WVU Extension Service: The Orchard Monitor: Committed to the Integration of Orchard Management Practices
July 14, 2008

Upcoming Events

Entomology

Pheromone Trap Counts Plant Pathology

 

UPCOMING EVENTS

August 14, 4:00-7:00 p.m. – Twilight Fruit Growers Meeting at Virginia Tech’s Alson Smith Agricultural Research and Extension Center, Winchester, Va.  The agenda will include a tour of 2008 research plots, seasonal updates by VA Tech Extension Specialists and a catered supper.  For more information contact the Frederick County Extension Office at 540-665-5699.

ENTOMOLOGY

Codling moth second generation egg hatch has begun and is estimated at 7% complete through July 13 based on an accumulation of 1269 DD since biofix on May 2 at the WVU-KTFREC.  Last week would have been the ideal time to initiate applications of either Rimon, Intrepid, Esteem, Assail, Calypso, or CM granulosis virus (Cyd-X, Carpovirusine).  Applications of either Altacor, Avaunt, Azinphos-methyl (Guthion), Delegate or Imidan should be initiated early this week in order to prevent fruit injury from early hatching larvae. An initial spray of any material should be followed by a second complete application in about 10-14 days (300 DD), or three additional alternate-row-middle applications 5-7 days apart.  Complete sprays of Cyd-X or Carpovirusine should be repeated every 7-10 days for a total of 3-4 applications.

Oriental fruit moth hatch of second generation eggs is about finished (99% complete), with third generation egg hatch just beginning (estimated at 3% complete through July 13), based on an accumulation of 1878 DD since biofix on April 10 at WVU-KTFREC. The third generation poses a threat to peach and nectarine fruits near or during harvest.  Larvae can enter anywhere on the fruit, resulting in the exudation of gum and frass (excrement) from the wound area.  As the gum ages, a sooty mold may form on it, turning the entire wound area black.  Larvae can also enter the fruit through the inside of the stem, and therefore leave no evidence of entry except for a small mark at the stem end of the picked fruit. 

Control of the third generation is justified where the pheromone trap capture exceeds 10 moths/trap/week in both peach and apple.  In peach and nectarine, apply either Assail or Intrepid at 2000-2100 DD (6-11% egg hatch); or Imidan, Altacor, Delegate, Lannate or Carbaryl (Sevin) at 2100-2200 DD (11-20% egg hatch).  A second application may be needed in about 2 weeks (300-350 DD), depending upon pest pressure and proximity to harvest.   Be sure to consider the following days to harvest limitations when selecting materials for application in peach and nectarine:  Imidan [14], Delegate [14 on peach, 1 on nectarine], Altacor [10], Assail [7], Intrepid [7], Lannate [4 on peach, 1 on nectarine], and carbaryl (Sevin) [3]. 

As a general guideline in apple, apply Rimon at 2300-2350 DD (30-35% egg hatch); or Assail, Calypso or Intrepid at 2350-2400 DD (35-42% egg hatch); or Altacor, Avaunt, Azinphosmethyl (Guthion), Delegate or Imidan at 2450-2500 DD (50-55% egg hatch).  A second application may be needed in about 2 weeks (450-500 DD), depending upon pest pressure.  Since actual egg hatch often falls behind DD based predictions in apple, it is best to treat within 7-10 days of exceeding the above trap threshold and to maintain spray intervals on a 2 week (complete) or 5-7 day (alternate-row-middle) schedule for as long as this condition continues.  Sprayable pheromone (CheckMate OFM-F) is also an option that can be targeted against adults to provide mating disruption in apple, peach and nectarine.  Pheromone traps should be used to monitor performance and schedule applications, which provide about 4 weeks of control.
Oriental fruit moth fruit injury
Western flower thrips larva on nectarine

Western flower thrips (WFT) is a potential threat to peach and nectarine fruits near harvest, especially if weather conditions become dry.  WFT adults are slender, about 1/16 inch long, yellowish, and hold their wings over their backs.  Larvae are smaller and wingless, but otherwise resemble adults.  Several generations occur per year as populations buildup in white clover and other weeds in and around orchards, as well as in field crops such as alfalfa.  Flight activity of WFT peaks in July through September in stone fruit orchards.  If conditions should become dry near harvest (doesn’t seem likely this year), ground cover hosts will become less attractive and make it more likely that thrips will move to stone fruit trees. 

Feeding on fruit near harvest results in silvering injury, a benign surface blemish that can be quite extensive if thrips populations are unchecked.  Injury usually occurs in protected sites, such as in the stem end, the suture, under leaves and branches that contact the fruit, and between fruit.  Inspect the earliest maturing varieties during final swell for silvering injury.  Monitor thrips by counting adults on 10 fruit at 5 locations in the orchard.  Sample fruit from the ends of branches in the lower third of the tree canopy.  Five adult thrips per 50 fruits and the presence of silvering injury may justify control, depending upon the potential market, because extensive silvering can result in downgrading of the fruit.  Control options [preharvest interval] include Delegate, SpinTor and Entrust [14 days on peach, 1 day on nectarine], and Lannate [4 days on peach, 1 day on nectarine].

