Scaffolds Fruit Journal, Cornell University NYSAES

Diseases | Insects | Credits


Volume 6, No. 8						May 12, 1997


COMING EVENTS

						     43F       50F
Current DD accumulations (Geneva 1/1-5/12):         312       142

Coming Events:                              Ranges:
Pear psylla eggs hatch                           111-402    55-208
Apple grain aphid present                        137-496    67-251 
Oriental fruit moth 1st catch                    129-587    44-338
Spotted tentiform leafminer 1st oviposition      141-319    48-154
Obliquebanded leafroller larvae active           149-388    54-201
Spotted tentiform leafminer 1st flight peak      180-544    65-275
San Jose scale 1st catch                         189-704    69-385
Comstock mealybug 1st gen crawlers in pear buds  220-425    82-242
White apple leafhopper nymphs on apple           236-708   123-404
Codling moth 1st catch                           273-805   141-491
European red mite egg hatch complete             361-484   183-298
McIntosh at bloom                                310-544   130-275

Phenologies (Geneva):  Apple (McIntosh) - Pink
                       Pear (Bartlett) - White Bud
                       Sweet Cherry (Windsor) - Full Bloom
                       Tart Cherry (Montmorency) - Early Bloom
                       Plum - Bloom
                       Peach - Bloom
          (Highland):  Apple (McIntosh) - Early Petal Fall
                              (Liberty) - Bloom to Petal Fall
                       Pear (Bartlett) - Petal Fall
            (Albion):  Apple (Idared) - King Bloom 5/11
                       Pear - Early Bloom
                       Tart Cherry - Early Bloom

PEST FOCUS
   Geneva: Obliquebanded Leafroller larvae active in apple terminals 
           4/30
 Highland: 1st Primary Apple Scab infections observed
   Albion: European Red Mite eggs hatching 5/7, 5/9

TRAP CATCHES (Number/trap/day)
Geneva:   
                                  4/24   5/1    5/5    5/8   5/12
Green Fruitworm                    0.2   0.1      0      0    0.1
Redbanded Leafroller               1.0   6.5    1.8    0.8    0.9
Spotted Tentiform Leafminer       43.7   301    278    122    456
Lesser Appleworm                     0     0    0.3*     0    0.6
Oriental Fruit Moth (apple)          0     0      0      0      0
Oriental Fruit Moth (peach)          0     0      0      0      0
San Jose Scale                       -     -      -      0      0

Highland (Dick Straub, Peter Jentsch):
                                  4/14   4/21   4/28   5/5   5/12
Green Fruitworm                    0.4      0    0.6   0.1      0
Redbanded Leafroller               2.4    8.6   18.1  18.8    5.9
Pear Psylla (eggs/leaf)            3.1    3.1    2.3   2.5    3.5
Pear Psylla (nymphs/leaf)            -      -      -   0.1    1.0
Spotted Tentiform Leafminer        0.8*  11.9   49.7  53.2   41.8
Oriental Fruit Moth                  0      0    0.6*  3.0    3.2

                                                       * = 1st catch


Diseases

APPLE SCAB UPDATE

by Dave Rosenberger
Plant Pathology, Highland

Recent Scab infection periods in Highland:

May 3-4  21 hrs wetting, 55F, 1.03 in. rain; trees at King Bloom
May 6    14 hrs wetting, 54F, 0.28 in. rain
May 9-10 12 hrs wetting, 51F, 0.11 in. rain; trees at 75% Bloom

The next 3-4 weeks may be the most critical part of the growing season for monitoring scab in commercial orchards. In orchards where scab infections are prevented prior to petal fall, the risk of significant fruit infections occurring during the remainder of the year are usually pretty low. In orchards where scab lesions become visible before petal fall, the risk of fruit infection is very high because millions of conidia become available while fruit are still very susceptible to infection.

If a few primary scab lesions are found during orchard monitoring, what are the best methods for preventing further spread of the disease? When the primary scab lesions are difficult to find (e.g., it takes more than three minutes of scouting to find each lesion), a weekly protectant application of captan or a mancozeb fungicide may be adequate to keep scab off the fruit given average weather conditions for the year. A safer option than using protectant fungicides alone would be to add an SI fungicide (Rubigan, Nova, or Procure) to the protectant in the next two or three applications. The SI fungicides will reduce the numbers of viable conidia that existing lesions can produce and will also help to eradicate any developing infections that are not yet visible in the orchard.

