Silver tip and green tip have arrived in most apple orchards and cultivars throughout NC. Given the importance of late silver/green tip applications for canker blight management, if you haven’t done it yet, this is a perfect time to dewinterize your sprayer and get it calibrated. For further information on airblast calibration, check out the 2020 SE Orchard Management Guide or contact your local extension agent.
The primary goal of disease management programs at late silver tip and early green tip in apple is to protect against fire blight cankers that will begin to ooze later in the season (likely not before pink bud or bloom) as well as protecting against early primary apple scab infections. A full rate (the higher rate on the label) of a fixed copper (e.g. Kocide 3000, COCS, Badge + several others) should be applied no later than green tip. Delaying applications of copper until 1/2″ green tip or beyond will increase the risk of chemical damage to developing tissue. Coppers that are “fixed” are more insoluble in water than soluble coppers (e.g. copper sulfate), which means that they should persist on leaf tissue longer during a rain event. In fixed coppers, copper ions, the toxic component of copper fungicides, will slowly be released during wetting events which is advantageous when you consider the time period between green tip and pink/bloom may be greater than 30 days. When applying copper at late silver/green tip, consider the following: Always follow the label-It’s the law. Choose spray adjuvants wisely (or do not use them at all). Penetrating adjuvants or those that cause excessive wetting can enhance the penetration of copper into leaf tissue (which is where you don’t want it to be). Check the pH of your spray solution. Low pH will result in coppers becoming more soluble and thus could reduce the residual activity of the fungicide and enhance the potential for phytotoxicity. The addition of hydrated lime can raise the pH of spray solutions, and can also assist in “fixing” more soluble coppers. Check with your chemical sales rep to determine if you should add hydrated lime to your copper application. Avoid applying copper under slow drying conditions. Again-Do not apply high rates of copper after green tip!
Below is a list of example coppers and rates of these coppers registered for management at the silver tip/green tip stage. As always, read the label before application.
Some Cultural Measures to Consider
Instead of binge-watching Netflix shows during the current outbreak, there are also some cultural steps you can take to help limit early infection:
- Remove fruit mummies. Mummified fruitlets can harbor several pathogens including Botryosphaeria (white rot, frogeye leaf spot and black rot), Colletotrichum (bitter rot), and I’d suspect even fire blight. Even if you can’t destroy them, the simple act of removing the mummies and tossing into the row middles should help limit spore spread.
- Prune out cankers. Yes, this should have been accomplished prior to green tip, but it’s not too late! Pruning cankers will help limit local fire blight inoculum which in turn should lower your risk of blossom blight infections.
- Apply urea and flail mow leaf litter. Again, likely should have been accomplished earlier, but you should get some boost in reducing the inoculum of pathogens causing apple scab, Glomerella leaf spot, Alternaria leaf blotch, Marssonina leaf blotch, plus other foliar diseases.