THE EFFECTS OF PRE-PLANT SEEDCANE TRE,ATMENT WITH THE FUNGICID-E,

ACYLALANINE

G. L. James Booker Agriculture International Limited, London, England, seconded to Ramu

Sugar Limited, Lae, Papua, New Guinea

ABSTRACT

Results from five trials carried out in Papua, New Guina, are reported, and the data show that downy mildew can be controlled in the plant crop by preplant treatment of the seedcane with acylalanine. The efficacy of the fungicide is shown t o persist into the first ratoon. Application of acylalanine as a foliar spray to four week old cane is also shown to control downy mildew, and the cost of this treatment in comparison to preplant seedcane treatment is discussed.

Increasing the length of time of preplant treatment in acylalanine did not reduce the levels in downy mildew infection which developed subse- quently. However fungicide concentrations significantly influenced stalk populations. Recommendations are made, therefore, for the lenght of treatment time and concentrations are made, therefore, for the lenght of treatment time and concentration of acylalanine for the preplant seedcane treatment of cy Q 90.

I t is concluded that the fungicide is useful in mantaining Q 90 in the spetrum of commercial varieties until an alternative varietyof equal agrono- mic and milling qualities, but with resistance to downy mildew, is foun.

II INTRODUCTION

Ramu Sugar Limited's state is 180 km west-northwest of the coastal port of Lae, and is also WNW of the Ramu-Markham Valley divide. The state lies at an altitude of around 400 m above sea level, and at an approximate latitude and longitude of 6" South 145' 53' East. The Ramu River forms the south-western border of the estate, and the foothills of the Finisterre range are to the nor- theast. When development is completed in early 1983, sugar cane will occupy some 5 500 ha.

The climated of the area is determined by the relative movements and interac- tions of the inter-tropical convergence zone and the south-easterly tradewinds. Consequently, a two-season weather pattern results, viz: a "north-west trade" season and a "south-east trade" season. From May through October south- easterly tradewinds predominate consisting of shallow surface air masses, while north-westerly winds made up of air masses which reach higher altitudes predomi- nate from December through March. There is a wet season from November through April with2a dry season from May through October. However, over 30% of the total annual rainfall can fall in the dry season. The annual rainfall mean for thirteen years is 1 818 mm.

Annual Mean S D of Monthly Means

Maximum temperature 30,4" C 1 ,o Minimum temperature 20,4" C 0,5 Mean temperature 25,4" C 0,7 Relative humidity 82 % 1,6 Daily open pan evaporation 6,8 mm 1,4

Temperatures and relative humidity show little variation throughout the year. The initial variety selection trials were planted in September 1979, and irraga-

ted nurseries, of those varieties selected for commercial planting, were established in 1980. The first of the commercial cane fields were planted in March 1981. The commercial fields are rainfed.

Q 90 was amongst those varieties chosen for commercial planting, because of its excellent growth and good juice qualities under the conditions obtaining on the estate; but high incidence of downy mildew symptoms were observed in this variety during the latter half of 1980. Consequently, expansion of Q 90, as one of the major commercial varieties on the estate, was curtailed. However, as acylala- nine (Ridomil 25 WP ") has been reported to control the ex ression of downy zP mildew symptoms both in the Philippines and Taiwan (Wilson ), a series of trials were initiated by the Agronomy Section of Ramu Sugar Limited to investigate its efficacy on Q 90. All these trials were laid down during the wet seasons of 198011981 and 198111982,

MATERIALS AND METHODS

Four initial trials were carried out in 1980 and 1981. In the first two acylalani- ne was used as a preplant seedcane dip. In the third trial acylalanine was applied to the setts in the planting machine; and in the fourth, acylalanine was applied as a foliar spray to four week old plant cane.

~ Trial 1

I Treatments ' : 1. Seedcane soaked for 1 h in 1 g a.i. acylalanine per litre I water. I 2. Seedcane soaked for 1 h in 2 g a.i. acylalanine per litre I water. ~ 3. Seedcane soaked for 1 h in water.

Design : Randomised block with ten replications. 1 Plot size : Two rows 5 m in length, 1,5 m spacing.

Variety : Q 90.

The percentage stalk infection was estimated at 21 and 36 days from planting.

