Leafminers' Generation Gap
While there are still some first generation leafminer pupae on hand, emergence and flight of second generation LM adults is well in progress. No sap-feeding mines of the second generation have been observed as yet. In orchards where parasitism of LM larvae is monitored, rates range from 10% to 50%, depending on the pesticide profile of the orchard.
Although an application of Provado against the first generation LM was certainly the treatment of choice this season, some growers have decided to concentrate their control efforts against the second generation. The first step toward effective control of second generation LM is careful monitoring of the density and development of first generation tissue-feeding mines. The level of incidence of tissue-feeding mines should be determined by sampling from middle-aged fruit cluster leaves.
If the treatment threshold of 7 mines per 100 leaves (for McIntosh) or 14 mines per 100 leaves (for non-McIntosh) is exceeded, then a treatment against the second generation LM is likely in order. For this treatment, there are three options. First, a treatment of Provado can be used; such an application should be made in the next week to 10 days. Second, a treatment of Lannate can be used. However, if Lannate is the material of choice, it should not be applied until after the second generation sap-feeding mines appear. The third option is to use a treatment of Thiodan against the second generation adults; such an application would need to occur in the next week or so. This material offers minimal control of the adults, and is not a very effective treatment. Whatever the choice material, the timing of a treatment against second generation LM is difficult, leaving treatment against the second generation LM less effective than treatment against the first.
All stages of mite development are now present in orchards. The hot, dry weather of the past few weeks is leading to rapid ERM multiplication; reminiscent of the 1995 growing season. In fact, in some orchards which received a pre-bloom application of Apollo or Savey, motile ERM are beginning to appear. Growers should pay close attention to the development of the mite populations, as populations of ERM can rapidly build to damaging levels if no action is taken. At this stage of the season, New York State's recommended treatment threshold is 65% of leaves containing 1 or more motile ERM.
Good News For Mite Control, Bad News For Mites
There is certainly good news on the mite control front. Ron appeared at the meeting last week called by the Massachusetts Pesticide Bureau to discuss registration of Pyramite as a summer miticide for use in Massachusetts orchards. There was much concern expressed about the impact of this material on aquatics, but the board took into consideration the fact that very few orchards contain significant bodies of water, and proceeded to approve the material for use.
Pyramite is active against all stages of mites, with the greatest effectiveness coming against nymphs, and it is less harmful to beneficials than either Kelthane or Carzol. A single treatment of this material in early July should offer good mite control for at least a month, and may reduce mite numbers to non-damaging levels for the remainder of the season. Pyramite represents a new class of chemical for orchard use, and the main concern centers around its high toxicity when inhaled. For this reason, it is packaged in water-soluble bags, like those used for Nova fungicide. These bags should not be opened when putting the chemical into the tank. The entire bag is introduced into the tank to avoid exposure to dust.
The Restricted Entry Interval (REI) for this material is 12 hours, and the pre-harvest interval is 25 days. The recommended dose for use on apples is 4.4 oz./acre, in no less than 100 gallons of water. This may pose a challenge in determining the number of bags which should be used per tank. As this is a new material for orchard use and recently labeled, we have no experience with the chemical and recommend cautious use until we gain more experience with its effects.
Potato leafhopper adults have been seen in several orchards in the last week. These adults have likely migrated from the midwest, with more to follow. PLH adults and nymphs can inject toxins into the leaf tissue, turning leaf margins yellow or brown. Young plantings are particularly susceptible to PLH infestation and injury. Growers should keep a close eye on blocks of younger trees. If the PLH population gets out of control, then a treatment of Thiodan, Sevin XLR or Provado is in order. This is also the optimal time to treat against the young nymphs of rose leafhopper and white apple leafhopper, using any of the materials previously mentioned.
Woolly apple aphid populations are building in several orchards. We advise that growers keep an eye out for WAA buildup, particularly on pruning cuts. Sugar, associated with both honeydew and the telltale white protective coating of the aphids, can spill out onto fruit and create an infestation of black sooty mold fungus. If 50% or more pruning cuts are infested, growers should consider using either a half-rate of Thiodan or a full rate of Lorsban for control.
Red sticky spheres for monitoring apple maggot fly populations should be hung this week. Please refer to last week's issue of Healthy Fruit for specific recommendations for sphere placement strategies.
Egg hatch of the new generation pear psylla is continuing, but no hardshell nymphs of this generation have been observed as yet. It is too late for an application of Agrimek, but there is still time to use Mitac, if necessary. Provado is also a viable alternative at this stage, but will likely be less effective than Mitac.
Two-spotted mites have been observed moving in moderate numbers into pear canopies; migration which is likely induced by mowing of the understory. Mites on pears can be controlled by use of Vendex, Carzol or Kelthane, and growers now have the option of using Pyramite on pears as well. Pyramite is also suitable for use on pears against psylla, but the rate at which it must be used to gain psylla control is high enough that the cost may outweigh the benefits.
ERM Reaches Peaches
European red mites have been observed on peaches in some orchards. If ERM populations grow to damaging levels on peaches, an application of Vendex, Carzol or Kelthane is recommended.