Agronomy

1 VELPAR - A NEW HERBICIDE FOR USE IN SUGARCANE

F.E. Richardson

Triomf - Farmers Organisation (Pty) Ltd., Natal, South Africa

I I ABSTRACT

The results of 26 field experiments with Velpar* (3-cyclohexyl-6-

I -(dimethylamino)-I-methyl-l,3,5-triarine-2.4 (1 H,3H)-dione) used alone and in combination with diuron, are presented. The herbicides were applied to a wide range of grass and broadleaf species in the sugar industries of Southern Africa. Velpar at low doses (0,68 kg a.i./ha) and low dose Velpar/diuron combinations (0,45 + 2,00 kg a.i./ha respectively) gave up to four months residual weed control when applied pre- and early post-emergence. Such low doses were not effective when late post-emergence sprays were applied and when grasses had tillered. There was some control of Cyperus esculentus but Cyperus rotundus was tolerant. The low doses used did not in- duce symptoms of phytotoxicity on ratoon crops. Newly planted sug- arcane was not sufficiently tolerant to post-emergence sprays and some leaf chlorosis occurred. At double doses the treatments were suitable for long residual weed control on sugarcane breaks and on road verges.

INTRODUCTION

Pre-emergence herbicides are being used increasingly in the sugar in- dustries of South Africa, Swaziland and Malawi. Herbicides such as alachlor and inetribuzin have tended to replace the phenoxy-group products MCPA and 2,4-D during the past few years. Grasses were developing as problem weeds and treatments effective for pre-emergence grass control were re- commended1~2f~4. In spite of the initial high costs of app!ication, most growers readily appreciated the advantages of a single long residual treatment, and combinations of alacl~lor/atrazine and metribuzin/diuron now form the most commonly used treatments.

Growers find that perennial grasses such as Panicurn maximum and Sorghum verticilliflorum are still difficult to control, mainly because of the ineffectiveliess of delayed spray applications. The sedges Cyperus esculentus and Cyperus rotundus have also proved to be difficult to control for any length of time. Screening and product evaluation continues with other products and combinations, in the search for treatments that have a wider spectrum of activity, a longer duration of control, and less dependance upon timing and associatkd lactors than present treatments.

* Velpar is the registered trademark of E.I. du Pont de Nemours and Co. Inc, Wilmington, USA

1341

AGRONOMY

Velpar (3-cyclohexyl-6- (dimdthylamino) -1 -methyl-1,3,5-triazine-2,4 ( lH, 3H) -dione), manulactured by E.I. duPont de Nemours, and previously coded DPX 3674, is an extremely active contact and residual herbicides.

Velpar has been screened for use in sugarcane at high rates of applica- tion, and at such doses it was phytotoxic to the ~ r o p ~ , ~ ] ~ . However there has been evidence of weed control activity at very much lower doses. A series of field trials was planned for Velpar alone, and Velpar in combination with diuron, during the 1975-76 growing season to evaluate this product further for selective use in sugarcane. This papef presents some of the results of 26 of the trials completed.

EXPERIMENTAL

The trials were conducted on a number of estates in South Africa, Swaziland and Malawi. The physical characteristics of the respective soils ?re presented in Table I which also includes information about the respective sugarcane crops.

TABLE I. Details of Experimental Sites.

Trial Series pH O.M. Clay Silt Sand C.E.C." Crop Variew % % % %

IV v VI VII VIII IX X XI XI1 XI11 XIV xv XVI XVII XVIII XIX XX XXI XXII XXIIT XXIV XXV XXVI

Alluvium "" Cartref Cartref Kroonstad Kroonstad

-Mayo Mayo Inanda Alluvium Trevanian Trevanian Habelo """ Tambankulu """ Somerling xxx

Somerling "" Balmoral Alluvium "" Clansthal Warrington Waldene Griffin Cartref Shorrocks Inanda Inanda Inanqa

Plant NCo3 10 Plant NCo376 4th ratoon NCo376 Plant N55/805 1st ratoon NCo376 Plant NCo376 4th ratoon NCo376 1st ratoon NCo293 Plant NCo376 Plant NCo293 1st ratoon NCo293 Plant NCo376 1st ratoon NCo376 Plant NCo376 2nd ratoon NCo376 6th ratoon NCo376 4th ratoon NCo376 4th ratoon NCo376 Plant NCo376 2nd ratoon NCo376 1st ratoon NCo293 1st ratoon N55/805 2nd ratoon NCo376 4th ratoon NCo376 1st ratoon N55/805 1st ratoon N55/805 , .

