May 28, 2002 Volume 11 No. 11 Update on Pest Management and Crop Development
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TRAP CATCHES (Number/trap/day)
Geneva: 1st Codling Moth and Lesser Peachtree Borer caught 5/23
Highland: 1st Variegated Leafroller and Tufted Apple Budmoth caught 5/28.
Warm, wet weather after shuck split may result in disease problems for peach growers caught off-guard. As the temperatures begin to (finally) rise, and with thunderstorms in the forecast for most of this week, be sure to keep an eye on the weather to avoid potential problems with bacterial spot of peach, and possibly peach scab.
Bacterial spot is a disease that affects virtually all stone fruits, but is particularly damaging to peaches, nectarines, and apricots. The disease is caused by the bacterium Xanthomonas arboricola. Temperatures above 65°F and wet conditions favor disease development, and it is likely to be a problem in orchards with a history of disease. Primary fruit and leaf infections occur as a result of frequent wetting from full bloom to 4 weeks after shuck split. Wind-driven rain or debris can damage leaves and developing fruit, creating small wounds that the bacteria can enter, and significantly affecting the occurrence and severity of fruit and leaf infection. Disease does not develop under hot and dry conditions.
Peach scab, caused by the fungus Cladosporium carpophilum, is more of a problem downstate, and on later peach varieties. It is capable of infecting all cultivars of peach, and is known to affect apricots, plums and nectarines. Once established, this disease can be extremely damaging. Infection and fungal growth are most rapid during periods of rainfall with temperatures between 6575°F. Symptoms develop after a very long incubation period of 4070 days. Because of the long incubation period, it is most often only the infections that occur between shuck split and pit hardening that develop fruit symptoms before harvest. Secondary infections may occur on twigs and late-season cultivar fruit. Although leaves and twigs may become infected, the fruit exhibit the most obvious evidence of the disease, developing small, greenish circular spots that gradually get bigger and darken as spore production begins. These spots appear when fruit are half-grown and are most common on the stem end of the fruit, but can occur over the whole surface.
Powdery mildew (rusty spot) is caused by the same fungus that causes powdery mildew on apple. This is a particularly favorable year for powdery mildew, so we expect to see rusty spot on peach varieties susceptible to the disease. Fortunately, fungicide programs targeted for control of brown rot or peach scab will often provide appreciable control of rusty spot. The SI fungicides (Indar, Elite, and Orbit) targeted towards brown rot management should provide good control against rusty spot.
Disease management. The most effective way of managing bacterial spot is to plant varieties resistant to the disease, yet this is not always practical. Maintaining proper fertility is essential, as excessive growth or poor nutrition increases a tree's susceptibility. Our limited choice of cultural control methods makes chemical control necessary when bacterial spot is a problem. If you had disease problems in the past and weather predictions look favorable for infection, applications of oxytetracycline will be necessary. If warm and wet weather conditions persist, oxytetracycline can be applied on a 710-day schedule from now until 3 weeks before harvest. Oxytetracycline is intended to be used in a preventive mode; it has very limited to no kickback activity. If conditions prohibit you from making an application 24 hours or longer after a known infection event, save your money, as an application at this time will probably be ineffective against these infections.
Recently, I have been hearing about the use of the foliar fertilizer Nutri-Phite Magnum as a means of managing bacterial spot. Nutri-Phite fertilizers are derived from phosphorous acid. Phosphorous acid forms a phosphite salt when neutralized with a base, as opposed to a phosphate salt, which results when phosphoric acid (the traditional source of phosphorous) is neutralized with a base. Phosphite has one less oxygen molecule than phosphate and, apparently, has a much higher degree of solubility and mobility. Its effectiveness against bacterial spot, at this point, is not known under New York conditions and, furthermore, I have not seen any published reports documenting its efficacy. We have included this product in our trials this year at the 2 pt/A rate, in order to evaluate its potential.
To prevent peach scab, pruning is helpful because it facilitates air movement through the canopy to reduce the length of wetting periods and improves spray penetration into trees. When control measures are needed, apply fungicide sprays at 1014-day intervals starting 10 days after shuck split and continuing until 6 weeks before harvest. These intervals may be lengthened during extended periods of dry weather. Several products are labeled for use in NYS for peach scab control, including Captan 50WP (2 lb/100 gal) or Captan 4L (1.5-2 pt/100 gal), Indar 75WS (0.8 oz/100 gal), Sulfur 95WP (5 lb/100 gal), or Topsin M 70WP/Captan 50 WP combination (6 oz/100 gal/ and 1 lb/100 gal, respectively). All of these fungicides are labeled for control of brown rot through either petal fall or shuck split. So, if you have been using these fungicides in your schedule for control of brown rot, you have been managing scab as well. It is important to maintain protection beyond shuck split through pit hardening for control of peach scab, especially under favorable weather conditions. These fungicides will also offer protection against brown rot and rusty spot (particularly sulfur) during this period.
