June 10, 2002 Volume 11 No.13 Update on Pest Management and Crop Development
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TRAP CATCHES (Number/trap/day)
Roundheaded Appletree Borer
Key CM management dates: 1st gen 3% CM hatch: June 12 (= first spray date where two sprays are needed to control 1st generation CM; 2nd spray is 2-3 weeks later). 1st gen 20% CM egg hatch: June 19 (= single spray date where one spray is needed to control 1st gen CM).
San Jose Scale
Roundheaded Appletree Borer
San Jose Scale
Plum Curculio. The spray cutoff for this pest is 340 DD (base 50°F) past petal fall. Sample numbers as of today, June 10:
Oriental Fruit Moth. In Niagara Co., using May 6 as the biofix for first flight, the 341 DD (base 45°F) accumulation puts us at 75% first brood larval hatch. Growers should have applied (or be anticipating soon) their second application of a pyrethroid for this insect (plus curc).
Codling Moth. With 250 DD (base 50°F) as a first spray date, we currently have:
Obliquebanded leafroller moths started flying in the Hudson Valley on June 3 and in Geneva on June 10, which puts us back on a nearly normal schedule for insect activity for the time being. First hatch is generally assumed to occur from about 300-360 DD (base 43°F) after the flight starts, and we'll be updating you each week with values for Highland and Geneva. OBLR management seemed not to be such a major challenge last year as it has been in the past, although the dry summer weather tended to obscure the evidence of infestations until the larvae started attacking the fruits. With an eye towards a perhaps more normal level of precipitation this season, this shouldn't be so much of a problem this year, which still leaves the perennial question of how best to manage these summer populations. Accordingly, a brief synopsis of last year's research efficacy trials might be in order.
Pesticide control programs for the first summer brood of OBLR were conducted in two Wayne Co. orchards in 2001, one of them an Empire/Cortland mixed planting, and the other McIntosh/Idareds. All sprays were applied in three applications starting 300 DD (estimated egg hatch) after the beginning of summer adult flight on 6/7 (which corresponded to 25-26 June), then followed at 14-day intervals thereafter (9-10 July and 23-24 July). Treatments were:
- Avaunt 30WG (5.0 and 6.0 oz/100) alone as well as in combination with Spintor 2SC (2.0 and 3.0 oz/100)
- Intrepid 80WP (3.0 oz/100); this is the 2nd-generation version of Confirm
- Lannate LV (48.0 oz/100)
- Spintor 2SC (6.0 oz/100)
- Intrepid 2F (4.0 oz/100) applied with Latron B-1956 (16.0 oz/100)
- Confirm 2F (20.0 oz/100) applied with Latron B-1956 (16.0 oz/100)
- Warrior T 1CS (3.2 oz/100); this is lambda cyhalothrin, a synthetic pyrethroid
- Asana XL (12.0 oz/100)
- Proclaim 5SG (4.8 oz/100) applied with Latron B-1956 (16.0 oz/100)
The initial levels of infestation in terminals from the summer generation of OBLR (20.0% and 50.0% infested terminals, respectively, in the two untreated check plots) are considerably higher in both orchards compared with those observed the previous season. However, as commonly observed in previous studies, levels of fruit damage in the research orchard were not highly correlated with infestations of the summer generation of larvae in terminals, as 30.0 and 7.8% of the fruit was damaged in untreated check plots at harvest, respectively, in these two orchards. The average fruit damage levels were generally higher among all of the treatments at the first site than in the second. Only three of the treatments applied in the first site -- Spintor, Proclaim, and the combination of Avaunt and Intrepid -- significantly reduced fruit damage below that observed in the untreated check plots. Apple cultivar and tree canopy size may also have affected the efficacy of the treatments in the different orchards, as the Empire and Cortland trees in the first block were larger and had denser canopies than the McIntosh and Idared trees in the second. All the treatments of Avaunt alone gave inadequate control, and damage was similar to that in the untreated check plots when data from the two orchards were combined. However, efficacy was improved when the material was used in a mixture with the other chemicals, and the most effective chemical in these mixtures was Intrepid.
