Abstract

Spinosad is one of the most widely used products for control of diamondback moth (Plutella xylostella) in Australia. Since the launch of Success* Naturalyte* in 1999, it has rapidly gained wide acceptance in all crucifer growing areas of the country. This has occurred, not only because spinosad is highly effective against diamondback moth, but because it also controls several other important lepidopteran pests such as heliothis (Helicoverpa spp.), cabbage white butterfly (Pieris rapae), cabbage centre grub (Hellula hydralis) and cabbage cluster caterpillar (Crocidolomia pavonana) at rates which provide growers with excellent value for money. Spinosad is highly active against loopers (Chrysodeixis spp.) and affords some control of cluster caterpillar (Spodoptera litura) and onion thrips (Thrips tabaci). There is no diamondback moth resistance to spinosad in Australia, the product has a favourable toxicological profile and it is selective to a range of beneficial predators and parasitoids.

The value of insect control is best gauged by assessing the quality of produce at harvest of the crop. In a small scale trial, a crop of broccoli infested with P. rapae, P. xylostella, S. litura and C. pavonana received a programme of six applications of spinosad at 7-10 day intervals. Spinosad at 48 g ai/ha resulted in 97.2% marketable heads, not significantly different (P>0.05) from the standard, prothiophos, at 750 g/ha which gave 100% marketable heads. Spinosad at 96 g ai/ha resulted in 98.7% marketable heads, reflecting superior control of S. litura at this higher use rate.

Keywords

Lepidoptera, yield, Plutella xylostella, Helicoverpa, Pieris rapae, Hellula hydralis, Crocidolomia pavonana, Chrysodeixis, Spodoptera litura, Thrips tabaci

Introduction

Spinosad is widely used for control of lepidopteran pests in crucifer crops in Australia. Success* Naturalyte* (containing 120 g/L spinosad, marketed by Dow AgroSciences) is labelled for use at 48 g ai/ha against diamondback moth (Plutella xylostella (L.) (Lepidoptera: Plutellidae)) and cabbage white butterfly (Pieris rapae (L.) (Lepidoptera: Pieridae), and at 48-96 g ai/ha for heliothis (Helicoverpa spp. (Hübner) (Lepidoptera: Noctuidae)).

There are several factors which have contributed to the market place acceptance of Success*, including cost-effectiveness against the key target pests P. xylostella and P. rapae, selectivity to a range of beneficial species and a favourable eco-toxicology profile.

In south-east Queensland, including the Lockyer Valley vegetable-basket region, brassicas are sporadically attacked by a number of lepidopteran pests in addition to those mentioned above. These include cluster caterpillar (Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae)), cabbage cluster caterpillar (Crocidolomia pavonana (Fabricius) (Lepidoptera: Pyralidae)) and cabbage centre grub (Hellula hydralis (Guenée) (Lepidoptera: Pyralidae)). Ability to control this spectrum of lepidopteran Brassica pests is a desirable trait in any product in this market.

This paper reports a single multiple application trial conducted at the QDPI Redlands Research Station in December 1999 by John Hargreaves in which lepidopteran insect control and its effect on broccoli yield was assessed.

Materials and methods

Seeds of the broccoli cultivar Dome (Yates Seeds) were sown into speedling trays containing a soilless mixture of peat and vermiculite (1:1), plus 100 g dolomite, 50 g potassium nitrate, 50 g superphosphate and 50 g blood and bone per 25 L of mixture. Seeds were sown on 05 November 1999 and sprayed once with sodium molybdate 1 g/L, Solubor^® 2 g/L and Nitofol^® 1.9 mL/L as the seedlings developed.

The transplants were planted into a 700 m² border of the Redlands Research Station on 13 December 1999. The red krasnozem soil had been pre-drilled with a basal fertilizer (Granular 4^®) at the rate of 0.1 kg/m. Rows were spaced 1.2 m apart and eight rows were drilled into the border with plants spaced 30 cm apart along the row. Four weeks after transplanting, plants were side-dressed with urea 9 g/m. Overhead irrigation was applied on demand and although conditions were wet through the period, overhead irrigation was generally applied once per week.

Four replicates of each treatment were laid out in a randomised block design. Plots were two rows wide by 30 plants long (24 m², 60 plants per plot). Five randomly selected plants from the middle of each plot were examined at each assessment.