Western flower thrips silvering injury on nectarine

PHEROMONE TRAP COUNTS
WEST VIRGINIA UNIVERSITY KTFREC

DATE - 2008 RBLR STLM OFM CM TABM DWB LPTB PTB AM
March 17 0
March 24 6 0
March 31 31 17
April 7 98 376 2
April 14 74 2688 84
April 21 109 1152 376 0
April 28 33 392 329 3 0 0
May 5 12 114 210 19 3 0 1
May 12 1 114 138 14 16 0 12
May 19 1 37 51 30 31 1 38
May 27 0 17 78 31 36 7 36
June 2 0 448 20 24 46 4 16 0
June 9 46 1504 13 19 42 27 27 0
June 16 127 1520 13 15 2 17 24 1
June 23 88 1792 45 9 8 6 12 2
June 30 43 1344 65 6 1 12 9 2 0
July 7 25 456 57 6 0 21 3 2 0
July 14 12 512 43 13 0 9 7 2 0

RBLR = Redbanded leafroller; STLM = Spotted tentiform leafminer; OFM = Oriental fruit moth; CM = Codling moth; TABM = Tufted apple bud moth; DWB = Dogwood borer; LPTB = Lesser peach tree borer; PTB = Peach tree borer; AM = Apple maggot.

PLANT PATHOLOGY

Infection periods and general disease update.  We’ve recorded seven additional infection periods since the last Orchard Monitor on June 30, 2008. Our disease pressure has been high for the past two weeks, with heavy rainfall amounts occurring in some locations (July 4 – 1.22 inches; July 13 – 1.99 inches (at WVU-KTFREC)). On June 30 – July 1, we had leaf wetting for 15 hours at 63 F with 0.24 inches of rain. On July 4, we had leaf wetting for 8 hours at 68 F with 1.22 inches of rain. On July 4 - 5, we had leaf wetting for 19 hours at 68 F with 0.09 inches of rain. On July 5 - 6, we had leaf wetting for 12 hours at 67 F with 0.01 inches of rain. On July 6 – 7, we had leaf wetting for 12 hours at 69 F with 0.48 inches of rain. On July 7 – 8, we had leaf wetting for 14 hours at 67 F with 0.14 inches of rain. Finally, on July 13 – 14, we had leaf wetting for 19 hours at 70 F with 1.99 inches of rain. Total rainfall to date for July is 3.99 inches (normal for the month of July is 3.3 inches). These most recent infection periods are favorable for the development of apple summer diseases.

Table 1. Dates and conditions for infection periods at the WVU - KTFREC, 2008.

No.

Date 2008

Hours/ degrees F

24.

June 28-29

14 hr/68 F

25.

June 29-30

8 hr/67 F

26.

June 30-July 1

15 hr/63 F

27.

July 4

8 hr/68 F

28.

July 4-5

19 hr/68 F

29.

July 5-6

12 hr/67 F

30.

July 6-7

12 hr/69 F

31.

July 7-8

14 hr/67 F

32.

July 13-14

19 hr/70 F

Accumulated wetting hours – threshold reached.  As of July 14, 2008, we have accumulated 362 wetting hours for a petal fall date of May 3 (last year at this time AWH = 247). Accumulated wetting hours are useful for predicting the appearance of sooty blotch on nonsprayed fruit. Symptom development for these diseases is highly dependent upon temperature and moisture conditions surrounding the fruit. The appearance of sooty blotch symptoms has been predicted with reasonable accuracy by using accumulated wetting hours (AWH). Visible signs of sooty blotch may appear following approximately 260 - 300 AWH (earlier in the season (260 AWH) if the disease was severe last year, later in the season (300 AWH) if not). The AWH threshold for making the decision to include Topsin-M in the spray program is 225 for high disease pressure and 275 for low disease pressure. Each of these threshold values presumes that 25 additional AWH will occur in the next 5 days after reaching the threshold. Sooty blotch was observed on nonsprayed fruit in research plots last week at the Winchester AREC (July 8).

Managing flyspeck on apples – how to interpret the accumulated wetting hour threshold and how to get the best control with currently available fungicides (adapted from an article by David Rosenberger, Cornell University).

Here is an in-depth application of the AWH threshold applied to flyspeck management. First, some biology. The fungi that cause flyspeck overwinter on and infect a wide range of host plants, growing on the external waxy cuticle of those plants.  What are "those plants"? For our discussion, we’ll say that "those plants" include most shrubs, bushes, vines, and trees that grow in orchard perimeters. Initially, these hosts produce ascospores, and then later, conidia, that blow into orchards. After a spore from one of the flyspeck fungi lands on an apple, the apple must be exposed to approximately 270 hr of accumulated wetting (AWH) before the flyspeck colonies become visible on the fruit.  Brown and Sutton in North Carolina were the first to identify the incubation period for flyspeck, and they found the best correlations when they ignored wetting periods of less than 3 hr duration. 

