University of Vermont

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.

By Terence Bradshaw

Forwarding from University of Connecticut Fruit Extension Educator Mary Concklin:

Attached is a guide for foliar nutrient applications based on an identified need as well as foliar nutrients and PGR for situations where buds have been damaged from frost and/or freeze situations such as we have had this spring.

Tree Fruit Foliar Nutrient Applications and Nutrients & PGRs for Frost-Freeze Situations.pdf

By Terence Bradshaw

Apple scab primary ascospore development is moving along in Vermont orchards, with most orchards having approximately 8-15% mature spores according to NEWA models. This will likely be our first significant infection period of the 2016 season, and growers should be prepared. Bud stages are all over the map right now depending on location, from earliest green tip in the colder uplands to late half-inch green tip / early tight cluster in the warmest valleys. Winds look a bit on the high side today but drop down to reasonable levels for spraying by late afternoon/this evening and through tomorrow, so this looks like the best window to apply protective materials.

By Terence Bradshaw

April 15, 2016

By later today most orchards in the Champlain and Connecticut valleys and Bennington area should be into green tip and disease management activities will need to commence soon for the 2016 season. The weather forecast for rain on Monday has been somewhat inconsistent with chances decreasing since last night, but growers should be ready for when any rains do come. That said, aside from the 30-40% chance called for on Monday, next week looks relatively dry. Depending on when we assume mature scab ascospores to be present in the orchard, we may have 2-6% ascospore maturity by Tuesday in most orchards. That may not seem like much, but many orchards had significant scab last year and 2% of a lot is still quite a spore load.

The threat of freezing weather is diminishing with forecast lows above freezing in the major fruit growing regions of the state after tonight. This means that both copper and oil should be okay to apply starting tomorrow through next week. I have seen and heard of increasing problems with San Jose scale in Vermont orchards, and a thorough oil application is the first line of defense against those insects as well as overwintering mites. Horticultural oil should be applied at 2% volume and in as much water as practical, certainly no less than 100 gallons per acre and more if you can on larger trees. This means slower travel and more refilling of the tank, so plan accordingly. Copper is the first line of defense against fire blight and while that disease was not present at high levels in Vermont orchards last year (in general…), it is out there and has become an increasing problem in the state in the past decade. A copper spray will also provide about seven days’ protection against apple scab and can be combined with oil. Fixed copper materials are best at this time, and specific materials and rates can be found in the 2015 New England Tree Fruit Management Guide. Care however must be taken with copper application, as the danger of phytotoxicity increases after green tip and especially by half-inch green tip. My suggestion is to get out there as soon as possible starting tomorrow and cover the whole orchard with a copper-oil mix before buds advance too far. When using oil, it is important to not use Captan for 7-10 days to avoid phytoxicity.

For orchards that have green tissue and were not covered with a fungicide, if an infection period occurs on Monday-Tuesday April 18-19, a kick-back fungicide may be called for to prevent infection because copper has no post-infection activity. The anilinopyrimidine (AP) fungicides Vangard and Scala have decent (48-72 hour) post-infection activity, work well in cooler weather, and are poor on fruit scab and are therefore good choices to use early in the season. Like all post-infection materials, there is potential for resistance development to the fungicide in local scab populations so a tank mix with a contact fungicide is recommended. I do not know of issues with copper and AP compatibility although there are no warnings on the label. If not using copper at this time, then mancozebs are another good material that will provide some protection against the disease (but have no kick-back activity of their own).

After this current round of treatment is completed, growers should begin their early season fungicide schedule going into the following week. Generally the mancozebs are the best candidates for maintaining protective coverage, although total use restriction must be followed (i.e. no more than four sprays through bloom at the six pound per acre rate of Manzate or equivalent or seven sprays up to the 77-day preharvest interval at the three pound per acre rate). After the seven-day ‘embargo’ following an oil application, Captan may also be used either alone or in combination with mancozeb (using a half-rate of each). If using Captan, recognize that there is a 40 pound per acre seasonal limit, so early season uses may limit its use later in the season for secondary scan and summer disease control.

Organic growers of course will be limited primarily to elemental fungicides including copper (apply that now, by the way) and sulfur materials. After the seven-day window that you buy with a copper spray, elemental sulfur applied at ten pounds per acre on a weekly basis or more often if more than one inch of rain falls is the primary line of defense against apple scab on susceptible cultivars. Growers do have the option of using liquid lime sulfur which has some post-infection activity but is very caustic, phytotoxic, and frankly nasty to apply, so good preventative coverage with elemental sulfur is important to manage the disease.

As always, apple scab and other pest management decisions should be made using best information on the conditions in your orchard. The apple scab primary ascospore infection season lasts roughly from green tip (judged by 50% of McIntosh buds having reached that stage) through 900 degree days base 32°F. Growers located near a NEWA station may use the models for the station closest to them, with the caveat that they may not be exact for their specific site. When using the scab model for a particular site, NEWA asks for a green tip date to be entered, and the default date is quite a bit ahead of what we are seeing in orchards. That said, entering an earlier date will allow you to be more conservative regarding ascospore development early in the season. For example, the default green tip date for Putney is March 30, which estimates 6% ascospore maturity by April 20, whereas entering a date of April 15 gives an estimated ascospore maturity of 2%. The only way to truly know the ascospore maturity level in orchards is to perform spore trapping or squash mounts using a microscope and very exacting and time-consuming technique, which is rarely done. The models are just that, computed estimates of biological activity in the orchard and only output what the model and entered conditions tell it to. That said, we know we are entering the scab season for this season, so growers should plan to apply coverage through the end of primary ascospore release. However, as we know that leaf wetness is required to initiate scab infection, extended dry periods will reduce the need for preventative coverage, but growers should be careful to not get caught entering a wet period without any coverage on trees.

New NEWA stations in Vermont! This spring we have brought one more NEWA station on-line in Bennington and have moved the Calais station from my house to a relatively new orchard in East Montpelier, which brings the total number of NEWA stations to ten, in addition to the airport sites located around the state. Remember that airport sites do not have leaf wetness sensors so apple scab and other disease models requiring that information cannot be run, but insect models will function fine.

Best wishes and good luck on the start of the season.

-TB