UMass Extension Fruit Program Invasive Pests

Healthy Fruit: Vol: 8 No: 14, Jun 27, 2000

Extra Inning

As discussed in the past several issues of Healthy Fruit, the residual effectiveness (or lack) of insecticides targeting plum curculio in the first week of June has dictated the buildup of PC injury in all monitored blocks. In orchards that received a border-row or whole-orchard treatment during (or soon after) the last week of May, we have recorded no significant buildup of PC injury in the past 3 weeks. However, in orchards vulnerable to early-June PC immigration, PC egglaying damage continues to build.

In one late-developing orchard, damage to unsprayed trees increased from 11% to 27% during the past week (6/19-6/26), indicating that PCs lingering in orchard blocks are still capable of inflicting substantial egglaying injury. In a separate experimental plot, tree-tapping surveys (6/26) yielded an average of 10 PC adults per mid-sized tree, substantiating evidence of apparently fresh egglaying scars on untreated trees.

For most commercial growers, the PC management front has been well in hand for the month of June—those whose orchards still harbor an active PC population may experience final buildup of PC injury over the next week.

Ball Game

The season's first apple maggot fly was observed on an unsprayed apple tree in Belchertown last week (6/19). Since that observation, we have captured a number of AMF adults on odor-baited red spheres placed in unsprayed trees.

Although AMF emergence has started right on time, we do not expect that invading AMF will pose a threat in commercial orchards for a couple of weeks. As always, we recommend that growers track AMF invasion by use of sticky red monitoring spheres, though yellow rectangle traps and rectangle/sphere combination traps (Ladd traps) are also available for use. Late June is generally the time of year to prepare and deploy sticky traps to monitor the annual invasion of apple maggot flies; this week is the optimal time for trap placement. Regardless of the trap type being used, proper trap placement is very important for accuracy in monitoring AMF density levels. When positioning traps in the tree canopy, it is critical that they be placed with abundant fruit and foliage beneath and to all sides. However, light is also a necessary component of effective placement as it enhances trap visibility to flies. The most effective position is one-third of the distance into the canopy from the outside of the tree; dwarf trees are the exception to this rule as their small size generally allows light penetration throughout the canopy. Foliage and fruit should not be within 6 inches of traps in order to keep the sticky surface free of interference and scraping from limbs and leaves. Traps should be placed at or near head height both to optimize captures and allow for easier monitoring.

Results from many years of data show that the capturing power of traps decreases for every week of field exposure—to maintain accuracy, traps should be examined at least once per week and should be cleaned of insects and debris every 2-3 weeks. Cleaning is best accomplished by picking accumulated debris from traps with a small, sharpened twig, removing as little of the sticky as possible.

Traps should be placed in susceptible varieties in areas where trouble will most likely arise. Although the details of cultivar susceptibility to AMF injury are still under study, common susceptible varieties are as follow:

Early-season: Early McIntosh, Gravenstein, Jersey Mac

Mid-season: Gala, Cortland

Late-season: Red and Golden Delicious, Fuji

A farm of 10 acres is best monitored using 10 traps, while a farm of 100 acres requires 20 evenly distributed traps for accurate orchard-wide monitoring. The treatment threshold for unbaited traps is a cumulative average of 2 AMF per sphere; when this threshold is reached, Guthion or Imidan should provide effective control. If the AMF population is low or moderate (as is typical in first sprays), a half or partial rate of either material should be sufficient.

Apple Crop Report From IDFTA

Over one-hundred-fifty fruit growers from throughout North America convened this week in Burlington, Vermont for the annual International Dwarf Fruit Tree Association Summer Tour. Hosted by growers and Extension personnel in Quebec, New York, and Vermont, the Organization spent three days touring orchards in the Lake Champlain Valley. The Champlain Valley region produces approximately five to six million bushels of apples annually. The predominant cultivar is McIntosh, followed by Cortland and Empire. The tour proved again to be an opportunity for like-minded growers to get together to see first-hand the latest dwarf fruit tree production techniques. Discussion of marketing issues and new cultivars were also hot topics as we toured New York apple orchards today.

Of interest to all is the status of this season's crop potential across North America. The following is a brief summary of the crop estimates of the major apple-crop producing regions in North America that we gleaned from our fellow tour participants.

Washington had a ‘small' crop in 1999, so 2000 is looking to be BIG. In fact, estimates range as high as 125 million bushels! Unfortunately, the 1999 crop is still not completely sold, and a new shipment of Chinese juice concentrate has hit America's shores. Expect a glut of Delicious apples and plentiful juice concentrate to keep prices low for West Coast fruit during the 2000-01 marketing season.

Michigan is coming off a record crop of thirty million bushels in 1999. The 2000 crop is looking moderate, with the exception of southwest Michigan where fireblight has run rampant this spring. Some are saying it is the worst fireblight ever to hit the region, and many acres of dwarf trees may be entirely lost to blight. Ohio too is reporting a moderate crop, with fireblight again a problem in some orchards.

The Mid-Atlantic region includes North Carolina, the Virginia's, Pennsylvania, and New Jersey. Altogether the region suffered a serious drought in 1999, and this has apparently had some impact on the 2000 crop potential. Estimates suggest the crop will be decent, but perhaps slightly below average. No major calamities have struck the region, although it is still very dry as you move south, and North Carolina in particular needs rain soon. Spotty hail in New Jersey and Pennsylvania may affect individual blocks.

The New England region includes Massachusetts, Maine, New Hampshire, Vermont, Connecticut, and Rhode Island. The apple-crop is best described as ‘moderate.' Again, a heavy crop and drought in 1999 has contributed to less-than-ideal fruit set in 2000. Weather during bloom was highly variable depending on location. For example, in Massachusetts, many orchards went from king bloom to petal fall within just a few days. Prolonged cool, cloudy weather followed bloom in much of New England. Macs are reported to be particularly light in many orchards, while later blooming varieties fared better. Hail has already damaged the crop in a few orchards in Massachusetts and Connecticut, including the UMass Horticultural Research Center in Belchertown.

