MTDC redesigned the steering system of the shielded herbicide sprayer (figure 19) with a tiller bar (figure 20) that actuates a wheel assembly. A mechanism was added to allow the width of the sprayer hood to be adjusted (figure 21). A gauge wheel was added to the back side of the individual in-row sprayer hoods and a gauge wheel was added to the front side of the wheel-row sprayer hoods. A mist barrier was added to the bottom of the sprayer hoods to reduce the chance that herbicide mist would escape (figure 22).

Figure 19—The second-generation MTDC Shielded Herbicide
Sprayer has adjustable spray hoods, a tiller steering system,
and a sun shade.

Figure 20—A closeup of the tiller bar used to steer the
MTDC Shielded Herbicide Sprayer.

Figure 21—The mechanism used to adjust the width of a
sprayer hood on the MTDC Shielded Herbicide Sprayer.

Figure 22—An adjustable spray hood with the height gauge
wheel and bristle mist guard on the MTDC Shielded
Herbicide Sprayer.

The second MTDC prototype was evaluated during field tests at the Augusta Forestry Center. According to Joshua McLaughlin, the unit was used for 6 days. It was used to apply Roundup Pro on five-row crops including white oak, northern red oak, bald cypress, sawtooth oak, and hazelnut. The seedbeds were about 4 feet wide. The chemical mixtures tested were 1 ounce per gallon or 2 ounces per gallon of Roundup Pro. A surfactant, Induce, was also added at a rate of 1 percent to quickly wet the plants and spread a uniform spray. Evaluators said they could not tell the difference in weed mortality between the 1- and 2-ounce mixtures. The tractor was operated at 1 ½ or 1 ¾ miles per hour. Even at the higher speed, enough herbicide was being applied.

A little herbicide escaped, damaging some trees. Evaluators were unsure whether the escape was human error or whether mist leaked from the hoods. The applicators did not notice herbicide leaking out. McLaughlin wondered whether the mixture might have been too concentrated. Some of the sprayer's tips and strainers were plugged, but evaluators attributed these problems to storage over the winter. When the sprayer was in full operation, there were no problems. The check valves did not leak. The flow-control gauges could not be evaluated because none of the spray units became clogged.

Evaluators started the spraying using the original nozzle tips (8001E and TR80-02) and worked some days with 8006 nozzle tips. Although the 8006 tips allowed more product to be applied, evaluators wonder whether these tips might have allowed a little herbicide to escape, damaging some trees.

Evaluators discovered that the steering wheels were not durable enough for their uses of the machine. Evaluators installed a sturdier wheel assembly (figure 23).

Figure 23—The improved version of the steering guide wheel
on the MTDC Shielded Herbicide Sprayer.—Courtesy of the
Virginia Department of Forestry

The new wheel assembly made it much easier to guide the sprayer unit. MTDC has incorporated this modification into the final design. The brushes on the bottom of each hood were seen as a plus, but the wheels on the back of each hood were installed too close to the hoods. Under wet conditions, mud built up between the wheels and the back of the sprayer hoods. Also, these gauging wheels were difficult to clean. The gauge wheels will be positioned farther back to correct the problem.