August 4, 2003 Volume 12 No. 21 Update on Pest Management and Crop Development
Codling Moth, Lesser Appleworm and San Jose Scale 2nd flights beginning.
Spotted Tentiform Leafminer 2nd flight began 6/23. The first sample of sap-feeding mines should have been taken at 690 degree days (base 43°F) following this event. If necessary, resample at 840 and 1150DD. DD43 to date = 1153
Rose Leafhopper and White Apple Leafhopper present on apple foliage.
Apple Maggots being caught throughout the region.
Roundheaded Appletree Borer
Peak hatch roughly: July 18 to August 5.
First Dogwood borer egg hatch roughly: Peak hatch roughly: August 8.
2nd generation 7% CM egg hatch: August 7 (rain-adjusted first spray date where multiple sprays needed to control 2nd generation CM).
2nd generation 30% CM egg hatch: August 18 (= single spray date where one spray needed to control 2nd generation codling moth).
Spotted Tentiform Leafminer
Third optimized sample date for 2nd generation STLM sapfeeding mines, if needed: August 4.
Roundheaded Appletree Borer
Peak hatch roughly: July 17 to August 4.
Peak hatch roughly: August 6.
2nd generation 7% CM egg hatch: August 3 (rain-adjusted first spray date where multiple sprays needed to control 2nd generation CM).
2nd generation 30% CM egg hatch: August 12 (= single spray date where one spray needed to control 2nd generation codling moth).
Spotted Tentiform Leafminer
Third optimized sample date for 2nd generation STLM sapfeeding mines, if needed: August 2.
Oriental Fruit Moth. Most problem orchards should have received a first spray against this brood 1-2 weeks ago, with the second application due as early as this week (assuming 1 14-day interval). According to the provisional PA model, hatch of the 2nd brood eggs should be essentially complete. The accumulated DD's (base 45°F) from the season's first biofix as of 8/3 are:
Codling Moth. In orchards not receiving protective sprays for apple maggot or oriental fruit moth and with potentially high codling moth pressure, the first application against the 2nd brood of this species is advised at 1260 DD (base 50F) after the season's first biofix. Geneva is at 1216 as of August 3, so the Orchard Radar prediction of August 7 should be accurate for a projected spray date; other sites in western NY would come due later in the week, and Highland reached this mark on July 27.
(Dave Rosenberger, Plant Pathology, Highland)
Wet postbloom weather, along with hot wet weather during July will probably make this a memorable season for development of summer diseases on apples in New York and New England. Summer diseases include flyspeck, sooty blotch, black rot, white rot, and bitter rot.
Flyspeck ascospores are released shortly after apples reach petal fall. On apples, the fungus requires roughly 270 hours of surface wetting time between early season infection and the time that symptoms become apparent on fruit. In northeastern United States, we are still uncertain of the exact details concerning disease development on apples. However, I believe that infection of fruit by ascospores is relatively unimportant in commercial orchards because our scab fungicides effectively protect fruit during the interval after petal fall.
Ascospores are probably very important for generating new infections in woods and hedgerows that border orchards. If we assume that infections on these other hosts (of which there are many) develop at approximately the same rate as infections on apples, then those infections should also become visible and begin producing conidia for secondary infections after approximately 270 hr of surface wetting. The conidia are far more abundant than ascospores, and conidia can blow into orchards from the border areas.
During a dry summer, the secondary infection cycle may not begin until early September and most infections that occur on apple fruit in September will not have enough time to develop visible symptoms before fruit are harvested. During wet summers such as the one we are currently experiencing, secondary infections on fruit can be initiated much earlier and symptoms on unprotected fruit will become visible during late summer. A wet summer may also allow multiple secondary cycles, thereby dramatically increasing inoculum that is available to blow into orchards during late summer.
Petal fall on McIntosh in the Hudson Valley occurred around 12 May this year. Peak ascospore discharge for flyspeck presumably occurred about 10 days later. Counting from 22 May, we reached 270 hr of accumulated wetting in the middle of the 91-hr wetting that occurred 19-23 June. Thus, conidia of flyspeck might have been available for infecting apples as early as late June. A flush of symptoms from those late June infections should appear on unsprayed apples within the next few days because we are nearing the completion of another 270-hr wetting accumulation (counting from 23 June).
The standard recommendation for controlling flyspeck in the northeast has been a combination of a benzimidazole fungicide (currently, Topsin M is the only choice) plus captan. However, research conducted over the past several years has shown that Sovran and Flint are at least as effective as Topsin+Captan, and that in some cases they are more effective. Sovran and Flint are more expensive than the Topsin+Captan combination, but this may be a year where one or two applications of Flint in August might pay dividends, especially if one adds the potential benefits that Flint sprays may have for bitter rot control.
Bitter rot is a sporadic disease in northeastern United States. We have not really had weather favoring bitter rot since the early 1990s. Bitter rot can be caused by several species of Colletotrichum. Infections occur during hot wet weather and often appear as decays on the sun-facing cheek of ripening fruit. Decays are tan and slightly sunken. Slimy pale orange spores may be evident in the center of fruit lesions during wet or humid weather. In North Carolina and other southern states, bitter rot spreads rapidly and can cause major losses within several weeks if fruit are not protected with fungicide during late summer.
