Insects
Using Bt
Bt (or Bacillus thuringiensis) is a biological control, a bacterium that works as an insecticide. To use Bt effectively the strain of Bt must be matched up with the pest it will be applied to control. Btk, or the kurstaki strain, is only effective against caterpillars, whereas the Bti, or israelensis strain, is effective against some species of gnats, mosquitos, and black flies. Regardless of the strain, Bt products are very selective. The advantage of this selectivity is that nontarget beneficial insects are not directly harmed by applications of Bt. Other advantages of Bt include a fairly short reentry interval.

Bt must be injested by the pest insect to work. Large caterpillars, especially those that are moving down off of plants are likely nearing pupation and are not going to be impacted by Bt applications because they are no longer feeding. Younger, and therefore smaller, caterpillars have the greatest chance to be controlled by Bt (and by conventional pesticides). Most insects stop feeding soon after injesting the Bt and most die within 2-3 days.

Sawflies often look like caterpillars but there are some important differences. Due to those differences they are not controlled by Bt. How can you tell if you have a caterpillar or a sawfly? Sawflies have 6 or more pairs of prolegs, caterpillars have 5 or fewer. Prolegs are short, stubby leg-like projections from the abdomen of the insect.

Source: Bt in your corner. NMPRO. November 2001.

Cultural

Tree Stake Options

Takiron/California Plastics - Plastic coated steel stakes ($2.50/8' stake): Some flexing to allow caliper. Some growers complain of plant damage from the point where ribs in the plastic designed to hold ties in place rub the bark, otherwise plastic coating prevents rubbing at top of stake and rusting. These stakes are generally not available larger than 8'. Bend in high wind (see below) causing cracks in plastic which leads to rust and shortened product life.
Bamboo ($1.00/8' stake): The portion below ground degrades limiting lifespan and size of trees that can be staked in following years. Doesn't flex in the wind. Some complain of rubbing on the trunk from the top of the stake. Can be split in half in order to wrap around the tree trunk when making a splint.
Metal All metal has the potential to bend in a strong wind. This bend is difficult to remove and leads to a dogleg in the trunk. (Price of steel has been increasing.):
Steel rods: Allow flexing for caliper development. Some complain of rubbing on the trunk from the top of the rod. Others have found plastic caps or sponge-like products from other industries to remedy this problem. Can be difficult to remove from the ground after a few years due to oxidation. Can be recycled.
Ultra Stake/Galvenized Steel Conduit ($2.45/8' stake): Doesn't flex. Can be recycled. Long life if not bent.
Smart Stake/Fiberglass ($2.50-$5.00/10' stake, price varies with diameter): Extremely flexible. Doesn't rot, bend, or break. Twenty year lifespan.
Tree-MATE-O ($5.00 + fencepost): Allows tree to flex but not bend or break. Ring on unit is large, impacts branching and can rub branches. Because fencepost is driven into soil, not pot, it doesn't blow over in high winds.

Thanks to these suppliers for providing information:
A.M. Leonard - Takiron, Galvenized Steel Conduit, and Bamboo stakes: 800-543-8955
Geotek Inc.- Fiberglass stakes: 800-533-1680
MacKenzies - Bamboo stakes: 800-777-5030
T-MATE-O - Tree-MATE-O: 877-854-5497

Staking is better than planting too deeply. With all of the attention planting depth is receiving from the green industry, be certain of your planting depth. Proper spacing can help reduce the need for staking - check out your liner supplier's spacing and compare it to others.

Source: Potter, M. J. 1991. Tree shelters. London: Forestry Commission Handbook 7.