In my opinion, captan is more effective against a running scab epidemic than are the mancozeb fungicides. In my field tests when the first fungicide applications are made after scab lesions are present on leaves, Captan 50W at 1 lb/100 generally provides better protection against fruit scab than does a mancozeb fungicide applied at 1 lb/100. The arresting action of captan is enhanced when hot weather (temperatures >80-85°F.) occurs several days after the captan application.

If an abundance of primary lesions are visible in trees, then more drastic action may be necessary to arrest the epidemic and prevent fruit infections. The full rate of captan (e.g., Captan 50W at 2 lb/100 gal) PLUS an SI fungicide should be applied in two or three sprays 7-10 days apart. When apple scab is well established in an orchard, the full rate of a contact fungicide is needed, both to protect fruit and unfolding leaf tissue and to minimize selection pressure for scab strains that are resistant to the SI fungicides.


Insects

AFTER THE BLOOM FADES

by Art Agnello and Harvey Reissig
Entomology, Geneva

Apart from some early varieties in a few inland sites, bloom hasn't really arrived yet, but most growers are already making the functional shift in their thinking to the pest management needs of their apples once the petals fall. This time of the season is when the effort to prevent insect pest problems begins its most active phase. The weather has turned unaccountably sluggish recently, but there's ultimately no stopping the trees at this point, so here are a few points to keep in mind for the petal fall insecticide sprays:

  1. To minimize the hazard to honey bees, apply pesticides only after ALL petals have fallen in the block and when no bees are actively foraging on blooming weeds (evening is better than early morning).

  2. Do not use Lannate on early McIntosh, Wealthy, or Dutchess because of possible injury to fruit and foliage.

  3. Postbloom use of any pyrethroid insecticide has on been known to encourage the build-up of mites and woolly apple aphid. If a pyrethroid (Asana, Ambush, Pounce) was used in any of the prebloom sprays, do not apply another pyrethroid at petal fall. Try to limit use of these materials to one application per season to delay resistance development and extend their useful field life.

  4. When choosing an insecticide for this application, keep in mind its range of activity, both adverse and beneficial. For example, if Sevin is applied for thinning, it will also help to control plum curculio and white apple leafhopper (even at the 1 lb rate). Carzol acts not only against European red mite, but will also control white apple leafhopper; however, it is not kind to predatory mites. Agri-Mek is recommended at petal fall for maximum efficacy against mites; this is also the timing at which it will have its greatest effect against white apple leafhopper nymphs and sapfeeding spotted tentiform leafminers. It is not likely to be very useful against rosy apple aphid.

  5. Be aware of the destructive effects of any spray materials on beneficial mites and insects (refer to Tables 8 and 12 on pp. 37 and 43 in the 1997 Recommends.)

  6. Do not use Vydate or Sevin during the first 30 days after bloom without taking into account their thinning effects.

MITES

Most areas of the state enjoyed relatively favorable conditions for whatever early season mite control programs were elected this year, so despite the potential confusion over what might be available for use later on, at least we haven't been in a panic over what to do and when to do it this spring. The approval of the Agri-Mek label has given growers the option of a post-petal fall application in blocks where the early season program may not have been adequately attended to. In addition, it is true that Pyramite was granted a federal label last week, but it is also true that its use status in N.Y. remains unresolved at this point; the matter is being pursued and we'll inform you of the results as soon as there is anything to report.

For the time being, we're pretty much in the same situation as we were last year at this date. Regardless of how the next 4-6 weeks pan out (and what was applied earlier), remember that it is always wise to keep an eye on the foliage throughout late June and July to detect unreasonable mite buildup, because a little warm weather can quickly boost numbers into the problem category. Until June 30, we recommend a threshold of 2.5 motile stages (anything except eggs) per leaf. You can determine the mite densities on the foliage by using the presence/absence technique:


European red mite adult female. J. Ogrodnick

Examine intermediate-aged leaves (from the middle of the fruit cluster) for motile stages. Check at least 50 leaves (5 per tree), for the presence of any number of mites; no treatment is recommended if <62% of the leaves examined are infested. A sequential sampling table (p. 90) and chart (p. 97) are provided in the Recommends. The choices are not numerous if you detect over-threshold levels; Kelthane can be used if you have no reason to suspect resistance in your populations, or if none has been applied in a given block for at least 5 years. Carzol is another choice if you don't mind eliminating any predator mites in the block; back-to-back sprays of this product would probably be needed.

