Evaluation of Multiple Herbicide Groups on Establishing Pearl Millet x Napiergrass Hybrids.

Field and greenhouse experiments were conducted from 2012 through 2014 to determine the phytotoxicity of multiple herbicide groups on pearl millet [Pennisetum glaucum (L.) R. Br.] x Napiergrass (Pennisetum purpureum Schum.) (PMN) hybrids.  In two greenhouse experiments, Plateau^®, Aim^®, Prowl^®, Dual^®, Metribuzin^®, Huskie^®, Permit^®, Aatrex^®, Warrant^®, and Direx^® were foliar applied post-crop emergence to PMN hybrids, specifically at the 3-5 and 5-7 leaf stages.  A chlorophyll content meter (Apogee Instruments model CCM-200) was used to determine total chlorophyll content of the leaves and visual ratings were made up to 30 days after treatment to assess the toxic effects.  Chlorophyll contents were correlated to herbicide activity through declining chlorophyll values which reached zero upon plant death.  Of the herbicides tested, only Dual^® (0.11 kg a.i. ha^-1) and Direx^® (0.59 kg a.i. ha^-1) resulted in lethality.  A field study was conducted at the Texas A&M AgriLife Research farm in 2014. The phytotoxic effects of the herbicides Plateau^®, Aim^®, Prowl^®, Dicamba^®, Huskie^®, Permit^®, Aatrex^®, Warrant^®, and Direx^® alone and in nine combinations were evaluated at the 5-8 leaf stage.  Chlorophyll content varied and could not reliably be used to detect differences.  Visual ratings, morphological measurements, and yield data revealed differences among herbicides and confirmed findings from the greenhouse studies in that Direx^® (0.59 kg a.i. ha^-1) will be detrimental in the establishment of PMN stands.  Results from greenhouse and field studies indicate that several herbicide groups have potential for negative phytotoxic effects on establishing PMN.  In addition, a greenhouse study evaluating seed-germination of PMN in two soil types with 3 pre-emergence herbicides (Dual^®, Guardsman Max^®, and Prowl^®) over 7 time intervals (seeding at 1 day through 8 months) is currently ongoing.