C.E.C.: cation exchange capacity m.e. %. "" Malawi. """ Swaziland.

I F.E. RICHARDSON

Field layouts generally consisted ol a randomised block design. Treatments were replicated four times and each plot was 0,0060 hectare in I

sprayed area. Unsprayed strips were left adjacent to each plot and these proved useful as control areas in addition to the replicated unsprayed plots. Though land preparation varied from trial to trial the application of the treatments and the methods of assessment were similar. I

Herbicides were applied by means of a "Cooper Pegler CP3" knapsack sprayer fitted with either a "Spraying Systems TKsW floodjet or a "Desmar- quest APM3" floodjet. Nozzle pressure was usually about 1,O bar and the spray output varied from 250 to 350 litres per hectare in the different ex- periments. The spray swathe extended from canerow to canerow across the interrow in those situations where the crop had emerged. There was some spray overlap on the canerow itself. If the trial was designed to evaluate phytotoxicity to the crop, the sprays were directed over the crop row. Treatments were applied as they have been were the fields being sprayed commercially.

\,

The soil moisture status at spraying was generally suitable for soil- applied and residual herbicides to be\ effective. With few exceptions warm humid growing conditions followed spray .application.

Visual ratings of weed control efficacy were made at regular intervals using a scale of 1 (= complete weed control) to 9 (= no weed control). A score of 4 represented the situation where the weed population was just acceptable and further control operations were not immediately necessary. A score of 5 was just unacceptable. Wherever possible an evaluation by species or species-group (e.g. broadleaf, grasses) was done.

Visual observations of the phytotoxic effects of the treatments were made during the development of the crops. Height measurements from ground level to the uppermost visible dewlap on the cane shoots were taken in some of the trials where double rates of application had been sprayed over the crop row. One hundred randomly selected shoots were measured for each treatment and these provided a method of assessing any growth setback.

Velpar 90% w.s.p. was used alone at 0,34; 0,68 and 1,35 kg a.i./ha. Velpar and diuron 80% w.p. were used at 0,23 + 1,OO; 0,45 + 2,00 and 0,90 + 4,00 kg a.i./ha respectively. It should be noted that the increasing rates of application doubled the previous dose, and that Velpar/diuron com- binations were used in the ratios of approximately 1 :4 on active material and 1:5 on formulated product. The treatments were compared with the sugar industry standards of Actril DS/diuron and metribuzin/diuron.

Technical details of the formulations used are given in Appendix I.

1344 AGRONOMY

RESULTS AND DISCUSSION

The results are discussed in relation to the different times of herbicide application :

a) the weed control that resulted from spraying the weeds pre-emergence, early post-emergence and late post-emergence.

b) the effect on the sugarcane itself from sprays applied pre-emergence and post-emergence in respect ol the crop.

EFFECT ON WEEDS:

Application pre-weed-emergence

Treatments were applied before the emergence of weed seedlings in nine experiments. The soil had been ploughed and disced in five of the sites and a crop had been planted. The soil surfaces of the other four sites had been disturbed during the post-harvest cleanup operation of a burnt ratoon crop. Carbon residues were usually worked into the top few millimetres of soil. The cleaning operation consisted of collecting burnt crop residues with a side delivery rake and deposit,ing the trash material into every fifth interrow. The "cleaned" interrows were essentially weed free in the trials reported here, but under most practical conditions a few small weeds are present. By the time sprays were actually applied a very early post-emergence si- tuation might also have developed. The results from six of the sites are presented in Table 11.

TABLE 11. Mean scores for grass control after pre-emergence application.