Populations of pests built up slowly and no insecticides were applied until plots received their prescribed treatments. Plants were examined for the presence of larvae of all species as well as the eggs of P. rapae, C. pavonana and S. litura. The pupae of both P. rapae and P. xylostella were also counted.

Sprays were applied 7-10 days apart, depending on rain, from the 8^th January. Initially 500 L of spray mix per hectare was applied by an Echo^® power knapsack sprayer delivering 800 kPa pressure through a horizontal boom. Two hollow cone, sintered aluminum nozzles (Albuz^® yellow 212) delivering 0.95 L/min, were spaced at 220 mm centres on the boom. An application speed of 1.9 km/h was maintained. On the 28^th January, the boom was increased to 4 nozzles, spaced at 220 mm centres, but changed to Albuz^® lilac 208 nozzles, delivering 0.45 L/min at 800 kPa. The wash volume was increased to 1000 L/ha. A non-ionic wetter was used with all treatments (Agral^® 600) at the rate of 0.1 mL/L. At maturity, terminal flower heads were harvested progressively over the period 10^th - 13^th March. A flower head was considered “prime” when inspection of the surface and floret bases showed no larvae present nor obvious signs of gross feeding. Processing grade allowed only a degree of scarring to the floret bases, indicative of earlier feeding.

Data were statistically analysed by analysis of variance using the QDPI ranb programme with appropriate transformations.

Materials used:

• Agral^® 600 a non-ionic surfactant containing 600 g/L nonyl phenol ethylene oxide condensate (CropCare Australia Ltd).
• Success* Naturalyte* containing 120 g/L spinosad as a suspension concentrate (* trademark of Dow AgroSciences (Australia) Ltd).
• Tokuthion containing 500 g/L prothiophos as an emulsifiable concentrate (trademark of Bayer Germany).

Results and discussion

No obvious phytotoxicity, with any concentration of spinosad, was noticed during the trial.

Crocidolomia pavonana (Table 1)

All treatments significantly reduced C. pavonana numbers at each assessment, but until the final assessment there was no difference between spinosad treatments and the standard, prothiophos. At the final assessment, spinosad at 6 g ai/ha gave a significant level of control, but itself was significantly poorer (P=0.05) than spinosad 12 g ai/ha and above, and prothiophos. Numerical equivalence with prothiophos was achieved with spinosad at 24 g ai/ha. Egg deposition by this species appeared to be unaffected by insecticide concentration.

Table 1. The numbers of cabbage cluster caterpillar, Crocidolomia pavonana (F.) larvae per broccoli plant after a range of insecticide treatments were applied to the foliage, Jan-Feb 2000

Treatment		Inspection date
		7 Jan 00	17 Jan 00	27 Jan 00	7 Feb 00	17 Feb 00	28 Feb 00
Untreated		2.0 a	4.7 a	33.2 a	9.3 a	23.7 a	27.1 a
Success*	50 mL/ha	1.5 a	0.0 b	0.4 b	0.3 b	3.5 b	12.1 b
Success*	100 mL/ha	0.0 a	0.0 b	0.0 b	0.1 b	0.3 b	1.6 c
Success*	200 mL/ha	0.0 a	0.0 b	0.0 b	0.0 b	0.0 b	0.1 c
Success*	400 mL/ha	1.8 a	0.0 b	0.0 b	0.0 b	0.0 b	0.0 c
Success*	800 mL/ha	0.0 a	0.0 b	0.0 b	0.0 b	0.3 b	0.1 c
Tokuthion®	1.5 L/ha	0.0 a	0.0 b	0.0 b	0.0 b	0.0 b	0.1 c

All treatments applied with Agral^® 600 at 10 mL/100 L. Values within columns, followed by a common letter, do not differ at the P=0.05 level of probability. Values quoted are re-transformed means from the √x + 0.5 transformation.

Spodoptera litura (Table 2)

Spodoptera infestation was low at the start of the trial, but gradually increased over time. The peak of infestation occurred in early February with an average of 50 larvae per plant in the untreated controls. Prothiophos showed excellent activity maintaining numbers at a very low level, matched by spinosad at 96 g ai/ha. Lower rates of spinosad, although not significantly poorer, were less effective numerically. The egg deposition by cluster caterpillar, Spodoptera litura, appeared unaffected by chemical concentration.

