Due to the presence of green tip on early varieties of apples combined with recent rain, we are in our first apple scab infection period for 2016. Extension Horticulturist Kari Peters tells us protection is needed for vulnerable green tissue; a copper spray will be useful for trees not at green tip.
Thanks to the early spring weather last week, some degree of green tip is occurring throughout Pennsylvania and Maryland. Last week’s scab spore test was not a fluke and Peters recovered mature spores from scabby overwintered leaves from the 2015 season.
Don’t be fooled by the cooler weather and think apple scab infection is not an issue. If the temperature is averaging 45 degrees, 18 hours of leaf wetness is needed. Since it has been persistently wet since March 13, it hasn’t taken long for leaf wetness hours to add up. At that temperature and wetness hours, symptoms will show up in about 17 days. We do have a little bit of a silver lining: since last year was a relatively light scab year, we are coming into this season with less available scab spores ready for action for 2016.
Green tip is a vulnerable time for scab and it is important to be vigilant, especially in blocks with known history. Once scab gets established, it is very challenging to get ahead of the disease.
For folks that have green tip peeking through, your best bet right now would be to use mancozeb at 6 lb/A. Copper use at green tip could run the risk of phytotoxicity. If you are not at green tip another copper application (2 lb metallic copper/A) would be a good idea since any copper applied last week most likely has washed off with the hard rain the last couple of days.
For more resources, visit the Penn State Tree Fruit Production website http://extension.psu.edu/plants/tree-fruit . For specific recommendations for disease management, visit The Disease Control Toolbox via the Tree Fruit Production website: http://extension.psu.edu/plants/tree-fruit/diseases/fungicides-and-antibiotics
When controlling for disease, weather and tree growth conditions need to be monitored at a local level within one’s own orchard. Before chemical products are applied, be sure to be in compliance by obtaining the current usage regulations and examining the product label.
If you have questions about fruit trees growing in your backyard, please contact your county Extension office and ask for Master Gardeners.