University of Vermont

May 7, 2015

by Terence Bradshaw

This is an important week for orchard activities, as you likely know. I’ll try to be brief but thorough:

Apple scab: Depending on whether or not you had green tissue showing on April 23 or (more likely) April 27-28, you may not have even seen an apple scab infection period in your orchard yet. We have had some false alarms as far as predicted wetting events, but things have overall been pretty dry. The chance of rain showers is there on Saturday May 9 and increasing daily through Tuesday, but no widespread soaker is expected, although localized showers may trigger an infection period in your orchard. Ascospore maturity is healthy, although in some orchards which have received no rain for seven or more days, development in the NEWA model has stalled, so the next wetting event will potentially trigger a significant infection period.

Spray conditions are good today Thursday May 6 and tomorrow May 7, with increased winds expected later Saturday and especially Sunday (check the conditions in your orchard prior to spraying, of course). Take home message- make sure you’re covered with a protective fungicide going into this rain event.

Pink-stage insecticides: Many orchards are at pink or approaching it now, and I expect first bloom in the Champlain Valley by Monday or Tuesday. If you have not already brought bees in, and tarnished plant bug or European apple sawfly are a problem in your orchard, an insecticide in the next spray may be prudent.

Fire blight: risk is still looking to be high for fire blight infection when blooms open in most orchards, and any wetting could trigger infection (including heavy dew or a spray application). Be ready to apply streptomycin within 24 hours of a wetting event, and reapplication will be necessary after a couple of days as new blossoms open and the material effectiveness wanes. Remember the conditions required for blossom blight infection: open bloom, wetting, sufficient bacterial population to infect (driven by weather in the past week or so, which has been warm), and warm weather during infection. Cooler weather in the middle of next week will likely reduce fire blight threat, but bloom and wet will likely occur before then.

General orchard activities: water if you can, especially newly planted trees. The potential showers in the next few days don;t look to be enough to give new trees what they need. Now is the time to apply nitrogen fertilizers, including prebloom foliar fertilizers (another thing to put in that pink spray).

May 5, 2015

by Terence Bradshaw

We have run the Maryblyt model for the UVM Hort Farm in South Burlington and, as I had predicted this morning, conditions for infection will occur this weekend if blossoms are open. We may not have flowers showing by this weekend, but growers are advised to be diligent in preventing infection.

This week’s edition of Scaffolds from the Cornell Fruit team has a very good, thorough set of recommendations for managing the disease: http://www.scaffolds.entomology.cornell.edu/2015/SCAFFOLDS%205-4-15.pdf

Good luck with it. As an aside, any comments on blossom stages at your site in Vermont would be helkpful to me in the next couple of weeks.

-Terry

May 5, 2015

by Terence Bradshaw

With the string of warm days that we have been experiencing this week leading into bloom, as well as the amount of fire blight that was around in 2014, I expect that we may be in for a tough year with this disease. I have not yet run the MaryBlyt program for Vermont orchard weather stations, but if you were to trick NEWA by recording yesterday as having bloom in the orchard (most orchards in the Champlain and Connecticut Valleys are at tight cluster), predicted fire blight risk is ‘High’ by Thursday and ‘Extreme’ by Friday and through the weekend. Remember, for blossom infection you need open blossoms (or other wounds, I would avoid pruning right now), heat accumulation significant for bacteria to multiply into an infective population, warm weather during infection, and wetting events. Heavy dew or spray applications may be enough to trigger infection.

First line of defense (after you pruned out all infected wood during the winter) was the copper spray that should have been applied at green tip. In most orchards it is too late to apply copper, except for the highest elevation sites. Do not spray fixed coppers after half-inch green bud stage.

The next step will be to have some streptomycin on-hand to apply within 24 hours of a rain event during bloom (remember, we need open blossoms for infection to occur). Now would be a good time to order your supply.

There is too much to the fire blight disease to discuss in this one notice, please review the pertinent section in the New England Tree Fruit Management Guide if you need a refresher.

We will run Maryblyt later today and I will send updates as the situation plays out.

April 30, 2015

by Terence Bradshaw

Cool weather has kept bud development in orchards behind ‘normal’, and I’m hearing reports ranging from late dormant in high elevation inland orchards through early half-inch green in the warmer valleys. Bud development will be moving fast with expected warm temperatures through Tuesday, when rain showers are expected to arrive. Ascospore maturation is increasing fast as well, and a significant infection period can be expected if wetting hours are sufficient. Because buds are developing so quickly, protective fungicide coverage should be applied as close to Tuesday as possible the ensure that material is on emerged tissue going into the infection period. Most orchards have applied little if any fungicide this season, so coverage will good spray coverage is critical since any ‘base coat’ of material is limited. Saturday through Monday look to have good weather (i.e. low wind speeds) for spray application. The point is, if you are among the majority of orchardists with green tissue showing, you should be applying a fungicide this weekend. With the dry weather and adequate warning going into this event, protective fungicides (EBDCs, Captan or sulfur (for organic growers)) should be adequate. Remember, do not use Captan or sulfur if oil was applied within the past 7 days.

