Warm, wet, summer weather, coupled with any lapses in orchard sanitation, can result in summer disease outbreaks. At Meigs, we are seeing the foliar stage of Botryosphaeria, aka frog eye leaf spot (Fig. 1).
Fig. 1
apple frog eye leaf spot
On the plus side, we won’t be surprised when we see black rot on the apples at harvest (Fig. 2).
Fig. 2
appleblackrotbeckerman
Fortunately, this only seems to be a problem in our Red Delicious block. Thankfully, the Honeycrisp haven’t shown any symptoms…yet. In general, frog eye leaf spot serves as an indicator that we should probably prepare for problems in the form of black rot on fruit. Red Delicious isn’t normally described as a susceptible host. Reportedly susceptible cultivars include Cortland, Empire, Northern Spy, and Honeycrisp. A few rows away is the Honeycrisp, and I’m hoping for a lot of rot for our fungicide trial. This frog eye leaf spot gives me hope. If I was a real grower, it would give me heartburn, as it is a warning of things to come.
At this point, summer disease management should focus on using protective fungicides for ‘cover’. Should disease pressures increase with wetter weather, or if you too are seeing frog eye leaf spot, supplement your protectant based cover schedule with either strobilurins (Flint, Sovran—remember your PHI) or an SDHI fungicide (Fontelis) or a strobilurin+SDHI premix—(Pristine, Merivon, Luna Sensation).
In the fall, make sure that you keep an eye out for any developing cankers (Fig. 3) being sure to remove in the spring, and burn.
Fig. 3
apple black rot cankers
Rigorous sanitation and removal of windfalls and mummies is also important. The Red Delicious block with frog eye leaf spot had both mummies in the tree, and uncollected windfalls in an attempt to ‘Bring on the Rot’!