Overview: Dry weather over the past few weeks have provided good conditions for copper and oil applications for disease, mite and scale management. Now that green tissue is showing, our options for controlling both arthropods and disease become more challenging.
For blocks that had San Jose scale (SJS) at pack out, multiple strategies should be considered and employed to manage SJS this season. Focusing on the pre-bloom period:
• Oil at 2% HIG and 1% TC on through the season will provide mite suppression and significantly reduce SJS. Yet, excellent coverage is essential for oil to smother European red mite eggs and scale as temperatures rise and as insects respire. Caution is recommended for applications this week as predictions of 28F and freeze events for Monday, March 30th will increase the chance for absorption of copper with oil leading to toxicity of green tissue. The same holds true for the use of Captan over oil residue. Uptake of these materials are phytotoxic to plant tissue if absorbed by developing foliage, resulting in deformed cluster leaves and loss of optimal photosynthesis for newly developing fruit and newly planted tree extension growth.
• Esteem 35WP @ 4-5 oz./A, Centaur 0.7WDG @ 34.5 oz./A, Sivanto Prime @ 10.5-14.0 fl.oz./A or Lorsban 75WG 2.0-2.67 lb./A will provide commercial control of SJS applied at the pre-bloom stage of apple. Additional strategies using Movento at petal fall and during the emergence period of SJS crawlers using contact insecticides should also be considered.
Fire Blight: As we now move past the dormancy and silver tip stage of apple into early green tip, copper will redistribute from rains over the past 48 hours to reduce early infections of apple scab and kill off inoculum of fireblight from cankers residing within the orchard.
Last year was a difficult year for growers given freeze events, hail and widespread fire blight, which warrants the use of copper in many orchards this season. Yet temperatures below 32F are predicted for Monday evening. If oil is used with copper and applied to green tissue on either side of freeze events, then copper ions will enter the plant tissue, killing plant cells. Postponing copper and using low rates of oil for later in the week should be strongly considered.
The majority of copper products used in tree fruit production tend to be “fixed” or relatively insoluble in water and safer to plant tissue. When added to water fixed copper becomes a suspension of copper particles. As the copper particles are stable on the plant surface, residing on the surface of leaves, stems and branches as the application dries, the copper ions are ‘released’ slowly, reducing the risk of phytotoxicity while providing residual disease management.
Some points to keep in mind this spring regarding copper.
(excerpts from Dr. D.R. Rosenberger (Scaffolds March 12, 2012, pg.6-9)
1. ‘Solubility of fixed coppers increases under acidic conditions. As a result, copper sprays will become more phytotoxic if they are applied in an acidic solution. Acidifiers such as LI-700 and non-buffered phosphite fungicides should not be tank-mixed with copper fungicides.’
2. ‘When buds are already showing green tissue, do not apply copper just prior to predicted frosts because the cells ruptured by frost crystals may resorb and be killed by the copper on the bud surfaces.’
3. ‘Adjuvants have highly variable and largely unpredictable effects on the efficacy of copper sprays. We know from years of experience that copper products can be combined with oil in delayed dormant or green tip sprays if oil is being applied to control mites. Otherwise, using one quart of spray oil per 100 gallons of finished spray solution may enhance coverage of the wood in these early season sprays, but using higher rates of oil does not “lock in” the copper deposits to enhance residual activity. No other adjuvants are necessary or recommended on tree fruits.’