I

* Ciba-Geigy Limited, Basle. Switzerland.

856

Plot size : Two rows 5 m in length, 1,5 m spacing. I Variety : Q 90.

The Q 90 seedcane was taken' from a field with a high incidence of downy mildew.

In order to reduce the movement of infection from one plot of Q 90 to another within the trial, each was separated from its neighbour by a block of Ragnar (2 rows of 5 m length) at either end and laterally by a single row of Ragnar. Ho- wever, to ensure that movement of infection was facilitated within each experi- mental plot of Q 90, the rows were aligned parallel to the prevailing wind.

Over 1 000 mm of rain were recorded during the experiment, and the mean relative humidity was around 84%.

The percentage stalk infection was estimated in the plant crop at eight weeks from planting. Shortly afterwards the experimental plots were cut back and the downy mildew infection estimated when the first ratoon crop was eight weeks old.

RESULTS AND DISCUSSION

Trial 1

Though the differences in percentage infection were not significant, the data in Table 1 indicate that both rates of acylalanine decreased the incidence of downy mildew. However, there was a significantly lower stalk population (P < 0,05) related to treatment with the higher concentration of fungicide at 36 days after planting.

Table 1 . Percentage Stalk Infection and Stalk Population in Trial 1

Stalk Population Seedcane Percentage Infection at 36 Days treatment At 21 Days At 36 Days ('000 Stalks

per ha)

1 g a.i./L 1.7 0 82.0 2 g a.i./L 1 .0 0 50.8

Control 7.2 6.1 67.0

Trial 2

There was a marked difference in downy mildew incidence between the cane grown from seedcane preplant treated with acylalanine and that untreated (Table 2).

I

Table 2. Percentage Stalk Infection in Trial 2

Seedcane Percentage Infection Treatments at 70 Days

0,4 g a.i./L 0 Control 43

Trial 3

No downy mildew developed in the treated or untreated plots of this experi- ment.

Trial 4

The overall percentage of tillers affected by downy mildew in the area of cane chosen for this trial was 27,7%. i On each of the three assessment dates, the incidence of downy mildew was lower in the treated plots than those which were left unsprayed, though the i differences were not significant. The intensity of downy mildew infection decli- 1 ned in both teatments with time (Table 3) . I

Table 3. Percentage Stalk Infection in Trial 4

Spray Treatment

Percentage Stalk Infection 1st 2nd 3rd

Assessment ' Assessment ' Assessment " 1,5 kg a.i.lha 19.8 Control 27,5

' 13 days after first spray 3 days after second spray. '36 days after first spray 26 days after second spray. "2 days after first spray 52 days after second spray.

Foliar sprays with acylalanine suppress the development of downy mildew symptoms. However, the rate of symptom expression declined dramatically du- ring the last 26 days of the trial. Though there wasfference in tiller populations between the sprayed and the non-sprayed areas (treated = 177 600 tillers per ha, control = 166 100 tillerstha), this was not significant.

Trial 5

Plant Crop

Downy mildew developed only in those plots in which the seedcane had recei- ved a preplant soaking in water alone.

859

I>

100 1 0 5 10 20 30 40

1

T~mes of treatment (min)

Figure 1. Number of stalks per ha In relation to treatment tlme averaged over concentrations. T r ~ a l 5. Plant crop data.

I

0 0,63 1,25 2.50 3.75

Fungic~de treatments (g a.l./L water)

Figure 2. Percentage ln fec t~on related to fungicide concentration, Trial 5- Angular trasformed data.

Examination of the plant crop stalk population data related to fungicide con- centrations revealed a significant linear response at the P<0,05 level. These populations were inversely correlated to fungicide concentritions, though the co- rrelation coefficient (r = -0,6707) was not quite significant at the 5% level of probability. Similarly, increasing periods of soaking reduced stalk population (significant at < 1% level) as shown in Fig. 1. The interaction between fungicide concentration and time of soaking was linear, being significant at < 1% probabi- lity.

Figure 3. Percentage infection in relation to treatment time and rate of treatment. Trial 5- Angular trasformed data.