Table 2. The numbers of cluster caterpillar, Spodoptera litura (L.) per broccoli plant, after a range of insecticide treatments had been applied sequentially to the foliage, Jan-Feb 2000

Treatment		Inspection date
		7 Jan 00	17 Jan 00	27 Jan 00	7 Feb 00	17 Feb 00	28 Feb 00
Untreated	-	0.0 a	1.3 a	18.6 a	52.4 a	38.6 a	33.3 a
Success*	50 mL/ha	0.0 a	0.1 a	13.0 a	18.2 b	44.8 a	30.0 ab
Success*	100 mL/ha	0.0 a	0.0 a	1.2 a	5.8 bc	28.8 bc	18.4 ab
Success*	200 mL/ha	2.1 a	0.8 a	7.5 a	3.7 bc	12.4 cd	16.2 b
Success*	400 mL/ha	0.0 a	0.2 a	8.7 a	1.0 c	7.0 de	1.6 c
Success*	800 mL/ha	1.7 a	0.7 a	0.9 a	0.5 c	1.9 e	0.7 c
Tokuthion®	1.5 L/ha	1.6 a	0.1 a	3.8 a	0.2 c	3.2 de	2.2 c

All treatments applied with Agral^® 600 at 10 mL/100 L. Values within columns, followed by a common letter, do not differ at the P=0.05 level of probability. Values quoted are re-transformed means from the √x + 0.5 transformation.

Pieris rapae (Table 3)

Pieris rapae pressure was constant throughout the trial and numbers in the untreated plots ranged from 3.7 larvae/plant in early January to 6.5 larvae/plant in middle February. At 48 g ai/ha spinosad and above, control of P. rapae was similar to that given by prothiophos 750 g ai/ha. At lower rates of spinosad, control was less effective (although not significantly so). Numbers of pupae tended to be low and a less sensitive indicator of control.

Table 3. The numbers of cabbage white butterfly, Pieris rapae (L.) per broccoli plant after a range of insecticides was applied to the foliage during Jan-Feb 2000

Treatment		Inspection date
		7 Jan 00	17 Jan 00	27 Jan 00	7 Feb 00	17 Feb 00	28 Feb 00
Larvae
Untreated		3.7 a	3.7 a	6.1 a	4.0 a	6.5 a	5.1 a
Success*	50 mL/ha	3.7 a	0.1 c	0.6 b	1.8 b	2.9 b	1.3 b
Success*	100 mL/ha	2.9 a	0.9 b	0.2 b	0.4 c	3.9 ab	0.7 bc
Success*	200 mL/ha	4.5 a	0.9 b	0.3 b	0.1 c	1.3 bc	0.1 cd
Success*	400 mL/ha	3.2 a	0.5 bc	0.4 b	0.2 c	0.5 c	0.0 d
Success*	800 mL/ha	2.3 a	0.1 c	0.6 b	0.3 c	0.4 c	0.0 d
Tokuthion®	1.5 L/ha	1.9 a	0.1 c	0.0 b	0.2 c	0.7 c	0.0 d
Pupae
Untreated	-	0.0	0.5 a	0.8 a	0.8 a	5.8 a	1.0 a
Success	50 mL/ha	0.0	0.2 a	0.1 a	0.2 a	1.2 bc	0.5 abc
Success	100 mL/ha	0.0	0.2 a	0.1 a	0.1 a	1.3 bc	0.6 ab
Success	200 mL/ha	0.0	0.1 a	0.1 a	0.1 a	1.9 bc	0.1 bc
Success	400 mL/ha	0.0	0.1 a	0.5 a	0.3 a	2.9 b	0.2 bc
Success	800 mL/ha	0.0	0.1 a	0.1 a	0.2 a	0.5 c	0.1 c
Success	1.5 L/ha	0.0	0.0 a	0.4 a	0.2 a	0.1 c	0.1 c

All treatments applied with Agral^® 600 at 10 mL/100 L. Values within columns, followed by a common letter, do not differ at the P=0.05 level of probability. Values quoted are re-transformed means from the √x + 0.5 transformation.

