If the lower limbs of your almond tree are turning brown, you have a problem.
While it is normal for some leaves on lower limbs to turn yellow because of being shaded by the growth above, lower limb dieback (LLDB) goes much farther and can kill your almond trees
Upper canopy or crown leaf loss is shade tree decline, a potentially fatal disorder caused by drought.
Symptoms of lower limb dieback
First seen in 2005, LLDB consistently appears in spring and on 7- or 8-year-old trees when leaves on lower branches turn yellow and brown, cankers develop, and brown discolorations are visible under the bark of infected branches. Cankers can girdle a limb and kill it.
Some almond varieties are more susceptible to lower limb dieback than others. Padre almonds are the most likely to get this disorder, with Butte being a close second. Install resistant varieties, such as Aldrich, Carmel, Fritz, Mission, NePlus Ultra, Nonpareil, Sonora, and Wood Colony, when possible.
While research is underway, we still don't know if lower limb dieback is a fungal disease or an environmental disorder. Two fungi have been found in trees exhibiting lower limb dieback (Botryosphaeria spp. and Phomopsis spp.). They may be causing the problem or are simply opportunists.
Preventing lower limb dieback
Low light levels, chemical overspray, soggy soil, and excessive fertilizer weaken trees, making them vulnerable to whatever causes this problem.
Specific conditions that seem to lead to LLDB include excessive water early in the growing season and compacted soil. Hull rot seems to make trees more prone to develop lower limb dieback, and scale insects may be involved.
Keeping your trees healthy is the best way to prevent lower limb dieback. This means proper irrigation, good drainage, the right amount of fertilizer (after a soil test shows a need), and control of scale insects.
Fixed copper and sulfur treatments are not effective. Fungicides may provide a cure, but we don't know yet.
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