Interest in controlling weed plants using radio frequency or microwave energy has been growing in recent years because of the growing concerns about herbicide resistance and chemical residues in the environment. This paper reviews the prospects of using microwave energy to manage weeds. Microwave energy effectively kills weed plants and their seeds; however, most studies have focused on applying the microwave energy over a sizable area, which requires about ten times the energy that is embodied in conventional chemical treatments to achieve effective weed control. A closer analysis of the microwave heating phenomenon suggests that thermal runaway can reduce microwave weed treatment time by at least one order of magnitude. If thermal runaway can be induced in weed plants, the energy costs associated with microwave weed management would be comparable with chemical weed control.

The growing list of herbicide-resistant biotypes and environmental concerns about chemical use has prompted interest in alternative methods of managing weeds. This study explored the effect of microwave energy on paddy melon (Cucumis myriocarpus) plants, fruits, and seeds. Microwave treatment killed paddy melon plants and seeds. Stem rupture due to internal steam explosions often occurred after the first few seconds of microwave treatment when a small aperture antenna was used to apply the microwave energy. The half lethal microwave energy dose for plants was 145 J/cm 2 ; however, a dose of at least 422 J/cm 2 was needed to kill seeds. This study demonstrated that a strategic burst of intense microwave energy, focused onto the stem of the plant is as effective as applying microwave energy to the whole plant, but uses much less energy.

Preliminary research has suggested that in vitro dry matter disappearance of some poor-quality fodder materials can be improved by microwave treatment. A laboratory-scale experiment that treated 50-g samples of lucerne hay in a 750-W microwave oven for 0, 40 and 80 s revealed that dry matter percentage increased by 1.7% as microwave treatment time increased from 0 to 80 s. The in vitro dry matter disappearance increased by 14.9% as microwave treatment increased from 0 to 80 s; however, there was no significant change in crude protein due to excessive variability in the results. This experiment was followed up with a larger-sample experiment in which 25-kg bags of lucerne fodder were treated for 7.5, 15, 22.5 or 30 min in an experimental 6-kW microwave chamber. Dry matter percentage increased by 7.2% as microwave treatment time increased from 0 to 30 min. Microwave treatment significantly increased dry matter disappearance during the in vitro digestion study; however, there were no significant differences between the various microwave treatment times. The 15-min treatment resulted in the greatest increase in dry matter disappearance (5.9%). The crude protein retained in the digestion residues increased by 19.2% as microwave treatment increased from 0 to 30 min. These laboratory studies were followed up with an animal response study in which 22 12–14-month-old Merino wethers were randomly allocated into either a group receiving a maintenance ration of untreated lucerne or a group receiving the same weight of microwave-treated lucerne. The average weight of the control group fluctuated around their starting weight during the 5-week-long trial, as would be expected from feeding a maintenance ration. By the end of the trial their average weight was 0.4% higher than when they started. However the group being fed the microwave-treated lucerne gained 8.1% of their initial bodyweight by the end of the trial.

Preliminary research has suggested that in vitro dry matter disappearance (DMD) of some poor quality animal fodder materials can be improved by microwave treatment. Laboratory scale experiments revealed that dry matter percentage of Lucerne hay increased by 1.7% as microwave treatment time increased from 0 to 80 seconds. The in vitro DMD of lucerne hay increased by 14.9% during the same microwave treatment. In addition it was also demonstrated that microwave treatment significantly increased starch digestion of oats compared to the control samples. These experiments were followed up with a larger sample experiment in which 25 kg bags of Lucerne fodder were treated for 7.5, 15, 22.5 or 30 minutes in an experimental 6 kW microwave chamber. Dry matter percentage increased by 7.2% as microwave treatment time increased from 0 to 30 minutes. Microwave treatment significantly increased DMD during an in vitro digestion study; however there were no significant differences between the various microwave treatment times. The 15 minute treatment resulted in the greatest increase in dry matter disappearance (5.9%). The crude protein retained in the digestion residues increased by 19.2% as microwave treatment increased from 0 to 30 minutes. These laboratory studies were followed up with an animal response study in which a Merino sheep group being fed the microwave treated lucerne gained 8.1% of their initial body weight by the end of the trial compared to a 0.4% increase in body weight for the control group.

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