I am trying out some 21st-century technology this week. First, I dictated my message while on my commute (with light editing), so the ‘writing’ style and length may be a bit different than folks are used to. Second, I recorded an update from the UVM orchard and placed on our YouTube channel. I intend to get one of those out on a fairly regular basis. Feedback is always welcome.-TB

Green tip bud stage was reached on McIntosh apples at the UVM Horticulture Research and Education Center in South Burlington today. This means that the active management season for apples has begun at our farm and likely has on many other farms around the area. Most farms in lower elevation warmer sites will see green tip by the end of the week; many upland sites may see it a bit after that. This stage is important because it signifies that there is susceptible tissue that can be affected by apple scab fungus. The fungus that causes apple scab and the apple tree co-evolved such that their early season lifecycles are very much in sync. The degree day model that we use to predict ascospore maturity and release starts at green tip on McIntosh and continues for roughly 900 degree days (base 32°F) after that. After this amount of accumulation has been reached, assuming normal conditions in the northeast regarding rainfall and humidity, we can assume that the overwintering inoculum for the apple scab disease has matured and will be released in rainfalls that occur during that period.

Under older conditions, growers were encouraged to maintain protective fungicide coverage from green tip through the end of ascospore release which commonly occurred around early to mid-June. However, a number of things have changed. The ability to closely monitor ascospore development and infection conditions using models such as those in the NEWA system allows us to better time our fungicide applications and reduce unnecessary, prophylactic treatments. We also have seen the bacterial disease fire blight increase in incidence in New England in the past 20 years. Fire blight can be considered essentially ubiquitous in the environment at this point, although it does not always reach infective potential many orchards. One of the key management techniques targeted toward fire blight is a delayed dormant application of a copper-based fungicide, which helps to reduce inoculum on the surface of plant tissues. This treatment, while technically still a chemical, is a relatively weak apple scab fungicide. However, the typically lower levels of mature ascospores, low amount of susceptible tissue exposed in the early season, and relatively cool temperatures experienced in early spring have typically lead growers to utilize this first fire blight management spray as their initial apple scab fungicide. If scab was relatively well-managed in your orchard last year, an application of a copper fungicide at full label rates should be sufficient to manage the disease for the next 7-10 days as long as it is applied before one quarter inch of green tissue is showing when looking at fruit buds from the side. That means there should be no leaves exposed from the emerging buds. Application of copper too late in the bud development can cause significant fruit russeting that can reduce the market value of your crop. This is an ideal week to treat orchard in the warmer production areas in the states with copper.

I have recently observed high levels of mites or scale insects in many orchards and how much of this due to reduction in the use of dormant or delayed dormant oil applications. While treating your trees with copper fungicide, it would be a good idea to include horticultural oil at a rate of 2% by solution (2 gallons in 100 gallons of actual spray material applied to the trees). Oil should be applied with very thorough coverage; I recommend 100 gallons of water per acre to fully saturate the trees. Oil works by physically smothering eggs and developing overwintering scale insects and therefore must thoroughly cover them to have affect. Oil should not be applied to orchards within 48 hours before or after a freeze event. Again, weather this week is conducive to oil application for most of the stakes, as we are not seeing significant risk of frost or freeze for the rest of the week.

Things tend to be pretty quiet on the insect front in this early season. Some growers may choose to hang white sticky cards at knee height in their orchard at about four traps per 10 acre block to monitor for tarnished plant bug. However, the vast majority of orchards in Vermont sell their fruit as pick-your-own or direct farmstand sales, and in my opinion TPB damage is insignificant and strictly cosmetic that should not need management for those that sell through those direct markets. For other farms that sell to wholesale markets, TPB can significantly reduce fruit quality that could lead to rejected fruit, so it may be managed on those farms. I recommend hanging TPB traps after the application of any copper fungicides in order to reduce the amount of spray that could make it difficult to read traps or make them less attractive to the insect. Pre-Bloom insecticide application for TBP may be warranted if there are more than three bugs per trap trapped in any given week. In order to reduce the likelihood of residues toxic to pollinators in apple pollen, I do not recommend the use of neonicotinoid insecticides (IRAC group 4A) prior to bloom. That leaves pyrethroid insecticides as the primary class that is typically used to manage TPB and other pre-bloom insects.

This is the perfect time to be preparing your soil and planting trees. When trees are planted in spring, growth in the first year is significantly better if planted during cool weather when roots are allowed to get established in soil before there is significant leaf and shoot development and therefore water and nutrient demand from the top of the tree. Ideally, apple trees should be planted by May 15, and certainly by the middle of June. For all new trees, whether on dwarf or semidwarf rootstock, irrigation should be immediately applied even if only only as a good thorough soaking from the water tank.

The UVM Tree Fruit and Viticulture Program is supported by the University of Vermont Agriculture Experiment Station, UVM Extension, USDA NIFA E-IPM Program, and USDA Risk Management Agency.

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