Arthropod Management Update


For those who do not have access to our website (http://orchard.uvm.edu/), the following is an update of accumulated DD (Base 50F) that can be used in conjunction with the table on arthropod 'events' that appeared in the April issue of the Vermont Apple Newsletter to get an idea of what to expect in terms of arthropod development.

European Red Mites (ERM)

The only place I saw ERM nymphs last week while scouting at the UVM Hort.Res.Center was in a block in which we did not use oil.  At this point in time, miticide options include Agri-Mek and, because of a recent change in its label, Apollo. The previous label for restricted its use to no later than Tight Cluster.  Now, Apollo can be applied on apples until 45 days before harvest.   Because of resistance concerns, you should not apply either Savey or Apollo in consecutive years.  Note that  Agri-Mek is also labeled for use against leafminers (see Leafminers section).

Leafminers (LM)

Reports from around New England indicate that LM moths have been very abundant over the past few weeks which may translate into high numbers of mines.  It is important to go out and check the undersurface of cluster leaves for the development of mines to determine if you need to apply an insecticide targeted at this insect.  The mines first appear as lightened areas on the undersurface of the leaf -- at this point the larvae are in the sap-feeding stage. As the larvae mature, they feed on tissue (i.e., tissue-feeding stage) and the mine becomes visible on the top surface of the leaf.

The leaf on the left has at least 5 sap-feeding mines on its undersurface. The arrow points to a cluster of mines.  The tissue on one mine has been peeled away.   The leaf on the right has a tissue-feeding mine.

Thresholds for first generation Leafminer mines are:

  • 7 mines per 100 leaves for McIntosh
  • 14 mines per leaves for non-McIntosh cultivars


Insecticides such as Provado, Agri-Mek and SpinTor  need to be applied during the sap-feeding stage in order to be effective.  (Note:  Both Agri-Mek and SpinTor should be applied with a penetrant.  See the 1998-1999 New England Apple Pest Management Guide and its 1999 Update for further details on the use of Agri-Mek and for a description of the new insecticide SpinTor.)


Please note that Provado and Agri-Mek have activity against Leafhoppers nymphs which are starting to make their appearance in the orchard.

Leafhoppers (LH)

                                            

White apple leafhopper adults are pale yellowish-white while the nymphs are pale white.  The insect overwinters on apple trees in the egg stage.  Eggs  begin to hatch around late pink. Nymphs and adults have stylet-type mouthparts and feed on the underside of mature apple leaves causing a stippling effect visible on the top sides of the leaves.  When feeding is extensive, the leaves can appear white.  The leafhoppers excrete a honeydew that can get on the fruit and cause black speckling.  Nymph and adults should be monitored starting at Petal Fall.  They often are found on the underside of leaves.  The threshold is 25 nymphs/adults per 100 leaves.  Provado and Agri-Mek are two options at this point in the growing season.  Growers using Sevin in their thinning sprays will get some control at the 1 lb rate. 

European Apple Sawfly (EAS)

The EAS overwinters as a larva in the soil.  It pupates in the spring and adults emerge during late pink and bloom.  The insect causes damage to the fruit by laying its egg near the calyx end.  The young larva tunnels just under the surface of the fruit leaving a winding scar.  The larva then migrates to another fruit where it will burrow into the core.

Some orchards in Vermont have a history of very high numbers of EAS -- one of those is the UVM HRC.  We started trapping EAS adults on white rectangular sticky traps on May 10, trapping as many as 32 on one trap. However, the cold temperatures arrived which slowed insect activity.   In orchards where EAS numbers are above threshold, the Petal Fall spray should not be delayed.  Insecticide options include Imidan, Guthion, and Lorsban.  Note that Lorsban is considered more toxic to the predacious mite T.pyri and may not give you as long a residual activity as Imidan or Guthion. Also note that the federal label for Guthion has recently been revised.  Changes affect the Personal Protective Equipment  required and extend the Re-Entry Interval (REI) to 14 days instead of the former 48 hours for certain activities.  If you purchase new product, make sure you read the label carefully so that you will be in full compliance with the new requirements.  Given the EPA public briefing and the information that has been released (see below), options other than Guthion (Azinphos-methyl) should be considered.

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