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Healthy Fruit 1997 Vol. 5:14

Jul 11, 1997

All Quiet on the Disease Front

There were some real challenges In getting on fungicides for scab this year. And in case you think it was all a waste of time, it wasn't, as indicated by non-sprayed trees at the Hort. Research Center last week, where fruit scab averaged 61% and cluster leaf scab 82%. In spite of that, barring any mistakes in timing, there is no significant scab in commercial orchards.

Fire blight is also a non-issue in the state so far. Apparently, fire blight activity didn't ever really start.

Time to Step Up Calcium Rates

Obviously, we think it is a good idea to apply calcium to apples on a regular basis over the summer. It develops fruit firmness, controls cork spot on susceptible cultivars, and even helps reduce flyspeck and sooty blotch. If you haven't started yet, anything you do from here on out will still be very beneficial. The recommendations are in the table below.


Applications should begin three weeks after petal fall and continue at two-week intervals until harvest.

Pounds per 100 gallons dilute
Calcium source
Until mid-July
After mid-July
Actual calcium
0.6 to 0.8
0.8 to 1.0
Calcium chloride (29% calcium)*
2.0 to 2.7
2.7 to 3.3
Calcium nitrate (19% calcium)
3.2 to 4.3
4.3 to 5.3

* Add 2/3 ounce vinegar per pound CaCl2.

Use of a surfactant in CaCl2 sprays may reduce the potential for foliar injury.

Leaf injury may be greater when captan or guthion is mixed with CaCl2.

Do not mix CaCl2 with SoluborTM.

Emerging Maggot

The recent rains have stimulated apple maggot fly emergence from pupae in the soil and trap captures on red sticky spheres have begun occurring in most monitored blocks. Trap-capture treatment thresholds have been developed over the course of years of study, largely in New York. For unbaited sticky red spheres, the treatment threshold is a cumulative average of 2 AMF per trap. For spheres baited with the fruit odor 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 Guthion or Imidan as the first AMF cover; waiting until the AMF season has progressed a bit before applying a full rate of either material. Soon after treatment, all AMF should be removed from the monitoring spheres, and accumulation of AMF toward the treatment threshold will begin again at zero. In order to maintain capturing power, sticky spheres should be cleaned of all debris at least every two weeks, as the spheres' ability to capture AMF is reduced by 25% for every week of exposure without maintenance.

Second Generation Leafminer

Flight of second generation adults continues, and the first wave of second generation sap-feeding mines has been observed. Treatments against the first generation appear to have turned out very positive results; blocks treated at petal fall or soon after show very low LM infestation. For treatment options against the second generation LM adults and larvae, refer to last week's issue of Healthy Fruit.

Mites and Miticides

As noted in last week's issue, mites are beginning to appear in moderate numbers in many blocks, even some which received an early season miticide application. At this point in the year there are 4 miticides available for use, aside from summer oil. Pyramite was recently registered for orchard use in Massachusetts; its recommended usage is discussed in the July 2 issue of Healthy Fruit. Kelthane, Carzol and Vendex are also available for summer use, but each has 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 New York, summer oil applications were effective as a maintenance treatment; they slowed increases in mite populations but did not significantly reduce the adult population already present. As with early-season oil applications, one must avoid applying Captan within a week or so of a summer oil treatment to avoid the foliar damage caused by material incompatibility.

Potato Leafhopper a Problem on New Plantings

Potato leafhopper adults have immigrated in large numbers this year from the midwest. Given these patterns of movement, no orchard in Massachusetts is immune to infestation of PLH. Nymphs have appeared in moderate numbers thus far, up to 10 nymphs per leaf. There are no data which indicate that PLH cause detectable injury to semi-dwarf or standard fruit-bearing trees. New plantings are most prone to PLH damage, and some research suggests that dwarf, fruit-bearing trees can also be damaged by PLH infestation. If the level of infestation warrants a treatment, Provado, Thiodan and Sevin are all available for use against PLH.

A Few Woolly Apple Aphids

Woolly apple aphid colonies are now moving from the basal areas of pruning cuts to new terminal growth. Most monitored orchards are showing some WAA colonies, but numbers to date have remained relatively low.

A Note on Psylla

Buildup of second-generation pear psylla is continuing, hardshell nymphs are present, and effective psylla control at this stage of the season is a real challenge. As would be expected, most control measures exercised against the first generation have been fairly successful, and areas which received no first-generation treatment show the greatest psylla populations.