University of Vermont

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.

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