Arthropod Management Update

**Insecticide/Miticide Note**
 
Please note that the Carzol label has a new restriction -- it cannot be applied after Petal Fall.  It is a material that not many growers use because of its toxic impact on beneficials in the orchard.   As always,  if you do have this material,  read the label carefully before use.

Update of General DD Accumulation

Potato Leafhopper

Potato Leafhoppers (PLH) are present on young terminal leaves in Vermont.   These insects migrate up to New England from the South.   They can cause extensive damage on young trees.   The insect has piercing/sucking mouthparts and as they feed, their saliva gets into the plant and causes a toxic reaction which results in "hopper burn"   -- the edges of the leaves turn yellow, curl,  and eventually turn brown.   The insect itself resembles the WALH in body shape but is lime green in color and will move very quickly (either forward or sideways) if disturbed.     A tentative threshold is one insect per leaf.  Table 16 on page 94 of the 2000-2001 New England Apple Pest Management Guide lists materials effective against  PLH.   Of the materials listed,  Provado and Thiodan would have the least impact on beneficials. 

Apple Maggot

Below is the total number of adult apple maggots trapped on the 19 baited traps we have hung at the UVM Hort. Res. Center.  You can see that trap captures are low.  However,  it is expected that trap captures will continue to increase as we enter the period of active migration into the orchard.  If you have had your traps out for 2-3 weeks, now is the time to clean them of debris.  Massachusetts researchers estimate that the trap's ability to capture apple maggot files decreases by about 25% for every week of exposure without maintenance.   Thresholds:  cumulative average of 2/trap on non-baited spheres or 5/trap for baited spheres.  If an insecticide for apple maggot is applied, trap captures should be discounted while there is effective residue present.    Since the adults are very active and spend much time on leaves and fruit where they feed on honeydew,   low rates of Guthion or Imidan are effective (i.e., 1/2 of full label rate). 

Leafminers

The graph below shows the average pheromone trap captures per date for spotted tentiform leafminers at  the UVM Hort. Res. Center.  The second adult flight seems to have peaked  on June 27.  We are currently seeing fresh sap-feeding mines.    Around the state,   first generation mines were below threshold in most of the orchards visited.   However, since LM can increase 8 fold per generation, it is important to watch for the development of new mines.   To sample second-generation leafminer, select mid-terminal leaves from both the interior and exterior portions of the canopy.  If second-generation mines exceed 2 per leaf, then treatment is advised.   If trees are under stress or are prone to late-season drop, a lower threshold of 1 mine per leaf is recommended.     Note:  Do not count first generation tissue-feeding mines when sampling for second-generation. 

European Red Mites

European red mites, in general, appear to be low in numbers so far.  As we progress farther into the growing season, the threshold continues to rise.  The following are the thresholds for the remainder of the growing season:

Dogwood Borer

"Infestations in apples of dogwood borer, a clearwing moth, are almost always located in burrknots or graft unions that are planted too high above ground level. Burrknots are aggregations of root initials that can develop on the above-ground portion of the rootstock; all commercial dwarfing and semi-dwarfing rootstocks have a tendency to develop burrknots. Some chemicals with hormone effects, such as NAA, can increase the expression of burrknots, as will failure to keep the area around the trunk weed-free and open to sunlight.

The adult seeks out these spots to lay eggs, particularly if they are surrounded by vegetation or protected by something, such as mouse guards. Moreover, mouse guards may frequently house weeds, and shield the lower trunk from incidental exposure to insecticide cover sprays. Sustained feeding by dogwood borer at the graft union may severely weaken the tree at this juncture, or girdle the trunk and cause a slow decline in tree health. Orchards in which mouse guards are emplaced should be examined for signs of damage.

White latex paint brushed on the exposed portion of the rootstock will prevent new infestations of the borers, and also protect against southwest injury to the bark. Dilute trunk applications of an insecticide with good residual activity can provide control of established infestations. Lorsban 50WP or Thiodan 50WP are the most effective materials if applied during the period between July 15 and August 15, bearing in mind the specific pre-harvest intervals. "

Please note that page 56 of the  2000-2001 New England Apple Pest Management Guide  has a section entitled "Trunk Painting for Bark Protection" which gives more details on using a trunk whitewash to deter borer egglaying. 

Additional information on borers can be found in the "In the Spotlight..." section of this newsletter.

Mullein Bug

Mullein bug damage has been observed on Delicious fruit in a few Vermont orchards.  Feeding on fruit by the insect results in upraised, pimple-like bumps.  Fruit often becomes misshapen as it increases in size during the season.   More details on the Mullein bug can be found on pages 39-40 of the 2000-2001 New England Apple Pest Management Guide.  Petal Fall is the time to manage this insect.

Cluster of Delicious fruit  with Mullein Bug damage

Mullein bug feeding damage on fruit  (raised bumps

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