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Squash mounts were performed this morning on leaves collected under abandoned apple trees on Orchard Hill in Amherst. The scab spores were just under the 10% mature spore level. The level is likely to be right at or slightly above 10% in low-lying areas to the east and south of Amherst, and with all the rain ending Monday some of the most "advanced" orchards might have had wetting periods. Orchards to the west and north of Amherst at high elevations are likely to be safe from infection so far, but keep in mind what we said last week about blocks that had scab late in the season last year!
Thus far, only a handful of tarnished plant bugs have been captured on white rectangle traps, with no orchards exceeding treatment thresholds. Given the pattern of the past several years, it is likely that we are in store for another light TPB year. However, below-threshold trap captures at this point may also be the result of weather patterns that are not conducive to TPB activity. TPB adults are not particularly active until the daytime temperatures reach 70 F or so—we certainly haven’t approached optimal TPB weather in the past couple of weeks. So, growers should keep an eye out for spikes in activity during the next warm spell, though we do not expect any major TPB problems.
Emergence of adult leafminers has slowed somewhat with the cool, wet weather of the past week. Even so, most orchards at or near tight cluster have exceeded treatment thresholds (based on trunk trap captures) and will likely require intervention of some sort. The density of LM emergence remains somewhat of a mystery to us—as mentioned last week, we expected that this year’s LM crop would be fairly light, given the remarkable season-long control achieved by most growers last year. However, emergence will likely flare again with some warm weather, and many growers will have to wrestle with heavy first-generation populations.
For early-season LM control, there are two basic strategies: prebloom treatments targeting adults and eggs, or treatment after petal fall targeting first- (or second-) generation sap-feeding mines. For prebloom LM control, pyrethroids (Asana, Ambush, Pounce) offer reasonable efficacy with a tolerable price tag. However, as we continually emphasize, use of pyrethroids is known to spark or exaggerate other pest management problems, notably long-term suppression of beneficial mites. Vydate and Thiodan are also available for prebloom use against LM, but we also caution growers to balance the risks of using these materials with their marginal efficacy.
Currently, the most effective, relatively benign treatments against developing LM populations appear to be those labeled for use post-bloom, including Provado, SpinTor, and Agri-Mek. However, none of these materials (pre- or post-bloom) offers a perfect solution; we will address the relative strengths and shortcomings of post-bloom materials in upcoming issues of Healthy Fruit.
Areas of the state with traditionally troublesome populations of thrips (particularly the Berkshires) may again face a real risk of damage from this invasive early-season pest. As was the case last season, the weather has been nearly ideal for thrips buildup and feeding damage. Adult thrips are able to enter apple buds (or other tree fruit crops) as soon as the buds begin to open, where they feed on the succulent, developing tissue within. The longer the bud tissue stays closed and soft, the greater the risk of damage. A slow, steady spring will maximize the potential for fruit loss from bud damage.
Early-season damage centers on developing leaf tissue, and as the leaves peel back from the buds, they may appear misshapen or brown at the tips. During tight cluster (after green tissue starts to harden), thrips adults are able to enter the flower buds, where they begin to feed on petal tissue and the fruit calyx. This is the most commonly observed damage, leading to shriveling and discoloration of petal tissue. This has two effects: damaging the fruitlets directly, and reducing the overall quality of the flower, reducing the probability of pollination.
Growers who have had problems with pear thrips in the past, have seen thrips active in buds this season, or who have orchards adjacent to stands of sugar maple should pay close attention to thrips presence and activity this spring. Studies done in the late 1980s showed that cutting and inspection of buds through pink gives the best indication of the potential for thrips damage. If thrips adults are found in flower buds, we recommend treatment if the population exceeds a provisional threshold of 3 thrips per bud.
The positive side of thrips management is that the thrips adults are controlled by nearly every prebloom insecticide. If the monitored population demands treatment, we recommend a low-rate application of Imidan, Guthion, or Lorsban no later than early pink. It is important to gain control of thrips prior to bloom; once the blossoms open, the bulk of the damage has been done.
Egglaying pear psylla adults have been present in low numbers for the past couple of weeks—no egg hatch has been observed thus far. As was the case last season, we expect that psylla numbers should be fairly light this spring, as most orchards kept psylla in check through last season’s harvest.
That said, the March 15 issue of Good Fruit Grower outlines some management strategies for pear psylla, and (like European red mites) a focus on prebloom tactics may be the key to effective season-long control. Oil may offer the greatest potential for prebloom suppression of egglaying and subsequent hatch, though Surround (kaolin clay) and Esteem (a growth regulator) are also labeled for prebloom use.
No hatch of European red mite eggs has been observed as yet. Given this, growers still have time to make an effective oil application—it appears that the weather will be favorable for such an application over the next several days.
In an average year, a single application of dormant oil will kill 60-70% of overwintering mite eggs, offering good control of ERM through late June. Two applications have been shown to reduce overwintering survival by 90-95%, resulting in control through mid-July.
As emphasized last week, oil offers reasonable mite control with no chance of resistance development—it only serves to smother eggs and young nymphs. We strongly recommend use of oil at 2 gal./100 through tight cluster and 1 gal./100 to mid-pink, after which the oil has little benefit. In fact, dormant oil shows its maximum effectiveness just prior to egg hatch (when mites need the most oxygen), if there is an appropriate period of dry weather after application. Given this, growers can still see real benefit from an oil application made in the next week or so, potentially alleviating the need for follow-on treatment with a miticide.
May 3, 2000
1:00 PM
Tougas Family Farm
246 Ball Street
Northborough, MA
Healthy Fruit is written by Dan Cooley, Ron Prokopy, Jon Clements, Starker Wright, 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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