Fig Leaves Showing Possible Disease Symptoms

Q. The leaves on my fig tree appear burned after this rain. I foliar sprayed it with Neem oil and soap and fish protein isolate, These trees were planted last fall and mulched with 1 foot of woodchips and looked amazing until now. They are watered three times each week in the summer.

A. The leaves do look like they are diseased. But I have a saying, “When the top looks bad, look at the ground.” First eliminate the easy problems before jumping to more difficult ones.

            I wonder if that 12 inches of surface mulch is rotting the trunk of the tree. It is easy to kill young trees if they sink, the bottom of the trunks buried in dirt, into the planting hole after planting. Or if woodchip mulch on the soil surface is piled against the trunk and kept wet.

            In both cases wet soil or wet mulch against the trunk can cause a disease called “collar rot”. The disease rots the trunk and “chokes” the top of the tree. When this happens, leaves look diseased or as if the plant isn’t getting enough water. This becomes very apparent during hot weather.

            Start on your knees and pull the mulch away from the trunk. Keep it there permanently, 6 to 12 inches away. Next, carefully remove the soil from around the trunk until you find tree roots coming from the trunk growing horizontally.

            If this small area of the trunk looks water soaked, there might be a problem. I will take a small penknife and cut away a narrow strip of the trunk that was buried in soil and mulch. The wood under the strip should be white or greenish white.

            If there is more than ½ inch of soil covering the trunk, or the trunk was buried in wet mulch, the tree may develop collar rot. All you can do is let the covered part of the trunk air dry and hope for the best.

            I have seen collar rot develop on the lower trunk young figs and pomegranate that are buried. Most figs and pomegranates are grown on their own roots. If the top of the tree dies, wait a couple of months and see if anything suckers from the roots or base of this tree. If it does, don’t replace the tree.

            These basal suckers will grow very rapidly into a new tree because the tree already has established roots. When one of the suckers is 12 inches tall, remove the others for a single trunk tree or select 3 to 5 for a multi-trunk tree.

            It’s possible these leaf problems are related to a leaf disease but I don't recognize it. Sometimes when dead areas develop from disease pathogens, the dead area of the is bordered by yellow. This yellowing is where the plant tissue is still dying. Sometimes this yellowing doesn't exist but only because the disease has stopped spreading.

            The humidity in Las Vegas is unusually high right now because of the so-called “summer monsoon” and rains. I expect diseases to pop up during this kind of weather. Having leaf diseases on fruit trees would not be uncommon during this time of year.

            Instead of spraying, driving using a passive approach towards controlling diseases. Remove extra leaves that might be blocking the movement of air and wind through the canopy. As you see leaf diseases, remove the infected leaves and dispose of them. The plant will grow new leaves in places where there is sunlight. Leaf diseases slow down or stop as the weather changes.