Yesterday three of our over 1,000 Crab Apple clients contacted us concerned about rapid leaf drop under their Crab Apple tree which we treat for them. Two of these clients have appreciatively been with us for over 15 years and the third for over 7 years and they were perplexed by what they were seeing as our Crab tree results have always been spot on. Although you may not currently see this happening under your Crab, it’s possible you may see something similar over the next few weeks if weather conditions remain cool and damp.
Understandably, the first thing that would come to mind is that these trees must have Apple Scab disease. After all, any leaf drop from Crab Apple trees is usually attributed to this disease as Scab is the most common and debilitating disease affecting Crabs. However, this current, albeit unusual occurrence, is not Apple Scab.
Yesterday and today we visited our clients homes to see things for ourselves. In addition to visiting these houses, we also drove to other Crab clients houses whose Crabs we treated the same days we sprayed the trees in question. Subsequently, all of the Crabs shared the same tank mix. After inspecting all 16 locations, only those same 3 Crabs were losing leaves. All of the other treated Crabs look great. Common sense would indicate that there is no way treating 16 Crabs, all of which suffer from Apple Scab yearly, would work perfectly well on 13 of the trees and not on 3 others all located within one square mile of each other. Either the treatment works entirely or it doesn’t work at all. We knew then that something else was going on.
In the photo above notice that the leaves are discolored, which to an extent, resemble leaves infected by Apple Scab. However, they are predominately bright green. Leaves affected by Apple Scab are never green when they fall and they never fall to this degree at this time of year. The leaves don’t all of the sudden discolor and drop mostly green as shown in the photo over just a few days.
What does cause this type of leaf drop? A different fungal condition called Anthracnose. We attribute this leaf fall condition to the same Anthracnose Fungus that we emailed you about a few weeks back and several times over past seasons. Anthracnose usually affects, and is most noticeable on Ash and Sycamore but it can affect many types of trees that catch the airborne Anthracnose fungal spores on just the right days and under the right conditions which we certainly had plenty of this Spring. These frequent, cool, damp conditions are why we recommended to all of our Crab clients the additional, 4th application this year. It’s just that kind of year.
One might ask why, if we are treating with fungicides to control Apple Scab, why wouldn’t it control Anthracnose fungus? Fungicides are like insecticides. There are Ant sprays, Wasp and Hornet sprays, Aphid sprays and so on. They all have different active ingredients that won’t kill insects they are not labeled for. The same is true of Fungicides. Unfortunately, just because a certain fungicide product works on one fungus that doesn’t mean it works on any and all fungal conditions. Fungicides are very target specific and while our tank mixture works phenomenally well on Apple Scab disease, they are not formulated to treat Anthracnose.
As we looked around yesterday morning, before last night’s winds, we could also see that Oaks, Maples, Lindens, Lilac’s and several other varieties of trees are also reacting to these fungal spores including those that cause Anthracnose.
In our opinion we feel this leaf drop could continue over the next several days but should subside as quickly as it started. Usually trees affected by Anthracnose will re-foliate as the Summer progresses if leaf drop is prominent enough. “IF” this leaf drop was caused by Apple Scab, which it was not, they would not re-foliate until the following year as they would continue to lose leaves non-stop from this point on until the trees would be almost barren of leaves by July and August as you experienced before we started treating your Crabs.