SCAFFOLDS Fruit Journal, Geneva, NY Volume 5 Update on Pest Management and Crop Development September 23,1996
43F 50F
Current DD accumulations (Geneva 1/1-9/23): 3374 2320
(Highland 1/1-9/23):
Coming Events: Ranges:
Lesser appleworm 2nd flight subsides 2775-3466 2002-2460
Oriental fruit moth 3rd flight subsides 2987-3522 2018-2377
Dave Rosenberger, Plant Pathology, Highland
A Correction and a Caution on Postharvest Urea Sprays to Control Scab:
In last week's issue of "Scaffolds", I noted that scab inoculum was unusually high in many NY apple orchards this year, that postharvest sprays of 5% urea could be used to reduce inoculum levels for next year, and that 5% urea equaled 5 lbs of urea/100 gallons of dilute spray. Upon rereading the article after it was published, I suddenly realized that 5% urea on a weight/weight basis is not 5 lbs/100 gallons, but instead would be 40 lbs/100 gallons (since 100 gallons of water weighs about 800 lbs). On the other hand, 5% urea might be construed as 5 lbs/100 gallons if the percentage was calculated on a weight/volume basis. So what does the recommended rate of "5% urea" really mean in terms of a rate per acre?
I called Dr. Bill MacHardy at the University of New Hampshire for his opinion. Dr. MacHardy recently completed a 545-page book, titled "Apple Scab: Biology, Epidemiology, and Management", in which he reviewed and summarized all of the published literature on apple scab. He is also actively involved in research on reducing overwintering scab inoculum with various kinds of postharvest sprays. Dr. MacHardy indicated that the standard rate of urea that he and other researchers have tested in postharvest sprays is 40 lbs urea/100 gallons. He applies about 100 gallons of dilute spray per treated acre. Dr. MacHardy did not believe that 5 lbs urea/100 gallons would be enough to significantly reduce overwintering apple scab.
Unfortunately, postharvest application of 40 lbs of urea per acre could have negative horticultural effects. If the spray is applied to leaves on the trees, this rate of urea might result in reduced winter hardiness, especially if leaves remained on the trees for more than a week after the application, thereby allowing much of the nitrogen to be translocated into buds and twigs. Applying the urea to the ground after leaf drop might be safer, but leaf coverage and effectiveness of the treatment are likely to be lower than when the spray is applied to leaves on the trees. The effectiveness of ground treatments with urea is significantly reduced if the soil surface freezes soon after the application, because the microbial degradation process is then arrested before the full benefits of the urea application can be realized. Even when applied to the soil, 40 lbs urea/A might cause excess tree vigor the following year, especially in McIntosh trees where fruit quality becomes a problem with high nitrogen levels in leaves.
The bottom line is that the overall benefits of urea treatments applied to reduce scab inoculum are questionable. Low rates of urea may not be effective for reducing scab inoculum, whereas high rates that are known to be effective against scab might have adverse effects on apple trees in our northerly climates. Applying urea at 5-10 lbs/A might have some benefits if weather conditions following application were ideal for enhancing leaf degradation and if this low-rate application was combined with one of the other postharvest treatments (leaf chopping, liming, or 2,4-D application) that was outlined in last week's "Scaffolds". However, there is no data to document effectiveness of such combined treatments. Growers with high inoculum orchards may still wish to experiment with some combination of postharvest treatments to reduce scab inoculum, but the benefits cannot be accurately predicted.
Fall Copper Sprays for Stone Fruits:
Weather conditions during spring and early summer of 1996 were conducive for development of bacterial diseases on stone fruits. Bacterial leaf spot caused by Xanthomonas pruni is rarely a significant problem in upstate New York, but it caused serious problems in some peach, plum, and apricot orchards in 1996. In one case, apricot trees that escaped spring frosts and set a full crop for the first time in several years ended up with no marketable crop because the fruit were completely destroyed by the black bacterial lesions.
Xanthomonas pruni can infect leaf scars on twigs as leaves drop in the fall. Bacteria overwintering in the leaf scars will initiate infections again next year if spring weather conditions favor infection. Where bacterial leaf spot was a problem in 1996, growers should apply a copper spray at leaf fall to reduce overwintering populations of this bacterial pathogen. Copper sprays applied at leaf fall are also effective against peach leaf curl. Note, however, that other fungicides registered to control peach leaf curl will not control bacterial diseases.
A copper spray applied at 25-50% leaf drop has also proven effective for reducing bacterial canker of sweet cherry. Bacterial canker is caused by the bacterium Pseudomonas syringae. Bacterial canker on sweet cherries can be prevented by copper sprays applied either at leaf fall in autumn or before bud break in the spring. (Some Hudson Valley cherry growers apply copper sprays in both fall and spring.) However, a copper spray applied to cherries in early spring can have adverse effects on pollination and cherry fruit set in years when there is little rainfall prior to bloom. In such years, copper residues in trees can be high enough at blossom time to affect the viability of pollen. Cherry growers concerned about inadequate fruit set may wish to control bacterial canker of cherries by using a fall application of copper rather than the dormant application of copper in spring.
