Kochia poses a challenge to vegetation management in both agricultural and noncrop areas. This species has developed widespread resistance to several herbicides with differing modes of action, including acetolactate synthase inhibitors and photosynthesis inhibitors. Resistance is also beginning to appear against the synthetic auxins and glycines. Therefore, alternative PRE and POST herbicides are needed for effective kochia management, especially in roadside bare-ground zones. Both PRE and POST herbicides were screened on rights-of-way in Pennsylvania. Mixtures containing diuron, flumioxazin, sulfentrazone, pendimethalin, prodiamine, and bromacil were evaluated for PRE activity in combination with glyphosate. POST kochia control was assessed for 15 noncrop herbicides. Results from all trials varied with kochia size and vigor at time of treatment. Although diuron is the current industry standard for PRE control in tank mixes, sulfentrazone appeared to have the most POST activity against vigorously growing kochia. All PRE herbicides evaluated performed better than the standard, sulfometuron plus chlorsulfuron alone. Dicamba, dicamba plus diflufenzopyr, fluroxypyr, and glyphosate performed best against kochia when applied POST. The recently available chemistries saflufenacil and aminocyclopyrachlor require further evaluation of application timing and use rates, respectively, for POST activity on kochia.
There were no differences in johnsongrass rhizome winter survival at central and southeastern locations in Pennsylvania in 1988 or 1989. At a 6-cm depth of burial, survival rates of 5 and 25% were found for rhizome segments 7.5 and 15.0 cm in length, respectively. Survival rates for rhizomes buried 25 cm averaged 86%, with no difference in survival between rhizome lengths. The majority of rhizome biomass produced by the biotype used in these studies was found at soil depths allowing a high percentage of survival.
For many of the shrub species invading temperate deciduous forests, extended leaf phenology contributes substantially to annual carbon gains, helping to make possible rapid growth and spread. We carried out a pair of proof-of-concept studies to evaluate the susceptibility of such shrubs to foliar herbicide treatment during the period of delayed senescence, i.e. well after it is typically attempted. We first evaluated leaf-level physiology in four species that lose leaves late in autumn; photosynthetic rates were comparable (80-111%) to those reported for the same species in summer. While preliminary, this finding provides a strong indication that diverse shrub taxa remain susceptible to control into late autumn. In addition, we conducted a field trial involving one of these species (Lonicera maackii) to directly evaluate the effectiveness of foliar treatment in November; applications included glyphosate and two concentrations of aminocyclopyrachlor plus metsulfuron methyl. Treatments killed (72%) or severely injured (14%) target plants, inducing greater cambial damage in plants that retained greater fractions of their canopy or had smaller canopy widths; there were no statistically significant differences among application types. This study demonstrated that late autumn can be a viable period in which to treat weedy species that delay senescence strongly, such as the many invasive Lonicera species in North America. Given that climate change and urbanisation are further delaying senescence in invasive plant populations, our study serves as a call for further investigation into what promises to be an increasingly viable opportunity for weed control in deciduous forests.
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