Diseases | Credits

SCAFFOLDS Fruit Journal, Geneva, NY                                   Volume 4 
Update on Pest Management and Crop Development                  April 24, 1995 


                                                     43F       50F
Current DD accumulations (Geneva 1/1-4/24):          186       78
                       (Highland 1/1-4/24):          188       68

Coming Events:                              Ranges:
Green fruitworm peak flight                       64-221     19-108
Rosy apple aphid nymphs present                   91-291     45-148
Pear psylla 1st egg hatch                        111-402     55-208
Green apple aphids present                       127-297     54-156
Pear thrips in pear buds                         137-221     54-101
Spotted tentiform leafminer 1st oviposition      141-319     48-154
European red mite egg hatch                      157-358     74-208
Redbanded leafroller 1st flight peak             180-455     65-221
Spotted tentiform leafminer 1st flight peak      180-420     65-217
Sweet cherry at white bud                        152-267     75-116
Peach at pink                                    152-269     68-119
McIntosh at tight cluster                        205-279     87-138
Pear at green cluster                            209-282     83-138
Tart cherry at white bud                         257-326    109-149

Geneva, 4/24
   Apple (McIntosh): Half-Inch Green
   Sweet Cherry (Windsor) and Tart Cherry (Montmorency): Bud Burst
   Pear: Bud Burst
   Peach: Quarter-Inch Green
   Plum: Swollen Bud
Hudson Valley Lab, Highland, 4/
   Apple (McIntosh): Tight Cluster
   (Golden Delicious): 3/4-Inch Green
   Pear (Bartlett): Green Cluster

TRAP CATCHES (Number/trap/day)
                                  4/13   4/17   4/20   4/24
Green Fruitworm                    0.3    0.3    0.2    0.3
Redbanded Leafroller                 0      0      0    1.0*
Spotted Tentiform Leafminer          0      0    1.2*   157
Oriental Fruit Moth (apple)          -      -      -      0
Oriental Fruit Moth (peach)          -      -      -      0
Lesser Appleworm                     -      -      -      0

Highland (Dick Straub, Peter Jentsch)
                                   4/11   4/17   4/24
Green Fruitworm                     1.0    0.3    0.7
Pear Psylla eggs (/terminal bud)    0.5    2.5   12.6
Redbanded Leafroller                0.5    2.6   10.4
Spotted Tentiform Leafminer           0   <0.1*  13.0
Oriental Fruit Moth                   0   <0.1*     0
Fruittree Leafroller                  -      -      0
                                                       * = 1st catch

   Redbanded leafroller 1st catch; Spotted tentiform leafminer increasing.
   Pear psylla eggs hatching; Rose leafhopper nymphs observed.


By: D. Rosenberger

Highland, NY:       Immature     Mature   Discharged   Tower shoot
4/20                   59%         37%       4.3%       804 spores

Spore maturity advanced very rapidly since our previous count on April 13 when we still had only 12% mature spores and virtually no discharge.

Apple scab infection periods:


By: Dave Rosenberger, Plant Pathology, Highland

Duration of wetting for the April 19 infection period was quite variable with location. At the Hudson Valley Lab, our electronic sensor indicated a slightly shorter wetting period (and therefore no infection period) whereas our string recorder indicated a 13 hr wetting period. With the relatively small number of ascospores that were mature at that time, we do not consider the April 19 wetting/infection period to be of commercial significance. However, significant spore discharge did occur during the April 21-22 wetting period. Note that the spore count information for April 20, the day before this rain, showed a huge discharge in our shooting tower test.

With trees at or near tight cluster, we are now entering the peak risk period for apple scab. Most of the apple scab ascospores that make it out of the ground cover will be released between now and petal fall. If apple trees are not adequately protected with fungicides during the next several weeks, the ascospores will initiate primary infections. Primary infections initiated between tight cluster and bloom usually occur on leaves. These infections become visible after 9-17 days. The primary infections produce the conidia that cause most of the fruit infections noticeable at harvest. Primary infections initiated between tight cluster and pink are especially troublesome because they can produce conidia during and shortly after bloom when fruit are most susceptible to infection.


