Why is there so much Scab in 1998? This is the question being asked throughout the Northeast -- not just in Vermont and New England but in New York and up into Canada. The following are some factors that potentially contributed to the scab in Vermont --

1. Winter set-up - We had a relatively warm winter. Parts of the state had adequate to good snow cover. The overwintering leaves remained insulated and wet. Therefore, the fungus had good overwintering conditions and was "ready" to mature as soon as it warmed up.

2. Earliness of spring -- We actually did have a spring this year and calendar-wise, it was early. Some growers were just not ready to spray so early. Unfortunately, as soon as there was 1/4" - 1/2" green tissue on the tree, some parts of the state had an infection period (i.e., April 16-17) and temperatures during that infection period were above 50F which is very favorable for ascospore release. Scab developed on the earliest "fingernail" size leaves on the fruit clusters. On non-sprayed McIntosh trees at the UVM HRC, lesions showed up from that early infection period on May 4th which was during bloom.

3. Bloom week - Bloom can be described by one word -- wet. Many growers just could not get into spray when they needed to. Plus, there was not only primary inoculum, but potentially secondary spores in the orchard at that time.

4. Continuation of wet weather -- All the wet weather we had in June and July was not only favorable for further disease development, it also depleted residues and made effective timing of fungicide applications difficult.

Looking over my notes from orchard visits, I saw scab in orchards on protective schedules and on SI programs. I saw situations where scab was present on the oldest fruit cluster leaves indicating that an early infection period was not covered. These were the orchards that had the most scab on the foliage and the fruit. [Note: It is often difficult to determine early scab infections because the infected leaves - usually those very small, fingernail-size leaves- drop from the tree.] In other orchards where infection occurred during the bloom period, the scab was not as bad. These were orchards where scab was first present on mid-or younger cluster leaves or on leaves near the base of terminals. Many growers in this situation were able to keep scab in check and off the fruit.

Because there is a higher level of scab this year, you may want to consider some sanitation practices this fall to reduce the potential overwintering inoculum. More on this will be in the next newsletter.

Please note that Table 14 on page 64 of The 1998-1999 New England Apple Pest Management Guide lists the "Maximum days from last spray to harvest" and the "Maximum rain from last spray to August 31" for the various fungicide options that manage these diseases. Cultural practices, such as summer pruning, can significantly reduce these diseases -- they should be your first defense.

Moldy Core -

Are some of your fruit turning red earlier than expected? If you cut into the core you might find that these fruit have moldy core -- a visible fungal growth in the seed cavity and core. A number of fungi are associated with this disease including Alternaria spp. Presumably, infection occurs through the calyx when it remains open for a prolonged period. It not surprising if we see more of this disease this year since the wet weather we had during bloom was favorable for infection.

Arthropod Management

Apple Maggot Flies -

Peak apple maggot fly flight is predicted to occur when 1387-1804 degree days have accumulated from January 1 (base 50F). At the UVM HRC, we were at 1523 degree days as of Aug. 3. In other words, we are in the 'high risk' period for apple maggot damage to fruit.

Trap captures around the region are variable, ranging from light to localized, high trap captures. The following is the weekly, new trap captures at the HRC -- you may have seen a similar pattern in your orchard.

 As we enter August, the question that always arises is: "When should I stop spraying?". The following is an excerpt from an apple maggot article written by Drs. Harvey Reissig and Art Agnello of Cornell University that appeared in Scaffolds, No. 19, July 27, 1998:

We regard these results as corroboration of our long-standing recommendations that a final spray be applied around the middle of August to effectively control apple maggot in most commercial orchards."

Another question that arises near harvest is: "Will picking up drops reduce my apple maggot fly population for next year?". In the same apple maggot article mentioned above, Drs. Reissig and Agnello stated:

"AM flies have a limited migratory capability, so all apple and hawthorn trees within 1/4-1/2 mile of commercial orchards should be removed if possible. Work by Ron Prokopy and his group in Massachusetts (Hu, X., J. Duan, J. Mason & R. Prokopy. 1996. Proc. Entomol. Soc. Ontario 127:107-114.) indicate that considerable work is involved in using the "dropped fruit removal" technique to mitigate AM populations. In theory, eliminating fruit drops will break the life cycle of flies in an orchard by preventing larvae from exiting the fruit and entering the soil. However, they found that, because of the breadth of the emergence period of larvae from dropped fruit, there was no case in which pickup of drops at a single point in time accounted for 80% or more of all larval exits collected from a given cultivar. Maximum benefit of drop removal occurred about two weeks before harvest for most cultivars. Since most growers currently pick up drops only once, usually well after harvest (mainly for cider apples), it is doubtful whether the economics would justify this pre-harvest initial drop removal in most cases."

Codling Moth -

Please note that we have entered the period, based on degree days, when it is predicted that 2nd generation codling moth larvae are vulnerable (i.e., period is from 1260 - 1370 DD from 1st codling moth trap capture; we were at 1343 as of Aug. 3 at the HRC.) If codling moths have been a problem in your orchard and you plan to treat, please take note of where you are in degree day accumulation in your orchard.

Borers -

The roundheaded apple tree borer (a beetle) is one of a number of borers that can attack apple trees.   Another borer is the dogwood borer (a clearwing moth).  These are the two most common borers observed in Vermont orchards. These and other borers that affect apple trees are described on page 27 of the 1998-1999 New England Apple Pest Management Guide. A picture of the adult roundheaded apple tree borer is on the UVM Apple Orchard website at http://orchard.uvm.edu/ uvmapple/ The adult beetles lay their eggs in the bark usually just above the surface of the ground from late June to early August. The larva is whitish with a brown head; it can reach 1 1/2 " long when fully grown. The larvae can tunnel in the tree for 2-4 years before it completes its life cycle. Its tunneling can severely weaken or kill the tree.

Borers are usually not a problem in orchards were orchard grass and weeds are kept low, close-fitting plastic vole guards are removed at petal fall, and summer insecticide sprays targeted at other pests reach the lower trunks of the trees. A clear area around the base of trees also allows woodpeckers, a natural predator, access to borer larvae.

Dr. Art Agnello, Cornell University, wrote the following about dogwood borers in an article that appeared in Scaffolds, No. 7, May 4, 1998:

"Infestations of this clearwing moth in apples 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."

Leafminers -

This insect has been a problem in some orchards around the state this season. The time to treat the 2nd generation mines has well passed. Third generation moths are flying. Usually, insecticides are not recommended against the third generation adults because of the difficulty in effectively timing an application and the negative impact of the potential insecticide option (i.e., Vydate) on beneficial arthropod species in the orchard.

The following chart appeared in earlier issues of IPM News but is included here again for your convenience. To conserve any T.pyri predator mites that might be in your orchard and thus enhance biological control, Pyramite would be the first choice if a miticide is needed. Thorough coverage is required for optimum control. Pyramite is restricted to two applications, with an application interval of 30 days between sprays. Note that the preharvest interval is 25 days.

** Take middle age leaves from anywhere