Dormant Sprays Not Reducing Lower Limb Dieback

Lower limb dieback (LLDB) continues to be a problem in some area almond orchards, especially in the Padre and Butte varieties.  Beginning in late April or early May, leaves on affected lower limbs begin to yellow and then turn brown.  Eventually, entire limbs die and by late summer, significant death of lower canopy wood can occur. Early studies indicated that species of Botryosphaeria and Phomopsis fungi played a significant role in this problem, but later efforts indicated that LLDB may not be a disease at all.  Multiple spring fungicide applications did not reduce limb death.  The bottom line is that LLDB is still not well understood although a compromised root system, especially from overly wet soils in the spring, may contribute to the problem. 

Some people have wondered if the industry’s move away from dormant sprays may have led to increased LLDB.   To test this hypothesis, we started a field trial two years ago in two young Butte & Padre orchards.  The six and seven-year-old orchards, which only had very minor signs of LLDB at the time, were divided up like a checkerboard; some areas receiving a dormant spray of 12 pounds of Kocide 2000® (4.2 lb. metallic copper equivalent) + oil in 100 gallons of water and some areas were not dormant sprayed.  In 2014, LLDB symptoms were substantial in these blocks.  Unfortunately there was no visible difference between areas dormant sprayed for two consecutive years and areas that were not dormant sprayed.  We will continue with this project for at least a third year to see if there are any long-term effects of dormant copper sprays on LLDB.  Thanks to John Starn for cooperating in this project.

 

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