The life cycle for bitter rot in the Northeast has not been adequately studied. I have noted the following scenarios for development of bitter rot under NY conditions:
1. Unsprayed fruit have no symptoms at harvest but develop bitter rot lesions if fruit are incubated at 100% relative humidity until they become senescent. This suggests that the fungus is often present on unsprayed fruit, but that it usually cannot cause decay until fruit become senescent.
2. The disease appears only on a few fruits near the orchard borders just prior to harvest. This occurs some years in my fungicide check plots where no fungicides are applied throughout the summer, but I rarely find more than 1-2% of fruit affected.
3. The disease may invade fruit after harvest and appear as a postharvest decay. In apple storage surveys conducted during the mid-1990s, we found that bitter rot accounted for 13% of the postharvest decays in one apple packinghouse in 1995.
4. Very rarely, bitter rot can become epidemic. This occurred in Michigan in 1995 (See Jones & Shane, Plant Disease 80:1294-1297) Annual epidemics occurred in one Long Island orchard during the early 1990s.
Why does bitter rot act so differently in different orchards and different years? No one knows, but all of the following are probably factors:
a. Inoculum levels probably vary greatly from year to year. In the Long Island case, we eventually discovered that horse chestnut trees (Aesculus hippocastanum) and sycamore maples (Acer pseudoplatanus) adjacent to the affected orchard were severely affected with Colletotrichum acutatum and were probably supplying inoculum for the orchard. The role of non-orchard hosts in the bitter rot cycle has not been investigated elsewhere in the northeast.
b. The time when inoculum becomes available is probably critical for infections in the northeast. Bitter rot infections occur best under hot, wet conditions. If inoculum does not reach orchards until September, it may be too cool for rapid development of infections.
c. Bitter rot is favored by long, warm wetting periods. Severity increases with duration of wetting up to 60 hr. In the northeast, we rarely have long wetting periods during August when temperatures are high enough to favor bitter rot infection.
So why be concerned about bitter rot this year? Extended wetting during May and June promoted bitter rot infections in non-orchard hosts. I have noted that horse chestnut trees in the Hudson Valley are already turning brown due to disease, something that has not happened in recent years. (Diseases other than those caused by Colletotrichum are also involved in blighting of horse chestnuts.) The hot, wet weather of the past week is likely to have allowed extensive dissemination of bitter rot spores in the Hudson Valley, and early ripening cultivars are already showing some evidence of infection at the Hudson Valley Lab.
Only two fungicides provide good activity against bitter rot at this time of year: Captan and Flint. However, captan must be applied at the maximum label rate; half-rates will not prove satisfactory. Heavy rains can presumably remove captan residues more easily than Flint residues because Flint tends to bind to the waxy cuticle of the fruit. Thus, Flint might perform better if our frequent rains continue. Either captan alone or Flint alone should provide adequate protection against bitter rot in most orchards. However, where extremely high disease pressure is expected (e.g., adjacent to wood lots or to known source trees such as horse chestnut), growers may wish to apply a combination of Flint at the full rate plus captan at one-half of the full label rate.
Neither fungicide is known to have post-infection activity against bitter rot, so timely protectant sprays are essential.
Sooty Blotch, Black Rot, and White Rot will all be controlled by sprays applied for flyspeck and bitter rot. However, given the wet conditions this summer, the interval between the last spray and harvest may need to be shortened to prevent late season infections by black rot and white rot.
Honeycrisp is especially susceptible to black rot and white rot, so this cultivar will need careful protection during August.
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SOMETHING NEW FOR THE FRUIT FIELD DAY
We're one month away from the annual N.Y. Fruit Pest Control Field Day, which will take place during Labor Day week on Sept. 4 and 5, as dictated by tradition. However, this year, in order to accommodate participants who may wish to attend other area tours earlier in the week, the dates have been shifted to the Thursday and Friday of the week, AND the Geneva installment will take place first (Thursday Sept. 4), with the Hudson Valley installment on the second day (Friday Sept. 5). Activities will commence in Geneva on the 4th, with registration, coffee, etc., in the lobby of Barton Lab at 8:30 am. The tour will proceed to the orchards to view plots and preliminary data from field trials involving new fungicides, miticides, and insecticides on tree fruits and grapes. It is anticipated that the tour of field plots will be completed by noon. On the 5th, participants will register at the Hudson Valley Laboratory starting at 8:30, after which we will view and discuss results from field trials on apples.
Also, this year the Geneva component will be preceded by a steak cookout and end-of-season social gathering at the scenic Geneva Country Club, 6:00 pm on Wednesday, Sept. 3. We're trying this out as a possible replacement for the long-held "Smelt Dip" spring cookout, which has been less successful in recent years at drawing industry cooperators for the pre-season get-together. In addition to a custom-grilled steak, the menu will include corn on the cob, salt potatoes, and tossed salad, with brownies and fruit for dessert, plus a cash bar. Cost is $21 per person; payment in advance is not necessary, but we do need to know that a sufficient number will be attending in order to hold the reservation. If you think you would be interested in attending, contact Harvey Reissig (315-787-2336 or firstname.lastname@example.org) to let him know. Save the dates.