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First-generation rose leafhoppers develop on rose bushes in the orchard periphery, then move (as adults) into adjacent blocks of apple trees to commence second-generation egglaying. With this one-generation delay in presence on apple, first-generation RLH are able to skirt treatments that often keep white apple leafhoppers in check, such as early-season treatments with Sevin (as a thinner) or Provado (targeting first-generation leafminer). Leafhoppers of both species are notorious for summer-long population expansion, until the harvest-time adult LH population is great enough to pose both an annoyance to pickers and a threat to fruit quality, largely from deposits of frass on fruit.
This appears to be a season of fairly dense RLH invasion; over the past week, substantial populations of early- and mid-instar RLH nymphs have become apparent in many monitored orchards. Any growers who are noticing high populations of LH nymphs now should be aware of the potential for population expansion through harvest, and treat accordingly. If the population appears to be excessive, bear in mind that nymphal stages of RLH are far more susceptible to treatment than adults—a low rate of Provado (1-2 oz./100), a half-rate of Thiodan, or treatment with Sevin should clear up RLH nymphs for the season.
Aside from hoping for the best, it is difficult to emphasize a particular management strategy for this season’s second-generation leafminer crop. As a result of the inconsistent weather patterns of May and June (and resultant LM egglaying), second-generation mine development has stretched out over several weeks—all growth stages, from early sap-feeding mines to substantial adult emergence, were noted in the past couple of days, and many orchards appear to building the potential for late-season population explosion (as seen in many orchards in 1998). Fortunately, few orchards are facing immediately damaging populations (in excess of 1 mine per leaf for the second generation), and this season’s above-average rainfall and minimal mite pressure (thus far) may partially offset some of the negative impacts of LM infestation.
Given little potential for effective further treatment of second-generation LM, coupled with the lack of benefit from treatment of third-generation mines, growers may choose to hold off on treatment of this season’s LM population and prepare for assessment of first-generation LM in 2001, when effective treatment is far more likely.
Thus far, European red mites haven’t mustered much of a threat in most sampled orchards. However, the first cases of damaging populations and early bronzing were observed in a few blocks of susceptible varieties (notably red delicious), suggesting that ERM may gain some steam in the next couple of weeks.
Consistent sampling of foliage is the best method to determine the level of threat posed by the developing ERM population. Although time-consuming, these samples can allow growers to effectively spot-treat vulnerable areas—saving time and chemicals in the long run. For sampling, we recommend inspection of middle-aged leaves (taken from anywhere in the canopy), and data from New York suggest that treatment should be considered if samples reveal that 80% of leaves are infested with 1 or more motile mites. If treatment is deemed necessary, growers have the options of Kelthane, Vendex, and Vydate (each with known drawbacks); Apollo (with a 45-day preharvest interval); and Pyramite, which is likely the best summer option, particularly for spot treatments.
Although we are still relatively early in the annual period of apple maggot fly invasion of commercial orchards, it appears that this year’s AMF population is pretty light. Only a handful of orchards have exceeded treatment thresholds on unbaited monitoring traps, and even fewer orchards (one) have built alarming numbers of AMF on baited perimeter traps.
If the AMF population does not generate an increased threat in commercial orchards over the next week or so, growers may be able to substantially increase the interval between AMF treatments, with treatments triggered by accumulation of 2 or more AMF per monitoring sphere. That said, it is important to bear in mind that the potential for additional AMF immigration is not over, as immigration and activity generally extend well into August.
As we regularly emphasize, a season of light AMF pressure (such as 1999) can add to the value of using traps to monitor the abundance of AMF. In a season such as this, growers may see a direct financial return from extending the interval between applications or reducing rates in response to slow-building, lighter AMF populations. In addition, regular monitoring of traps may alert growers to later-season invasion and buildup of AMF, which is still a distinct possibility this year.