86 1

First Ratoon Crop

The levels of downy mildew ififection which developed in the first ratoon were shown to be very significantly affected by fungicide concentrations in the preplant soak, and that this response was linear (P < 0,001). Figure 2 illustrates this. Ho- wever, the lenght of time of preplant soak had no significant effect on the percentage of downy mildew infection.

The interaction between times of soaking and fungicide concentrations prior to planting had a strong linear effect on percentage downy mildew infection levels (P < 0,Ol). Figure 3 illustrates these data.

As in the plant crop, first ratoon stalk populations per-ha were shown to be affected by length of preplant soaking (P < 0,Ol). The data in figure 4 show that this response was linear and negatively correlated to the time of soaking.

40 I

0 5 10 20 30 40

Times of treatment (rnin)

Figure 4. Number of stalks per ha in relation to treatment time (averaged over concentration).

In contrast to the plant crop, the stalk populations per ha in first ratoon showed a very strong quadratic response to fungicide concentrations (P < 0,001). These data are illustrated in figure 5.

Whilst the interaction between times of preplant soak and fungicide concentra- tions for stalk populations per ha in the plant crop were strongly linear, these data showed a very strong quadratic response (P < 0,001) in the first ratoon (Fig. 6).

I

0,63 1.25 2.50 3,75

Fungic~de treatments (g a.i./L water)

Figure 5. Stalk population per ha related to fungicide concentration.

CONCLUSIONS

The data reported above confirm observations in the Philippines (Wilson 2 , and Taiwan (Hsieh ') that preplant treatment of seedcane with acylalanine will control the development of downy mildew in the plant crop of two susceptible varieties, Pindar and Q 90 (see Tables 1 and 2), and that this systematic effect persists into the first ratoon (see Fig. 2.). Though the reduction of the plant and first ratoon crops to eight weeks each in trial 5 does not parallel what happens to commercial seedcane, the intensive ratooning will give some idea of the period of efficacy of acylalanine through the crop cycle, with respect to downy mildew control. In this light, it is interesting to note observations made at Ramu during 1981 and 16,2 ha on Q 90 nursery plots. The seedcane for these plots was treated prior to planting in acylaline at a rate of 0,4 g a.i. per litre of water for 30 min. This treated cane was planted in February and March 1981. Inspections during the plant crop revealed no downy mildew; consequently seedcane was taken for planting commer- cial fields in October and December 1981. Subsequent inspections of these com- mercial fields showed an overall percentage stalk infection of less than I % , and there were only 9 , l infected stools per ha in the nursery plots four weeks after the cane had been cut for seed. However, while the commercial cane fields of Q 90 still show a very low incidence of downy mildew, there was a dramatic increase in disease levels in the nursery plots following a period of very wet weather. There were over 1 600 infected stools per ha (cf above, 9 , l at four weeks). Conseque- tly, the development of downy mildew within the second and subsequent ratoons in trial 5 will. be observed with interest.

The data from trial 4 show that foliar sprays with acylalanine at 1,5 kg a.i. per ha applied to four week old Q 90 also controls downy mildew. However, the cost of one application is significantly more expensive than preplant treatment of the seedcane.

Results from trials 1 and 5 show that acylalanine reduces stalk populations (see Table I) , and that these talk populations are negatively correlated to the time of treatment (see Fig. 1 and Fig. 4). However, increasing the length of time of fungicide treatment had no effect on downy mildew infection levels. While the plant crop stalk populations in trial 5 showed a negative though non significant correlation with fungicide concentracions, the same data in the first ratoon crop

u o o ~ e ~ IS.I!J 'luarulea~l 30 ale1 pue aruy luaruleall 01

uo!leIaJ u! eq ad s y ~ e l s 30 JaqrunN '9 a~na!d

showed a very strong quadratic response (see Fig. 5). Consequently, the following recommendations can be made for the preplant treatment of Q 90 seedcane:

- Concentration of acylalanine - 1,25 g a.i , per 1 of water - Time of soak - no more than 5 min

and as foliar spray:

- 1,5 kg acylalanine a.i. per hectare.

