SVERIGES LANTBRUKS UNIVERSITET

Weeds and Weed Control
24th Swedish Weed Conference
Uppsala 26-27 January 1983

Vol 1. Reports

WIPING GLYPHOSATE ON CUT SHOOTS OF AGROPYRON REPENS

Lido Dobrovich, Hjalmar Nilsson and Sigurd Håkansson
Department of Plant Hurbandry

SUMMARY

The effect on Agropyron repens of glyphosate (in Roundup) applied by wiping onto cut shoots and by applying the herbicide onto the actual cut areas or on limited parts of the stem/leaf surfaces further down was studied in pot experiments. When the cut area was completely fresh almost the same effect was obtained by placing a small quantity of herbicide on the cut surface as by wiping a totally much larger quantity along the stems and leaves in addition to the quantity that also adhered to the cut surface. Good effect was also obtained when applying only to stems and leaves without the herbicide coming into contact with the cut surface. No noticeable effect was observed when applying only to the cut surfaces when they were two days old and had dried out. When wiping along stems and leaves, when also the cut surfaces became treated, no significant difference in effect was noticed between treatments where the cut surfaces were fresh and those where they were two days old.

INTRODUCTION

Methods for wiping glyphosate, in Roundup, onto weeds have become of interest during recent years. Roundup is applied in a fluid with considerably higher concentration than in normal spraying and the spray volume per unit of area will be smaller. The method of application is of particular interest as a method of controlling Agropyron repens in conjunction with cereal harvest. The wiping is then done on Agropyron repens where the longer shoots have been cut off at combining. The following questions have arisen in this connection. Is the effect obtained by uptake in the actual cut surfaces or does the uptake occur effectively only through the epidermis/stomata on leaves and stems? What importance for the effect has the age of the cut surfaces following the cutting? An experiment was conducted during the summer-autumn 1982 in order to give a preliminary answer to these questions.

MATERIALS AND METHODS

The experiment was arranged as a pot experiment in the experimental enclosure at the Department of Plant Husbandry. Agropyron repens runners were dug up from arable soil on 9 June 1982. Among runners formed during the year, 5 cm long pieces with two buds on each were cut off. The pieces were planted on June 10 in Mitscherlich pots filled with sandy soil of moderate organic content, 5 pieces per pot at a depth of 5 cm. The pots were repeatedly watered as needed. On June 22 and July 14 NPK fertilizer was supplied in the form of 50 ml per pot of a water solution of NPK fertilizer (Superba S, 280 ml per 10 l water).

The treatment with Roundup was done on September 2. At that time the plants of Agropyron repens had reached a development that can be considered to correspond to a development that is normal at the time of cereal harvest in Central Sweden. It had above-ground shoots of very varying lengths, which is typical. Leafy shoots without stems ranging from 5 to 25 cm in length and shoots with stems of 40-60 cm length (with and without spikes) occurred together. Below the soil surface there was a well-developed system of new runners, often several dm long and more or less branched.

The shoots were cut with scissors, 25 cm above soil. All stems and leaves that reached higher than 25 cm were cut approximately as at cereal harvest. Shorter shoots remained uncut. Cutting was done either two days before or immediately before herbicide application.

Roundup was applied with Wettex cloths moistened with Roundup solution of different concentrations - by wiping along the cut shoots or by pressing either onto the cut surfaces or onto limited parts of the stems/leaves. (The Wettex cloth consists of ca. 35 % cotton and 65 % cellulose and has the ability to absorb the liquid to an amount of 10-20 times its own weight).

Wiping along the shoots (methods 1.1 and 1.2) was done as follows. A long and narrow vessel, open in the top through a narrow slit, contained Roundup solution. A Wettex cloth was placed in the vessel through the slit and was allowed to hang over the front edge of the vessel and the freely down to a level about 15 cm under the bottom of the vessel. The horizontal lower edge of the cloth reached about 5 cm above the upper rims of the Mitscherlich pots, which were placed on a conveyor underneath the cloth. The pots were transported on the conveyor under the wiping apparatus at a speed of 1 m/sec. As the Agropyron shoots and the Wettex cloth were bent backwards during the passage under the application apparatus, the shoot parts above a height of 10-12 cm were wiped. Lower shoot parts and lower shoots were not treated. Pressing onto limited surfaces was done with a wooden block (8x8x4 cm) wrapped in Wettex cloth moistened with Roundup solution. When pressing the cloth onto the cut surfaces (methods 2.1 and 2.2) the shoots were held gathered in the hand (as done earlier when cutting) and the surfaces were touched by the Wettex cloth in three rapid, light applications. The pressing against the shoots 6-8 cm below the cut surfaces was also done with the shoots gathered in the hand and with three rapid applications with one of the edges of the block onto the shoot group, from three directions with ca. 120º difference.

