Crepe Myrtle Bark Scale (Acanthococcus lagerstroemiae) and Sooty Mold (Capnodium sp.) Decrease Bloom and Fruit Number in ‘Natchez’ Crepe Myrtle (Lagerstroemia ×fauriei ‘Natchez’)

Crepe myrtle bark scale (CMBS) ( Acanthococcus lagerstroemiae ) is an important pest of crepe myrtle in Texas, and infestations are accompanied by excessive growth of sooty mold (SM) that will cover stems, and, in severe cases, leaves. These combine to create significant stress on the plant, and anecdotal evidence suggests a decrease in bloom number under heavy infestation. In an existing planting of 24 ‘Natchez’ crepe myrtle in four blocks, three trees were randomly chosen in each block and treated with either a dinotefuran (year 1) or imidicloprid (year 2) drench. The three remaining trees were untreated. In February of year 2, all visible signs of CMBS and SM were removed from all trees using a high-pressure water spray. Beginning with onset of blooms [July (year 1) and May (year 2)], trees were scored weekly using a 0 to 10 scale for CMBS severity and SM incidence, with a score of 0 indicative of no observable CMBS or SM and 10 representing complete coverage. Blooms were counted weekly by creating a standard number of blooms per small, medium, and large clusters. Once blooms ended, all fruit were removed and counted. During year 1, treated plants had lower season-end average CMBS scores (5.2 vs. 8.5), lower season-end SM scores (4.9 vs. 8.3), and higher total number of blooms (2314 vs. 1017) than untreated trees. In year 2, treated trees again had lower season-end CMBS scores (0.7 vs. 2.2), lower season-end SM scores (0.2 vs. 2.2), and higher total bloom number (5284 vs. 2144) than untreated trees. Treated trees had higher fruit numbers in year 1 (3770) and year 2 (7031) than infested trees, 998 and 2009 in years 1 and 2, respectively. CMBS infestations can have a devastating effect on crepe myrtle, even at low infestation levels, and CMBS infestation, along with the corresponding presence of SM, decreases bloom in CM.