By mid October, you can really see the difference fungicide applications make towards preserving pecan leaf health. This past year we made three fungicide applications to all of our orchards at the Pecan Experiment Field except for a five acre block of native trees that did not receive any pesticides.
The photo at above shows our fungicide treated pecan trees in mid-October. The leaves on these trees are still healthy and green. Healthy leaves capture energy from the sun and covert that energy into carbohydrates. Carbohydrates are then used to fill this year's pecan kernels and promote pistillate flower production next Spring. Maintaining healthy foliage throughout the growing season is the best way to reduce a pecan tree's natural tendency for alternate bearing.
Now look trees that did not receive fungicides during the growing season (photo above). By mid-October, some of the native trees had lost most of their leaves while most had taken on a bronzed appearance. These trees are already shutting down for winter. Lesser amounts of carbohydrates are created by damaged foliage and that limited supply of energy is totally directed towards filling this year's crop of nuts. This leaves little of no energy for pistillate flower formation next year. Unchecked pecan foliar disease ultimately accentuates the alternate bearing pattern.
Pecan diseases not only impacts leaf health but they can have direct effects on nut yield. The photo at right shows two clusters of Stuart pecans. The cluster on the left is covered with scab. On the right, the nuts still show signs of scab infection but to a much lesser degree. All of these nuts appear to be splitting open but the heavily infected nuts are one half the size. Pecan scab causes yield losses in three ways; early nut abortion, reduction in nut size, and a reduction in percent kernel.
The primary reason we apply fungicides to pecan trees is to control pecan scab. However, the secondary impacts of disease control on leaf health is equally as important. The introduction of pecan scab resistant pecan cultivars will make disease control easier but does not eliminate the need for fungicide applications. The control of leaf disease, especially during wet summers, is important for maintaining tree health and productivity.