Ascospores from the overwintering flyspeck fungi are released at around petal fall stage of apple fruit development. Therefore, flyspeck colonies initiated by ascospores may begin appearing on unsprayed fruit at 270 AWH after petal fall. Because sprays for scab, mildew and rust usually prevent infection of apple fruit by the flyspeck ascospores, ascospore infections are not usually seen in commercial orchards. However, a lot of activity is taking place on those wild hosts we mentioned earlier. Infections initiated by ascospores on those wild hosts begin releasing conidia coincident with their becoming visible (after 270 AWH).  When those infections produce conidia, orchards are exposed to a continuous supply of conidia blowing around and around throughout the remainder of the summer and fall.  If fungicide residues on fruit drop below effective levels, then the conidia will initiate flyspeck infections on fruit.

In experiments where trees are left unsprayed after 2nd cover (i.e., they are protected from flyspeck ascospores but not from conidia), flyspeck incidence and severity on fruit increases dramatically around 540 AWH.  Thus, flyspeck requires 270 AWH to produce conidia on wild hosts and another 270 AWH to infect and produce visible colonies on apples.

In New York, the results of two recent trials suggest some limitations to our currently available fungicides:

1 - Two inches of heavy rain may be enough to eliminate fungicide residues. Pristine has the best residual activity, but none of the fungicides had adequate residue to completely protect against flyspeck after about 2 inches of rain.

2 - Fungicides applied after flyspeck infections have been initiated can arrest growth of the flyspeck fungus temporarily, but they do NOT eradicate the infections.  Sovran is better than Pristine or Flint for suppressing infections but it is not better than Topsin-M + Captan. So, Pristine provides the best residual protection, but Sovran and Topsin M provide the best post-infection activity.

Based on the above, what we know about the biology and the activity of our fungicides can be summarized in statement form to help us formulate our management options:

  • The period of least risk for significant flyspeck infection occurs between petal fall and 270 AWH (for the reasons noted above).

  • After 270 AWH, fruit should be continuously protected with fungicides. Any gaps in protection after 270 AWH may allow flyspeck infections to be initiated.

  • Two inches of rain can remove virtually all fungicide protection.

  • Fungicides applied after infections are initiated do not eradicate all infections. Post-infection sprays will arrest incubating infections for varying (and at this point, unpredictable) periods of time. When the fungicide residues drop below inhibitory levels, the surviving flyspeck infections begin growing again. Predicting when suppressed lesions resume growth is difficult because we can't accurately predict when fungicide residues are exhausted.

  • The 270 AWH incubation period for flyspeck can perhaps be viewed as a "grace period" for lapses in fungicide coverage.  If apples are consistently protected from infection during summer and fungicide residues are removed by heavy rains on September 1st, then flyspeck will not appear on fruit so long as fruit are harvested AND COOLED before they are exposed to 270 hr of wetting.  However, if apples are left unprotected through 90 hr of wetting in July and/or August after conidia are being released, then part of the grace period will have been used in July-August and flyspeck may appear on fruit more quickly than otherwise expected in September.

  • In real life, the total grace period for lack of fungicide protection during the growing season is probably less than 270 AWH because flyspeck can continue to grow on wet fruit surfaces after harvest until fruit are cooled below about 45 F.  Fluctuations in air temperatures as storage rooms are filled can cause condensation on surfaces of cold fruit already in the room, and that moisture can allow continued growth of flyspeck.  I don't know how much of a 270 hr incubation period can be completed after harvest, but I suspect that up to 70 hr of the required 270 hr incubation period could occur after harvest if fruit are not cooled rapidly.  Application of a postharvest fungicide drench might suppress growth during the cool-down period after harvest, but I am not aware of any data that address this question.

  • Given all of the above, the safest approach for controlling flyspeck will be to maintain fungicide coverage throughout summer after the 270 AWH threshold has been reached.  If extended rainy periods preclude timely re-spraying of blocks after heavy rains, then that lapse in coverage may use up part of the preharvest "grace period."

  • Wet autumn weather such as we have had in recent years may be contributing to elevated inoculum levels in hedgerows and woodlots.  Thus, extra caution (i.e., extra sprays in September and perhaps even in early October for late varieties) may be warranted until we get a dry summer-fall combination to break the current high inoculum cycle.

  • Late summer sprays for flyspeck can be compromised by incomplete coverage of fruit surfaces.  Including a surfactant with the fungicide during late summer may be helpful, but an excess of surfactant will only cause excessive run-off, thereby leaving less residue on fruit than a spray applied with no surfactant.  Probably the best way to improve coverage in late summer sprays is to reduce tractor speed and increase the volume of water applied per acre.

  • Conclusions:  Control failures with flyspeck usually occur either because of poor spray coverage during the latter part of the growing season or because trees were left unprotected through more than 270 hr of wetting during the preharvest interval.  Fungicide protection on fruit is exhausted after 2 inches of rain, so fungicide sprays may be needed in September if heavy rains occur with more than 25 days remaining before fruit will be harvested.

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