New, sustainable insights into combating tobacco thrips

Thrips parvispinus, sometimes known as tobacco thrips or simply thrips, is found across the world and is well known in countries like Indonesia, India and China. However, it also poses a serious threat in Kenya (specifically in papaya cultivation), in the US and on the Hawaiian Islands. In Europe, it has been prevalent in Greece for more than 25 years, and it made its appearance in Dutch horticulture in 2019. Since then, it has been found in many ornamental plants and has also become a major, perennial pest in Anthurium cultivation.

Thrips causes significant damage to plants and is difficult to control. It is crucial for the entire agricultural sector to be alert to signs of tobacco thrips so that early interventions can be made. To gain a better understanding of thrips and how to combat it sustainably, research into the effectiveness of different green crop protection products and a diverse range of biological control agents has been launched in collaboration with Koppert.

A conscious decision was made in this research not to use regular chemical plant protection products, as they will be phased out in the coming years. One of the research goals was to gain knowledge about effective green approaches to the troublesome Thrips parvispinus. With this research, we aim to contribute to combating tobacco thrips sustainably.

VERTIFY trial provides confirmation and new insights

The trial was conducted with PP1L Anthurium plugs. A total of 180 plugs were distributed across two trays with 90 per mesh cage. Two treatment types were employed in the trial: one with natural enemies and one with green insecticides.

For the natural enemy treatments, two preventive introductions were made with Thrips parvispinus females. For the insecticide treatments, three to four applications were conducted at intervals of five or seven days.

The initial application of green insecticides occurred 11 days after the first introduction of Thrips parvispinus. The application volume was 1,000 l/ha. Motto (an effluent) and Attracker (a thrips attractant) were added to all treatments. Foliar applications were made with a spray lance targeted at the top and bottom of the leaves. The treatments are summarised in the table below.

Treatment		Products used	Dosage	Timing	Time of day
1	Motto + Attracker (untreated)	Sugar derivative and fatty amine	0.03% + 0.1%	T1, T3, T5	-
2	NoFly + Motto + Attracker	Paecilomyces fumosoroseus	0.25% + 0.03% + 0.1%	T1, T1, T4, T6	End
3	Code A + Motto + Attracker	Metarhizium anisopliae	0.125% + 0.03% + 0.1%	T1, T1, T4, T6	Morning
4	Neudosan + Motto + Attracker	Fatty acids and potassium salts	2% + 0.03% + 0.1%	T1, T1, T4, T6	Morning
5	Spruzit + Motto + Attracker	Pyrethrins	0.6l/ha + 0.03% + 0.1%	T1, T3, T5	Morning
6	Code B + Motto + Attracker	Liquid organic fertiliser	10l/ha + 0.03% + 0.01%	T1, T1, T4, T6	Morning
7	Velifer + Motto + Attracker	Beauveria bassiana	0.05% + 0.03% + 0.1%	T1, T1, T4, T6	End
8	BotaniGard (WP) + Motto + Attracker	Beauveria bassiana	0.0625% + 0.03% + 0.1%	T1, T1, T4, T6	End
9	Code C + Motto + Attracker	Mycotal	2 kg/ha + 0.03% + 0.1%	T1, T1, T4, T6	End
10	Entonem + Motto + Attracker	Steinernema feltiae	500,000/m² + 0.03% + 0.1%	T1, T1, T4, T6	End
11	NeemAzal-T/S + Motto + Attracker	Azadirachtin	0.25% + 0.03% + 0.1%	(6 applications at Anthura) T1, T3, T5	Morning
12	Code D + Motto + Attracker (Chemical reference)	Vertimec (abamectin)	0.15% + 0.03% + 0.1%	T1, T3, T5	Morning

