Digitaria ischaemum (Schreb.) Schreb. ex Muhl. and Poa annua L. are competitive, early successional species which are usually considered weeds in agricultural and turfgrass systems. Bacteria and fungi associated with D. ischaemum and P. annua seed may contribute to their competitiveness by antagonizing competitor forbs, and were studied in axenic culture. Pantoea spp. were the most common bacterial isolate of D. ischaemum seed, while Epicoccum and Curvularia spp. were common fungal isolates. A variety of species were collected from non-surface sterilized P. annua. Certain Pantoea spp. isolates were antagonistic to competitor forbs Taraxacum officinale, Trifolium repens. All bacterial isolates that affected T. officinale mortality were isolated from D. ischaemum seed while none of the P. annua isolates affected mortality. Two selected bacterial isolates identified as Pantoea ananatis were evaluated further on D. ischaemum, T. repens (a competitor forb) and P. annua (a competitor grass) alone and in combination with a Curvularia sp. fungus. These bacteria alone caused >65% T. repens seedling mortality but did not affect P. annua seedling mortality. These experiments demonstrate that Pantoea ananatis associated with D. ischaemum seeds is antagonistic to competitor forbs in axenic culture. The weedy character of D. ischaemum could at least in part stem from the possession of bacteria that are antagonistic to competitor species.

The annual bluegrass weevil (ABW; Listronotus maculicollis Kirby) host preference for annual bluegrass (Poa annua L.) is well documented, but ABW efficacy for annual bluegrass control in mixed turfgrass stands has not been researched. This study evaluated threshold-based insecticide ABW control for annual bluegrass control in mixed-species golf course fairway turfgrass. To investigate integrated pest management programs for annual bluegrass control in fairways, the effects of creeping bentgrass (Agrostis stolonifera L.) overseeding, three insecticide programs (preventative, threshold-based, and no insecticide), and the plant growth regulator paclobutrazol (280 g ha-1 , applied monthly) were evaluated for annual bluegrass control in field experiments conducted over 2 yr on golf fairways in North Brunswick and Bloomfield, NJ. Treatments were replicated four times and arranged in a split-split-plot randomized block design. Overseeding (whole-plot factor) did not affect annual bluegrass cover at either location. Paclobutrazol (split-plot factor) reduced annual bluegrass cover each year at both locations. At the North Brunswick site, paclobutrazol resulted in 0% annual bluegrass cover, compared with 37% in the nontreated control at the conclusion of the 2-yr experiment. Insecticide program (split-split-plot factor) only affected annual bluegrass cover at the North Brunswick site. In the absence of paclobutrazol, the no insecticide program had lower annual bluegrass cover (23%) than the threshold (37%) and preventative (44%) programs at the conclusion of the experiment. These findings show that monthly paclobutrazol applications during the growing season can reduce or eliminate annual bluegrass after 2 yr. This is the first study to show that omitting ABW insecticidal control can also reduce annual bluegrass, although efficacy was site specific. 1 INTRODUCTION Annual bluegrass (Poa annua L.) is more sensitive to biotic and abiotic stresses than other cultivated cool-season turf-Abbreviations: ABW, annual bluegrass weevil. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Background: Turfgrass managers reported poor Eleusine indica control following applications of the mitosis-inhibiting herbicide dithiopyr in cool-season turfgrass. Field, glasshouse, and laboratory experiments were conducted to understand the response of these biotypes to dithiopyr and prodiamine. Results:In field experiments at two locations with putative dithiopyr-resistant E. indica, preemergence applications of dithiopyr provided no E. indica control. Single applications of the protoporphyrinogen oxidase (PPO)-inhibitor, oxadiazon, provided > 85% control at these locations. When subjected to agar-based bioassays, root growth of putative resistant biotypes planted with 0.01 mmol L −1 dithiopyr was slightly reduced (< 25%) whereas roots were completely inhibited in the susceptible biotype. Glasshouse whole plant rate-response experiments found that the cytochrome P450 inhibitor, piperonyl butoxide (PBO), did not increase the sensitivity of these putative resistant biotypes to dithiopyr. Sequencing of ⊍-tubulin 1 (TUA1) revealed a Leu-136-Phe substitution in both dithiopyr-resistant populations. Conclusion:Eleusine indica biotypes with resistance to dithiopyr are present in cool-season turfgrass systems in the United States. Resistance is possibly related to a single nucleotide polymorphism (SNP) of an ⊍-tubulin gene. If turfgrass managers suspect resistance to dithiopyr, oxadiazon can still be an effective alternative for preemergence control.

The annual bluegrass weevil (ABW) is typically regarded as a pest of fine turfgrass, but recent research has found withholding insecticides for ABW control can reduce annual bluegrass cover. The objective of this research was to evaluate threshold-based insecticide and paclobutrazol programs for annual bluegrass control. The effect of three insecticide programs (preventive, threshold, and no insecticide) and four rates of paclobutrazol (0, 70, 105, or 210 g ha−1 applied monthly) were evaluated. Replicate experiments were conducted from April to November in both 2018 and 2019 on a mixed creeping bentgrass and annual bluegrass fairway in North Brunswick, NJ. By the conclusion of both experiments, all paclobutrazol programs reduced annual bluegrass cover compared to the nontreated. In threshold and no insecticide programs, reduction in annual bluegrass cover was enhanced by paclobutrazol at 105 g ha−1 in both years, and at 70 g ha−1 in the 2019 experiment. Paclobutrazol at 210 g ha−1 reduced annual bluegrass cover to < 20% regardless of insecticide program. In 2019, threshold-based ABW control without paclobutrazol provided similar annual bluegrass control as monthly applications of paclobutrazol at 70 and 105 g ha−1 with the preventive insecticide program. Turfgrass quality reductions from threshold-based insecticide programs persisted for a shorter duration than the no insecticide program, regardless of paclobutrazol treatment. Threshold-based ABW insecticide programs that allow ABW feeding damage to occur can reduce annual bluegrass cover. These reductions were further enhanced by paclobutrazol applications. The combination of threshold-insecticide programs with moderate rates of paclobutrazol (70 to 105 g ha−1) provided reductions in annual bluegrass cover similar to the highest rate of paclobutrazol (210 g ha−1) without ABW damage. Turfgrass managers integrating the threshold insecticide approach and monthly paclobutrazol applications can achieve greater annual bluegrass control than either strategy alone if temporary reductions in turf quality can be tolerated.

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