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San Jose Scale is a somewhat overlooked pest that can result in reduced orchard productivity and tree death. Scale literally sucks the juice out of the host plant, including apples and stone fruit. Although generally controlled by spring oil applications, it may become more prevalent during periods of mild winter weather and where pesticide programs become ‘softer’. Look for slow, otherwise unexplained, dye-back of shoots and limbs as a sign of scale infestation. Close inspection of the branches will reveal the small, white, waxy covering of young scale insects mixed with a sooty black covering as they mature -- it almost looks like a coarse salt and pepper mixture. Red ‘stippling’ of fruit at harvest is also a good sign of scale infestation. Scale multiplies very rapidly if left unchecked -- good spray coverage and an effective insecticide directed at the crawler stage will help keep San Jose Scale from finding your orchard. For more information, see the Index of Fruit Insect Pest Photographs at West Virginia University www.caf.wvu.edu/kearneysville/wvufarm9.html.
In the past two weeks, we have seen no indication that any additional late-emerging plum curculios have moved into orchard blocks from overwintering sites. However, in some orchards the tail end of PC immigration (6/1-6/3) encountered a lack of residual spray coverage. In a few cases, these late-arriving PCs have enjoyed periods of optimal egglaying conditions on virtually untreated trees. The statewide PC damage levels have risen substantially over the past week, but it is important to note that the majority of damage has occurred in blocks in which residual insecticide coverage lapsed before 6/1-6/3. Over the past two weeks, the level of PC damage in monitored orchards has risen as follows:
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Given variable treatment tactics, differences in orchard-specific PC damage have become even more exaggerated over the past week—currently, damage (assessed in border-row trees) ranges from 0-22%. As mentioned last week, we feel that growers who had residual insecticide coverage through early June should not face risk of further PC damage. However, in orchards where coverage ran out in late May, growers face the risk of substantial accumulation of damage from the relatively small but highly energetic PC population currently in the orchard. If facing this situation, it is not out of the question to consider an additional application targeting PC to stop further damage. For any grower who has doubt about the efficacy of residual insecticide coverage in early June, we highly recommend inspection of fruit in traditional hotspots to determine whether an additional treatment is necessary.
The first potato leafhopper of the season was spotted in our region about a week ago—this is traditionally the time of year when invading PLH adults ride the winds north from overwintering sites far to the south and somewhat west of Massachusetts. PLH invade as adults, and these adults along with nymphal stages are capable of damaging apple trees by injecting toxins into terminal tissues and new shoot growth.
Because PLH immigrate over such long distances and are largely reliant on wind power for transport, it is very difficult to predict the threat posed by PLH invasion from one year to the next. Mature, fruiting trees are at very little risk of PLH damage, with the exception of mild discoloration of terminal leaves. New plantings, however, are prone to heavy damage to terminal growth, which can dramatically stunt the photosynthetic capability and growth of small trees.
When the population of PLH reaches a damaging level, terminal leaves will curl, with discoloration ranging from yellowing at the mid-rib to browning of the leaf margins. Such damage can appear at an alarming rate in young trees, and is often confused with viral infections or nutrient deficiencies. If PLH damage becomes an issue, a single treatment of Imidan, Guthion, Thiodan, or Sevin should remedy the problem.
Although moderate populations of white apple and rose leafhoppers have been observed in and around orchards, it is still too early to target these species. Most LH observed are still adults, and treatments aimed at adult LH are generally ineffective—nymphal populations are much more susceptible to treatment either with Thiodan or Sevin. Because of this, we do not recommend treatment for a couple of weeks, when the next generation’s nymphs are present.
In a few monitored sites, eggs of European red mites are apparent on leaves, but very few motile mites have been found in any sampled areas. For the moment, there seems to be a general lack of mite pressure—as mentioned last week, even during periods of low risk (such as now) growers are advised to keep abreast of mite population development to better gauge the potential for late-season problems.
Over the past two weeks, moderate populations of green peach aphid have been observed, particularly in areas that traditionally experience buildup. The telltale sign of GPA infestation is curling of new growth—like PLH infestation on young apple trees, GPA infestation can dramatically stunt tree growth. Green peach aphid colonies also produce large amounts of honeydew which, as it drizzles onto tree and fruit tissues, can lead to troublesome development of sooty mold fungus.
If a substantial aphid population is observed, treatment is likely necessary to alleviate both the risk of direct tree damage and the indirect effects of sooty mold development. Traditionally, Lannate has been the material of choice for control of active GPA colonies; we will include information on efficacy of some newer materials for GPA control in next week’s issue of Healthy Fruit.
According to recent information from the U.S. Apple Association, the current agreement between the EPA and Dow AgroSciences does allow for currently labeled use of chlorpyrifos through the 2000 growing season. Some of the details of the agreement are under review; U.S. Apple is encouraging the EPA to modify the agreement to permit postbloom use of chlorpyrifos as a trunk spray targeting borers. The outcome of this debate will likely hinge on residue studies to determine the potential impact of trunk applications on fruit residues.
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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