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Nursery best management practices study

A project is currently underway at general Andrews State Forestry Nursery to develop best management practices for the continued production of low cost, high quality, native, bareroot seedlings with minimal environmental impact. Key areas of investigation include soil water management, weed control and fumigation practices related to the production of white pine and black walnut seedlings.

Soil water management tests will study sub-soiling regimes and equipment choices such as rototillers and tines, to reduce soil compaction. Irrigation techniques will be studied using new commercially available technology to determine timing and amounts of water needed for each irrigation event. The movement of water through nursery seeding and rooting zones is a critical factor in the potential impact of damping off and root rot agents.

Weed control is a primary challenge in bareroot nursery operations. All practices, sequences, and timings of organic management, fallow, cultivation and chemicals use will be reviewed.

Fumigation using sodium methydithiocarbamate (Vapam HL or Sectagon 42) will be tested against untreated fields. Fumigation is cheap insurance for bareroot operations, but its efficacy needs to be continually reviewed in relation to cost, impact on non-target organisms and health and safety issues.

Walnut ( a one year product) results will be available in the Spring of 2000 and white pine ( a three year product) results are to be reported in 2002.

Bt = Microbial insecticide

Bt is the common abbreviation for Bacillus thuringiensis subspecies kurstaki.. It is a common, naturally occurring soil bacteria found in most regions of the world. A German scientist named Berliner first isolated Bt in l9l5. Bt was produced and sold as an insecticide as early as l960. It is registered and sold as an insecticide in over 50 countries for use against Lepidoptera caterpillars. There are several other subspecies of Bt that are used to control mosquitos, black flies, potato beetles, and several tree leaf beetles. To work, a Bt product must be eaten. It is more effective when eaten by younger larvae. Bt can remain viable on foliage for four to ten days. Timing of the application and good coverage of the foliage are essential.

The insecticidal agents of Bt consist of bacterial spores and crystals. When eaten the crystal dissolves and paralyzes the insect gut, causing it to stop feeding, and death may occur during the next few days. The insect gut lining begins to break apart and may permit spore germination and growth of the bacterial spores in the body cavity. This causes a general infection which leads to death.

Bt is registered for use against hundreds of insects on a world-wide basis to protect crops, shrubs and trees. In Minnesota, Bt can be used for caterpillar control on forest and shade trees. Major insects affected include tent caterpillars, gypsy moth, jack pine and spruce budworm. In addition, bagworm, spanworm, red humped caterpillar, cankerworm, and saddled prominent can be controlled with Bt. It does not control sawflies, bees, grubs, maggots, or any adult insects.

In general, Bt is very safe to use. The EPA has found no hazards to human health associated with the use of Bt. It has no known carcinogenic or mutagenic properties at field application rates or in laboratory studies. There are no known poisonings or chronic exposure problems. However, in concentrated form, it may cause sensitization in hypersensitive individuals following long inhalation exposure or accidental injection. The EPA considers Bt sufficiently safe that it has exempted it from food residue tolerances, groundwater restrictions, endangered species labeling, special review requirements, spray area reentry interval, and protective clothing for applicators. Bt does kill the caterpillar stages of most butterfly and moth species. In some instances, killing non-target caterpillars is be of concern. Be especially aware of are rare or beneficial species of butterflies in the area to be treated.