Treatment		Dosage
13	Franklinothrips predatory thrips	10/m²
14	Amblyseius Swirskii + Carpoglyphus lactis/artemia	200/m² + 2000/m²
15	Transeius montdorensis + Carpoglyphus lactis/artemia	200/m² + 2000/m²
16	Chrysoperla carnea (egg)	100/m²
17	Amblydromalus limonicus + Carpoglyphus lactis/artemia	200/m² + 2000/m²

Treatments applied

Assessment and results

Regular weekly assessments were conducted until 14 days after the final application. On each assessment date, thrips (larvae and adults separately) were counted on 12 plants. On the final assessment date, thrips were counted on 40 plants. Crop damage caused by thrips was scored from 1-5 (1=no infection, 5=high infection). At the end of the trial, the fresh weights of 15 plants were measured. On each assessment date, assessments were also conducted on general crop condition, phytotoxicity and visible spray residue.

Two introductions — one with 17 and one with 11 female Thrips parvispinus — occurred at a weekly interval in each cage. The thrips were cultured on pepper plants with a good level of infestation. First applications with insecticides were performed on relatively low numbers of Thrips parvispinus.

Conclusion: treatment with insecticides

1. Thrips numbers
After repeated applications, none of the treatments significantly reduced Thrips parvispinus. A tendency was seen with Code A, Neudosan, and Code D (chemical reference) in which relatively small numbers of thrips were discovered during each assessment.

2. Crop damage
At the end of the trial (16 days after the most recent application), there were significant variations in crop damage caused by thrips. The treatments Code D, Neudosan and NeemAzal-T/S resulted in the lowest amount of crop damage. There was no difference between the other treatments and the untreated plants.

	Crop damage (1-5)
Treatment	23-4	30-4	7-5	16-5	22-5	31-5
Untreated	0.8	3.0	2.8	2.8	3.8	4.5	c
NoFly	1.0	2.5	3.0	3.0	3.5	4.5	bc
Code A	1.5	2.3	2.8	2.5	3.3	4.3	bc
Neudosan	1.3	3.0	3.3	2.5	3.0	3.3	ab
Spruzit	1.3	3.0	3.3	3.0	4.3	5.0	c
Code B	0.5	3.0	3.5	2.8	3.8	4.8	c
Velifer	1.3	2.8	3.5	3.3	4.0	4.8	c
BotaniGard (WP)	1.0	3.8	4.3	3.8	4.5	5.0	c
Code C	0.8	3.5	3.8	3.5	4.3	4.8	c
Entonem	1.5	2.8	3.0	3.8	4.0	4.8	c
NeemAzal-T/S	1.0	2.3	2.3	4.3	3.0	3.3	ab
Code D	1.0	2.5	2.0	3.8	2.3	2.5	a
fprob	0.242	0.366	0.053	0.148	0.058	0.004
lsd	0.8	1.2	1.3	1.3	1.3	1.4

Crop damage caused by thrips in the plants treated with insecticides

Spray residue or phytotoxicity was not observed in any of the treatments. Motto and Attracker were added to all treatments so as to compare them equivalently. However, in practice, some of the agents used do not require the addition of an adjuvant. Faster drying by Motto in insect-parasitic fungi could also have had a detrimental effect because a prolonged wet period can enhance penetration of the fungi into the insect.

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Conclusion: treatment with natural enemies

Thrips numbers:

After two preventive and six curative introductions of natural enemies, a significant reduction in the number of thrips (larvae, adults and total numbers of thrips) was found with all treatments compared to the untreated plants. No significant differences were found between the treatments with natural enemies.

Crop damage:

After two preventive and two curative introductions of natural enemies, a significant reduction in crop damage was found with all treatments compared to untreated plants.
After seven introductions, significant differences were found. The treatment Amblyseius Swirskii + Carpoglyphus lactis/artemia resulted in relative low crop damage, and the treatment Amblydromalus limonicus + Carpoglyphus lactis/artemia resulted in relative high crop damage.
However, after eight introductions of natural enemies, no significant differences were found between the treatments (except untreated).