Interpretación de los resultados Su discusión

Like the field trial (Chapter 2), the herbicides were applied when the plants were beginning to senesce as this was thought to be the best time to apply the herbicides as the plant was most likely to be transporting sugars to the underground organs as the leaves were senescing. Thus the herbicides would also likely be translocated to the underground organs. This senescence and the dying off of the aboveground parts is also the reason why these initial results do not show the full effects of the herbicides as the normal death of the aboveground parts of the plant would affect the health of the plant and not be able to be fully separated from the herbicide effects when scoring. Furthermore the initial measurements are only able to measure the

aboveground effects of the herbicides and not whether the herbicides have affected the belowground organs, which for C. silvatica is the most important part to target as

that is where regrowth is likely to occur from. However some information about the initial effects of the herbicides on C. silvatica was obtained.

Triclopyr/picloram/aminopyralid was the fastest and most effective herbicide applied to affect the health of C. silvatica initially. Whether applied to the upper portion or lower portion the entire plant was 100% affected two weeks after herbicide

application. The same results were found in the field trial (Chapter 2).

Metsulfuron and 2,4-D were the next best herbicides to affect C. silvatica initially and the treated and untreated portions were quickly affected. Metsulfuron also initially affected the plants in the field trial (Chapter 2), although it appears as though the plants were affected faster in the glasshouse than in the field. Hornby (2011) found that C. silvatica was affected by metsulfuron initially and Heering & Peeper (1991) found metsulfuron affected C. arvensis by 80 – 96% eight weeks after treatment, depending on the rate used. The trial presented in this chapter found that metsulfuron had initially affected C. silvatica by a similar amount eight weeks after herbicide

application. Unlike metsulfuron, 2,4-D was not trialled in the field trial (Chapter 2) due to limited plots available.

Fluroxypyr and 2,4-D/dicamba also significantly affected the C. silvatica plants initially, including the untreated portions. When applied to established plants in the field (Chapter 2), 2,4-D/dicamba was one of the most effective herbicides although the untreated portion was affected slower than the rest of the plant. In the current trial 2,4-D/dicamba affected the untreated portion quicker. This could be because the plants were smaller than those in the field or because a set dose was applied to all of the leaves in the treated portion with the addition of surfactant.

In this trial glyphosate showed slower effects than in the field trial (Chapter 2). This could be because those plants in the glasshouse only had herbicide applied to 50% of the plant, whereas those plants in the field had herbicide applied to 90% of the plant, and those plants in the glasshouse only had 1 ml of herbicide applied, which may not have been a fatal dose. Rahman and Sanders (1992) also found that glyphosate only provided some initial control of C. silvatica and Matic and Black (1994) only found some knockback initially in a trial on C. arvensis.

The two remaining treatments, aminopyralid and clopyralid, both showed poor initial results. Aminopyralid did not affect the C. silvatica plants as significantly as the other treatments, and only showed localised herbicide effects on the leaves and vines. Those plants treated with aminopyralid in the field (Chapter 2) showed better and faster results than those found in the glasshouse. Again this is likely due to the fact that the herbicide was applied to 90% of the plant in the field and only 50% in the glasshouse. Clopyralid also showed poor results initially and the plants were often as healthy as

those in the untreated controls. The field trial (Chapter 2) showed better results and where the health of the plants was affected faster. This difference could be because the glasshouse plants only had herbicide applied to half the plant. Other trials have also found that clopyralid shows only some knockback of C. silvatica (Rahman & Sanders 1992), C. sepium (Rahman et al. 2002) and C. arvensis (Matic & Black 1994).

3.4.2 C. silvatica spring regrowth

The pots were moved to the shadehouse after the initial measurements. While the pots were in the shadehouse new shoots did not emerge until 5 October 2012, a considerable period of time after shoots had emerged in the field (22 August 2012), as seen in Chapter 2. This could be because those plants in the shadehouse were smaller and thus had less reserves or because they were in damper conditions with less exposure to full sunshine than those plants in the field. In the shadehouse the pots were also more exposed to colder temperatures than they were when they were in the glasshouse. This could have delayed new shoot growth. The shoot growth may also have been delayed because the plants were grown quite late and their normal growth pattern may have been disrupted because of this. There were also few shoots in the untreated control 24 and 28 weeks after herbicide application and as a result few treatments were significantly different from the untreated control.

Shoots emerged sooner in the metsulfuron treatments than in any other treatment. The same was found in the field (Chapter 2) where more shoots had emerged in the metsulfuron treatments by 22 weeks than any other treatment. Heering and Peeper (1991) and Matic and Black (1994) found that C. arvensis also grew back after

treatment with metsulfuron. Metsulfuron may have stimulated the shoots to regrow early, but further investigation would be required to confirm this. After 28 weeks, the pots in which 2,4-D was applied to the lower portion of C. silvatica, also had more shoots emerge than the untreated controls. Other trials which used 2,4-D found that while it can provide good initial control of C. arvensis there is significant regrowth in most cases (Wiese & Lavake 1986; Schoenhals et al. 1990; Matic & Black 1994). Because the regrowth occurred later in the season, the first two initial regrowth measurements do not show the whole picture about which treatments gave long term control of C. silvatica. Those measurements taken at 32 and 37 weeks however show a more accurate picture of the long lasting effects of the herbicides on C. silvatica as the shoots had emerged in most cases and accurate measurements were able to be taken and at 37 weeks the roots and rhizomes were able to be destructively sampled to show the effects the herbicides had on the roots and rhizome.

After 32 and 37 weeks had passed several pots treated with 2,4-D/dicamba,

three herbicides therefore showed long lasting control of C. silvatica and were the three best treatments out of those tested in the current trial. These results were better than what was found in the field trial (Chapter 2) where although there was some long term control, by 33 weeks these three treatments had several plants regrow. This difference is probably because those plants in the field would have had more extensive root systems than those smaller plants in the glasshouse. However these results do show that these three herbicides show potential for the control of C.

silvatica and should be investigated further.

These results are similar to what has been found on C. silvatica in a separate trial. Hornby (2011) found that triclopyr/picloram and aminopyralid showed long term control of C. silvatica.

The other herbicides didn’t show the same level of control and for the most part the upper and lower treatments of the herbicides showed similar results to the untreated controls and thus there was little control of the C. silvatica and its below ground parts. Previous trials with 2,4-D showed only partial control of C. arvensis long term as there was regrowth (Wiese & Lavake 1986; Schoenhals et al. 1990; Matic & Black 1994). The current trial found similar results, despite the species differences. C. arvensis also grew back after applications of fluroxypyr (Matic & Black 1994), as did the C. silvatica in the current trial. Neither 2,4-D nor fluroxypyr were trialled in the field due to limited available plants. Clopyralid, glyphosate and metsulfuron were trialled in the field (Chapter 2) and all three herbicides showed similar efficacy on C. silvatica in the field as in the glasshouse. Trials using metsulfuron, clopyralid and glyphosate also found that C. arvensis (Wiese & Lavake 1986; Heering & Peeper 1991; Matic & Black 1994), C.

sepium (Rahman et al. 2002) and C. silvatica (Rahman & Sanders 1992; Hornby 2011) usually grew back after herbicide treatment.