WHITE APPLE LEAFHOPPER

WALH nymphs can be numerous in some blocks, especially in the eastern part of the state. Provado has proven itself effective against this pest, and a petal fall application also gives leafminer control. Growers using Sevin in their thinning sprays will get some control at the 1 lb rate. Alternative choices for control include Thiodan and Lannate; Agri-Mek or Carzol used for mites now will also do the job, but Carzol will be harmful to predator mites. The damage potential of this first generation should be evaluated carefully before deciding on the need for a specific control of this pest.

PLUM CURCULIO

Plum curculio adults move into orchards from overwintering sites in hedgerows or the edges of woods and are present in the trees from late pink to early bloom before the fruit is susceptible to damage. Adults are active in the spring when temperatures exceed 60F. Adult females oviposit in fruit during both day and night but feed mostly at night. Depending on temperature, overwintering adults remain active for two to six weeks after petal fall. Although adults may feed on blossoms, apples are not susceptible to damage until petal fall, at which time adults damage fruit by both feeding and ovipositing. Unlike fruit injured by other pests, many apples damaged by plum curculio will remain on the tree until harvest. Because adults are not highly mobile, orchards near overwintering sites, woodlands, and hedgerows are most susceptible to attack. Fruit damage is usually most common in border rows next to sites where adults overwinter.


Plum curculio adult. J. Ogrodnick

Monitoring for plum curculio is not currently recommended in New York because of the amount of time and labor involved and because plum curculio is generally assumed to be present in every orchard. However, various techniques have been used in other areas to monitor plum curculio damage and the presence of adults:


Dried sap produced by plum curculio feeding and oviposition wounds on apple

Several species of wasps parasitize eggs and larvae of plum curculio. Ants, lacewings, and ground beetles prey on larvae in the soil, and some fungi kill larvae. These organisms are not usually sufficient to regulate populations of plum curculio in commercial orchards. Plum curculio is difficult to control completely with insecticides. Relatively high rates and persistent applications are important because adults may be active for two to six weeks after petal fall depending on temperatures. In normal orchards that are not near woodlots or hedgerows and have not suffered previous damage, a single application at petal fall will provide seasonal control. In problem orchards, a petal fall application followed by a second spray 10 to 14 days later will provide adequate control. In orchards with chronic problems, or in seasons when adult activity is prolonged by unusually cool and wet weather, two cover sprays applied 10 to 14 days apart after petal fall may be necessary to prevent late damage.


Plum curculio oviposition scars on apple

This recommendation derives from a developmental model tested several years in the field at Geneva, which predicts that control sprays are no longer necessary whenever the last spray has been applied with 10-14 days after the accumulation of 340 DD (base 50°F) from petal fall. Guthion, Imidan, Lorsban, and all pyrethroid insecticides are effective at controlling plum curculio. These materials will also control codling moth later on.

MANAGING PHYTOPHAGOUS MIRID BUGS

by Dave Kain, Art Agnello, Joe Kovach & Harvey Reissig
Geneva

In a previous article, we gave an overview of the biology and management of mullein plant bug (MPB) and apple brown bug (ABB). For the past three seasons we have been monitoring the spring generations of MPB and ABB on apple, and conducting trials to determine action thresholds and best chemical control strategies for these pests.

In 1994, we evaluated the efficacy of a number of insecticides, under different timing programs. Damage was not severe in any treatment that season; all treatments appeared to work well. In 1995, additional compounds were tested, but were applied only at petal fall. Although there were no significant differences among the various treatments, all were significantly better than the check. However, only one treatment resulted in less than 3% damage to fruit at harvest.