Treatment Trial No. Days after application

Product Dose I1 VI IX X XIV XV kg a.i./ha 103 98 55 85 40 40

Velpar Velpar Velpar

Velpar 3. diuron Velpar 3. diuron Velpar I- diuron

Metribuzin + diuron Actril DS " + diuron

* expressed as litres product/hectare.

t F . E . RICHARDSON 1345

Very good weed control was given by most of the treatments and this persisted for a long time. Velpar at 0,68 kg a.i./ha, and the Velparkdiuron combination at 0,45 + 2,00 kg a.i./ha eventually gave nearly four months of commercially acceptable grass control. Many common broadleaf weeds were prevented from germinating. Weed species normally controlled at such rates are listed in Appendix II.

The lowest doses of Velpar and Velpar/diuron were not adequate for long residual control. It appears that the Velpar threshold level for effective weed control and no crop growth setback is between 0,45 and 0,75 kg a.i./ha. Diuron should not be added at rates greater than 2,5 kg a.i./ha.

. One of the experiments was in an area of very heavy sedge infestation. The effect of the treatments on Cyperus esculentus was much better than that on Cyperus rotundus and the latter species was confirmed as tolerant to Velpar/diuron conlbinations at practical rates of application.

It will be seen from Table I11 that there was excellent pre-emergence control of both species at high rates of application but symptoms of leaf chlorosis developed on a iew plants and the products cannot be recom- mended for use in plant crops of sugarcane at such high rates.

It should be noted that under the conditions of the experiment (with a soil of low clay content and with continuous wet weather after spraying) treatment with metribuzin + diuron at 1,40 and 1,60 kg a.i./ha respectively, gave better control of the Cyperaceae than did the test products.

TABLE 111. Mean scores for sedge control 55 days after pre-emergence application (Trial IX).

Treatment Cyperus Qperus

Product Dose kg a.i./ha

csculcntw rotundus

Velpar Velpar Velpar

Velpar + diuron Velpar + diuron Velpar + diuron

Metribuzin f diuron Actril DS + diuron

Application post-weed-en-er-qence

The treatments were applied post-emergence to weeds in fifteen ex- periments. It became clear that timing was of critical importance, and that,

AGRONOMY

for Velpar to be used successfully, the sprays have to be applied at an early post-emergence stage of weed growth.

When the treatments were applied to grasses at a late post-emergence stage (i.e. already tillering, culms over 60 mm high, more than 6-8 leaves unfurled) the results were generally unsatisfactory. Velpar is used at high rates for industrial weed control. It can be seer1 from Tables IV slkd V that the grass control was excellent when the very high rates were used, even when sprays were applied late post-emergence. Such treatments show promise for use in sugarcane breaks and on road verges.

TABLE IV. Mean scores for grass control after early post-emergence application.

Treatment Trial No.

Days after application

Dose I IV XI XI1 XXII I11 111 Product kg a.i./ha 36 74 57 40 45 53 103

Velpar Velpar Velpar

Velpar + diuron Velpar + diuron Velpar + diuron

Metribuzin + diuron Actrii DS -1 diuron

TABLE V . Mean scores for grass control after late post-emergence application.

Treatment Trial No.

Days after application

Product Dose VIII XIV

kg a.i./ha 70 40 XVI XIX

44 21

Velpar 0,34 7,9 5,s 6 5 - Velpar 0,68 4,9 3,9 5 s - Velpar 1,35 1,3 2,9 2,3 - Velpar + diuron 023 + 1,00 6 3 4 0 5,8$ 7 8 Velpar + diuron 0,45 + 2,00 1,8 3,s 4,o 4,o Velpar + diuron 0,90 + 4,OO 1 , 1 2,6 2,1 -

Metribuzin + diuron 1,40 + 1,60 1,8 3,9 3,4 2,O Actril DS + diuron 1,251 + 2,OO 2,1 4,9 4,6 4,o

Velpar/diuron mixtures at 0,45 + 2,00 kg a.i./ha were satisfactory for use within sugarcane fields if applied early post-emergence. under ad- verse climatic conditions this combination was better than Velpar alone at 0,68 kg a.i./ha. Velpar is highly water soluble (32,000 ppm) and diuron is consistently effective when used under warm wet climatic conditions. The best results were seen when applications were made during humid conditions and when the weeds were actively growing.