As previously observed, Intrepid provided slightly better control of OBLR fruit damage than Confirm, particularly in the first orchard, in which OBLR pressure was higher. Spintor was slightly more effective than Confirm or Intrepid in protecting fruit in this orchard. Fruit damage in the plots treated with the synthetic pyrethroids, Asana and Warrior, was very similar to that in the check plots in the first orchard, which indicates that the OBLR populations in this orchard are uniformly resistant to all of these materials. In contrast, the pyrethroids were as effective as the better standard and experimental materials in the second orchard and significantly reduced fruit damage below that in the check plots. The current materials tested that are considered to be "standards", Confirm, Spintor and Lannate, all reduced fruit damage below that in the untreated checks, although Spintor was the only material that gave a significant reduction in both of the test orchards. Spintor provided the best overall performance in the trial, reducing fruit damage to less than 7% when the data from both orchards were combined. This indicates that growers are already using the most efficient tool for OBLR control. Proclaim also gave good control when the orchard results were combined, although this product is not yet registered; it may provide a material available for future consideration. Manufacturers suggest that this product be applied with oil as an adjuvant, but Latron B-1956 was substituted because one of the growers used Captan in the test orchard, apparently with no loss of efficacy.
(Dave Rosenberger, Plant Pathology, Highland)
Some orchards in the Hudson Valley and other parts of the state have no crop this year because of freeze damage, hail, or a combination of both. For some growers, this is the third consecutive year of weather-related disaster losses. These losses, combined with a decade of low prices for fruit crops, have convinced some growers to quit the fruit-growing business. Their orchards will be abandoned until the land can be sold or converted to other uses.
For fruit growers who plan to stay in business, the objective in a disaster year is to minimize inputs while still controlling pests that could potentially cause tree mortality or reduce the cropping potential for next year. Following are disease management suggestions for orchards with no harvestable crop.
Where primary scab was effectively controlled, no additional fungicide sprays should be necessary, except for cultivars that are highly susceptible to mildew. Apple trees can tolerate considerable mildew, so 100% control is not essential. Nevertheless, for mildew-susceptible cultivars such as Ginger Gold, Cortland, Paulared, and Rome, additional mildewcide sprays may be needed during June and early July to keep foliage healthy and to limit the amount of carry-over inoculum for next year.
Sulfur is the cheapest mildewcide, and it should provide adequate protection for trees with no crop. Sulfur is often used during summer at rates of 3-5 lb/A because of concerns about injuring fruit with higher rates and also because sulfur is usually applied with some other scab fungicide. In orchards with no crop, better mildew control might be achieved by applying sulfur at 10-15 lb/A. Even at these higher rates, sulfur will be easily removed by rains. Mildew-susceptible apple cultivars should be resprayed with sulfur at about 14-day intervals or after rains of one inch or more.
Where scab lesions are present in trees with no crop and sulfur is not needed for mildew control, a single application of captan at the maximum label rate in early to mid-June will limit secondary spread of scab to new leaves. Secondary spread of scab in summer is often limited by hot weather. Temperatures above 85°F significantly reduce viability of conidia. If, however, the weather stays cool and wet, another application of captan may be needed in early July to slow secondary spread of scab, especially in vigorous trees where shoot growth may continue unabated. Where considerable leaf scab is evident in late summer, a captan spray in late August or early September can help to limit the spread of scab to the undersides of leaves during autumn. Preventing spread of scab during autumn can significantly reduce the amount of carry-over inoculum for next year. Again, there is no need for 100% control of scab in an orchard with no crop. So long as the foliage remains reasonably healthy, it will be more cost-effective to control scab next year (perhaps by using urea sprays applied to fallen leaves) than to spend money for fungicides this summer.
