Protect peaches with a dormant copper spray to limit bacterial spot and peach leaf curl this season. Photo: K. Peter, Penn State
The 70 - 80 °F days during the third week in February made me wonder if Punxsutawney Phil was joking around when he said there was going to be six more weeks of winter. Regardless, the season is on our doorstep and there are few housekeeping items on the disease management to-do list before the 2018 season gets into full swing.
Dormant sprays to manage fungal and bacterial diseases
Growers are encouraged to apply dormant copper sprays on apples and pears for fire blight and scab; and on peaches (and other stone fruit) for bacterial spot and peach leaf curl. Ziram and chlorothalonil (e.g. Bravo) are alternatives to copper and will also control peach leaf curl. Since peach leaf curl can only be managed when leaves are off the trees, applications should be made prior to bud swell If using copper, growers will want to aim for 2 lb/A of metallic copper: pay attention to the % metallic copper equivalent (and amount of metallic copper per unit) listed on the label of the copper you use. Also, during dormant sprays, it is okay to mix oil and copper. Since minimal green tissue is present, the risk of phytotoxicity from the copper-oil mix is very low. Consequently, emergence of green tissue will want to be monitored when this combination spray is used.
Since we had a spike in warm weather, time will only tell if any significant bud swell occurred in the peaches. Last year, there was a high incidence of peach leaf curl on early varieties and it was most likely due to bud swell occurring during the warm weather experienced during February 2017. If bud swell occurred and your dormant fungicide spray had not been applied yet, the peach leaf curl fungal spores may be protected from sprays. Time will only tell how the unseasonable temperatures during the third week in February 2018 will have affected the peach trees and fungicide sprays applied after this time.
There is still time to get rid of overwintering scabby leaves
Out of principle, we will begin to monitor our overwintering leaves with apple scab for spore release during the first week in March. Ascosopore release from infected leaves typically coincides with green tip. So far, green tip hasn't occurred. Fingers crossed it won't happen for another month… There is still time to keep apple scab in check if you haven't done so already. Apple scab can be managed by reducing the number of available overwintering spores in last year's leaves present in the orchard through sanitation. Remember: orchards are self-infecting when it comes to scab since spores can travel about 100 feet.
Options for reducing spores:
- Apply urea sprays (40 pounds per 100 gallons of water per acre) to the orchard floor including the sod row middles. Spores need leaf tissue to survive and urea helps the breakdown of the tissue thereby eliminating the food source for the spores. If urea is applied, your spring nitrogen applications need to be reduced based on the amount of urea applied to the tree rows.
- Shred leaf litter using a flail mower or remove leaf litter by raking, sweeping, or vacuuming. Shredding leaf litter assists the decay of the plant material, as well as aids in the reorienting the leaves, thereby disrupting ascospore discharge.
Remove mummified fruit from trees while pruning
While growers are finishing up their winter pruning, it is very important to remove any mummified fruit hanging in the trees. This is especially critical for brown rot in stone fruit trees. Mummified fruit left hanging in the trees will become spore factories during the season and cause infection on blossoms and fruit. Fungicides will be overwhelmed with such high inoculum pressure. Consequently, sanitation is important for fruit rot prevention.
2018 - 2019 Penn State Tree Fruit Production Guide
If you haven't already done so, please consider investing in the 2018-2019 Penn State Tree Fruit Production Guide. All previous versions are considered out-of-date and should be discarded. Significant additions, updates, and improvements have been made to the 2018-2019 guide giving growers the most current information for commercial tree fruit production.
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