May 1, 2006 Volume 15 No. 7 Update on Pest Management and Crop Development
Geneva: 1st Oriental Fruit Moth catch today, 5/1.
Mullein Plant Bug
Oriental Fruit Moth
San Jose Scale
Spotted Tentiform Leafminer
White Apple Leafhopper
Perhaps more than at any other time of the season, orchard duties these days are directly impacted by weather patterns, which translate into fruit bud developmental stages. The spring so far has been marked by fairly dry weather, and rather warm spells alternating with 'extreme clear' patches that have produced regular nighttime frost warnings (see Julie Carroll's article in this issue). Just like the guy with one foot in a bucket of acid and the other in a bucket of lye, we're doing OK 'on the average', but the situation at any one moment might be troubling. We're still a little ahead of that notorious normal schedule that never really exists, but the cool spells have had a delaying effect on the trees' march to pink bud. I think this should be taken as a good opportunity to get prepared for the crush of pink pest management duties that always seems to coincide during too short a period, so a brief assessment of where we stand with insect pests might be useful at this point.
The potential pests of most concern just now are probably rosy apple aphid (RAA), oriental fruit moth (OFM), and tarnished plant bug (TPB), with European apple sawfly and plum curculio lurking in the wings. Unlike the past two years, OFM could be making its appearance in most orchards well before bloom this season, very likely this week with the 70-degree highs predicted over the next few days. In blocks with a history of internal worm infestations, you might put up 1 or 2 traps and check them fairly regularly until pink bud to be sure there's no great flush of moths that might indicate a particularly high-risk population this year. Then, of course, comes the question of how to respond when the numbers start building.
According to the philosopher Yogi Berra, it's always tricky making predictions, especially about the future. However, I'm going to make a completely unfounded assumption here and suggest that, even though we may get quite a few moths flying during pink and bloom, the overall temperature ranges we're expecting will result in very little egg hatch until petal fall, when the newly emerged 1st brood larvae will be best handled. Most growers will be using an OP like Guthion or Imidan at petal fall, possibly tank-mixed with a Bt or Intrepid for OBLR, and all of these will have some effect on most OFM populations. In particularly high-risk situations (that is, where you had a hard time managing internal leps last year, and you know good and well that they'll be back this year), you might want to substitute a more lep-active material like Avaunt (or Calypso, if the label comes through in time, as is being speculated by some in the industry) for one of your petal fall or first cover sprays. This way you might get an extra jump on the OFM/CM complex during their first generation, while covering the need to protect against other petal fall regulars like plum curculio and European apple sawfly. (Assail could technically be used as well, but might be put to better use if saved for the 2nd broods of these leps.)
According to your personal philosophy, RAA and TPB can be either perennial challenges, puzzling but non-fatal occurrences, or else a complete flip of the coin. Do you have them, do you need to treat for them, are you able to control them if you do, and does it matter if you don't? These pests also have been slow to tip their hand this season. It's possible to scout for rosies at pink, but this is often not practical, given all the other hectic activity at this time; TPB is not a good candidate for scouting, and if the bloom period is prolonged by cool, wet weather, a pink spray is of little use. If RAA is your main concern, you could elect a pink spray (using something like Lorsban or Actara) IF you have the luxury of a suitable application window.
However, if you think it's justified to go after both of these pests, one option (aside from a more traditional approach of using a pyrethroid at pink) would be to apply Assail during bloom at the 2.5-oz rate. Its labeled use in apples covers this use, provided you avoid spraying when bees are actively foraging. The ability to time this spray closer to the susceptible period of the newly set fruitlets should do a much better job of controlling both species than anything applied at pink, and it can go in the tank with most scab materials you might be using at bloom. Assail won't do too much for any PC that have made it into your trees during the bloom period, but it does have good activity against EAS and mullein plant bug, if you have been experiencing difficulty getting early enough protection from these pests .
During the wet 2005 summer in the lower Hudson Valley, several peach growers noticed a declining level of brown rot control after they had applied Indar for controlling fruit rot. The same decline of Indar performance was reported for a peach orchard in Niagara County. In this orchard, blossom blight had been managed with captan, followed by three consecutive sprays of Indar against fruit rot. This program, which had been successful in the past, failed in 2005. Approximately 20% of peaches had brown rot at the time of harvest.
Prior to the 1995 registration of Indar for brown rot control in New York, Wayne Wilcox, the New York fruit and berry pathology extension leader at the time, had conducted an extensive survey on the sensitivity of strains of the brown rot fungus to Indar and other fungicides belonging to the same SI class of fungicides. With his baseline sensitivity data on file, we were able to test and compare the sensitivities of strains isolated from diseased fruits from the peach orchard in Niagara County.
We discovered that the control failure experienced with Indar was caused by resistance. The pattern of resistance development was very typical for the SI class of fungicides. Strains of the brown rot fungus most sensitive to SI fungicides before they were ever used had been eliminated. Instead, 20% of the strains we tested in 2005 were up to 40 times less sensitive to these SIs than the strains tested in 1993.
How were these resistant strains selected? The spray history for this peach orchard in Niagara County was available for 1996 to 2005. Blossom blight had been managed with 3-5 captan sprays. Fruit rot had been managed with two Indar treatments, starting at 'turn of color'. This would add up to a total of 20-25 Indar applications. Would this total of sprays be sufficient for developing resistance to Indar?
Most likely not. Immediately adjacent to the peach orchard had been a small, old, "fresh fruit" nectarine orchard with notorious brown rot problems. There, Indar had been used much more often and starting with blossom blight control. We must assume that SI-resistant strains of the brown rot fungus were selected in this small "fresh fruit" nectarine orchard, and that these SI-resistant strains had found their way into the adjacent peach orchard.
