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Healthy Fruit 1997 Vol. 5:12

Jun 25, 1997

Summer Starts

We've started summer, with REAL humidity and heat over the past couple of weeks. The estimates from the HRC are shown below.

Plum Curculio Resurgence

The extremely warm weather this past weekend did indeed spark a resurgence of egglaying activity in most areas of the state, as fresh scars were seen in several early- and mid-developing orchards this week. We have now exceeded the 340 DD threshold in most areas, and early to mid-developing orchards which had a protective cover in place through the weekend should be clear of any significant threat of further PC immigration.

Leafminer Update

In orchards where Provado was used as a leafminer treatment at petal fall or shortly thereafter, the surviving population of mines appears to remain very low. In areas where no application was made or where coverage was poor, LM development ranges from late sap-feeding mines to early pupation. It is still much too early for a treatment against the second generation LM, either with Provado or Vydate.

Apple Maggot Fly Approaches

Emergence of adult apple maggot flies will soon be upon us, making this coming week a good time for placement of red sticky monitoring spheres in orchards. The following information details placement of spheres and treatment thresholds.

The key to accurate monitoring of AMF populations is accurate trap positioning. It is critical that traps be positioned with abundant fruit and foliage underneath and to all sides of them. However, light is also a necessary component of effective placement of spheres as it enhances their visibility to flies, so the most effective positioning is 1/3 of the distance into the canopy from the perimeter of the limbs. Dwarf trees are the exception to this rule as their low foliar density permits light entry deeper into the canopy. Foliage and fruit should not be within 6" of traps in order to keep the sticky surface free of interference and scraping by limbs and leaves. Traps should be placed at least at head height, if not slightly higher. Results from many years of data show that the capturing power of traps decreases for every week of exposure, so for accurate results traps should be examined at least once a week and should be cleaned of all flies of AMF size and larger at least every 3 weeks. Cleaning is best accomplished by picking flies off the traps with a small, sharpened twig (removing as little of the sticky as possible) while holding the trap by the hook with a pair of vise grips.

Traps should be placed in susceptible varieties in order to watch areas where trouble will arise. The susceptible varieties are as follows:

Early season: Early McIntosh, Gravenstein, Jersey Mac

Mid season: Cortland

Late season: Golden and Red Delicious

A farm of 10 acres should have 10 traps hung, while a farm of 100 acres should have 20 traps hung. The treatment threshold for unbaited traps is a cumulative average of 2 AMF per sphere. When this threshold is reached, Guthion or Imidan should provide effective control. If the AMF population is low or moderate, a half or partial rate of either material should be sufficient, while a high population should be well controlled by a full rate.

Apple Bark and Twig Borers

Borers of several types remain as a relatively minor pest of apples in Massachusetts. However, over the past several years there has been increased attention paid to borers as a potentially problematic pest, particularly in low-spray orchards. In recent years, several New England states have reported increases in sightings of the roundheaded appletree borer; growers in Pennsylvania have noted the presence of dogwood borer on dwarfing rootstocks; and in one Massachusetts orchard, there was a sizable outbreak of the twig boring apple pith moth.

Prevention is the best medicine in dealing with borers, so if you are using a reduced spray program in your orchard, you should make every effort to practice cultural techniques which will reduce the threat of infestation. Preventive maintenance measures include periodic examinations of mouseguards for hidden borer activity, control of burr knots, removal of host plants from the orchard perimeter (unmanaged apple trees, hawthorn, shadbush and mountain ash) and meticulous management of the orchard understory. Lack of cover around the bases of trees not only discourages oviposition but also allows access to larval holes by woodpeckers, which are the predominant natural predator of borers.

During peak emergence, usually between late June and early August, a trunk application of Lorsban or Thiodan should provide good control of the adult borers. For larval control, growers should inspect the lower portion of the trunks for evidence of larval infestation (pinholes with sawdust exuding). If evidence of larvae is seen, then efforts should be made to kill the larvae before damage to the tree is irreversible. This can be accomplished by inserting a wire or awl into their hole, digging them out with a knife, or injecting a mixture of para-dichlorobenzene moth flakes and cottonseed oil or 1.5% rotenone extract and ethyl alcohol into the hole with a grease gun. Any trees within the orchard which are irretrievably damaged should be removed from the orchard and burned to prevent further infestation.

Pyramite Update

Today, Ron is in attendance at the meeting of the Massachusetts Pesticide Bureau, at which state registration of Pyramite as a summer miticide is being discussed. We are hopeful that this meeting will result in good news, and will report on the progress of the registration in next week's issue of Healthy Fruit.