Plutella xylostella (Table 4)

Plutella xylostella numbers were relatively low for the early part of the trial, although high numbers infested plants in the middle of February (14.1 larvae/plant in the untreated plots). Spinosad gave very good control of P. xylostella at 12 g ai/ha and above, and at 48 g ai/ha performed as well as prothiophos 750 g/ha. Although pupae were counted, these proved a less accurate measure of a treatment’s performance than did larvae. The trial was harvested and produce graded according to commercial standards (Table 5). The highest proportion of “prime” broccoli came from the standard prothiophos plots (89.9%), although this was not significantly superior to rates of spinosad 48 and 96 g/ha which gave 76.4% and 87.5% of "prime" broccoli respectively.

Table 4. The numbers of immature diamondback moth, Plutella xylostella (L.) per broccoli plant after a range of insecticide treatments had been applied sequentially to the foliage

Treatment	Inspection date
		7 Jan 00	17 Jan 00	27 Jan 00	7 Feb 00	17 Feb 00	28 Feb 00
Larvae
Untreated		0.0	0.5 a	1.4 a	2.7 a	14.1 a	5.1 a
Success*	50 mL/ha	0.0	0.1 a	0.1 b	0.1 b	1.4 b	1.2 b
Success*	100 mL/ha	0.0	0.3 a	0.0 b	0.1 b	0.1 b	0.1 c
Success*	200 mL/ha	0.0	0.1 a	0.1 b	0.0 b	0.4 b	0.1 c
Success*	400 mL/ha	0.0	0.1 a	0.1 b	0.0 b	0.2 b	0.0 c
Success*	800 mL/ha	0.0	0.2 a	0.0 b	0.0 b	0.1 b	0.0 c
Tokuthion®	1.5L/ha	0.0	0.1 a	0.0 b	0.3 b	0.2 b	0.0 c
Pupae
Untreated	-	0.0	1.0 a	1.3 a	1.6 a	5.5 a	3.5 a
Success*	50 mL/ha	0.0	0.1 b	0.1 b	0.2 b	0.7 b	0.8 b
Success*	100 mL/ha	0.0	0.0 b	0.2 b	0.2 b	0.6 b	0.1 b
Success*	200 mL/ha	0.0	0.1 b	0.2 b	0.1 b	1.4 b	0.1 b
Success*	400 mL/ha	0.0	0.1 b	0.1 b	0.0 b	0.1 b	0.1 b
Success*	800 mL/ha	0.0	0.1 b	0.1 b	0.0 b	0.2 b	0.1 b
Tokuthion®	1.5 L/ha	0.0	0.0 b	0.0 b	0.0 b	0.8 b	0.1 b

All treatments applied with Agral^® 600 at 10 mL/100 L. Values within columns, followed by a common letter, do not differ at the P=0.05 level of probability. Values quoted are re-transformed means from the √x + 0.5 transformation

The mean number of all species of larvae per plant found on broccoli after the fourth application of insecticide is shown in Figure 1.

Figure 1. Number of lepidopteran larvae on broccoli assessed eight days after fourth application of insecticide.

Combining “prime” and “processing” grade heads together to create a “marketable” category, the result was no different, with prothiophos giving 100% marketable heads, while spinosad at 48 and 96 g/ha gave 97.2 and 98.7% marketable heads respectively (Figure 2).

Table 5. Quality assessments at harvest for 20 plants per plot of broccoli sprayed with a range of insecticides, in terms of caterpillar damage

Treatments		% broccoli heads by quality category
		prime grade	prime + processing	Unmarketable
Untreated	-	0.3 c	6.2 f	93.8 a
Success	50 mL/ha	2.6 c	33.6 e	66.4 b
Success	100 mL/ha	41.0 b	87.5 cd	15.5 c
Success	200 mL/ha	52.7 b	90.7 bcd	9.3 cd
Success	400 mL/ha	76.4 a	97.2 abc	2.8 de
Success	800 mL/ha	87.5 a	98.7 ab	1.3 de
Tokuthion	1.5 L/ha	89.9 a	100.0 a	0.0 e

All treatments applied with Agral^® 600 at 10 mL/100 L. Values within columns, followed by a common letter, do not differ at the P=0.05 level of probability. Values quoted are re-transformed means from the √x + 0.5 transformation.

Figure 2. Percentage of broccoli heads classified as unmarketable due to insect feeding damage in field trial of spinosad.

Acknowledgements

This trial was conducted on behalf of Dow AgroSciences by John Hargreaves at the Queensland Department of Primary Industries research facility at Redlands.

References