The control given by early post-emergence applications was less satisfactory than that from pre-emergence ones. The scores for Trial I11 (Table IV) show a rapid breakdown of weed control after about 50 days. Trial IV was conducted under extremely wet and humid conditions and the results were consequently very good. Broadleaf weed control was gen- erally satisfactory but perennial grasses such as Panicum maximum and Panicum laevifolium remained lairly tolerant unless sprayed at an extremely young stage. Paspalum urvillei and Cynodon dactylon were not controlled. Cyperus rotundus was tolerant but Cyperus esculentus was readily con- trolled at economic levels of application (Table VI).

I TABLE VI. Mean scores for Cyperus esculentus control after post-emergence ap- plications.

Treatment Trial No. Days after application

Product Dose '

kg a.i./ha IV XXII XXIV xxv 46 60 30 14

I Velpar 0,34 1,3 - - - Velpar 0,68 1,8 4,O 3,3 6 3 Velpar 1,35 1,o 2,3 1,8 3,3

I Velpar + diuron 0,23 + 1,00 2 4 6,O 2 3 Velpar + diuron 0,45 f 2,00 1,o 4,O 1,o Velpar + diuron 0,90 + 4,OO 1,3 3,O 1 3

Metribuzin + diuron 1,40 + 1,60 1,3 4,8 1 3 6 3 Actril DS + diuron 1,251 + 2,00 2,3 5,3 1,8 5 3

Effect on sugarcane

The phytotoxic effects on sugarcane ol high doses of Velpar have already been reported4~6. Symptoms include %,leaf chlorosis and leaftip ne- crosis. Stunted shoots, poor growth and dead result from increasing doses. Sugarcane was present in all the experiments. A few sites were particularly suitable for evaluating the effect on the cropl and measurements were taken to support visual observations where necessary.

1348 AGRONOMY

Plant crops

Plant crops were more susceptible than ratoons to sprays applied to emerged sugarcane. Phytotoxic symptoms were more apparent on cane growing on some of the sandier soils. When the treatments were applied pre-emergence to newly planted sugarcane the effects were less noticeable. No statistically significant reduction in plant growth from the herbiddes was measured, even from high double doses, but some of the leaves did show signs of chlorosis in a few of the trials. As may be seen from Table VII unchecked weed growth had marked effects on shoot populations and

, lengths.

TABLE VII. Crop growth measurements of plant cane sprayed pre-emergence. (Trials I1 and XI.

Treatment Shoot lengths Population " ( 4 per .metre

Products Dose I1 X X

kg a.i./ha 174 days 133 day 133 days

Velpar Velpar Velpar

Velpar + diuron O,23 + 1,00 - 40,s 16,2 Velpar + diuron 0,45 + 2,OO 81,l 38,3 17,6 Velpar + diuron O,90 + 4,OO 82,9 39,3 16,4

Metribuzin + diuron 1,40 + 1,60 79,9 41,3 18,6 Actril DS + diuron 1,251 + 2,OO - 38,3 17,6

Weeded control , Unweeded control

Standard error k 2 , 7 k 1,86 k 1,79 C.V. % 6,7% 9,56% 22,5% L.S.D. 5% 8,3 5,46 5 4 4

, ,& " Assessed by counting the number of shoots in 100 metres of cane row for each treatment.

With care the test products can be successfuflfksed in plant cane but the safety margin is very low. There is little room for error during field applications, eitther with the dose actually applied or with delays in the timing of the sprays. Consequently Velpar and Velpar/diuron combinations should be considered phytotoxic to plant cane even at low doses.

Ratoon crops

After a burnt ratoon has been harvested the development and emer- gence of new shoots is usually very rapid. Under normal summer conditions ratoon shoots are well developed by the time weed control sprays are ap-

F.E. RICHARDSON 1349

plied. Only in winter and early spring is growth sufficiently slow for sprays to be applied pre-emergence of cane. For practical purposes herbicide sprays in ratoons can be considered as being post-emergence of the crop.

