The biological control of strawberry in Japan
Yoko Saiki, Tetsuo Wada
Arysta LifeScience Corporation,
St. Luke’s Tower, 8-1, Akashi-cho, Chuo-ku, Tokyo 104-6591, Japan

Abstract: The easy introduction method of Phytoseiulus persimilis and Aphidius colemani in strawberry makes good control of Tetranychus urticae, Myzus persicae and Aphis gossypii. This method is easy enough for the aged growers and the usage of these natural enemies are growing year by year. On the other hand, the effective method to control Frankliniella occidentalis biologically is not established yet, and chemical measure not to disturb above beneficials was taken for the insects.

Key words: Phytoseiulus persimilis, Aphidius colemani, Tetranychus urticae, Myzus persicae, Aphis gossypii, Frankliniella occidentalis, strawberry

◆Introduction

In Japan, the main pests of strawberry are spider mite, aphid and thrips. Since strawberry cultivation period from September to April, and sometimes growers do not use heating system throughout the cultivation, it is said to be difficult to use the biological control agent in strawberry. But recently, the scheduled introduction of Phytoseiulus persimilis and Aphidius colemani is found out to show the stable efficacy to control spider mites and aphids.
Through 1998-2003 the biological method to control thrips which occurs from February has been evaluated. Amblyseius cucumeris, Orius strigicollis, Amblyseius degenerans and Franklinothrips vespiformis has been tested but made no good results. Also, Beauveria bassiana and Verticillium lecanii are not effective enough under low temperature climate. At present, spraying of biologically compatible chemical pesticides are used against thrips.

◆Methods

Control of spider mite　
The concept is to introduce Phytoseiulus persimilis before the occurrence of Tetranychus urticae and not to make T.urticae occur through the end of year, since it is difficult for growers to find the first occurrence of T. urticae, and explosive growth of P. persimillis cannot be expected during the winter time.
In Japan, the planting of strawberry is done in September without roof and most growers use granule pesticides such as Acetamiprid or Imidacloprid to control various early pests. In October, house roofs are covered by plastic 7-10days after roofing, and then P. persimilis is introduced at the rate of 2/m2 without checking the occurrence of Tetranychus urticae. If growers notice that there is already occurrence of T. urticae, they should spray Fenbutatin oxide or Hexythiazox before introduction.
One month after the first introduction, the second introduction will be done at the same rate. If there is one or two hot spots of T. urticae, P. persimilis should be sprinkled there heavily. If there are more hot spots or even occurrence throughout the field, Fenbutatin oxide, Hexythiazox or Bifenazate should be sprayed to lower the population of T.urticae.
In the end of January or the beginning of February, just before spring occurrence of T.urticae, third introduction of P. persimilis should be made at the rate of 2/m2. The timing is decided according to the climate condition. Also spraying should be considered if T.urticae exists.
The fourth introduction is optional. If the cultivation continues till May or, controlling of T.urticae is not satisfactory enough, the fourth introduction should be done one month after the third introduction.
For growers to search for T.urticae at ordinal 1,000m2 plastic house, they should choose 4 beds, and from each bed, evenly choose 20 plants. For each 20 plants, they should look for 1 leaf to find the occurrence of T.urticae.

Table 1. Introduction schedule of P.persimilis
Control of aphid
Contrary to spider mite, in strawberry, usually the introduction of Aphidius colemani, after growers notice the occurrence of Myzus persicae or Aphis gossypii, is effective enough, since the aphid population growth is slow in autumn and winter.
If the aphid is just found on the back of leaves, A.colemani should be introduced at the rate of 0.5/m2 for 2 weeks. If some aphids are found on the stems, introduction rate should be 2/m2, 3weeks. If the stems are covered by aphid colony, A.colemani introduction should be after spraying of Pymetrozine. Also, after introduction, when some hot spots of aphids are found, the spot spraying of Acetamiprid is effective.
If the mummies of A.colemani are found 2 weeks after the first introduction and aphids do not increase rapidly, it could be analyzed as aphid is almost controlled. And if the parasite rate increases to 80% 4-6 weeks after the final introduction, the control is successful. When aphids are growing throughout the crop, the Pymetrozine should be sprayed.

Table 2. Introduction of A.colemani (upon occurrence of aphids)

Control of thrips
Frankliniella occidentalis usually starts to build up population from February. Some exists in green house through the winter and many of them invade into the house when growers open the side window.
Some biological methods have been tested but not effective enough and so as biological compatible pesticides, Lufenuron and Flufenoxuron are used.

◆Results and discussion

Test results of introduction of P.persimilis and A.colemani
Those are test data of spider mite and aphid control.

Table 3. Population of spider mites per compound leaf : P. persimilis : Spray of mitecide
(Adopted from Takemoto, 2001)



Figure 1. Efficacy of A.colemani against aphids (Takemoto, 2003)

The usage of biological control method in strawberry
This method drives forward many growers to IPM. They have hesitated to try natural enemies since it was difficult for them to decide the introduction timing. In the season of 2003 autumn ? 2004 spring, about 700ha (estimate) of strawberry growers use biological control methods, which is about 10% of total 7,300 ha cultivation of strawberry in Japan. And it is expected to rise to 20% in the near coming years.


Figure 2. Estimated area of introduction of P.persimils (Strawberry)

◆Acknowledgements

　We wish to express our gratitude to Mr. Hiroyuki Takemoto, Fukuoka Agricultural Research Center for technical advice and his dedication to biological control in the prefecture.

Takemoto, H. 2003: How to control aphids by the parasitic wasp in early raising strawberry. Fukuoka.(in Japanese)