May 9, 2005 Volume 14 No. 8 Update on Pest Management and Crop Development
(Highland): San Jose Scale model degree days (base 50 F)
Mullein Plant Bug
Oriental Fruit Moth
San Jose Scale
Spotted Tentiform Leafminer
White Apple Leafhopper
Roundheaded Appletree Borer
Mullein Plant Bug
Oriental Fruit Moth
San Jose Scale
Spotted Tentiform Leafminer
White Apple Leafhopper
Before the internal worm management decision process gets started in earnest this season, here is a synopsis of a small-plot efficacy trial conducted against oriental fruit moth in Wayne Co. last year.
The effectiveness of different schedules of Imidan were compared against oriental fruit moth in commercial WNY apple orchards in 2004. Tests were set up in two small plots (approx. 1/3 A), in two commercial orchards in Wayne County. Both of these small plots had been used in the past for OFM studies and were heavily infested during the 2003 growing season. Many of the unsprayed trees in 2003 had a 40-60% infestation level of OFM at harvest. In order to time sprays, a network of 24 OFM traps was maintained throughout western NY, and checked weekly throughout the season. The first egg hatch for each generation was estimated to occur at 175-200 DD (Base 45 F) after the biofix (first sustained catch of moths). Four treatments were compared in each orchard:
(1) Protective Schedule: Imidan was applied at pink (6 May), petal fall (21 May) and as cover sprays on 3, 16, and 30 Jun; 20 Jul; and 2, 17, and 31 Aug.
(2) Optimum Timing: Imidan was applied at the estimated first hatch of eggs against each generation. The first generation spray was applied at pink (6 May) based on pre-season estimates of OFM phenology. The second generation spray was applied based on a pheromone trap biofix and DD calculations on 20 Jul. The third generation of OFM was delayed until after the third flight had started during the last week in Aug, and applied on 31 Aug. A fourth spray in this treatment was never applied because the flight continued throughout September and growers were reluctant to spray after Labor Day.
(3) Late Season Control: The first spray was applied on 20 Jul at the estimated first hatch of eggs of the second generation using methods described for the Optimum Timing schedule, followed by another cover spray on 2 Aug. A final spray was applied on 31 Aug, and a fourth spray was not applied after September because of concerns outlined above.
(4) Untreated Check: No insecticide sprays were applied to a small block of 12-16 trees along the outside edge of the research plot.
The same rate of Imidan 70W (3 lbs/A) was applied in all applications in all treatments with a high-pressure handgun sprayer to ensure adequate coverage. Damage from the first generation was estimated on 23 Jul by inspecting 100 fruits on each of 5 trees in each treatment. Apples were sampled again on 10 Sept (100 fruits on 3 trees/trt) to estimate cumulative damage from the first and second generations of OFM. Fruit was picked on 8 Oct, which is a normal harvest date for late maturing apple cultivars in NY, and 100 fruits on 4 trees/trt was examined to estimate seasonal damage from all three generations of OFM. Data from the two combined orchards was subjected to an AOV with SuperAnova. Means were separated with Fisher’s Protected LSD Test (P<0.05). Data was transformed Arcsin (Sqrt X) prior to analysis.
OFM damage was considerably lower in the Untreated Check plots throughout the season than in 2003, probably because of the unseasonably cool and rainy weather throughout the summer (Table 1). After the first generation, 13.4% and 5.0% of the fruit was infested in the checks in the two orchards, and damage in the combined orchards averaged 9.2%. When data from the combined orchards was analyzed, only the Protective schedule significantly reduced damage from the first generation below that in the Untreated Checks. Since no OFM sprays had yet been applied in the Late Season treatment, damage in this plot should have been similar to that in the check. However, the lack of control in the Optimum Treatment suggests that the single spray at pink was ineffective against the first generation, probably because flight of the first generation of OFM was later than normal and did not even begin until bloom in 2004.
Average fruit injury in the combined Check plots increased to 15.7% after the second generation, and only the Protective treatment significantly reduced fruit damage, although damage was lower than that in the Check plot in the Late Season combined treatments. At harvest (8 Oct), damage in the combined orchards Checks (17.4%) was only slightly higher than the average damage resulting from the first and second generations, which suggests that damage from the third generation of OFM was relatively insignificant during 2004. The results from this study show that Imidan can still adequately control OFM in problem apple orchards in NY if it is applied frequently at high rates with thorough coverage. In these heavily infested orchards, neither of the 3-spray programs, the Optimum Timing or Late Season Schedule, were as effective as the Protective Schedule, although damage in both of these treatments at harvest was lower than that in the Check. Even though the effectiveness of both of these reduced-spray schedules was similar during 2004, it is possible that results from these strategies could vary from year to year, depending upon seasonal weather patterns that may affect OFM phenology.
Nine fungicides (Syllit; Topsin M or Methyl-T; Nova, Procure and Rubigan; Flint and Sovran; Vangard and Scala) belonging to four classes of chemistries are labeled for the post-infection control of apple scab. Unfortunately, many of these materials have lost their activity because the scab fungus developed resistance. In response, we have worked on the site-specific management of resistance (SMOR). The SMOR concept is simple: Test the sensitivities of individual orchards and only use the post-infection materials that are still active. Who would do the sensitivity tests to find out where individual orchards stand? We are prepared to provide this test service for the 2005 season for a cost-covering fee of $800.