Roundheaded Appletree Borer
Mullein Plant Bug
Oriental Fruit Moth
San Jose Scale
Spotted Tentiform Leafminer
Roundheaded Appletree Borer
Oriental Fruit Moth
San Jose Scale
Apple growers in N.Y. have not traditionally applied insecticide sprays specifically targeted against internal Lepidoptera. Early season control sprays directed against the plum curculio have provided adequate control of the first generation of internal Lepidoptera, and later sprays applied during July and August to control apple maggot have controlled later season generations. Most growers have used broad-spectrum organophosphate (OP) insecticides to control all of these pests that directly injure fruit and have usually obtained almost perfect control at a reasonable cost. However, in the future, it appears that changing pesticide regulations may affect the availability and use patterns of organophosphates. Also, as growers attempt to implement more sophisticated IPM programs using more selective "reduced risk" insecticides, which usually have a narrower activity range, for control of plum curculio and apple maggot, it may become necessary to apply specific treatments to control internal Lepidoptera throughout the growing season.
Three species of lepidopterous larvae can infest apple fruit in New York State: codling moth (CM) Cydia pomonella (Linnaeus); oriental fruit moth (OFM) Grapholita molesta (Busck), and lesser appleworm (LAW) Grapholita prunivora (Walsh). This species complex of apple pests is commonly referred to as internal Lepidoptera. Seasonal development differs slightly for all three species. However, since codling moth is the most common pest found in fruit in commercial orchards, this entire complex of pests can be managed by directing control measures on a schedule designed to control CM. Since these pests can be found commonly infesting apples in unsprayed orchards and wild apple trees, natural enemies, predators and parasites will not provide adequate control in commercial apple orchards. Therefore, for the foreseeable future, it is likely that specific control tactics will have to be used in order to obtain acceptable control of CM in commercial N.Y. apple orchards.
It should not be necessary to apply additional special sprays for CM control in apple orchards that continue to be treated with even minimal schedules (2-3 sprays during the season) of OP or other broad spectrum insecticides for control of the plum curculio and apple maggot. During the past few years, however, with the advent of trapping-based spray decisions for apple maggot, and a resulting decrease in cover sprays in some cases, there have been more opportunities for an unwelcome return of low-level CM infestations. In such cases, if it becomes necessary to apply special sprays for CM control in orchards that are not being treated with standard insecticides, timing control sprays by using CM developmental models based on heat unit accumulation is a very effective management strategy.
The Michigan model for predicting CM development gives fairly accurate predictions of codling moth activity in N.Y. As many as two insecticide applications may be made for each of the two generations per year, depending on the severity of pressure. Degree days are accumulated from the date of first sustained moth catch, and the first spray is applied at 250 DD (base 50°F), which corresponds with predicted 3% egg hatch. A second spray may be applied 10-14 days later. If pressure is not too severe, one spray will suffice, applied instead at 360 DD after the biofix date. To control the second generation, the timing is 1260 DD after this same biofix date.
We will again publicize suggested codling moth treatment windows this season, for those growers who don't necessarily spray certain blocks for maggot each year, and who have evidence (or suspicion) that codling moth is starting to pose a significant threat. We're calling the biofix May 23 in Geneva and May 13 in Highland; we will be providing regular updates to identify imminent spray dates.
Insecticide trials conducted in N.Y. over a number of years in research orchards heavily infested with CM and other species of internal Lepidoptera have shown that most currently available IPM-compatible, "reduced risk" insecticides (Dipel, Confirm, and SpinTor) are slightly less effective in preventing fruit injury than are standard OP insecticides such as Guthion and Imidan. However, it is likely that these selective materials applied on a schedule of 2-3 sprays/generation of CM, based on predictions from a CM developmental model, will provide adequate control in normal commercial apple orchards that are not located adjacent to abandoned orchards or extensive acreages of feral, unsprayed apple trees. However, since some of these materials have limited contact activity against young CM larvae, and are only effective when ingested, they may be more effective if they are applied 5-7 days earlier than the estimated first hatching date predicted by the developmental model for each generation of CM. This type of scheduling ensures that eggs are deposited on residues of the material so that hatching larvae are more likely to ingest a lethal dosage of the compounds before entering the fruit.
