As was advocated last year, it is important again to 'rotate' your miticides in order to manage the development of resistance. If you used either Apollo or Savey last year, you should not use either of them this year or if you had instead used Agri-Mek, you should switch to Apollo or Savey or possibly just a pre-bloom application of oil. The best situation would be for European Red Mites (ERM) to remain under threshold levels - which is a real possibility if the predacious mite T.pyri is present.
Over the past three years, we have been participating in a
collaborative, New England-wide project led by Dr. Jan Nyrop from Cornell University to
introduce the predacious mite, Typhlodromus pyri, as a biological control agent for
ERM. Three sites in Vermont were involved in this project: Larrabee Point
Orchard in Shoreham, Allenholm Farms in So. Hero, and the UVM Hort. Res. Center in South
Burlington. At each site, T.pyri were released in designated trees.
Also in each orchard 'control' trees located away from the release trees were flagged and
were monitored each growing season. Results of the project have been presented at
the Vermont Tree Fruit Growers Association Meetings in 1998 and 1999. A summary of
the first two years of the study is available at: /~fruit/?Page=treefruit/tf_ipm/tpyri/tpyrireport9697.html
The good news is that not only did T.pyri become established in
the release trees in each orchard, it was found naturally occurring in other trees in the
orchard as well.
One of the stipulations of participating in the project was that pesticides known to
be harmful to the predacious mite would not be used. It appears that this has
allowed not only the released predators to survive but also has allowed naturally
occurring populations to increase in number.
The following graphs summarize the data collected in 1998 on the # of
ERM/leaf and the # of predacious mites/leaf (i.e., Phyto/leaf) during May, June,
July and August in each orchard. In each of the orchards, ERM did not reach
threshold levels on the monitored trees and, in most cases, T.pyri outnumbered
ERMs.
The first step is to not use materials that are toxic to T.pyri such as: pyrethroids, dimethoate, Carzol, Lannate, and Vydate. Mancozebs or Polyram should be limited to pre-bloom applications. Also, if possible, avoid using Lorsban, Agri-mek, and Kelthane. If this is not possible on your whole orchard, perhaps you can establish a 'nursery' block where you could avoid these materials and try to encourage T.pyri populations. Dr. Nyrop is investigating ways to distribute T.pyri from orchard to orchard or block to block - I will have more on this in a future newsletter.
Biological control of ERM by T.pyri is an exciting prospect for Vermont!! Try to encourage the development of T.pyri populations in your orchard !
Larrabee Point Orchard, Larrabee
UVM Hort. Research Center