Dave Kain and Art Agnello, Entomology, Geneva
As with our recollections of the year's weather, we're often surprised when we see our perceptions of pest events compared with hard data. Keeping this in mind, here is our annual comparison of some of the pest events that occured this season (in Geneva) with calculated "normals". In general, with the late spring and cool summer, most events occurred a week or so behind schedule for the entire season (unlike most years, when everything "catches up" after a little warm weather).
DATE DEGREE DAYS (BASE 43 F)
__________________________ _________________________
EVENT Normal (+/- days) 1996 Normal (+/- DD) 1996
AMERICAN PLUM BORER
1st catch 18-May (+/-7) 20-May 425 (+/-120) 379
1st flight peak 2-Jun (+/-6) 17-Jun 684 (+/-147) 962
1st flight subsiding 28-Jun (+/-7) 5-Jul 338 (+/-217) 1396
2nd flight start 10-Jul (+/-3) 18-Jul 1587 (+/-261) 1748
2nd flight peak 27-Jul (+/-6) 1-Aug 2183 (+/-241) 2092
2nd flight subsiding 13-Sep (+/-8) 9-Sep 3326 (+/-222) 3122
APPLE MAGGOT
1st catch 28-Jun (+/-8) 8-Jul 1336(+/-168) 1481
Peak 3-Aug (+/-15) 8-Aug 2354(+/-194) 2292
Subsiding 5-Sep (+/-11) 26-Aug 2984 (+/-148) 2764
CODLING MOTH
1st catch 8-May (+/-7) 28-May 479 (+/-106) 510
1st flight peak 3-Jun (+/-12) 13-Jun 769 (+/-195) 851
2nd flight start 17-Jul (+/-14) 28-Jul 1843 (+/-350) 1998
2nd flight peak 10-Aug (+/-8) 22-Aug 2475 (+/-369) 2649
2nd flight subsiding 10-Sep (+/-8) 16-Sep 3142 (+/-237) 3257
COMSTOCK MEALYBUG - Adult males
1st catch 1-Jul (+/-4) 5-Jul 1448 (+/-136) 1396
1st flight peak 8-Jul (+/-5) 15-Jul 1639 (+/-82) 1661
1st flight subsiding 20-Jul (+/-10) 1-Aug 1983 (+/-137) 2092
Crawlers present 5-Aug (+/-12) 22-Aug 2397 (+/-186) 2649
GREEN FRUITWORM
1st catch 4-Apr (+/-9) 15-Apr 79 (+/-28) 61
Peak 15-Apr (+/-11) 22-Apr 140 (+/-62) 122
Subsiding 5-May (+/-10) 30-May 310 (+/-92) 527
LESSER APPLEWORM
1st catch 11-May (+/-10) 16-May 392 (+/-155) 283
1st flight peak 23-May (+/-8) 24-May 599 (+/-193) 466
1st flight subsiding 20-Jun (+/-11) 17-Jun 1185 (+/-266) 962
2nd flight begins 10-Jul (+/-18) 15-Jul 1623 (+/-492) 1661
2nd flight peak 16-Sep (+/-7) 9-Sep 3175 (+/-156) 3122
LESSER PEACHTREE BORER
1st catch 26-May (+/-8) 3-Jun 588 (+/-155) 602
Flight peak 5-Jul (+/-17) 17-Jun 1486 (+/-434) 962
Flight subsiding 10-Sep (+/-8) 5-Sep 3140 (+/-192) 3011
OBLIQUEBANDED LEAFROLLER
1st catch 11-Jun (+/-5) 17-Jun 917 (+/-86) 962
1st flight peak 20-Jun (+/-8) 20-Jun 1163 (+/-195) 1034
2nd flight begins 7-Aug (+/-10) 22-Aug 2500 (+/-181) 2649
2nd flight peak 21-Aug (+/-13) 3-Sep 2882 (+/-191) 2957
ORIENTAL FRUIT MOTH
1st catch 2-May (+/-6) 9-May 300 (+/-99) 227
1st flight peak 13-May (+/-11) 20-May 418 (+/-93) 379
2nd flight begins 2-Jul (+/-6) 1-Jul 1441 (+/-162) 1305
2nd flight peak 8-Jul (+/-11) 29-Jul 1778 (+/-451) 2018
3rd flight begins 12-Aug (+/-10) 19-Aug 2594 (+/-251) 2561
3rd flight peak 24-Aug (+/-11) 9-Sep 2912 (+/-317) 3122
PEACHTREE BORER
1st catch 17-Jun (+/-11) 13-Jun 1061 (+/-290) 851
Flight peak 10-Jul (+/-21) 1-Jul 1666 (+/-515) 1305
