Fungal Fiesta

Unfortunately, the only news to report is that diseases which are not usually a problem are a problem. Fresh scab lesions are still showing up. Check the red spots on fruit which look like scale injury - if there's an olive green center it is more likely scab. The symptom is one that probably comes from partial control, with the centers of the spot still producing conidia. And scab is still wide-spread.

Reports of blossom end rot are now coming in. At this point, there is no treatment.

Powdery mildew is also showing up in susceptible varieties, like Cortland, Paulared, and of course, Ginger Gold. The damage does not appear to be economically important, but it is an indicator of how wet it has been.

Similarly, we are seeing occasional rust spots, particularly on Golden Delicious.

This always has been a blessedly boring time of year, disease-wise. It still is, but only because the single word still is, "spray!"

Mites, Summer Oil and Captan a Problematic Mix

In blocks which received either an early-season miticide or a full oil program, the cool, wet conditions have not yet inspired a break in mite control. However, in some blocks which only received 1 early-season oil treatment, the ERM populations have reached levels of moderate risk. In an extreme case, a block which received no oil or miticide, pockets of significant bronzing were observed, along with 10-30 ERM per leaf. For reference, if you are monitoring the abundance of ERM in your orchard, middle-aged leaves (from anywhere on the tree) should be sampled. We recommend that a treatment be considered if more than 65% of sampled leaves contain 1 or more motile mites.

If treatment is necessary, there are 4 miticides available for use during July and August, aside from summer oil. Pyramite stands as the most highly recommended, but Kelthane, Carzol and Vendex are also available for use, each with significant drawbacks. ERM resistance to both Kelthane and Carzol has been noted, and both (particularly Carzol) are especially toxic to predaceous mites. Vendex has been demonstrated as being less effective when used as a July/August miticide than when applied in May.

In studies performed in recent years in New York, summer oil applications were effective as a maintenance treatment; they slowed increases in mite populations but did not significantly reduce the population of adults already present.

Since captan use is up to keep on top of scab flourishing in the orchards, oils can be a real problem. As with early-season oil applications, one must avoid applying captan within a week of a summer oil treatment to avoid the foliar damage.

Bora's Borin'

Over the past several years there has been increased attention paid to borers of several species as a potentially problematic pest of both apples and peaches, 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 and New York have noted the presence of dogwood borer on dwarfing rootstocks; one Massachusetts orchard had a significant outbreak of the twig boring apple pith moth; and several blocks of peach trees in Massachusetts fell victim last year to the peachtree borer.

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 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 (depending on the species), 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 (small holes with sawdust exuding). If evidence of larvae is seen, then efforts should be made to kill the larvae before damage to the trees is irreversible. Unfortunately, larval control is extremely labor intensive, but it can be accomplished by inserting a wire or awl into their hole or digging them out with a knife. Any trees within the orchard which are irretrievably damaged should be removed from the orchard and burned to prevent further infestation.

Maggot Fly Doing Well

In some high-risk blocks, unbaited monitoring spheres continue to capture large numbers of apple maggot flies, up to 20 AMF per sphere. However, these heavy captures are generally occurring in blocks which are at the most risk of AMF pressure, particularly those immediately adjacent to unmanaged apple trees. Statewide, roughly half of orchards have reached threshold levels of AMF capture, but no egglayings have been observed thus far.

For AMF, treatment thresholds based on trap captures have been developed over the course of years of study in New York and Massachusetts. For unbaited sticky red spheres, the treatment threshold is a cumulative average of 2 AMF per trap. For spheres baited with butyl hexanoate, a treatment threshold of 5 AMF per trap is recommended.

If these thresholds are reached, an application of Guthion or Imidan is advised. We do advise use of a reduced rate of either material as the first AMF cover; a reduced rate controls light to moderate AMF populations quite well. If such an application is made, all AMF should be removed from the monitoring spheres and accumulation of AMF toward the treatment threshold will begin again at zero. As emphasized regularly, sticky spheres should be cleaned of all debris every 2-3 weeks, as the spheres' ability to capture AMF is reduced by ~25% for every week of exposure without maintenance.

Mr. Potato Head

The nymphal population of potato leafhopper has all but disappeared. No growers that we know of applied a spray directed at PLH, so it seems that even early, low-rate sprays of Guthion and Imidan targeting AMF have taken a chunk out of the PLH population. However, growers should remain wary of PLH populations developing on young, nonbearing trees which do not receive the standard treatment against AMF.

Healthy Fruit is written by Dan Cooley, Ron Prokopy, Starker Wright, Wes Autio, and Karen Hauschild except where other contributors are noted. Edited by Dan Cooley. Publication is funded in part by the UMass Extension Agroecology Program, grower subscriptions, and the University of Massachusetts IPM Program. Healthy Fruit is available on the Web at The Massachusetts Tree Fruit Advisor, (click here). A text version can be e-mailed to you if you contact me, at dcooley@microbio.umass.edu. Please cite this source if reprinting information.