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About 10 years ago, pear thrips caused quite a scramble in the maple industry, inflicting tremendous damage to sugar maple stands across the Northeast. The massive infestations of maple trees in the late 1980s carried over into apples (a preferred thrips host) as well; a few orchards in western Massachusetts suffered substantial crop losses to this unpredictable insect. From the early 1990s through 1997, pear thrips have put in an early-season appearance in most orchards across the state, but have not built to such numbers to be of economic concern.
Several factors seem to be coming together this season which may set the stage for significant damage from pear thrips in apple orchards. First, the presence of thrips in orchards last year was greater than it has been in the recent past, with monitored orchards harboring populations of 1-2 thrips adults per blossom: enough to cause damage, but not necessarily enough to warrant treatment. The wider presence of thrips active in orchards last year does not bode well for this year. The second critical factor leading to outbreaks of thrips damage is weather. Unfortunately, the weather thus far this spring has been nearly ideal for thrips 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 for 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 leaf tissue begins 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 seen and generally most severe injury. As soon as the pink tissue starts to unfold, damage is seen as shriveling and discoloration of petal tissue, which has two effects: damaging the fruitlets directly and reducing the overall quality of the flower, so that it is no longer attractive to pollinating insects.
Growers who have had problems with pear thrips in the past, have noted their presence 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 a treatment threshold of 3 thrips per bud.
The good side of managing thrips is that they are controlled by nearly every pre-bloom insecticide. If the monitored population warrants treatment, we recommend an application of Guthion or Imidan 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.
Very few tarnished plant bugs have been captured on visual monitoring traps thus far. This holds with the pattern of the past several years, and we may be in store for another light year on the TPB front. However, below-threshold trap captures at this point may also be the result of sub-optimal weather for TPB activity. TPB adults are not known to become particularly active in orchards until the daytime temperatures reach 70 F or so, and we have experienced only a few periods of activity thus far.
As one might expect with below-average trap captures, damage to buds has been sparse as well. However, a few oozing buds have been spotted: damage which likely occurred during the brief warm spell of 4/7 to 4/8.
As expected, there is high variability statewide in captures of adult leafminers on trunk traps. Population levels noted during harvest last year are a good indicator of what is to come this spring. Logically, orchards with heavy LM infestation when the leaves dropped will see a similar early-season population this year. Trap captures in a handful of orchards have already reached 100 per trap (a good indication that treatment will be necessary), others average 10-20 LM per trap, while traps in many cooler locales have yet to show many captures. This could be another banner year for LM infestation, and we highly recommend early-season monitoring as the first step in management.
For pre-bloom control of leafminer, growers can use a pyrethroid (Pounce, Asana, Ambush) or Vydate. The ideal timing for use is early pink, though use of any of these materials comes with substantial risk. Pyrethroid use has been directly linked to outbreaks of European red mites due to profound suppression of mite predators, and Vydate has been shown to have a severe negative impact on buildup of T. pyri. Because of its well-known effects as a thinner, Vydate should not be used beyond early pink. We will dive into post-bloom LM treatment options in subsequent issues of Healthy Fruit.
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 be 90-95%, resulting in control through mid-July or so.
Along with reasonable early-season mite control, there is no possibility that ERM can develop resistance to oil; it has no chemical effect on the mites, and 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), given that there is an appropriate period of drying after application.
Pear psylla adults have been active for several weeks, and oviposition was noted early last week (4/13). Egglaying has been light thus far in most areas, and we do not anticipate heavy early-season activity as most blocks were relatively psylla-free at harvest.
Bloom in peaches has yielded disappointment in many orchards in the region. Primarily in central Massachusetts, apparent winter injury has taken its toll, with projected fruit losses of up to 95%. As with last year's weather-related injuries in apple, damage is highly variable between (and within) orchards.
The message this year is "Don't delay". The reason behind this is one that this approach should reduce risk of an early season infection. It's an old-fashioned approach to managing scab that assumes no one was out counting scabby leaves last fall.
However, if you really wanted to get a read on whether your orchard needs to be sprayed early this spring, last fall was the time to do it. As outlined in the New England Apple Pest Management Guide, in order to know how important the an infection period is, you need to know four things:
For the time being, ignore 2, 3 and 4, and focus on the amount of inoculum in an orchard. The only way to know how much inoculum is there was to measure the potential ascospore dose (PAD) by counting scab-infected leaves last fall. Those leaves are becoming this year's inoculum. If you didn't do it, then the only thing to do is take a guess.
Some may be tempted to use last year's packout evaluations to estimate scab. This is really a poor approximation. In a study we did a few years ago, we showed that the agreement between PAD and percent fruit scab was poor. But we do know that there were a lot of scabby fruit last fall, and that in the orchards scab was a larger problem than it has been in many years. So, in general, we know there is a lot more inoculum than usual.
That means, in general, that delaying the first spray application until pink or until after the first three infection periods, isn't a good idea this year. However, a block that didn't have scab last year and isn't bordered by abandoned trees is still a good candidate for delayed sprays. The problem is, unless a PAD evaluation was done, no one knows what the inoculum situation really is.
That points out an important aspect of IPM. By gathering some information, you can save some sprays and reduce the risk of damage. Without the information, the only way to reduce risk is to spray.
With that in mind, be ready for this week's showers. The safest approach will be an application of a protectant fungicide prior to the first infection period. The second-best approach will be following the first infection period with an SI application.
Healthy Fruit is written by Dan Cooley, Ron Prokopy, Starker Wright, Wes Autio, and Duane Greene except where other contributors are noted. Edited by Dan Cooley. 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.