By Terence Bradshaw

It didn’t take long after I posted my last recommendations for someone to point out to me that it’s unlikely that apple scab ascospores can be released through two inches of snow. Point taken. This cool weather has put things into that slow, on-hold pattern a bit, but activity will pick up today and tomorrow as temperatures get into the 50s. In warmer southern Vermont predicted ascospore maturity is getting up around 10%, which is when we should be taking scab more seriously. In the Champlain Valley, where ascospore maturity is estimated around 5-7%, buds appear to be hovering around the half-inch green stage. Upland and inland, still at silver tip. Rains Sunday and Monday are expected to bring an infection period, so orchards with significant tissue exposed should be covered with a fungicide in the next two days.

Weather is looking good for oil application today and tomorrow, assuming that your site isn’t expecting freezing weather in the next couple of days. I am a proponent for putting oil on as late as possible, up to tight cluster or even pink. The rate should be adjusted down as buds open more: 2-3 gallons per 100 gallons water (straight % in tank, not adjusted for tree for volume or per acre) is good from dormant through green tip; 2 % GT-tight cluster; and 1% as you approach pink. Oil should be put on dilute- slow down and open up your nozzles if you can. For most orchards, 100 gallons of water per acre should be the minimum for applying oil. That means recalibrating your sprayer in many cases.

For growers with substantial bud development and concern about cold temperatures the past week, you may want to pinch some buds and look for browning in the developing ovaries…or not. There’s not much you’ll do about it now, anyway, but come bloom, it would be wise to observe flowers and be ready to adjust thinning if more than 20-30% damage is observed. I’m pretty hopeful that most sites have been fine, the critical temperature for 90% bud kill at tight cluster is 21°F, although some damage may be seen at 28. For half inch green, we can expect buds to be all right down as low as 23 or even colder. Trees at silver or green tip should be fine. Remember, if you suspect bud damage from cold temperatures, it is important to contact you crop insurance agent ASAP to get the claims process started.

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

The label is the legal document for the product use.

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The UVM Tree Fruit and Viticulture Program is supported by the

University of Vermont Agriculture Experiment Station, a USDA NIFA E-IPM

Grant, and USDA Risk Management Agency Funds.

By Terence Bradshaw

Here’s a real quick update. Bud stage in warmest Vermont orchard sites is around half-inch green (HIG). At that point, copper should not be applied unless you know the crop is going to cider, as copper applied at any effective rate for this time of year will russet the fruit finish. Frost is expected, again, the next few nights. At HIG, buds are hardy to around 20°F. I see no immediate issues in that regard. But, frost means that oil and/or captan should not be used in the orchard, at least until late next week. Early season scab fungicides of choice should be mancozeb or scala/vanguard. Sulfur, of course, is the main material for use in organic orchards.

In the Champlain Valley, we’re still closer to green tip for now. That means that copper is still a viable material, but be sure to not apply it after the first two “mouse ear” leaves emerge from the bud. See the bud stage link (above) for a visual. Otherwise, default to those listed above.

Buds are around silver tip or even dormant in upland and inland sites. Hold tight there, although you could get a prophylactic copper on for fire blight, but that won’t help much against scab.

BUT, this doesn’t suggest that anyone needs to spray. Modeled ascospore development is around 1-7%, more in southern areas. Potential for rain is pretty solid today and fairly spotty until midweek. You need rain and extended wetting to cause infection. Here’s my take: orchard at HIG or later should maintain coverage, especially if you have an orchard that takes substantial time to spray. Time it as close to rain as possible; if you were uncovered going into today’s rain, cover as soon as this rain is done with a protectant + Vangard or Scala for some kickback. If you were covered or are in one of the lower risk sites (decent scab control last year, green tip or earlier bud stage), hold off until we get a better idea of the chance for rain later in the week. Of course, use NEWA to keep an eye on scab development in your area.

Insect notes: if tarnished plant bug is a concern in your orchard (less so in pick your own than wholesale orchards), then get traps up soon. We use white sticky traps from Gemplers or Great Lakes IPM. Set three per block, knee-high, on a lower scaffold out in the drive row. Check weekly, giving enough time to apply prebloom insecticide if needed. Trap thresholds are listed in our monitoring guide located here. Print that out and out it on your wall in the shop.

If you’ve had mite or scale problems, think about your options for managing them in the next few weeks. Oil is a great first line of defense, but if you have high populations, especially of scale, you may need to consider adding a stronger material prebloom. Esteem is most recommended for scale, applied around HIG to tight cluster. If mites have been a problem, there are a number of materials available for prebloom use, you’d best check the New England Tree Fruit Management Guide for recommendations.

Be safe out there.

Terry

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

The label is the legal document for the product use.

Disregard any information in this message if it is in conflict with the

label.

The UVM Tree Fruit and Viticulture Program is supported by the

University of Vermont Agriculture Experiment Station, a USDA NIFA E-IPM

Grant, and USDA Risk Management Agency Funds.

By Terence Bradshaw

Yesterday, April 9, we ‘called’ green tip at the UVM Horticulture Farm, orchards. This signals that buds are beginning to open, and therefore green tissue is present that may be susceptible to apple scab infection. The apple scab ascospore maturity model, which predicts the presence of mature overwintering inoculum that could infect, given appropriate weather conditions, uses ‘McIntosh’ green tip as a biofix to start accumulating degree days. It is best to record your own green tip date, and if you are using NEWA to track infections, use the station that is closest to your farm (or buy your own station, and I can help you to connect it to the NEWA network).

Presently, the orchards in the warmest parts of the state (Bennington and Putney) are predicting 2-5% of ascospores mature; in Addison, Chittenden, and Grand Isle counties, it’s more like 1-2%. Inland and upland sites likely aren’t even at green tip yet, but will likely advance once the warm weather returns. What does this mean? In warmer areas, I would get copper on as soon as you can get in- remember, after the buds reach ½” green tissue, your window for high-rate copper is closed. Wind is looking pretty fierce on Monday (rainy too) and Tuesday, and both of those days look to be in the 50s-60s. So I’d try to get some copper on this weekend. Hold off on oil, as it’s looking like frost conditions Saturday night. For orchards that are closer to the very beginning of green tip and which have less chance of advancing beyond half-inch green on Monday and Tuesday, I would wait until Wednesday or so and apply copper (and oil if you can). For inland and upland sites with no bud break- hold off.

It’s important to recognize that early season infections when <5% of ascospores are mature typically won’t cause much if any scab, especially if your inoculum is low to begin with. Some orchards had terrible scab problems last year, and if you had any noticeable scab, assume that you’re high inoculum and need to take a more conservative strategy this year. But, if you had low scab (as in, none that you know of), and/or you perform orchard sanitation, you can relax a little bit in the early season. You still have time to flail mow leaves and / or apply urea to the orchard floor to reduce scab load for this year. However, copper is important not just as a (relatively weak) scab protectant, but also as a fire blight management tool, so I strongly urge growers to get copper on before the window closes if you’ve had any whiff of that disease in the recent past.

Don’t Forget- The New England Tree Fruit Management Guide is now housed at: http://netreefruit.org.

-Terry

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

The label is the legal document for the product use.

Disregard any information in this message if it is in conflict with the

label.

The UVM Tree Fruit and Viticulture Program is supported by the

University of Vermont Agriculture Experiment Station, a USDA NIFA E-IPM

Grant, and USDA Risk Management Agency Funds.