New York picked a record crop of nearly 30 million bushels in 1999, so the 2000 crop is anticipated to be on the lighter side. Hail has already ruined several thousand acres in the lower Hudson Valley and Columbia County, resulting in a reduced crop potential of at least 50% in that region. Western New York has reported no problems, so the crop is looking average there.

In summary, the East is looking at about two-thirds of an average crop. But, the big crop potential in the West plus continued pressure from Chinese juice concentrate will likely mean a continuation of less than optimal returns to growers for the 2000-01 apple crop.

Honeycrisp -- the Good, the Bad, and the Ugly

Also at IDFTA, a group of Honeycrisp ‘experts' were convened in a grower's orchard next to a large planting of young Honeycrisp. There has been a lot of hype about this new apple, so an attempt was made to be pretty blunt about its potential to make inroads into the market as well as be a profitable gem for growers. Included in the discussion were: David Bedford, University of Minnesota Honeycrisp breeder; Chris Watkins, Cornell University post-harvest physiologist; Susan Brown, Cornell University fruit breeder; Paul Wooley of E.C. Marketing; and several growers from as far away as Minnesota, Wisconsin, and Michigan who have experience with Honeycrisp.

After much discussion, it was unanimous that Honeycrisp has the potential to do "Good" for growers in traditional McIntosh country. But, Susan Brown cautioned it has some characteristics that are not so desirable -- she says the "Bad" and the "Ugly." In a nutshell, here is how Honeycrisp stacks up in her eyes. (And the others were pretty much in agreement!)

The Good -- clearly, Honeycrisp has excellent texture and flavor when picked at the right maturity. Both consumers and growers acclaim it's "explosively crisp" eating quality, and mention it in the same breath as the highly desirable and good-eating Gala and Fuji. Plus it keeps remarkably well in ‘plain-Jane' air cold storage.

The Bad -- now here it gets a little strange, but unfortunately there has been a lot of variability observed in Honeycrisp's fruit appearance, and -- in some cases -- eating quality. For example, Honeycrisp are supposed to be a blush-red apple, although they have been reported to be striped too. Sometimes Honeycrisp fruit is washed-out in appearance, and usually these do not eat as well. This is more likely to happen when the tree is under stress with too heavy a crop load. Speaking of stress, it was advised to make sure Honeycrisp grow rapidly during the early establishment years. Otherwise, once they slow down, they may not be inclined to grow vigorously again. (Honeycrisp is inherently a weak grower -- does irrigation sound like a good idea???)

And the Ugly -- here things get even worse, as Honeycrisp storage issues remain a serious bugaboo. In particular, they are susceptible to soft and ribbon scald and bitter pit. (Although at least one grower claims calcium sprays easily rectify the problem.) Also, the best storage environment and temperature regimen remains to be worked out. Fortunately, there is some active research addressing these serious storage problems.

All of the Honeycrisp experts agreed the apple deserves serious grower trial, but before going too gung-ho and planting large acreages, growers may want to wait until some of the "bad" and "ugly" characteristics of Honeycrisp are better understood and can be more easily managed.

Phenologically Speaking

Apples measure 1.45-1.65 inch this week.

Scab Well-managed

The scab situation has stabilized with most orchards showing few new infections despite continued weather conditions favoring scab development.

Fire Blight Warning

Fire blight infections are showing up in several sites. So far it looks as though sites which have had chronic low level infections in previous years will have significant infections this year. Infections first started showing up last week. Fresh infections were observed yesterday "with foliage just beginning to wilt (no blackening yet)". Affected cultivars: 'Paula Red', 'Gala', 'Jonagold', 'Idared', 'Cortland', 'Fuji'.

This May Be a Banner Year for Summer Diseases

Unless we get a prolonged dry spell, this should be a big year for flyspeck and sooty blotch due to frequent and extended wettings. At orchards in eastern MA, for example, the hours of accumulated wetness total 200 hours in June 2000 compared with 34 hours in June 1999. In western MA, the accumulation from May 15 to June 14 this year is 256 and at the HRC in Belchertown, MA it is 237 hours. When the numbers are adjusted for a start date of ten days after petal fall (the earliest you could expect flyspeck primary inoculum to be mature) and for duration of wetting period and run through the "Sutton" flyspeck prediction model they are much lower: 94 for Belchertown and Deerfield as of June 14. However, there has been quite allot of rain since June 14 and we will continue to update these numbers. We "expect" to see flyspeck on apples when the "Sutton" model numbers reach 273. This is rarely before the 20th of July and sometimes as late as Sept 1. This system works more consistently for North Carolina where it was developed. We, in MA, Glen Koehler in ME, and Dave Rosenberger in NY are working on different aspects of flyspeck prediction to provide a model that works well here in the Northeast. We are developing methods to rate a block of apple trees for flyspeck risk based primarily on the density of alternate host plants in the orchard borders and the density of flyspeck on those plants. Glen Koehler is improving the accuracy of the leaf wetness accumulation data by adjusting the numbers down if the temperature is higher or lower than the optimum 68 o F for flyspeck development. Dave Rosenberger has determined the rate of removal of fungicide residues by different amounts of rainfall. Here in MA we will start to examine new canes of blackberry on a weekly basis. The first place we see flyspeck is on these canes at ground level, usually two weeks before we see it on apples. The overwintering inoculum on the second-year canes was mature on 6/5, so the fungus has already had three weeks to germinate and grow "invisible" mycelium on suitable host plants.