Biology and Control of Maryland Meadowbeauty (Rhexia mariana L.) in Blueberry (Vaccinium spp.) in North Carolina

Abstract

North Carolina is the fifth largest producer of blueberries (Vaccinium spp.) in the U.S. with approximately 5,000 acres harvested in 2006. A study was conducted to determine if a positive correlation exists between the weed populations in field drainage ditches and weed populations in the field interior, and to inventory the weed species present in the ditches and the field interiors. Sixty-six species were inventoried over a two year period. A second study was conducted to define the seed biology of Rhexia mariana L., an aggressive perennial weed in blueberry, by determining temperature effects on germination, average seed number per capsule, seed number in the seed bank, and seed dormancy. Maximum seed germination was observed at day/night temperatures of 20/35C. Seed germination ranged from 47 to 86% and dormancy ranged from 14 to 53%. The number of seed capsules produced per infested area was different among locations and ranged from 500 to 1125 capsules/m2. Across locations, seed capsules produced an average of 74 seeds each. On average, 27 R. mariana seeds were present in each 273cm2 sample of soil. A single m2 of R. mariana infestation has the potential to produced 12,375 seed capsules and 915,750 seeds. Of those seeds, roughly 604,395 would be viable, 519,779 could germinate as freshly mature seeds, and an additional 84,615 seeds would be dormant. An estimated 1000 R. mariana seeds could germinate from 1m2 of the soil seed bank. A third study was conducted to determine the efficacy of flumioxazin on R. mariana and the tolerance of blueberry to flumioxazin. The data indicate that flumioxazin does not injure blueberry when applied PRE. Flumioxazin applied PRE in a single or a sequential application does not have a negative effect on blueberry yield, even at rates that exceed the registered rate. Control of R. mariana with a single application of flumioxazin at the registered rate of 0.42 kg ai/ha ranged from 83 to 100% at 60 days after treatment (DAT). Sequential applications of flumioxazin at 0.21 kg ai/ha per application resulted in control greater than 96% 30 d after the last of two applications. The data indicates that flumioxazin applied PRE at the registered rate of 0.42 kg ai/ha in a single application or 0.21 kg ai/ha in a sequential application in a 12 month period would give effective control of R. mariana. A final study was conducted in which a grower survey was used to determine the current weed management practices employed by blueberry growers in North Carolina. A 41-question survey was mailed to 241 blueberry growers in February 2008. A total of 58 valid responses were returned and were entered into the data set. Respondents represent 24% of the survey population. Thirty-eight percent of the survey population grows a combination of rabbiteye and highbush blueberry types. The highbush variety ‘Croatan’ was the most frequently planted variety in total hectacreage, and the rabbiteye variety ‘Premier’ was the most common variety of that blueberry type. Growers use a combination of mechanical cultivation, hand removal, and herbicides to control weeds in blueberry. Greenbriar species (Smilax spp.) were reported as those species that are increasing in severity, are the hardest to manage, and that interfere most with harvest. Sethoxydim and hexazinone are the most common herbicides used in non-bearing and bearing blueberries, respectively. Growers indicated that their greatest concern in weed management is crop safety to herbicides. Results from all four studies will aid in the development of a comprehensive weed management plan to address the specific needs of North Carolina blueberry producers.