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The average size of apples is 3/4 inch in the East and 1/2 inch in the West. Peaches are averaging 7/8 inch and pears are averaging 1 inch.
Infections that occurred during primary scab season are showing now as leaf lesions, but the good news is that most commercial orchards came through a very tricky primary season with extreme scab pressure very well. Unsprayed trees are full of scab. Many have reported that Flint has performed well.
A somewhat early and relatively wet Spring has contributed to flyspeck development. The primary inoculum (the sexual or ascospore stage) is mature and is being released in Eastern and Southern orchards, with Western orchards lagging about a week behind. Research at UMASS indicates that this release is occurring mostly from the flyspecks that have survived the winter on brambles, wild grape, oak, maple, and other plants that have the proper waxy cuticle (cuticle that has not completely hardened or dried-out over the winter). The consensus among experts is that this primary cycle happens mostly within the woods and hedgerows, perhaps reaching a couple of rows into an orchard block and that it is not until a few weeks later that the secondary stage of the fungus (the asexual or conidial stage) spreads its spores from a larger range of host plants (that have the right waxy cuticle to support this stage of the fungus in June and July) much further into the orchard block. While we mostly agree with this scenario, we feel that the importance and impact of the primary inoculum may be underestimated and that a spray with a material like captan or Flint about three to four weeks after petal fall, especially in the 3 or 4 rows of apples adjacent to woods or hedgerows may reduce the potential for a flyspeck problem later in the summer. This could be combined with the last curculio spray or could come after that. The timing of subsequent sprays could be fine-tuned for each block according to "Flyspeck Risk" if a survey of the woods or hedgerow is done to determine the abundance of the alternate host plants and the density of flyspecks on those host plants. The tree fruit disease lab at UMASS is conducting these surveys as part of a replicated experiment. One outcome of the study will be to develop a condensed, user-friendly survey for growers and scouts to use.
So far, there has been no sign of fire blight in pears.
A severe thunderstorm originating near Northampton and traveling east through Amherst, Belchertown, and the Warren-Brimfield area last Friday afternoon took its toll on crops in the region, including some orchards. Damage was localized but severe where it occurred. A local Food Bank’s early vegetable planting was destroyed, and orchards that did get hail reported 50 to 100% fruit damage. At the UMASS Horticultural Research Center in Belchertown, the storm lasted less than thirty minutes, but two rounds of hail during that time resulted in significant damage (50% plus) to the Research Center’s apples and peaches. Nearly two inches of rain also fell during the storm. The Hudson Valley of New York has already seen their share of hail during mid-May storms that damaged nearly 5,000 acres, and we understand Columbia County N.Y. was hit hard during last week’s severe weather too. Needless to say, growers with hail-damaged orchards are now facing the challenge of whether to abandon or salvage the crop. The growing season is young, so we certainly hope these recent storms are not a precursor of more to come!
Across the board, fruit set is quite variable -- Empire and Golden Delicious are looking good, however, McIntosh, Cortland, and Delicious fruit set ranges from light to moderate, being very dependent on orchard location and condition. A short bloom and poor weather following bloom likely contributed to the less-than-ideal set. Similarly, light fruit set on McIntosh has been reported in Maine and Southeast Vermont. The traditional thinning window (up to 12 mm fruitlet size) has passed in most areas, however, it is not too late to use ethephon (Ethrel, Aventis CropScience; Ethephon, Microflow) on blocks or trees that still have too many, or heavily clustered, fruit. (Remember, the crop always seems to get much larger as the growing season passes!) A recommended rate for thinning with ethephon is 0.5 to 1.5 pints per 100 gallons, using the lesser amount on Macs (easier to thin) and the higher rate on Delicious and Empire. Ethephon works best with warm temperatures (both during and following application) and will help return bloom the following season when applied to trees with fruit in the 15-25 mm. size range. Caution is advised on easier-to-thin varieties such as McIntosh and Cortland, because over-thinning can result with ethephon application. Further, we have had little experience with ethephon in Massachusetts. If fruitlets are still in the 10-15 mm size range, an NAA plus Sevin application might be a safer and equally effective late thinning application. As always, read product labels for more specific usage directions.
In all monitored areas, plum curculio activity increased with the high temperatures late last week (6/1-6/2). This period also stimulated a late flush of captures on traps intercepting PC crawling or flying into orchards, suggesting that a few stragglers were in fact holed up in areas outside of orchards through mid-week.
In unsprayed orchards, damage to fruit rose dramatically by Saturday—reaching 90% damage over the two-day stretch of activity. In monitored commercial orchards the trend (though not the scale) was the same, as evidence of PC feeding and egglaying increased statewide from 0.5% (through 5/31) to 1.8% (through 6/3).
The pattern of damage in commercial orchards indicated that this late immigration was not particularly heavy, but that the few PC arriving on border-row trees were stimulated to a high level of both feeding and egglaying activity. As is usually the case with newly arriving PC, border-row trees sustained the greatest damage, and multiple stings were observed on most damaged fruit.
For growers who are tracking degree-day (DD) accumulation as an indicator of the end of PC activity, our monitored sites range from 109-170 DD accumulated since petal fall, placing us 1/3-1/2 of the way through the projected PC season. From here, a stretch of moderate weather (high temperature = 75o, low temperature = 55o) will yield 15 DD per day—indicating that 10-15 days remain for PC coverage.
We do, however, feel that the late immigrants of last week are likely the last substantial invasion of the season. Given this, growers who applied a border-row treatment late last week should be clear for the season; those who have lost residual activity may want to consider a final border-row application.
Nearly all leafminer larvae observed in the past 3 days have reached the tissue-feeding stage, indicating that it is too late for any chemical treatments to have much impact against first-generation LM. Recent samples have revealed a significant disparity in mine development—LM growth stages already range from early-instar (sap-feeding) larvae through well-developed pupae.
Although mine densities are relatively low in orchards assessed thus far, the statewide LM population has shown a trend toward extreme late-season expansion. Growers are advised to keep an eye on development of potentially explosive mid-season populations; as mines become apparent on fruit-cluster leaves, we advise sampling of mine density in consideration of treatment targeting second-generation LM.
Healthy Fruit is written by Dan Cooley, Ron Prokopy, Jon Clements, Starker Wright, Arthur Tuttle, Wes Autio, and Duane Greene except where other contributors are noted. Publication is funded in part by the UMass Extension Agroecology Program, grower subscriptions, and the University of Massachusetts IPM Program. A text version can be e-mailed to you if you contact Doreen York. Please cite this source if reprinting information.
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