By: Art Agnello, Entomology, Geneva

A minute insect that is actually in the trees for only a brief period during early spring can cause not only tattered foliage in sugar maple trees, but also large decreases in fruit set of apples in the Northeastern U.S., including parts of New York. The pear thrips (Taeniothrips inconsequens [Uzel]) is an unusual insect about 1/20 inch long, with fringed wings and asymetrical mouthparts. The adult pear thrips is slender and brown, with short antennae and a swelling behind the head; the wings are long and narrow, with fringes of long hairs. Young pear thrips are small and white with red eyes ("thrips" is the term used both for one or several of the insects.) Its mouthparts consist of a pair of stylets for puncturing plant tissue, plus a cone with a rasp-like surface, which is used for roughening the wound and then sucking up the juices.

Pear thrips originally came from Europe, but were introduced into California at the turn of the century, where they exhibited a taste for plums, cherry, apple, and pear; other favored hosts are basswood, birch, beech, ash, and of course, maples. It is the adult thrips that show up on host trees in great numbers and do the most extensive damage. Generally speaking, they arrive just before or during the opening of fruit buds (late April for New York apples and pears). They enter the bud, or else start feeding on the bud tip and gradually work themselves in. Eggs are laid under the bud scales, petals and sepals, on stems and in other succulent flower and leaf parts. The larvae feed voraciously for about 3 weeks, adding to the damage already caused by the adults. After the larvae finish their feeding period (early June in N.Y.), they drop off the tree and enter the ground, often to depths of a foot or more, where they enter a diapause stage until fall. Sometime in September or October, they pupate in their earthen cell, and remain until the adults emerge the next April. Under natural conditions, the duration of a single adult's life probably covers a period of 4-6 weeks.

On fruit trees, feeding is usually concentrated on the tender flower parts, which gives the blossom buds a shriveled, scorched appearance, or may cause them to fall off completely. Leaf damage in hosts such as maples is caused by the insects' feeding on the developing leaf tissue; this results in leaves that are dwarfed, mottled yellow to green-brown, and distorted. Small scars resembling blisters show up along the leaf veins and stems. The tree will consequently have a thin crown, possibly suffer some moisture stress, and may even drop its leaves prematurely in the fall.

Because much of this pest's life is spent underground, control of damaging populations is very difficult. Insecticides have been suggested by some, but their effectiveness is difficult to measure, because most growers are not aware of the damage until after it has already been done, although thrips are sensitive to nearly any prebloom insecticides used in most commercial orchards. On fruit trees, an oil spray is advised against the egg-laying adults as they emerge, timed between the bud burst and green cluster stages of pear and plum (usually the 2nd or 3rd week of April). This can be a prudent treatment to apply in any case, as a preventive measure against other pests such as mites or pear psylla. Massachusetts guidelines suggest that it can be useful to examine fruit buds at this time to determine whether thrips are present.


By: Art Agnello

It's probably safe to say that this won't be an early spring after all; that opportunity passed with the snowfall and cool fronts a couple of weeks ago. The trick now is to avoid getting surprised by what might be called the "spring potential" that's lurking in each fruit bud and insect brain until just enough warm weather accumulates to set everything off like a chain reaction. A few thoughts about the pink bud period would be in order now, because depending on the weather pattern over the next week or two, this stage might not last too long. The last of the prebloom sprays should be applied at pink for the most effective control of a variety of arthropod pests. In general, the three most important insects to be concerned with are tarnished plant bug, rosy apple aphid, and spotted tentiform leafminer. If all three are present in sufficient numbers to warrant a treatment at this time, the only materials with enough broad sprectrum activity and residual effectiveness to do a good job are the pyrethroids, Asana, Ambush or Pounce.

Tarnished Plant Bugs: As a rule, pyrethroids give the best control of plant bugs because they have sufficient residual activity to protect against the extended adult feeding and egg-laying period of this insect. Cygon and Thiodan are other possible alternatives; Thiodan is easiest on mite predators, but probably least effective against TPB. If your fruit has been showing no more than 2-3% plant bug damage at harvest, a spray is of questionable value, because low-level damage is difficult to eliminate completely, and packout studies have shown that any increases in packout gained by spraying for TPB are usually offset by the cost of the spray. If TPB is not a problem, but rosy aphids and leafminers are at threshold, a recommended option would be Vydate; for rosy apple aphid control alone, use Lorsban 50WP at 12 oz, or Thiodan at 1 lb of the 50WP (2/3 qt of the 3EC) per 100 gallons.