We must have 50 apple leaves with scab lesions to do these sensitivity tests. There are two modes of testing, a 'forward mode' and a 'rescue mode'.
In the 'forward mode', a scab control failure has not been a problem in previous seasons, but a grower wants to know for how much longer the post-infection fungicides used will last until resistance sets in. Naturally, leaves with at least one visible scab lesion will not be found easily. In this case, six trees at the opposite corners of a typical orchard block must be left unsprayed until scab lesions develop on cluster leaves. The 50 leaves with scab lesions are then collected and submitted to our test facility. After that, the corner trees are included in all subsequent treatments. Alternatives to such corner trees are unsprayed trees close (no more than 1,000 feet) to the orchard block, or a recently abandoned (no more than two seasons) orchard where scab had been managed with the same fungicide program.
In the 'rescue mode', leaf scab develops unexpectedly after post-infection fungicides have been applied. In this case, finding leaves with scab lesions will not be a problem. However, the leaves submitted for testing must be collected before a 'rescue' spray is applied. Otherwise, the scab spores already sprayed will not germinate and, therefore, cannot be tested.
The collection and shipment of leaves to our test facility are crucial steps in the procedure:
Leaves are sent to (no weekend delivery):
Diana Parker, Cornell University, Department of Plant Pathology, 630 West North Street, Barton Laboratory, New York State Agricultural Experiment Station, Geneva, NY 14456. (Telephone 315-787-2400).
The minimum requirement included with the shipment of leaves will be the name, the address and the telephone/e-mail number of the submitter. Much appreciated would be a 'warning' to Diana Parker, either by phone (315-787-2400) or by e-mail (firstname.lastname@example.org) prior to the shipment.
What happens next ?
The submitter will be contacted before sensitivity tests are initiated. A brief form with simple questions will be sent (mail, fax, e-mail). This form will include the assurance that a fee of $800 will be charged after a sensitivity diagnosis has been provided for the orchard sampled. The test submission form and instructions can also be obtained from Cornell's regional extension tree-fruit specialists.
In northeastern United States, blossom-end rots of apple are caused by at least three different fungi: Sclerotinia sclerotiorum, (the cause of white mold on beans), Botrytis cinerea (the gray-mold fungus), and Botryosphaeria obtusa (the black rot fungus). When blossom end rot is caused by B. obtusa, symptoms usually develop only as fruit begin to ripen in autumn, even though the sepal infections may have occurred earlier in the season. Symptoms of blossom-end rots caused by the other pathogen appear during summer.
Blossom-end rot, caused by B. cinerea, is sometimes called "dry eye rot." I have seen only a few apples with dry eye rot during 25 years of fieldwork in southeastern NY. The disease develops when B. cinerea colonizes dying petals and then moves into sepals and eventually into the fruit. Botrytis infections in sepals may remain quiescent until after harvest and then develop into fruit decays during storage, but the relationship between sepal infections at petal fall and subsequent incidence of gray mold decay during storage has not been proven.
Most of the blossom-end rot seen in NY and New England should be called calyx-end rot because it is caused by S. sclerotiorum. The key difference between dry eye rot caused by B. cinerea and calyx-end rot cause by S. sclerotiorum is that the former usually appears as a circular rot centered on and completely encompassing the calyx, whereas the latter is almost always offset to one side of the calyx. Calyx-end rot infections often stop expanding and die out when lesions reach a quarter to a half-inch diameter. Fruit with these dried out lesions will appear normal at harvest except for the small dry lesion visible at the calyx. In some years and on some varieties, however, calyx-end rots attract attention in midsummer because affected fruit color prematurely. Fortunately, fruit that ripen prematurely usually drop from the tree before harvest.
No one has studied the epidemiology and control of S. sclerotiorum on apples. Most of what we know about the life cycle and effective controls for this fungus comes from other crop systems. The fungus can colonize a wide range of broad-leaved plants and forms sclerotia (black pebble-like resting structures) that allow it to survive over winter. These sclerotia germinate and produce wind-dispersed ascospores in spring. The ascospores germinate and grow on senescing flower petals and then invade the subtending plant tissues.
Calyx-end rot in apples has been observed primarily where growers relied exclusively on mancozeb or mancozeb-SI combinations for scab control, but it never showed up in ALL orchards using those fungicide programs. Presence/absence of this disease may be related to the prevalence of certain broad-leaved plants in the ground cover. However, we have no data to indicate which ground cover plants in apple orchards are most likely to harbor the disease or why it occurs in some orchards and not others.
Because of the sporadic and unpredictable nature of this disease, and because losses are usually minimal even when the disease shows up, it is rarely cost-effective to target sprays specifically for calyx-end rot except for blocks where the disease was observed in previous years. Where there is historical precedent for concerns about calyx-end rot, captan or Topsin M applied during bloom and/or at petal fall will probably provide adequate control. Topsin M was very effective against S. sclerotiorum in bean fields, but resistance to this fungicide developed in some fields after it was used for many years. No one knows whether S. sclerotiorum has developed resistance to Topsin M in apple orchards.
Vangard and Scala are very effective against Botrytis diseases, but they have proven less effective against S. sclerotiorum in vegetable disease trials conducted at Geneva. No one has data to show whether Vangard and Scala are more effective than captan for controlling calyx-end rot on apples. Given that uncertainty, the decision to use Vangard or Scala in bloom and petal fall sprays should be based on their cost-effectiveness for scab control rather than on the possibility that they will control calyx-end rot.