Acquisition and Transmission of Fusarium oxysporum f. sp. vasinfectum VCG 0114 (Race 4) by Stink Bugs

Fusarium oxysporum f. sp. vasinfectum VCG 0114 (race 4; i.e., FOV4) is an emerging pathogen that causes severe root rot and wilt of cotton. FOV4 is seed-borne, but the mode of seed invasion is uncertain. In an initial study, seeds in bolls that were puncture inoculated with FOV4 conidia when they were 25- or 30-days old became infected but remained viable. Because stink bugs can ingest and introduce bacterial and yeast pathogens into cotton bolls, we hypothesized that stink bugs may ingest and transmit FOV4. Southern green stink bugs and brown stink bugs were exposed to potato dextrose agar cultures of FOV4 and subsequently caged with cotton bolls to assess transmission potential. Both species fed on the cultures and acquired FOV4, and brown stink bugs transmitted FOV4 to cotton bolls. Thus, management of FOV4 may require management of stink bugs to mitigate the spread of the disease in cotton.

Soil-Borne Pests of Peanut in Growers' Fields with Different Cropping Histories in Alabama1

Pest levels and yields of peanut were monitored in growers' fields in 1991 through 1993. Yields ranged from 2085 to 6440 kg/ha and averaged 3947 kg/ha over the 3 yr. Incidence of southern stem rot (SSR) (caused by Sclerotium rolfsii) averaged 7.6 foci (up to 30 cm in length) per 30.5 m row and ranged from 0 to 31.0 foci. Peanut yield tended to be inversely related to incidence of SSR and directly related to the number of years between peanut crops. Incidence of SSR was inversely related to number of years between peanut crops and was consistently greater in fields cropped to peanut every other year compared to other fields with less intensive peanut production. Yields obtained from irrigated fields averaged 11.4% greater than those without irrigation. Leaf spot control programs used by growers provided consistent levels of control. Peanut seed invasion by aflatoxigenic fungi and plant damage by larvae of the lesser cornstalk borer (Elasmopalus lignosellus) generally were low. Seed invasion by Aspergillus flavus-type fungi was positively correlated (P < 0.05) with damage due to lesser cornstalk borer in 1993. Juvenile populations of root knot nematodes (Meloidogyne incognita) were positively correlated (P < 0.001) with incidence of SSR in 1992.

Les successions secondaires sur sites mésiques dans le Haut-Saint-Laurent, Québec, Canada

Secondary succession on mesic sites was studied in 10 forest stands in the Haut-Saint-Laurent region, using diameter-class distribution and dendrochronological analysis. Size-class ordination allowed the determination of two seral successions associated with forest communities of clear-cut or abandoned field origin. Forest cutting favors vegetative resprouting of Tilia americana, Ostrya virgininiana, and Prunus serotina rather than seed invasion of species from neighbouring communities. Fraxinus americana, Betula populifolia, and Ulmus americana colonize abandoned fields. Whatever the nature of the disturbance, strong regeneration and high shade tolerance leads to the eventual dominance of the sugar maple and to what appears to be succession convergence. However, a situation where the sugar maple is replaced by the American beech is an old community raises questions concerning the stability of the so-called climax maple forest.