Mirid Bug Control - 1994

                             % DAMAGE
TREATMENT             JUNE 28       AUG 30
Asana @ pink           1.2 a          0 a
Asana @ PF             3.0 a        0.5 a
Asana @ pink & PF      0.7 a        0.3 a
Imidan @ pink & PF     0.3 a        0.5 a
Imidan @ PF            3.8 a        0.5 a
Diazinon @ PF          3.0 a        0.3 a
Lannate @ PF           1.7 a        0.5 a
Thiodan @ PF           1.5 a        0.3 a
Check                 13.7 b        7.3 b


Mirid Bug Control - 1994
(All treatments applied at petal fall)

                             % DAMAGE
TREATMENT             JUNE 22       OCT 2
Asana                   3.7 a       0.5 a
Lorsban                 5.0 a       3.2 a
Thiodan                 6.0 a       4.5 a
Imidan                  7.0 a       3.2 a
Carzol                 17.2 ab      5.0 a
Diazinon               18.7 ab      5.5 a
Beauvaria bassiana     19.3 ab      7.5 a
Check                  29.0 b      20.5 b


1996 Trials
Timing of insecticide application for mirid control is critical but difficult to determine, as eggs hatch during bloom. In 1996, an experiment was conducted to determine the best timing for insecticide application. Asana, an effective insecticide against mirid bugs with a relatively long residual period, was applied at pink, petal fall, or pink+petal fall. This was compared with a treatment of Imidan, which has a shorter residual period but is less harmful to predatory mites. Imidan was applied at petal fall and petal fall+1st cover. In addition, Carzol applied at bloom, which is a standard practice in Washington, was included as a reference; there was also an untreated check. Nymphs disappeared shortly after hatching in pink treatments, and shortly after spraying Carzol. Hatch was essentially 100% complete by petal fall. Differences in fruit damage between pink and petal fall treatments were not significant, but pink applications resulted in significantly less fruit damage than the check, while petal fall applications did not.


Timing insecticide application to prevent damage by MPB and ABB
(Fruit evaluation, September 1996)

                       % DAMAGED FRUIT IN CATEGORY
TREATMENT            CLEAN     FANCY      #1 + CULL
Asana @ pink        98.5 a      0 a         1.5 a
Asana @ pink+PF     99.0 a    0.5 ab        0.5 a
Carzol @ bloom      93.0 ab   0.5 ab        6.5* ab
Imidan @ PF         96.5 a    0.5 ab        3.0** a
Imidan @ PF+1C      95.0 ab   0.5 ab        4.5 ab
Asana @ PF          93.0 ab   0.5 ab        6.5 ab
Check               86.5 b    2.5 b        11.0 b

* This rating is probably erroneous owing to confusion with severe plum curculio 
damage in this treatment.
**  Mirid nymph numbers were comparatively low in this treatment.


In another experiment, Asana was applied to 3-4 foot sections of tree limbs bearing flower clusters, which afterward were caged using mesh cloth bags, to preclude nymphs that might immigrate from untreated parts of the tree, at different periods of crop development. Mullein plant bugAsana was applied at full bloom, petal fall and when fruit were 10 mm. Bloom and petal fall treatments were also sprayed with Asana, through the mesh bag, at weekly intervals until fruit were 10 mm to ensure that any later hatching nymphs inside the bag would be killed. Using this method, any damage that appeared in a treatment would have had to occur prior to the time of the first Asana application. Therefore, damage to fruit in the bloom treatment would have occurred before full bloom, damage to fruit in the petal fall treatment would have occured before petal fall and damage to fruit in the fruit @ 10mm treatment would have occurred prior to when fruit were 10mm.

It appears from these two experiments, data from other Station blocks, and the trials conducted in 1994 and 1995, that much of the damage caused by mirids occurs before petal fall, and that pink applications of insecticides control 1st generation mirid nymphs better than petal fall applications. However, pink sprays result in no less damage and are not warranted until nymph numbers are above some threshold number.


Phenological stage in which MPB and ABB damage fruit
(Fruit evaluation, September 1996)

Phenological stage in which MPB and ABB damage fruit
(Fruit evaluation, September 1996)
                       % DAMAGED FRUIT IN CATEGORY
TREATMENT            CLEAN     FANCY    #1      CULL    #1 + CULL
Asana @ bloom       95.8 a     1.8 a   0.6 a   1.8 a      2.4 a
Asana @ petal fall  85.2 a     2.5 a   7.4 a   4.9 a     12.3 b

(Fruit 10 mm and check treatment data not included because very few fruit were left 
in September owing to premature drop.)


