

Even with the best expert systems, on-farm weather stations, and predictive forecasts, sometimes we have to rely on common sense when making management decisions in the orchard. The forecast for most of Vermont is for rain showers to begin Sunday, with higher likelihood in southern Vermont. By Monday, we’re looking at 50-60% chances. With average temperatures around 50°F, we only need 11 hours leaf wetness to cause an infection, and at 57° that lowers to seven hours. Primary ascospore maturity is estimated at around 25% by Sunday, which presents a very good load of inoculum for infection.

However, NEWA is not predicting an infection period for this weather event. (You’ll notice an April 1 date entered for green tip, I did this to be conservative in estimating ascospore maturity development to reflect the weather in early April conducive to spore maturation which has a base temperature of 32°F vs 43° or so for tree bud stage development).

On the other hand, I am running a trial of another proprietary modelling system from Europe, RIMpro, which uses a different forecast model and predicts a pretty significant infection event:

I am only running this at two sites in the state and don’t have the ability to make it ‘live’, so I’m using it as supplemental to NEWA for now. The graph has a lot of information: rain and leaf wetness at the bottom in blue, and various stages of spore release, germination, and development in the curves above the maturation chart. The red “infection value” line represents the overall risk for infection, and anything over 300 is considered a severe infection risk in unprotected orchards. The white portion of the curve represents germinating spores that may be susceptible to contact fungicides, the orange curve represents spores that have developed primary stroma into leaf tissue and the beginning of ‘infection’.

Since we’re pretty early in our use and interpretation of this system, and it is all based on predictive weather data ay our specific site in South Burlington anyway, please don’t take the model as indicative of actual orchard conditions yet. That said, there appears to be good likelihood of a potentially severe infection period starting Monday. In general, calm winds are expected over the weekend so there should be ample time to get a protective spray on. However, overnight and early morning temperatures are expected to be below freezing, so follow the usual precautions: no oil application, avoid captan as well if possible, and protect pumps, booms, and lines from freezing.

By Terence Bradshaw

Despite my warning from Sunday about an impending apple scab infection period early this week, the cool/cold temperatures and short wetting event associated with yesterday’s snowfall (!) did not trigger infection in any Vermont orchards. At this point, most orchards have not experienced an infection period yet this spring. Dry weather is expected through the weekend, so sprayers can be put away for the time being and attention turned to planting trees and watering. Soil conditions are dry across the state, and developing fruit buds will tax moisture resources in some orchards. Newly planted trees especially should receive water, as well as high density plantings. Next week looks showery, so plan on protecting against the next infection periods prior to the arrival of the wet weather.