Green tip through tight cluster is a good time to apply nitrogen fertilizers in the orchard. Applications are best informed by foliar nutrient analyses which should have been conducted last summer. Many orchards on heavy soils with high organic matter content may not need any nitrogen applications in most years. Another concern is that overapplication of nitrogen may increase susceptibility of trees to fire blight infection. A conservative rate of nitrogen to apply in most orchards is 30 of actual nitrogen per acre. Recommended fertilizer materials can be found in the 2015 New England Tree Fruit Management Guide.

I go away for a week and nothing happens in the orchard. Not quite, but with the cool weather, trees have been advancing slowly. We reached green tip on McIntosh on Friday, April 24 at the UVM Hort Farm in South Burlington. This signals the real start of pest management season for us. Other, warmer sites likely had green tip earlier and I have heard a few reports of half-inch green showing.

Last week’s rains likely occurred before emergence of green tissue susceptible to apple scab, but rain today and tomorrow cause enough wetting for an infection period. Estimated ascospore maturity based on degree day modelling is relatively low right now at 2-3%, but actual maturity may be higher. If you sprayed copper in the last week, you should be okay, but if not, and significant wetting occurs, application of a fungicide with kick-back activity may be important, especially if you had high levels of scab last year which would provide ample inoculum for infection this spring. Strobilurin and DMI fungicides may be effective if resistance is not an issue in your orchard, but they would be better used later in the season when their activity against other diseases that aren’t yet a threat such as cedar apple rust and powdery mildew are active. The anilinopyrimidine (AP) fungicides Scala and Vangard would be better choices now because they are effective at cool temperatures (<50 F) and have little to no activity against fruit scab which limits their at later times. Kick-back fungicides should be combined with at least a half-rate of a protectant material (EBDCs or Captan, but no Captan within 10 days of an oil application) to reduce development of resistance in the local apple scab population.

White rectangle traps may be hung at three traps per ten acre block any time for monitoring tarnished plant bugs in the orchard. A cumulative capture of three bugs per trap for wholesale orchards or five per trap for retail orchards by tight cluster may indicate a need to treat before bloom.

Weather continues to look good for tree planting this week.

-Terry

Friday, April 17:

I will be away starting Saturday April 18 through the 25th. I am sending this notice in anticipation of activity next week in my absence, but please recognize that it is made based on a fairly long-range prediction.

We have seen no green tissue yet in South Burlington on any cultivars, and most are at early/just barely silver tip. Degree day accumulation since January 1, base 43 F is just about 47, and green tip is expected at about 100. Warmer sites than South Burlington have little more accumulated degree days, including Dummerston (50) and Shoreham (54). Other sites are at or below this level generally. Daily accumulations are in the 5-10 range when temperatures range from lows in the 30s to highs in the 60s. This is all estimations, guesses, and (informed) conjecture, but the point is that there is little to no green tissue out there now, and I don’t expect much development over the weekend, although the warmest sites may see some green tissue by Monday.

Next week we’re expecting two days (Monday & Tuesday) of rain followed by three days of showers, all with highs in the 50s and lows in the upper 30s and low 40s. Bud stages will advance slowly, and although scab ascospore maturity is likely very low to zero as of today, the fungus matures just a little faster than your trees so that when green tissue emerges, mature inoculum may be present in the orchard.

I recommend that growers in the Champlain and Connecticut Valleys use any time this weekend or between rains next week to get a copper fungicide on for management of fire blight, which will also buy you a week or so of time before scab season really hits. If you have time, go slow and add your spring oil treatment to thoroughly wet the canopy at dilute-2x concentration. If green tissue emerges by mid-late next week and copper coverage was questionable, nonexistent, or washed off from 1″ or more of rain since application, and you had any scab last year (or didn’t conduct a thorough evaluation in fall to assess), you may want to follow up with a kickback fungicide after the rains stop. Vangard and Scala are recommended particularly for the cool weather that is expected next week.

Anything else I offer is pure speculation based on very extended weather forecasts. Keep your eye on NEWA in the coming weeks (I mean every morning), there are a few new stations that have added in recent years. If you need to extrapolate very far for a station, and that includes on host site farms with varied topography, remember that NEWA is just one tool to help you in your pest management decisions, but to also use your experience and to trust observation made on your own farms.

I’ll make another plug for the 2015 New England Tree Fruit Management Guide, which has the specific answers an any materials I have suggested or alluded to.

Other activities next week: if your site is prepped, it looks like good timing to plant trees. If anyone is planting cider apple trees, please let me know what you have and how you have planted them, and I may also be able to visit when I get back. We need to set the stage for good cider apple research now so that it may pay off down the road in good, scientifically-sound research results.

Thanks. Remember, I will not have email access next week, so avoid sending me anything until April 27. Questions regarding spray guides or administrative issues can be sent to Sarah Kingsley-Richards at: skingsle

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The UVM Apple Program is supported by the University of Vermont Agriculture Experiment Station, a USDA NIFA E-IPM Grant, and USDA Risk Management Agency Funds.