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Healthy Fruit 1997 Vol. 5:9

Jun 4, 1997

Growth and Weather

While some of the later-developing areas of the state have only progressed to 80% petal fall, the growth stage of McIntosh in early to mid-developing areas ranges from 1/4" to 1/2" fruit. Peaches are generally at shuck-fall or a bit later.

A spell of warm weather (several days in a row with temperatures in the mid-70s or higher) may still trigger a significant invasion of PC; leaving rapidly-developing fruit, even on the interior trees, particularly susceptible to PC injury.

We are still about 5 to 7_F below the average temperature this season. This means tree development is slower, and some key pest development is either slower or nonexistant.

Warm Weekend Brings Curculio

On average, members of the UMass IPM crew have been examining 1500-2000 fruits per day across 48 commercial orchard blocks for evidence of plum curculio activity. Each of these blocks is visited and sampled every three days as part of a large experiment to determine whether a correlation exists between captures of PC in black pyramid traps and PC injury levels within the orchards. Up to today, PC injury has averaged 0.4% across all sampled blocks, and all of these blocks received a treatment against PC shortly after petal fall. This level of damage (0.4% as of 6/4) is very low relative to the past couple of years.

From ongoing studies of PC movement in some unmanaged orchard sites, we have reason to believe that a significant proportion of the overall PC population has yet to immigrate into orchards. The reason behind this is that with the exception of last Friday and Saturday (5/30 and 5/31), the weather has not been favorable for PC immigration by flight. Warm spells, such as occurred last week, are necessary to trigger invasions of PC from the woods surrounding the orchard and to inspire egglaying activity within the trees. In fact, in one early-developing, unmanaged site, PC damage increased from 1% to 15% between last Friday and Sunday (5/30-6/1).

In our judgment, the relatively cool weather pattern that has been in place will probably translate to a long, drawn-out PC season. Our extensive program of scouting will allow us to monitor PC activity throughout the month of June, and we will keep you updated as the PC season progresses.

The question of PC control now is whether the second application against PC should be a whole-farm or a border row treatment. In deciding between these options, an important consideration is that the fruit at this stage of development are growing very rapidly, and fruit may be partially unprotected if a well-timed protective cover is not in place. Given the slow development of PC populations within orchards, In next week's issue of Healthy Fruit, we will include the specifics of the New York State degree-day model, which aids in determining the end of the PC egglaying season.

Rain Signals End to Primary Scab Season

Primary scab is practically over in all parts of the state. With the rains of the past weekend, the last significant ascospores of the season were released. Any infections from that release (given adequate wetting in your part of the state) should show up by the middle to end of next week. If you don't have scab by then, then you won't have primary scab this year.

Leafminer Development Varies

Development among leafminers ranges from a few remaining egglaying adults to a few scattered tissue-feeding mines, and everything in between. As we are expecting with plum curculio, this appears to be a drawn-out LM season. It is too early to make an accurate assessment of potential LM populations, as LM in most areas of the state are only at an early sap-feeding stage. Sap-feeding mines will become more evident over the next week.

Growers who have concerns about developing LM populations should sample interior fruit cluster leaves for evidence of sap-feeding mines. As outlined in the 1997 March Message, our treatment thresholds for first-generation sap-feeding mines under Massachusetts weather conditions (dryer than some surrounding states) are 7 mines per 100 leaves for McIntosh and 14 mines per 100 leaves for non-McIntosh varieties. These thresholds may seem conservative to some, but judging from recent years' experience, LM have a great capacity for rapid multiplication from one generation to the next. In other words, even a relatively small number of first-generation mines often translates into a much greater number of mines in the subsequent generation. These thresholds for treatment represent our best estimate from over 10 years of accumulated data.

Several orchards scouted by Polaris Orchard Management are already at 15-25 mines per 100 leaves, which is beyond the threshold which warrants treatment. If a post-petal fall treatment against first-generation LM is necessary, most areas of the state still have time this next week for an application of Provado or Agrimek; applications should probably not occur beyond 1/2"-2/3" fruit.

Omite Replacement on the Horizon

In blocks receiving only oil as the pre-bloom treatment for mites, some adult ERM and first generation eggs can be seen. However, the numbers at this point remain very low. No adult ERM or eggs have been observed in blocks which received a pre-bloom treatment with either Apollo or Savey.

Under cool weather conditions, ERM populations tend to build slowly, but growers intending to use Agrimek for leafminer and ERM control ought to make the applications before the leaf tissue hardens off, to allow proper penetration of the chemical. There are still several days remaining for such treatments to occur.

