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According to the latest interception trap data, there was little arrival of immigrating plum curculio over the holiday weekend. Despite ideal conditions for immigration of overwintering PC, only a few straggling arrivers were detected, so it seems that the bulk of this year's population arrived 5/21-5/22. This is good news from a management standpoint, suggesting that growers who had good residual coverage through the weekend have likely evaded the majority of the PC threat.
In our principal unsprayed research blocks, the warm, humid weekend weather inspired a high level of egglaying activity: damage increased slightly from 5/24 (31%) to 5/27 (34%), then doubled through 5/31 (69%). This pattern is predictable, given that there was a large, uncontrolled PC population in the orchard, with ideal egglaying weather through the weekend.
In commercial orchards, PC egglaying damage has remained remarkably low. In the most current samples, the statewide average is below 0.2%, the lowest injury levels recorded in recent years. It remains difficult to predict if any PC are yet to immigrate, though we predict that the peak damage potential has passed. In the past 2 years, however, the majority of PC injury has accumulated in the second half of the season, usually at the tail end of the residual coverage of the first or second sprays.
Even with the light PC population, growers are advised to continue monitoring perennial hotspots for flushes of injury. In addition to regular visual inspection of fruit, a degree-day model was developed in New York to assist growers in determining when PC season is nearing its end. According to this model, the last treatment against PC should be applied such that the residual effectiveness of the material (10-14 days, depending on formulation and weather) will protect the orchard through the accumulation of 340 degree days (DD), measured after petal fall. To calculate DD, take the average of the day's low and high temperatures (F), then subtract 50 to determine the day's DD total. Depending on the region, we are only 1/3 to 1/2 way to 340 DD; although the potential for widespread losses to PC may be less than in recent years, growers should continue to monitor for late damage buildup.
Tissue feeding mines are appearing in untreated areas, and a small proportion of mines in early sites have begun to pupate. Orchards receiving Provado, Agri-Mek, or SpinTor appear relatively clean so far, though it is still too early to get a good read on the density of the surviving population.
In early- to mid-developing orchards, it is getting late for use of these three materials. Once first-generation mines begin to develop into the tissue-feeding stage, the only realistic option for treatment is Lannate. For optimal LM control from this material, treatment should be made when mines begin tissue feeding, ideally when less than 10% of mines have moved beyond the sap-feeding stage.
Apparently the hard rains of last week have set the European red mite population back a bit, as most monitored blocks are relatively mite-free. Those individuals that are present are predominantly adults, and spotty egglaying has been observed. Along with low levels of ERM, some two-spotted spider mites have begun to appear, though not yet in threatening numbers. As is always the case in mite management, hot and dry weather in June can inspire rapid expansion one generation to the next.
In monitored blocks, psylla have progressed into hardshell nymph to adult stages, making chemical control very difficult. If the population present is posing a threat, then the next available window for gaining control is when the summer generation eggs begin to hatch. According to 1998 trials by NEFCON, a single treatment of Pyramite in mid-June offered excellent psylla control through August. In this trial, 1 application of Pyramite far outperformed 2 applications of Mitac, with Pyramite contributing some level of ovicidal effects. It may be too late in most orchards to use Agri-Mek for psylla control (due to hardening of plant tissue), so the best available options are Pyramite, Provado, and Mitac.
Many growers across the state have begun to plant plots of peach trees in place of apple in response to consumer market demand. While it is certainly a good idea to capitalize on the public's desire for local peaches, positioning new plantings of peach trees within blocks of apple can have a few drawbacks. The critical factor to keep in mind is the difference in timing of bloom and harvest between apples and peaches. When in very close proximity, a pre-bloom insecticide application on apple may impact pollination of peaches. The same will be true of a post-bloom insecticide application on peaches, which can have a negative impact on pollination of apple. A second (and potentially more severe) threat comes near harvest of peaches, which generally occurs at the height of apple maggot season. Residues present on peaches at harvest have come under close scrutiny in the past several months, and growers should take all precautions that sprays applied to apple do not impact near-harvest peaches.
A variety of plant bugs are capable of inflicting high levels of catfacing injury on peaches between shuck fall and 3/4" fruit. Times of orchard mowing often hold the most risk; as the understory is mowed, the bulk of the plant bug population will move into the tree canopies for shelter.
Given the increased risk of catfacing injury, we recommend that an active, protective insecticide cover be in place for a couple of days prior to mowing. Research over the past decade has shown that common OPs (such as Guthion and Imidan) are at best 50% effective in preventing catfacing injury. Therefore, we suggest use of a full rate of Guthion or Imidan in conjunction with a one-third labeled rate of a pyrethroid. We feel that because of the tendency of pyrethroids toward absorption into the bark of the trees (and slow release from the bark), the reduced rate of pyrethroid offers a good compromise. Such a treatment will enhance the residual effects of Guthion or Imidan, while limiting the destructive effects against mite predators.
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.