1 Though acylalanine does control downy middew, its fungicidal activity is only fully effective in the plant crop, and there is a recrudescence of disease in the first and subsequent ratoons. Consequently, the expense in using acylalanine as a preplant dip and foliar spray, in order to retain Q 90 in the spectrum of commer- cial varieties at Ramu, is only justified until a downy mildew resistant variety of equal agronomic and milling qualities is found. Hopefully, this will be in the near future. In the meantime, acylalanine will be used in the "holding campaign" for Q 90 against downy mildew.

ACKNOWLEDGEMENTS

I would like to thank Mr. B J Dyer, Agricultural Manager, for his encourage- ment and interest in this work, and Mr. A Beever, General Manager, for his permission to publish these data.

REFERENCES

1. Hsieh, W. H . (undated): Preliminary Test Results of Ridomil 25 WP for Control of Downy Mildew on Sugar Cane. Mimegraphed Report of Taiwan Sugar Research Institute.

2. Wilson, N . L. (1981): Personal Communication.

EFFETS DU TRAITEMENT AU FONGICIDE ACYLALANINE APPLIQUE AUX BOUTURES AVANT

DE LES PLANTER

G. L. James

Booker Agriculture International L td , Londres, R . U . , R a m u Sugar Ltd, Lae , Papouasie-Nouvelle-Guinke

L 'au teur fait p a r des rksultats d e cinq essais rkalises e n Papouasie- Nouvelle-Guinke; selon lesquels l e mildiou peut &re contr81k dans le cas des cannes d e nouvelle plantat ion e n t rai tant les boutures avec d e l'acylala- nine avant d e les planter . Les effets d u fongicide persistent jusqu'h la premiere repousse.

L a pulvkrisation foliaire d'acylalanine su r des cannes d e qua t r e semaines

a contribuC B contrbler le mildiou. L'auteur compare le coat de ce trait- ment B celui administre aux boutures avant de les planter.

La prolongation du traitment B l'acylalanine avant de planter les boutu- res n'a pas rCduit l'infection, laquelle s'est rCpandue ulterieurement. Nkan- moins, la concentration du fongicide exerce une influence notable sur les populations de tiges. L'auteur fait des recommandations pour la durCe du traitment et la concentration en acylalanine pour le traitement des boutures de la variCtC Q 90 avant de les planter.

L.L'auteur aboutit B la conclusion que le fongicide est utile pour mainte- nir la variCt6 Q 90 dans le spectre des variCtCs commerciales jusqu'h ce qu'une nouvelle vari6tC aux qualitCs agronomiques et usini2res similaires, mais rCsistante au mildiou soit obtenue.

EFECTOS DEL TRATAMIENTO DE LA CANA DE SEMILLA ANTES DE LA SIEMBRA, CON EL FUNGICIDA ACYLALANINE

G. L. James Booker Agriculture International Limited, Londre, Inglaterra, en apoyo

de Ramu Sugar Limited, Lae, Papua, Nueva Guinea

RESUMEN

Los resultados de cinco ensayos efectuados en Papua, Nueva Guinea, se han dado a conocer y 10s datos demuestran que el mildiu lanoso puede ser controlado en la cosecha de planta mediante un tratamiento previo de la caiia de semilla, usando acylalanine. La eficacia del fungicida se ha com- probado que persiste hasta la primera cosecha de retofio. La aplicaci6n de acylalanine como rociado foliar, realizado a la caiia de cuatro semanas de edad, tambiCn se ha demostrado que controla el mildiu lanoso, y el costo de este tratamiento, en comparaci6n con el tratamiento a la semilla de caiia previo a la siembra, es objeto de discusi6n.

El aumento en el tiempo de tratamiento previo a la siembra, con el uso de acylalanine, no redujo 10s niveles de la infecci6n con mildid lanoso, que se desarroll6 subsiguientemente. Sin embargo, las concentraciones del fun- gicida influyeron significativamente en las poblaciones de tallos. Se hacen recomendaciones, por tanto, respecto a la duraci6n del tiempo de trata- miento y la concentraci6n de acylalanine para el tratamiento previo de la caiia de semilla de la variedad Q 90.

Se llega a la conclusi6n de que el fungicida es util para mantener a la Q 90 en el espectro de las variedades comerciales, hasta tanto se encuentre una variedad alternativa de iguales cualidades agron6micas y para el proce- so industrial, per0 con resistencia a1 mildiu lanoso.