Flight subsiding 26-Aug (+/-13) 26-Aug 2876 (+/-296) 2764
REDBANDED LEAFROLLER
1st catch 18-Apr (+/-7) 22-Apr 185 (+/-87) 122
1st flight peak 4-May (+/-9) 20-May 298 (+/-85) 379
2nd flight begins 3-Jul (+/-6) 1-Jul 1515 (+/-225) 1305
2nd flight peak 14-Jul (+/-7) 15-Jul 1783 (+/-328) 1661
2nd flight subsiding 5-Aug (+/-11) 25-Jul 2383 (+/-258) 1927
3rd flight begins 20-Aug (+/-12) 29-Aug 2758 (+/-208) 2841
SAN JOSE SCALE - adult males
1st catch 16-May (+/-8) 6-Jun 475 (+/-116) 660
1st flight peak 31-May (+/-7) 6-Jun 675 (+/-56) 660
2nd flight start 15-Jul (+/-10) 18-Jul 1686 (+/-203) 1748
2nd flight peak 14-Aug (+/-10) 5-Aug 2392 (+/-210) 2192
2nd flight subsiding 29-Aug (+/-12) 16-Sep 2857 (+/-305) 3257
SPOTTED TENTIFORM LEAFMINER
1st catch 19-Apr (+/-7) 25-Apr 175 (+/-67) 136
1st flight peak 5-May (+/-6) 20-May 313 (+/-75) 379
2nd flight begins 14-Jun (+/-7) 20-Jun 1067 (+/-134) 1034
2nd flight peak 10-Jul (+/-8) 11-Jul 1681 (+/-225) 1305
2nd flight subsiding 27-Jul (+/-9) 1-Aug 2220 (+/-235) 2092
3rd flight begins 8-Aug (+/-8) 8-Aug 2531 (+/-170) 2292
3rd flight peak 23-Aug (+/-10) 19-Aug 2878 (+/-207) 2561
3rd flight subsiding 12-Sep (+/-7) 12-Sep 3311 (+/-96) 3197
DATE DEGREE DAYS (BASE 43 F)
__________________________ _________________________
CROP PHENOLOGY Normal (+/- days) 1996 Normal (+/- DD) 1996
APPLE-MCINTOSH
Green tip 11-Apr (+/-6) 22-Apr 108 (+/-42) 122
Half-inch green 21-Apr (+/-7) 29-Apr 176 (+/-29) 158
Tight cluster 27-Apr (+/-6) 9-May 228 (+/-24) 227
Pink 3-May (+/-6) 16-May 295 (+/-30) 283
Bloom 9-May (+/-6) 20-May 377 (+/-40) 379
Petal fall 17-May (+/-5) 24-May 494 (+/-51) 466
PEACH
Swollen bud 5-Apr (+/-4) 25-Apr 126 (+/-38) 36
Bud burst 22-Apr (+/-4) 2-May 136 (+/-5) 179
Half-inch green 27-Apr (+/-7) 7-May 186 (+/-29) 209
Pink 28-Apr (+/-9) 13-May 215 (+/-31) 263
Bloom 5-May (+/-6) 16-May 298 (+/-58) 283
Petal fall 12-May (+/-9) 24-May 406 (+/-123) 466
PEAR
Swollen bud 14-Apr (+/-5) 22-Apr 123 (+/-42) 122
Bud burst 23-Apr (+/-7) 29-Apr 159 (+/-52) 158
Green cluster 1-May (+/-5) 9-May 240 (+/-30) 227
White bud 5-May (+/-7) 16-May 297 (+/-53) 283
Bloom 8-May (+/-7) 20-May 344 (+/-50) 379
Petal fall 15-May (+/-8) 24-May 436 (+/-57) 466
PLUM
Swollen bud 17-Apr (+/-8) 2-May 148 (+/-38) 179
Bud burst 27-Apr (+/-4) 9-May 173 (+/-49) 227
Green cluster 1-May (+/-5) 14-May 239 (+/-35) 266
White bud 5-May (+/-5) 16-May 239 (+/-17) 283
Bloom 7-May (+/-5) 20-May 329 (+/-49) 379
Petal fall 13-May (+/-5) 24-May 393 (+/-53) 466
SWEET CHERRY
Swollen bud 12-Apr (+/-5) 22-Apr 100 (+/-32) 122
Bud burst 23-Apr (+/-6) 29-Apr 177 (+/-30) 158
White bud 1-May (+/-6) 6-May 222 (+/-31) 206
Bloom 5-May (+/-6) 13-May 267 (+/-36) 263
Petal fall 13-May (+/-4) 20-May 383 (+/-61) 379
TART CHERRY
Swollen bud 15-Apr (+/-6) 22-Apr 117 (+/-61) 122
Bud burst 27-Apr (+/-6) 2-May 210 (+/-42) 179
White bud 9-May (+/-5) 13-May 281 (+/-26) 263
Bloom 11-May (+/-4) 20-May 365 (+/-59) 379
Petal fall 18-May (+/-4) 24-May 462 (+/-65) 466
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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