It is normal practice to direct herbicides so as to avoid, or to minirnise as far as possible, spraying the cane leaves. This is normally achieved by the use of wide angle floodjets. These are positioned in the centre of the interrows and the spray swathe extends from cane row to cane row.

Velpar and Velpar/diuron had no marked effect on the crop when this method of application was used. A few chlorotic leaves were observed on plants growing on sandier soils when sprayed at double doses. Leaf chlorosis symptoms seemed to occur only when the treatments had been applied during very hot and humid conditions. As a result two phytotoxicity experiments (Trials XVIII and XX) were further established during mid- summer. Spays were applied directly over the rows of well grown ratoon crops (Variety NCo376). When sprayed, the 4th ratoon crop (Trial XVIII) had a mean canopy height of 50 cm with 7-9 leaves unfurled per shoot. The 2nd ratoon crop (Trial XX) had a mean canopy height of 30 cm with 3-4 leaves unfurled per shoot. Air temperatures ranged from 28-32OC.

Slower growth rates resulted when double doses were applied. The effects from double Velpar/diuron combinations were less than those from double doses of the 2,4-D/diuron standard. From Table VIII it will be seen that the differences were still present 5-6 months after application.

Although double doses gave less phytotoxicity than did double doses of the standard, it is considered that only directed sprays should be used, and that Velpar or Velpar/diuron combinations should never be applied directly over the crop.

TABLE VIII. Crop growth measurements of ratoon cane sprayed late post-emergence during summer.

Treatment Shoot lengths Population (cm) per metre

Products Dose per ha. Trial XVIII Trial XX Trial XX kg a.i. or a.e. 182 days 160 days 160 days

Velpar + diuron , 0,45 + 2,OO 173,3 147,8 101 Velpar + diuron 0,90 + 4,OO 160,5 148,O 78 2, 4-D + diuron + 2,88 + 4,OO 153,3 145,O 74 Weeded control - 163,3 155,8 107

Standard error _+7,75 +2,55 - C.V. % 933% 3,4% - L.S.D. 5% 24,7 cm 8,2 cm -

AGRONOMY

CONCLUSIONS

Velpar (at 0,68 kg a.i./ha) and Velpar/diuron combinations (at 0,45 + 2,00 kg a.i./ha) are suitable for certain weed control uses in sugar- cane fields. At the above rates of application a number of weed species are controlled for long periods without damage to the crop. Pre-emergence applications give more satisfactory results than do ones that are post- emergence of the weeds. However Velpar does not have a wide margin of selectivity between crop and weed. Carelessly controlled applications may lead to crop phytotoxicity. Plant cane does not appear to be as tolerant as ratoon crops and the use of treatments containing Velpar is not recom- mended in plant cane situations. Directed sprays should be used whenever possible in ratoon crops. At higher rates of application Velpar and Velpar/ diuron treatments are suitable for use in sugarcane breaks and on field edges.

ACKNOWLEDGEMENTS

The co-operation of many estates in providing sites for herbicide trials is greatly appreciated. Thanks are extended to the Director, South African Sugar Experiment Station, Mt. Edgecombe, for the analysis of sbil samples. Thanks are also due to the field advisory staff of Triomf-Farmers Organisation (Pty) Ltd., and in particular Mr. J.G. Hardy, who assisted with the experiments. The Velpar was donated by Messrs E.I. du Pont de Nemours and Co. (Inc.), Geneva, and the results form part of the data submitted for the registration of Velpar for use in sugarcane in South Africa.

REFERENCES

1. Richardson, F.E. (1970). The results of pre-emergence herbicide screening trials for sugarcane in Natal. SASTA Proc. 44: 148-154.

2 . Richardson, F.E. (1973). The results of recent pre-emergence herbicide screening trials in sugarcane, 1970-73. SASTA Proc. 47: 173-178.