Pear blocks with no crop must be protected from Fabraea leaf spot. Trees left unprotected will defoliate early and will not produce flower buds for next year. Bosc is the most susceptible of the commonly grown varieties in New York.
Epidemics of Fabraea leaf spot are usually initiated between petal fall and July 1. Epidemics usually occur as a result of primary infections that become established during the three to four weeks after petal fall. These primary infections appear as nondescript, round leaf spots that usually escape notice. If fungicide protection is inadequate during June or early July, a few primary infections will provide the inoculum for a rapidly developing epidemic. Foliar symptoms can appear almost simultaneously on many leaves throughout much of the tree canopy during late June or early July.
Fabraea can build up more quickly than diseases like apple scab because only young leaves are susceptible to scab (except in autumn), whereas all leaves are susceptible to Fabraea throughout summer. Thus, when epidemics develop in early summer, all of the existing leaves can become infected in a short time if inoculum is present and trees are left unprotected.
To avoid Fabraea epidemics, pear trees should be protected with fungicide from petal fall through July 4. These sprays will prevent the primary infections that subsequently produce the abundant conidia that cause the epidemics. If trees are protected with fungicides applied on a 14-21-day interval through July 4, then the chances for late season development of Fabraea are minimized.
The heavy rains of the past two weeks may have allowed Fabraea to become established in pear orchards in the Hudson Valley. Therefore, pear growers should monitor Bosc orchards carefully over the next several weeks. Where Fabraea is already present in orchards, fungicide protection will be needed throughout summer.
The mancozeb fungicides are very effective in controlling Fabraea. Mancozeb sprays during summer are usually limited by the 77-day preharvest interval for these fungicides. However, in orchards with no crop, mancozeb can be used later into the summer so long as the total amount applied for the season does not exceed the 21 lb/A/year as noted on the label. Several growers have reported that Flint and Sovran also provide excellent control of Fabraea leaf spot. No one has researched the effectiveness of Flint and Sovran for controlling Fabraea, but these fungicides may be more effective than mancozeb for controlling Fabraea in orchards where initial infections are already present.
Symptoms of Fabraea leaf spot are virtually identical to those caused by Botryosphaeria obtusa, the black rot fungus. However, the leaf spotting caused by the black rot fungus usually occurs in limited areas of the canopy and can be associated with identifiable sources of inoculum. Inoculum for black rot leaf infections can come from dead branches or spurs, or from a mummified fruit. Leaf spotting caused by Botryosphaeria generally does not spread from leaf to leaf. By comparison, Fabraea leaf spot is often more uniformly distributed within the tree, especially after the epidemic becomes established. Presence of Fabraea in leaf spots is easy to confirm with a microscope because all Fabraea lesions produce an abundance of characteristic conidia that are not present in leaf spots caused by other fungi.
Cherry leaf spot has many of the same life-cycle patterns as Fabraea. Cherry leaf spot can spread rapidly during the summer, and severe infection will result in premature defoliation. Trees that defoliate early are more susceptible to cold damage the following winter. Therefore, non-cropping cherry trees will need to be protected from leaf spot thoughout the summer.
During the ongoing azinphosmethyl review of the past months, the list of registrations provisionally being proposed for immediate cancellation included plums and prunes, and because we were fairly certain that this decision would not be reversed in the final ruling, we opted not to include Guthion or generic AZM in the Tree-Fruit Guidelines for this commodity group. Naturally, the regulatory wheels turned a bit more slowly than expected, but last week, a letter from Bayer was finally sent to the EPA that formally requests the voluntary cancellation of products containing AZM technical for this crop group (together with grapes, strawberries, and a number of non-fruit crops). Therefore, once these products begin to be sold with this "new" label, those cancellations will in fact go into effect. However, all the Guthion and generic azinphosmethyl currently in growers' hands and in the channels of commerce can continue to be used as labeled until all stocks are depleted.
This material is based upon work supported by Smith Lever funds from the Cooperative State Research, Education, and Extension Service, U.S. Department of Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.
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