In a number of Experiment Station blocks in 1996, nymph numbers during bloom were compared against damage to determine a provisional action threshold. This comparison (Fig. 1, below) showed that, if 3% downgraded fruit is chosen as an acceptable level of damage, the action threshold is 23 mirid nymphs (MPB and ABB combined) per 40 limbs tapped at full bloom. This result is similar to guidelines currently in use in Canada, where mirid damage is more common. In Ontario, a threshold of 5-7 nymphs per 25 tapped limbs is employed; this is based on a 2% damage threshold. If we had chosen 2% as a damage threshold, the corresponding numbers of nymphs/tapped limb would be about 12/40 limbs, or 7.5/25 limbs, which is very close to the Ontario value. The threshold in Nova Scotia is 8/20 limbs or 16 per 40.

This threshold is preliminary and should be developed further before being relied upon. It is also based on data from blocks treated at petal fall (efficacy of material is assumed not to be a factor). Therefore, if this threshold is reached in full bloom limb-tapping samples, then a petal fall spray alone will not prevent unacceptable damage, and a pink spray would have been warranted. In this case, we need to be able to predict, before pink, whether the threshold would have been reached.

Pheromone traps were used in late summer/early fall 1996 to monitor MPB migration from mullein back into apple trees to lay overwintering eggs. Adult male MPB were caught in traps in all of the blocks that were monitored. Total numbers caught varied widely and should provide a good range of values to compare with numbers of nymphs found in limb-tap samples in the spring of 1997. We will continue to trap MPB over the next 2-3 seasons to evaluate whether traps catches can be used to predict the need for insecticide application at pink the following spring.


Mirid damage on apple

It is worth noting that we observed mirid bugs and/or mirid damage, ranging from slight to severe, in 5 commercial apple blocks during the 1996 season. Although this number seems low, there were likely more blocks where damage was done but was not noted or was confused with other damage. Experience with this bug precludes making any predictions about its appearance in the future, but its potential for causing severe damage warrants caution.

BORING

by Dick Straub
Entomology, Highland

Recently, without apparent purpose, I removed the mouse guard from a tree in one of our experimental blocks and noted that the graft union was infested by dogwood borer. Further examination under mouse guards of approximately 200 4th-leaf and 5th-leaf trees revealed that 50% were likewise infested. Subsequent examination of approximately 100 4th-leaf trees without mouse guards in an adjacent block revealed no infestations. My conclusion that mouse guards can be problematic with regard to this insect will come as no surprise to many orchardists and fieldmen.


Burrknot tissue on clonal rootstock of apple, dogwood borer feeding sites


Dogwood borer adult female. J. Ogrodnick

Infestations are almost always located in burrknots or graft unions that are planted too high above ground level. The clearwing moth (Lepidoptera: Sesiidae) seeks out these areas to lay eggs, particularly if they are surrounded by vegetation or protected by something - such as mouse guards. Moreover, mouse guards may frequently house weeds, and shield the lower trunk from incidental exposure to insecticide cover sprays.


Larva of dogwood borer. J. Ogrodnick


Collections of frass produced by feeding of dogwood borer on burrknot surface

Sustained feeding by dogwood borer at the graft union may severely weaken the tree at this juncture, or girdle the trunk and cause a slow decline in tree health. Orchards in which mouse guards are emplaced should be examined for signs of damage. For more detailed information on identification and control measures, see Cornell Tree Fruit IPM Fact Sheet #14 and/or Cornell Recommends, p. 71. Chlorpyrifos is excellent for treatment of bark boring insects.


Scaffolds is published weekly from March to September by Cornell University - NYS Agricultural Experiment Station (Geneva), and Ithaca - with the assistance of Cornell Cooperative Extension. New York field reports welcomed. Send submissions by 3 p.m. Monday to:

Scaffolds Fruit Journal
Editors: A. Agnello, D. Kain
Department of Entomology, NYSAES
Geneva, NY 14456-0462
Phone: 315-787-2341
FAX:315-787-2326
E-mail: ama4@cornell.edu


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Color photographs courtesy of New York State Integrated Pest Management Program.