You’ve probably heard it by now. The National Oceanic and Atmospheric Administration (NOAA) predicts an above-normal Atlantic hurricane season for 2020. NOAA predicts “a 60% chance of an above-normal season, a 30% chance of a near-normal season and only a 10% chance of a below-normal season.” This translates to 6-10 hurricanes (>= 74 mph winds), including 3-6 major hurricanes with winds of 111 mph or greater.
What does this forecast have to do with tree fruit production? These high winds may cause tree fruit roots to crack and split. Wounds created by this activity allows for entrance of the Phytophthora root rot pathogen. Flooding also facilitates movement of pathogen spores through the soil. Once infected, cankers and root rot develop during subsequent months, leading to tree death this fall or next spring and summer.
Although Isaias is only a tropical storm, winds may get high enough to cause some damage to anchoring roots. Nevertheless, we still have four more months of the Atlantic hurricane season remaining, which runs from June 1 through November 30. Given the potential for loss and the above normal risk for hurricane development, it is probably prudent to review some basic information on disease development and control.
Peach and apple trees at 3 to 5 years of age are most susceptible to wind injury and subsequent infection by Phytophthora species. If trees are leaning to one side, or there is open space around the collar, this is a good indication of “tree whipping” and therefore root injury. Younger trees tend to be more flexible and therefore less likely to be damaged, especially when the soil is softened by excessive rainfall. Older trees with large, well-developed root systems are more likely to fend off the wind; limb breakage and fruit loss may be a bigger concern on these trees. Of course, wind speed plays an important role in the severity of damage across all age groups.
If injury is thought to have occurred, fungicide application should be considered immediately after the storm subsides to limit Phytophthora root and crown rot development. Ridomil Gold, applied to the soil, is the recommended fungicide. Foliar applications of a phosphorous acid material, such as Aliette, Agri-Fos, Phostrol, etc… are alternative controls. If damage is severe across all age groups, one approach would be to apply Ridomil to 3-5 year old trees and a phosphorous material to young and old trees.
If time and weather permits, application of root or foliar fungicide prior to the hurricane may help “immunize” the trees before infection can occur. Both types of fungicides are highly systemic. However, one needs to allow time for the Ridomil to move through the soil and be absorbed by the roots. Excessive storm flooding could wash away the fungicide before it has a chance for root absorption. Of course, once these materials are applied, the hurricane will most likely change course! Hence, the disadvantage of applying before the storm.
For details on application and rates of Ridomil Gold and Aliette, see the NJ Tree Fruit Production Guide (2016 issue) and product labels.