The following treatments with regard to combinations of cutting and type of Roundup application were used:

1. Wiping along the shoot
1.1 Cutting 2 days before application
1.2 Cutting immediately before application

2. Pressing onto the cut surfaces
2.1.Cutting 2 days before application
2.2 Cutting immediately before application

3. Pressing onto the shoots 6-8 cm below the cut surfaces
Cutting immediately before application

All the above treatments were sub-divided with regard to the application of Roundup as follows:

- No application of Roundup
- Application of a solution with 5 % Roundup
- Application of a solution with 20 % Roundup
- Application of a solution with 50 % Roundup

Each sub-treatment was represented by five pots, distributed into five different blocks.

At different times following the treatment, changes in the above-ground shoots were determined according to the following scale with regard to the total amount of shoots in a pot:

0. Shoots completely green
1. Weak changes in colour
2. Comprehensive red shade
3. Largely brown and withered
4. Completely dead

On the 35th day after the treatment the above-ground shoots of Agropron repens were cut off. The underground stems and roots were then taken up from the pots. Together with the soil they formed a cylindrical mass. This was divided into four equally large parts by two cuts at right angles. One of these parts was chosen randomly and its rhizomes and roots were shaken out and placed in pots with new soil, where they were distributed and covered with about 5 cm soil. All pots were taken to a glasshouse with a temperature of ca. 8ºC (night) and ca. 15ºC (day) for determination of the emergence of new shoots as a test of the regeneration ability of the runners. The number of shoots were counted on 3 November, thus 27 days after transplanting, when the shoots were also cut at the soil surface and weighed. The re-growth of above-ground shoots after another 8 days was counted and weighed, on 11 November (Table 1).

RESULTS AND DISCUSSION

Wiping along the shoots gave approximately the same herbicide effect in treatments 1.1 and 1.2. With this treatment the herbicide solution was not only wiped along the shoots below the cuts but also onto the cut surfaces. However, the quantity that adhered along the shoots below the cuts was judged to be many times larger.

Pressing against the cut surfaces in methods 2.1 and 2.2 was judged to have left a quantity of herbicide on these surfaces of the same magnitude as on the corresponding surfaces in methods 1.1 and 1.2. It was judged that almost as much herbicide was deposited on the shoots immediately below the cut surfaces as on the actual cut surfaces themselves. The 2 days old cut surfaces, as well as stems and leaves down to 4-7 mm below these surfaces, had dried out at the time of the herbicide application. The results in Table 1, treatment 2.1, suggest that there was no effect of importance achieved by applying herbicide to these dry tissues. When applying the herbicide to the freshly cut surfaces (treatment 2.2) the effect was, on the other hand, almost as good as when applying by wiping, despite that perhaps 100 times as large amount was applied by wiping along the shoots as by pressing onto the cut surfaces.

Table 1. Result of treatments. Pots treated with Roundup: means of 5 replications. Pots not treated with Roundup: means of 10 (1.1 and 2.1) or 15 (1.2, 2.2, 3) replications

Click here for Table 1

Application by pressing onto the shoots 6-8 cm below the cut surfaces (treatment 3) was judged to have deposited a larger amount of herbicide on the shoots than the application according to 2.1 and 2.2, but only a fraction of the quantity according to 1.1 and 1.2. It is, then, interesting that the effect was at least as strong or stronger in treatment 3 than in 1.1 and 1.2.

Even the relatively low doses in treatment 3 have, thus, been sufficient to give good effect. There are also negligible or almost no differences in effect between the 5 % and the 50 % concentrations in the different treatments. The differences between various doses and between methods 1.1, 1.2, 2.2 and 3 that can be distinguished, appear to be fairly random. They are to a considerably extent a result of certain low shoots not reacting at all to the Roundup application because they originated from planted rhizome pieces, which had not developed any shoot of such length that it came in contact with the herbicide. Short shoots that were in connection with longer shoots via the mother rhizome or those that originated as lateral shoots from the base of longer shoots, were generally influenced as strongly as the longer shoots on which the herbicide was applied. Thus the herbicide must have been transported very effectively in the plants.

It was very difficult to sort the underground stems into living and dead groups or into different degrees of viability. The number and weight of new shoots that emerged after transplanting were judged, however, to give a very good reflection of the quantity of viable underground stems present at the time of transplanting.