In the May 14th issue of Healthy Fruit, we briefly discussed the progress toward registration of Pyramite as a summer-use miticide on apples in Massachusetts. This chemical represents a reasonable replacement for Omite; although more harmful to mite predators than Omite, it is less toxic to these predators than Carzol. As mentioned previously, Pyramite has received federal approval for use as a summer miticide on apples. However, registration in Massachusetts is turning out to be more complex than we had initially thought. Pyramite represents a new class of pesticide, which commands the attention of the entire Pesticide Bureau during an upcoming meeting. Thus, the registration process cannot be resolved by a conference call as we had previously thought. We are hopeful that the registration can be cleared by some time in July, and we will keep you posted on the progress.

Check for Rosy Apple Aphid

A fair number of rosy apple aphids have been observed on Cortland and Gravenstein over the past week. Cultivars like Cortland, Gravenstein, Ida Red and Golden Delicious are especially susceptible to RAA damage, and should be considered for treatment with Lorsban, if necessary.

Time for Pear Psylla Treatment

Pear psylla nymphs have progressed into the hardshell stage in some of the earlier-developing areas of the state. Sites which have not yet received treatment against psylla are developing significant populations and are showing accumulation of honeydew on foliage. In orchards where an application of Agrimek against pear psylla is being considered, this week is likely the time in which these treatments should occur. In orchards where psylla numbers are low (less than 1-2 nymphs per leaf), the application can be delayed another week without any major problems.

Peach Plant Bugs II

In last week's issue of Healthy Fruit, we incuded a brief outline of plant bug management strategies on peaches. Because of the omission of the punchline, we are reprinting that discussion in its entirety.

Shuck fall is the time to pay particular attention to signs of attack by tarnished plant bug, oak plant bug and hickory plant bug. Feeding by these insects peaks between shuck fall and when the fruit reach 1/2"-3/4" in diameter. It is important to protect fruit at this stage against 'catfacing' injury caused by plant bugs. Research has shown that either Guthion or Imidan alone are at best 50% effective in preventing plant bug injury. Therefore, we suggest use of a full rate of Guthion or Imidan in conjunction with a one-third labeled rate of a pyrethroid such as Asana, Ambush or Pounce. We feel that because of the tendency of pyrethroids toward high absorption into and slow release out of the bark of the trees, the one-third rate of pyrethroid offers a good compromise; extending the residual effects of the chemical while limiting the well-known destructive effects against mite predators. If mowing is planned in blocks of peaches, it is important that an active protective insecticide cover be in place at the time of the mowing. This will limit the effect of plant bugs, which are numerous in the groundcover, when they are pushed into the canopies by mowing.

Shift Brown Rot Strategy at Shuck Fall

As peaches leave shuck split, brown rot managment should change. While managment during around bloom to shuck split, and during the final stages of ripening, can be critical to brown rot control, the time from pit hardening to early ripening is less critical. Peach fruit are more resistant to brown rot during this period. Last year, the fruit team did a trial on peaches at the HRC which eliminated or reduced fungicides during this period. There was no difference in the amount of brown rot regardless of whether we applied 5 fungicides from shuck-split to harves, or only two fungicides over that period. If we continue to have wet weather, don't eliminate fungicide sprays after pit hardening. However, a couple of applications over that period, even during wet weather, should be adequate.

A far more critical period occurs when the fruit starts to color and ripen. At that point, consider using the newer SI fungicides labelled against brown rot on peaches: Indar, Elite and Orbit. While these fungicides are pricey, they are also very effective. To quote from Wayne Wilcox, who has done several years of trials on these fungicides,

"Indar, in particular, has provided outstanding control of brown rot for the last 3 years in our sour cherry trials in Geneva, even when we inoculate fruit and really turn up the disease pressure. For instance, under the most severe evaluation regime last summer, 80% of the unsprayed fruit were infected; fruit sprayed with 2 oz/100 gal of Nova had 59% infection; fruit sprayed with 2 lb/100 gal of captan had 25% infection; fruit sprayed with 12 oz/100 gal of Rovral had 19% infection; and fruit sprayed with 0.8 oz/100 gal of Indar had 3% (!) infection. ...Indar is also two or three times as active as Orbit in lab assays of active ingredients, although these assays are not always perfect reflections of what happens in field."

In addition to being very effective, Indar, Elite and Orbit have either a 1 (Indar) or 0 days preharvest interval. The goal of most peach growers in Massachusetts should be to supply as ripe and rot-free a peach as they can. These fungicides, applied as needed around harvest, are probably the best option for this purpose.