Root-knot nematodes are parasitic, microscopic and omnipresent worms that cause considerable damage to horticultural and field crops in sub-tropical regions, resulting in significant financial losses to growers and gardeners. Until recently, fumigation of the soil with methyl bromide (MBr) before planting was the primary method for controlling root-knot nematodes in valuable vegetable crops. However, since the discovery that it has severe negative effects on the stratospheric ozone layer, the use of MBr has been phased out in the United States.

To combat parasites like root-knot nematodes without the use of chemical pesticides, scientists are focusing more research on developing new, parasite-resistant varieties of vegetables. Dr. Judy Thies, a research plant pathologist at the United States Department of Agricultures Agricultural Research Service, was part of a research team that developed the Charleston Belle variety of bell pepper, the first nematode-resistant bell pepper. Dr. Thies and her colleagues tested the stability of two types of bell peppers Charleston Belle and Carolina Wonder, the only nematode-resistant varieties available to commercial growers and home gardeners. They tested the peppers for resistance to nematodes in sub-tropical climates to determine if the cultivars were stable when grown in Florida under high soil temperatures.

The study results showed that nematode-resistant varieties such as Charleston Belle and Carolina Wonder are viable alternatives to MBr for managing southern root-knot nematode in bell pepper in sub-tropical environments. Contact: Mr. Michael Neff, American Society for Horticultural Science, 113 South West Street, Suite 200, Alexandria, VA 22314-2851, United States of America. Tel: +1 (703) 836 4606; Fax: +1 (703) 836 2024; E-mail: mwneff@ashs.org.

Source: www.eurekalert.org

GPS-guided, shank-applied, spot treatments with fumigants are among experiments by the United States Department of Agriculture (USDA) and the University of California Davis (UCD) scientists seeking solutions to long-standing problems with replant disease in almond and stone fruit orchards. Without soil fumigation and/or other steps before planting, severe Prunus replant disease (PRD) kills or prevents growth in about half of replacement almond or stone fruit trees in California.

PRD is associated with a complex including soil conditions, fungi, bacteria and moulds from the preceding crop. Parasitic nematodes can also play a role. We sometimes find aggressive pathogens such as Armillaria, Phytophthora or Verticillium, said Dr. Greg Browne, a USDA plant pathologist at UCD, who leads the Pacific Area-Wide Pest Management Programme for Integrated Methyl Bromide Alternatives. Dr. Brownes team is probing several practices to find alternatives in view of regulations on methyl bromide (MBr), Telone formulations and other fumigants. Results, based on tree growth indicated by trunk diameter, of research in orchards have revealed findings that may contribute to solutions, including:

Chloropicrin and mixtures of it and iodomethane, Telone or MBr are more effective than the latter three alone.
Short-term rotations with Sudan grass, wheat followed by mustard, or a single fallow season can reduce effects of PRD.
Over- or under-irrigating almond trees replanted without pre-plant soil fumigation after removal of almond on peach rootstock can worsen PRD.
GPS-controlled shank treatments applied to tree sites before planting with chloropicrin/Telone, or drip irrigation-applied spot treatments with a formulation of the two chemicals, appear nearly as effective as strip or broadcast treatments.

The spot-fumigation system, developed by Prof. Shrini Upadhyaya, UCD Agricultural and Biological Engineering Department, in co-operation with TriCal Inc. is basically a conventional shank-rig mounted on a tractor. It is controlled by a GPS computer for automatic and precise injection of fumigant in a prescribed grid of rectangular areas where trees will be planted. The method saves considerable material compared with broadcast application.


Source: www.westernfarmpress.com

Scientists from CSIRO Entomology of Australia and Agricultural Research Service of the United States Department of Agriculture have jointly assessed the efficacy of ethanedinitrile (EDN) at low temperatures (3-22C) against pathogens in cereal feed grains. EDN, patented by CSIRO as a new fumigant against insects and micro-organisms, is being investigated by CSIRO Australia as an alternative to methyl bromide (MBr) for a range of other uses, including soil and timber fumigation.

The study reported preliminary assessment of efficacy at low temperatures against target pathogens including Tilletia indica Mitra, Peronosclerospora sorghi (sorghum downy mildew), Tilletia controversa Khn (dwarf bunt) and Ustilago maydis (DC) Corda (boil smut). EDN has a threshold limit value (TLV) of 10 ppm, which compares favourably with 5 ppm for MBr. Treatments included: (1) naked spores; (2) bunted seed, when present as a propagule in the pathogen life cycle; and (3) spores dusted on maize.

EDN-treated material and untreated control spores of T. indica, T. controversa and U. maydis were seeded onto water-agar medium to assess viability based on spore germination. As oospores of S. sorghi germinate poorly on artificial medium, a bioassay on susceptible plants was used. Treated oospores were mixed into the upper layer of soil in a plastic pot and planted with seeds of a highly susceptible sorghum cultivar, and placed in a growth chamber for disease development.

In general, though data indicate EDN was more toxic at higher temperatures, good control was obtained at the lowest temperature of 3C. Overall, T. indica, with its large teliospore, was the most tolerant of the smut fungi. Naked teliospores were more easily controlled than spores still contained within the fungal structure of T. indica and T. controversa. All three smut species treated were controlled to a high level at all temperatures and at dosages likely to be useful in treatment schedules. No vital stains were shown to be effective with oospores of P. sorghi, which could be because of annual dormancy of the oospores. Contact: Mr. J. E. van Someren Graver, CSIRO Entomology, G.P.O. Box 1700, Canberra, ACT 2615, Australia.

Source: www.mbao.org

Researchers at the University of California Davis, the United States, studied the efficacy of a soil disinfestation system comprising steam treatment and solarization as a methyl bromide (MBr) alternative for field-grown cut flowers and strawberry. High energy costs and lack of appropriate steam applicators have limited the use of steam in commercial fields. Injecting steam into finished plant beds with a mobile steam generator under clear polyethylene mulch would allow steam to supplement solarization as needed. The research aim was to develop an economical combined solarization and steam heat, soil disinfestation system.

Pathogen (Verticillium sp.) and weed seed (common chickweed, knotweed, purslane, little mallow and yellow nutsedge) samples were first installed in the planting beds. Viability of the weed propagules was determined using tetrazolium tests. Treatments included drip application of MBr + chloropicrin (MBrPic, 67:33) at 350 lb/acre, control (no MBrPic, solarization or steam), solarization alone, steam alone, and steam + solarization. For steam + solarization treatments, beds were solarized before and after steam application. For steam treatments, steam was injected to raise the bed temperature to 70C for 30 min.

Solarization alone did not have the same efficacy as MBrPic. Steam, with or without solarization, resulted in weed control similar to MBrPic. Peak temperatures of >78C in the steam treatments did eliminate weeds as well as MBrPic.

Source: www.mbao.org