Lagenophora schmidiae (Asteraceae), a critically threatened new species from Aotearoa / New Zealand

Lagenophora schmidiae de Lange & Jian Wang ter sp. nov. (Asteraceae) is described, illustrated and differentiated from L. montana Hook.f. The new species was first recorded from Aotearoa / New Zealand in 1974, when it was identified as L. montana. This relatively recent recognition reflects in part the fact that the new species is extremely uncommon, and has often been confused with the superficially similar L. barkeri Kirk, with which it often grows. A conservation status for L. schmidiae of ‘Threatened / Nationally Critical’ using the New Zealand Threat Classification System is proposed, as the new species is known only from small populations, many of which are threatened by alien weed invasion.

POTENTIAL USE OF Coronopus didymus (L.) SM. IN PARTHENIUM MANAGEMENT

This study aimed to assess a brassicaceous weed Coronopus didymus (L.) Sm. as a source of potential natural herbicides for management of an alien weed parthenium (Parthenium hysterophorus L.). Initially, the effect of aqueous leaf, stem, root and flower extracts (0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0%) of the weed was checked on germination and growth of the target weed. Leaf and stem extracts showed the best herbicidal activity and a 2.5% extract of the each plant part completely inhibited germination of parthenium seeds. The lowest extract concentration (0.5%) of leaf and stem reduced germination by 56 and 46%, shoot length by 43 and 12%, root length by 59 and 62%, and biomass of whole plant by 44 and 15%, respectively. Root and flower extracts were less herbicidal and reduced parthenium germination by 23–52% and 33–56%, respectively. In a pot experiment, soil was incorporated with 0.2, 0.4, 0.6, 0.8, 0.10, 1.2% (w/w) crushed dry biomass of C. didymus, parthenium seeds were sown after one week and the effect of amendment on germination and plant growth was recorded after 45 days of sowing. All the doses of soil amendment significantly suppressed root length by 21–48% over control. A 1.2% soil amendment significantly reduced biomass of parthenium seedlings by 23%. This study concludes that leaf and stem extracts of parthenium possess potent herbicidal potential for control of parthenium.

Low and high input agricultural fields have different effects on pest aphid abundance via different invasive alien weed species

We conducted field surveys to detect the population density of the most important invasive weed species and their associated virus vectoring aphids in crops grown under high input field (HIF) vs low-input field (LIF) conditions, with and without fertilizers and pesticides. The most frequent invasive weed species were Stenactisannua, Erigeroncanadensis and Solidagocanadensis. These species were hosts predominantly for the aphids Brachycaudushelichrysi and Aulacorthumsolani in both management systems. The 13% higher coverage of S.annua under LIF conditions resulted in a 30% higher B.helichrysi abundance and ~85% higher A.solani abundance compared with HIF conditions. Host plant quality was assessed by measuring peroxidase enzyme activity. There was a significantly increased POD activity at 10 μmol min−1 mg protein−1 unit in S.annua under LIF conditions, suggesting a higher stress by aphids under this management regime. The high colonization intensity of B.helichrysi on maize, potato and alfalfa crops were detected from both S.annua and E.canadensis. We conclude that new and faster methods need to be used to prevent colonization of such virus vectoring aphids and their host plants, even under low input regimes.