3. Anon. (1975). Weed control in the South African Sugar Industry. S. Afr. Sug. Ass. Expt. Stat. 1-31.

4. Iggo, G.A. (1975). Results of screening pre-emergence herbicides for sugarcane. SASTA Proc. 49: 122-125. '

5. Allison, D.A. and Joyce, T.D. (1974). 3-cyclohexyl-6-(dimethylamino)-1-methyl 1,3,5-triazine - 2,4 (lH, 3H)-dione (DPX 3674) - a new non-selective herbicide with contact and residual properties. Proc. 12th Br. Weed Control. Conf., 279-284.

6. Anon. (1974). 22nd Annual Report. Mauritius Sugar Industry Research Institute, Mauritius. p. 48-50.

7. E.I. du Pont de Nemours and Co. (Inc.) (1975). Personal communication.

8. Macvicar, C.N. (1973). Soils of the Sugar Industry, Bulletin 19. South African Sugar Association Experiment Station.

I Details of herbicides used

I Common name Trade name Manufacturer Formulation

hexazinone" Velpar du Pont 90% W.S.P. diuron Karmex du Pont 80% w.p. metribuzin Sencor Bayer 70% w.p. 2,4-D amine Farmers 2,4-D Dow 720 g.a.e./c 2,4-D iso-octyl ester Actril DS May Baker 600 g.a.e./r + ioxynil octanoate + 100 g.a.i./~

I * (proposed)

APPENDIX I1

I Common weed species norlnally controlled pre-emergence or early post- emergence by Velpar (0,68 kg a.i./ha) or Velpar/diuron

(0,45 f 2,00 kg a.i./ha).

Grasses

Brachiaria eruciforrnis Digitaria ternata Panicum rnaxirnum Chloris pycnothrix Eleusina africana Rhynchelytrum repens Cl~loris gayana Eleusina indica Setaria sphacelata Digitaria adscendens Panicum Iaevifoliun~ Setaria ~~erticillata Digitaria sanguinalis Panicurn glabrescens

Broadleaf Weeds

Chenopodium rnurale Galir~soga parviflora Acalyplza ecklonii Chenopodiunl album Gnapkalium luteo-album Argemone rnexicana Commelina diffusa Hibiscus trionum Ageratunz conyzoides Cosmos bipinnatus Lepidium bonariensis Apium leptophy llum Lepidium divaricatunz Ainaranthus hybridus Datura stramoniunz Nicandra physaloides Amaranthus spinosus Emex australis Portulaca oleraceae Amaranthus thurlbergii Erigeron floribundus Richardia brasiliensis Bidens pilosa Erigeror~ canadense so la nun^ nigrum Commelina benghalensis Eupatorium odoraturn Siegesbeckia orientalis

VELPAR - UN NUEVO YERBICIDA . A ,;USARSE g~ LOS CAMPOS DE CANA DE AZUCAR

I

F.E. Richardson I

RESUMEN

Se presentan 10s resultados de 26 experimentos con Velpar (3 - cyclohexyl - 6 - (dimethylamino)- 1 - methyl - 1, 3, 5 - triazine - 2, 4 (AH, 3H)-dione) usado sol6 y en comb,inacion con diur6n. Los

1352 AGRONOMY

yerbicidas se aplicaron a una garna arnplia de yerbajos de hoja ancha y grarnineas. El Velpar a razon de 0.68 kg a.i./ha y dosis bajas de la cornbinacion con diuron (0.45 + 2.00 kg a. i./ha, respectivamente, tuvieron efectos residuales en el control de yerbajos por cuatro rne- ses si se aplicaban corno pre y posternergente. Tales dosis no tu- vieron efectos favorables cuando 10s yerbajos habian retofiado. Se registr6 cierto control de Cyperus esculentus per0 el Cyperus ro- t u n d ~ ~ result6 tolerante. No hub0 sintornas de fitotoxicidad en el retofio de cafia. En cafia nueva sernbrada se observ6 cierta clorosis por efectos postrnergentes del yerbicida. A dosis dobles, 10s trata- rnientos fueron adecuados para control yerbajos que crecen en 10s bordes de 10s carnpos de caiia.