Leafminers: Despite last year's late summer leafminer reprise, first generation STLM won't necessarily turn out to be a problem this year; in our experience, there's been a low predictability between third brood numbers in an orchard one year and first brood in the same block the next year. Moreover, this generation tends to be the least problematic overall and in many cases might even be ignored completely (even if eggs do reach the 2-3 per leaf level), considering the availability this year of Provado later on, rather than having to use a more conventional material that generally does your predator populations no good.

Nevertheless, for those who may opt for a traditional first brood management strategy, Vydate applied at pink will act as an ovicide against the eggs, 90% of which are generally present by bloom, and its long residual activity will also work against the larvae as they hatch. Lannate is also effective at pink, but has a shorter residual life, which may be a concern if egg-laying gets slowed down by cool weather. Also, there is little or no ovicidal action with this material, so you are aiming at the young larvae. These materials can also be used at petal fall, but Vydate thins the fruit, so if you don't want this thinning action, Provado or Lannate at petal fall are preferred. Be sure all the blossoms have fallen. The recommended threshold for this brood of STLM is 2 eggs per fruit cluster at pink. Examine leaves 2, 3, and 4 on three clusters from each tree sampled, and use the sequential sampling table (No. 16, p. 84 in the Recommends) or chart (Fig. 1, p. 88) to determine how many trees to sample.

Remember that a decision can also be made by sampling with a threshold of 1 sap-feeding mine per leaf at petal fall (same table, or chart on p. 90, Fig. 3). For rosy apple aphid at pink, 1 infested cluster per 100 (check 10 on each of 10 trees) warrants treatment.

Leafrollers: Growers may feel it is necessary to control obliquebanded leafroller in their pink spray. A number of materials, most notably the pyrethroids, are suitable for this purpose; however, even if you do kill some larvae during the pink stage, it will still be necessary to come back again after bloom to finish the job, because not all of the population has emerged from their overwintering sites by this time. We consider petal fall to be a preferable time to control these caterpillars, if indeed you elect to do so. Frankly, considering 1) the low level of fruit damage caused by this brood, 2) the complete lack of any benefit in controlling the summer generations obtained by wiping out the overwintered brood, and 3) the increased selection pressure for resistance being exerted on this species, and its apparent willingness to oblige, we are gradually becoming converts to a more laissez-faire approach for the overwintered generation of this pest as well. More on this nearer to petal fall.

Mites: If oil was not used earlier for red mites, a contact miticide should be included now -- Kelthane, Omite, and Carzol are possibilities; however, Morestan performs very well against mites at pink, and because no resistance to it has been seen (and it can't be used post-bloom anyway), it remains our strongest recommendation for a pink miticide. Be sure to use adequate water with any of these miticides. No contact miticide should be necessary at pink if oil was applied previously. Vydate or Lorsban may also provide some mite suppression if used at this time.

Plum curculio: Some growers favor a pyrethroid at pink to help take care of the first curcs immigrating into the block during bloom, because they don't feel they will get in soon enough with a petal fall spray to control every single one. This is an especially popular practice in mixed plantings, where some varieties are still in bloom while others have already reached petal fall. Although it may be possible to kill some curculios this way (and it may not be very many if the residue has to last through a very protracted pink and bloom stage), the majority of adults begin damaging the fruit clusters after the petals fall; in fact, Sieg Lienk found that it takes a couple of warm days after this point until any are actually working in the trees. Despite the philosophy that ANY curcs that can be killed justify a spray, it is our opinion that the long-term effects of excessive pyrethroid sprays constitute a strong argument against this practice. Multiple-year field trials conducted by Harvey Reissig have shown that the addition of a pink pyrethroid spray does not reduce fruit damage by curculio when compared with normal programs consisting of petal fall-plus-cover sprays. You would come out ahead by spot-treating the trees that reach petal fall earlier, or by making a quick border row spray to hold off the invasion for a few days while the straggling varieties catch up, after which a full cover petal fall spray could be applied.


Through an editing error, the rate for Vydate 2L to control STLM during the summer (p. 67) was listed incorrectly. It should read 1/2-1 pints/100 gal.

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
Dept. of Entomology, NYSAES
Geneva, NY 14456-0462
Phone: 315-787-2341 FAX:315-787-2326

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