By Kari A. Peter
Although there is still snow on the ground in some parts and the nights are still quite chilly, it won’t be long before the trees wake up from their slumber. Consequently, it’s time to start thinking about those dormant spray applications to limit bacterial and fungal diseases for the coming season.
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 before 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, the emergence of green tissue will want to be monitored when this combination spray is used.
There is still time to get rid of overwintering scabby leaves
As a matter of principle, we began to monitor our overwintering leaves with apple scab for spore release last week, and no spores have been detected. This was expected since 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. Leaf litter can still be shredded if urea had been used, too. This will aid in the breakdown of the leaf tissue more.
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 can be overwhelmed with such high inoculum pressure. Consequently, sanitation is important for fruit rot prevention.