Before we know it, apple harvest season will be here. As always, it is important to harvest apples at the proper maturity depending on their use – be it for immediate fresh market sales, short-term refrigerated storage, or long-term Controlled Atmosphere (CA) storage. Of course taste is a good indicator of maturity, and still used effectively by many growers to help judge fruit maturity and suitability for harvest. Still, it is nice to have as much information as possible for estimating proper harvest maturity. Once again, Valent BioSciences Corporation (formerly Abbott Laboratories) is offering a weekly ‘Harvest the Potential’ report to bring you information on how the apple crop is evolving in our area. Included will be information on fruit quality, size, color, and harvest time -- all useful information for helping decide when to pick. For southern New England, our own Dr. Duane Greene contributes to the weekly report. ‘Harvest the Potential’ is free via e-mail or FAX. If interested, send e-mail to valentbiosciences@valent.com, or FAX 847-968-4802. Include your name, address, phone and FAX numbers, and e-mail address.
In the eastern part of the state, apples were measuring in at 2.4-2.7 inches during the last few days. The crop continues to size well.
Even though many blocks of apple trees had significant scab infections in May, early eradication efforts were successful and secondary spread has not been a problem in June and July in the vast majority of blocks. This is noteworthy in light of the continued periodic rainfall.
A recent evaluation of a replicated 1995 planting of 25 cultivars at the HRC (part of the NE 183 Trials) showed that some cultivars had significantly more scab on the leaf terminals and clusters than others. The cultivars which had the most scab on the terminals (20 % or more of the terminals examined) were: Shizuka, NY 429, Ginger Gold, Orin, Golden Delicious, Sunrise, Braeburn, and Golden Supreme. The same cultivars had the most scab on the leaf clusters, although the scab levels were not quite as high (16 % or more of the leaf clusters examined). The most resistant cultivars were Gala Supreme, Goldrush, Pristine, Enterprise, NY 75414-1, Honeycrisp, and Fuji.
The high rainfall and tricky infection periods in May also resulted in enough leaf scab on the 1999 NE 183 planting at the HRC (24 cultivars and 5 reps) to warrant a count. Eight of these cultivars had scab on 25 % or more of the terminals examined: BC 8525-33, R. Macintosh, MN 1824, NJ 109, Hampshire, Pinova, Runkle, and BC 8526-50.
Although new strikes seem to have slowed somewhat in cultivars initially infected, troublesome levels of shoot blight continue to become apparent over the past two weeks in other cultivars such as Mutsu where no indications of infection were noted previously. Given the conflicting information concerning management of shoot blight during the growing season, growers are divided between removing infected terminals as they appear and waiting until after tissues dry out for removal in late summer.
The accumulated rainfall for the HRC in Belchertown from April 15 to July 15 was 17.5 inches. The UMASS weather station in northwest Deerfield has been registering even more rainfall during most of the season. The other UMASS weather stations in Sterling and Northboro received less rain (about 13 inches by June 15). Together with moderate temperatures this is good weather for growing summer diseases. We have been searching for new flyspecks on alternate hosts in the borders around apple orchard blocks as well as on sprayed and unsprayed apples and so far nothing, but it can't be too far behind. In Amherst on July 14 we trapped more flyspeck conidia in an infected patch of blackberries (more than 250 conidia on 1 tiny plastic "rotorod" and several other rods with more than 50 conidia per rod) than we have ever seen. Surely rows of apples trees nearest to large inoculum sources have been getting some conidia, and if rainfalls or heavy dews continue it should not be too long before we start
seeing specks. The various prediction models that are driven by leaf wetness and temperature are indicating that in the absence of fungicides, specks should be showing up soon. We are not trying to alarm anyone, but this would probably not be a good year to decide to stop spraying fungicides in July. For high risk areas (nearest dense woods that have maples, oaks, blackberry canes, grapevines, Viburnum spp., and other hosts, a spray with captan or captan +Benlate or one of the new strobillurins (Flint or Sovran) every 2-3 weeks is a good idea as long as preharvest intervals allow. Late-ripening and lightly-colored cultivars are of course the most problematic. For medium or low risk blocks a three week interval is still reasonable. For those brave souls who have very low risk situations (no close inoculum sources, well-ventilated site, very open canopies, etc.) and are willing to take the risk a four week interval is still possible.
Healthy Fruit is written by Dan Cooley, Ron Prokopy, Jon Clements, Starker Wright, Arthur Tuttle, Wes Autio, Bill Coli, 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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