Some of the newer selective contact insecticides being developed show promise as potential replacements or rotational complements to the standard OP programs currently used for internal lep management. The results of a recent test in heavily infested research orchards at the NYSAES are shown in Table 1, below. The first generation of internal Lepidoptera was controlled well by all of the treatments. However, at the end of the second generation, internal lep damage in the seasonal programs of Calypso, Actara, and Guthion/Spinosad were not statistically lower than that in the untreated check plots. The standard treatment of Guthion gave the best overall control of internal leps, but the Warrior treatment and programs using mixtures of materials provided statistically comparable control.
Table 1. Efficacy of OP-Replacement materials, 2001.
Means within a column followed by the same letter are significantly different (Fisher's Protected LSD Test), P<0.05).
Oriental Fruit Moth
During the last decade, OFM management in peach orchards in the province of Ontario, Canada, has been increasingly dificult because populations throughout the area have become resistant to organophosphate insecticides. During the last several years, OFM damage has also been increasing in peach orchards in nearby Niagara Co., which is located in relatively close proximity to the peach production regions in Canada that have been experiencing OFM outbreaks. During 2001, trials were conducted to: (1) Monitor the efficacy of a standard OP insecticide against OFM in a typical "problem" orchard in Niagara Co. (2) Test the feasibility of using a heat-driven egg hatch model to time insecticides against different broods of OFM, and (3) Compare the effectiveness of new insecticides against OFM. Dilute to run-off sprays were applied with a handgun sprayer (450 psi) at several different timings according to degree day accumulations (base 45oF) since 1st adult catch (1st gen) for both broods. Applications were made against both generations, at either early egg hatch alone or followed by a second spray; mid-egg hatch alone; or at late egg hatch.
Treatments, including an untreated check, were replicated 4 times on single-tree plots and arranged in a RCB design. First brood early sprays (5-10% egg hatch) were applied on 14 May (150 DD), and a second spray was applied on 29 May (265 DD). Single-spray mid-egg hatch treatments were also applied on 29 May. Single late hatch sprays were applied on 11 Jun (395 DD). Second brood sprays started on 19 July (1130 DD) for the early hatch plots and were reapplied on 1 August (1400 DD). The mid-hatch sprays were also applied on 1 August. Late hatch sprays began on 9 August (1635 DD). Larval counts for the first brood were taken on 18 June by examining 100 terminals per tree in each replication. Fruit damage was evaluated on 100 randomly selected fruit per tree on 9 September. Results are given in Table 2.
Treatments with lower percentages of infested terminals generally also had low levels of fruit injury, except for the single application of Asana applied at the beginning of hatch of each brood, which had low terminal damage, but relatively high levels of fruit injury. Even though the second brood of OFM is the first generation to significantly damage fruit, shoot infestation from the first brood may have a bearing on subsequent fruit injury. The 2-spray treatments of Asana and Calypso were the most effective programs in protecting fruit from OFM injury. The single applications of Asana were not as effective as the 2-spray program, and the single sprays applied later in the season were more effective than the single treatment applied at first hatch. The 2-spray program of Intrepid was also more effective in protecting fruit than any of the single sprays, but, in contrast to Asana, the most effective single-spray program of Intrepid was the application begun at first hatch. These differences may be due to the different residual effectiveness and modes of action of the two compounds. Avaunt also significantly reduced OFM fruit damage below that in the untreated check plots, and was almost as effective as the better programs of Calypso and Asana. Esteem was not as effective against OFM as the other new materials tested. The 2-spray Imidan program did not significantly reduce OFM fruit damage, which suggests that field populations of OFM in this orchard have developed low-moderate levels of resistance to this material and probably also to other types of OP insecticides.
For estimates of the optimum treatment dates according to a developmental model of this pest, check the Orchard Radar Digest in this and subsequent issues. Although we only list predictions for Geneva and Highland, an approximate date for other areas in the state can be established by interpolation.
Table 2. OFM Terminal Infestation and Fruit Damage, 2001
Means within a column followed by the same letter are not significantly different (Fishers Protected LSD Test, P<0.05). Data transformed using Arcsin (Sqrt X) prior to analysis.
This material is based upon work supported by Smith Lever funds from the Cooperative State Research, Education, and Extension Service, U.S. Department of Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.
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