Delayed Dormant Copper and Adding Oil or Not and How Much?

A standard recommendation for delayed dormant copper is applying it on apples between Silver Tip and until but not beyond quarter inch green tip (QIG). QIG is determined by looking at the floral apple buds which are wider in appearance and situated on spurs. Leaf buds are pointy and narrow instead. Looking at the a floral buds, QIG is an apple growth stage which ensues when 50% of floral buds are open and visibly expressing the stage QIG. Applying the copper after 50% QIG stage is a risk for bud injury and fruit russetting later on. If you decide to risk it and to apply copper at the 1/2-inch Green Tip (HIG) i.e. later than QIG, you should definitely see first if the label allows this growth stage use, and if yes, then use the so called “softer” formulations like Cueva, or use much lower equivalent metallic copper rate per acre of your copper material of choice. There is a risk from many factors to allow copper to injure buds or cause fruit skin rusetting later:

– Did you read the copper pesticide label and checked if HIG stage is allowed for application of that specific material? Which rate? If not, do not use it at this stage.

– Did you count the buds in a sample of 100 randomly chosen buds walking through the orchard and tallied buds in 5 categories: Dormant, Silver Tip, GT, QIG, HIG, and did your tally show 50% of buds HIG? If you are anywhere beyond 50% of buds at HIG, you risk an injury by copper. Do not use it, if you were late to spray.

– Did you fix your sprayer on time and got it calibrated i.e. up and running before the window between Silver Tip and QIG? If you did, go for it, but if not, do not risk to apply the copper material not labeled for HIG stage use just because your tractor or sprayer was not ready on time.

– Did you look at the ruts in the orchard, is it muddy from this week’s rains? Or the oncoming weather forecast shows we will have days with slow drying conditions? Be tactical: muddy midrows might delay you to apply copper pushing you to do it beyond QIG risking bud injury, or if slow drying conditions are oncoming based on weatehr forecast, reconsider applying copper, choose lower rate, or use less injurious formulation of the copper.

We just do not recommend applying copper beyond QIG as we do not know what weather conditions we will have ahead. Even very low rates of copper are risky in slow drying conditions which can can cause copper to trigger fruit russetting (you wont see it now, it will be later, when fruit enlarge beyond 20 mm). If you have an orchard that had fire blight last year, you should definitely consider applying copper this year from silver tip to QIG bud stage, but you do not need to apply it necessarily, if you had no fire blight and you had no scab last year in that block. Also, do not apply copper near frost events (I hope we do not have any this spring). If you are at Green Tip and up to QIG, and you want to apply delayed dormant copper, it is not advisable to apply copper and/or oil in the situations where hard frosts are announced. Anything spray-applied on the plant surface, following freezes, will get sucked into the green tissue plant cells as frost crystals melt and injure the bud tissue. Oil or copper, alone, can exacerbate frost injury, but mixing them together is potentially even more damaging to injured green tissue by frost. Although, we can’t say we have seen injury of this mix after frost, being worst than either compounds alone, it is concerning to apply this mix near a hard frost.