How do I protect my newly planted trees from deer browse?
First of all, sports hunting should be allowed in your area (bow hunting in more urban areas) to help in preventing population expansion of white tail deer. Once the deer population gets very high, shooting damage-causing deer is not very cost effective in that deer simply move in to replace deer that are removed.
You should know what to look for to distinguish deer browse from rabbit browse. You can look for hoof prints on the ground and telltale droppings near the damage. Deer don’t have upper incisor teeth so they tend to tear off the vegetation as they browse. Rabbit damage is two feet or less from the ground and they leave smooth cuts when they browse. Remember that deer tend to browse young tender growth in it’s early stages and may not be very noticeable, yet by nipping plants "in the bud" you have lost much potential growth of a tree for the season.
There are two basic ways of preventing deer damage — repellents and barriers (fencing). Repellents in general only provide moderate protection and may be only a temporary fix as deer learn to ignore the repellents. Fencing on the other hand is permanent and can provide good to excellent protection depending on the extensiveness and how well the fencing is maintained.
Area repellents are applied near plants and repel deer by smell. Examples are small bars of soap, human hair, moth balls, chicken eggs (20% eggs/ 80% water), coyote urine, and commercial products such as Hinder and Big Game Repellent (Deer-Away).
Contact repellents are applied directly to trees to repel deer by taste. Examples are Hot Sauce (6% Hot Sauce/ 94% water), Habanero peppers (8% pepper/ 92% water), Thiram, and commercial products such as DeerGuard or DuraPel (both contain bitter tasting Bitrex). These repellents should be applied as needed, as new growth appears and after heavy rainfall.
A deer’s learning ability tends to make repellents fail over time and truly hungry deer will ignore repellents. It’s a good idea to switch repellents periodically as a counter measure.
If deer browsing is heavy or you need rather complete and permanent protection, then a physical barrier (exclusion) is necessary. Physical barriers range from woven wire fencing 8-10 feet high or electric fencing, to protecting individual trees with welded wire hoop cages or using tree shelters (tubes).
Tree fencing requires the least maintenance but is costly to install. A common style electric fence used at the Horticulture and Agroforestry Center (HARC) consists of sevenfoot steel posts with six electric cord strands with a solar charger. Care must be taken to keep the fence well maintained, by keeping vegetation off the wires or deer will easily jump or crawl through the fence.
Individual trees can be protected using wire hoops. Five-foot tall welded wire (2x4 inch grid) cut into five-foot sections formed into a hoop and fastened to the ground with a four-foot section of rebar is being used at HARC. The downside is that its harder to maintain the trees with the hoop in place and during windy periods the trees may rub against the top of the cage causing trunk damage. Plastic tree tubes are also used to protect individual young trees. Problems have been observed using tree tubes such as spindly stem growth and winter damage. There are now tubes that are made with coarse mesh or fine mesh (openings about 1/8th inch). These tubes require more extensive staking from top to bottom to hold them up. The coarse mesh tubes have the problem of allowing the side branches to grow out the sides of the tubes allowing browse, while the fine mesh tubes prevent this problem. The mesh tubes do not have the winter damage problem of the solid tubes and also do not harbor mice and wasps. Wire hoop cages and tree tubes have the benefit of protecting from rabbit damage that electric fences lack. Floodplains that have frequent flooding will cause debris buildup on fencing and caging.
Cages and tree tubes can even be pushed over by debris and the current of the floodwater. Cages and tubes should be removed as soon as branches are above most of the browse damage. These trees are still small enough to be vulnerable to buck rub. At HARC, two steel posts are positioned alongside each tree trunk to help prevent total girdling from buck rub. This is not necessary in the electric fence exclosure areas.
I suggest you research the pros and cons of the many treatments for deer damage control in regard to your particular situation and to check out the many resources on this subject on the internet.