Where do we go from here? Indar has been the most effective brown rot material among several other SI fungicides. As expected, all brown rot strains resistant to Indar were also resistant to Orbit, Elite and Nova. If declining brown rot performance with Indar becomes a problem, switching to Orbit, Elite or Nova will not solve this emerging problem of resistance. We must remember though that the SI fungicides also provide good control of powdery mildew, which apparently remains sensitive. SIs also control cherry leaf spot. Unfortunately, the cherry leaf spot fungus has also developed SI resistance in Michigan.
Our thoughts about brown rot control in the future are as follows: We do not know how widespread Indar (SI) resistance of the brown rot fungus has become or will become in the years ahead. If a declining performance of Indar (or Orbit) has been noticed, these SI fungicides should be replaced by alternative brown rot fungicides, at least during the fruit protection phase. Alternatives for both blossom blight and fruit rot management are the protective captan formulations (most now have a 24-hr REI). Another very active alternative would be Pristine. Pristine is a mixture of two fungicides and provides very good control of brown rot, powdery mildew and cherry leaf spot when used on a protective schedule. Pristine can be used five times during a season, but only twice in sequence.
When 'kick-back' activity is needed during blossom blight control, Rovral/Iprodione would be alternatives to Indar or Orbit. Use of these iprodione products is limited to two treatments per season for blossom blight control. Ronilan, which is no longer registered in the US, was a very similar fungicide, and resistance of the brown rot fungus to the class of dicarboximide fungicides has been found in other US states and many countries abroad. At present, we do not know where we stand on resistance to Rovral/Iprodione in New York. We can only speculate that resistance to these fungicides will not be a limiting problem, because they have not been used extensively in the past.
Some 'kick-back' activity during blossom blight control is also provided by the two anilinopyrimidines (APs) Vangard and Scala. However, neither fungicide is labeled for fruit rot control, and they have use restrictions on cherries (phytotoxicity).
What is the 'bottom line' for managing brown rot in 2006? The 'standard program' in the past has been to manage blossom blight with a protective fungicide such as chlorothalonil or captan, followed by Indar (or Orbit) for fruit rot control. This routine may no longer apply, because the brown rot fungus has developed resistance to Indar (and Orbit) in a peach orchard in Niagara County.
What can or should we do in 2006? Many things. We have numerous fungicides, in addition to Indar (or Orbit), for the control of blossom blight, and some provide post-infection control. We should utilize these fungicide options. Do we have a 'silver bullet' for the control of fruit rot in orhards where Indar (or Orbit) performances have noticeably declined? At this moment there is only one 'silver bullet' option: Pristine.
We have compiled an 'up to date' list of brown rot fungicides labeled in New York for 2006. This long (3-page) list can be obtained from your regional Extension Educators, or online at: http://www.nysaes.cornell.edu/pp/extension/tfabp/index.html.
The first scab lesions showed up late last week in unsprayed trees in our research plots. The lesions I found were on the underside of the first and second cluster leaves and presumably resulted from the light Mills infection period that occurred April 7-8 when trees were between quarter-inch and half-inch green. Lesions were difficult to find even on unsprayed Jerseymacs: I found three lesions in about 30 minutes of searching. Thus, the April 78 infection period was relatively unimportant orchards that had low carry-over inoculum and/or that had fungicide applied prior to the infection period.
In the Hudson Valley and southern New England, the time when sweet cherries are blooming is a critical time for managing X-disease. During cherry bloom, seedling Mazzard sweet cherry trees can be detected in hedgerows and woodlots next to stone fruit orchards because of their showy white flowers. Seedling sweet cherry trees often become established as a result of seeds carried by birds from cultivated cherry trees. These seedling trees can harbor X-disease and provide an inoculum source for infecting commercial peach, nectarine, and sweet cherry orchards. I have seen at least four cases in the Hudson Valley where one or two seedling Mazzard trees left in woodlots or hedgerows have resulted in significant commercial losses in adjoining sweet cherry and peach orchards. While the seedling Mazzards are in bloom, they should be marked for removal, and removal should be completed before June 1.
Do not confuse Mazzard seedling trees with shadbush (Amelanchier species) that bloom slightly earlier than the Mazzard seedling trees. Shadbush trees have a more wispy twig structure and the trunks on shadbush lack the large horizontally oriented lenticels common to trunks of Mazzard seedlings. When removing potential hosts for X-disease, it is important to note that wild black cherry (Prunus serotina) is NOT a host for X-disease and need not be removed from orchard perimeters to control X-disease. Black cherry blooms later in the spring and has a much different flower structure than Mazzard seedling trees.
X-disease is still one of the most difficult diseases to manage in peach, nectarine, and sweet cherry plantings. The pathogen that causes X-disease is a phytoplasma, a phloem-limited organism previously known as a mycoplasma-like organism or MLO. Several leafhopper species are able to acquire the phytoplasma from infected chokecherry (Prunus virginianae) or sweet cherry trees and then transmit the pathogen to orchard trees. Transmission occurs during summer, and insecticide treatments are not very effective for preventing transmission if infected chokecherry or sweet cherry trees are present within 500 feet of susceptible stone fruit crops.
Peach and nectarine trees are dead-end hosts for the disease, apparently because peaches and nectarines develop disease symptoms and die before titers of the phytoplasma become high enough to allow feeding leafhoppers to acquire the pathogen from diseased trees. With infected chokecherries and sweet cherries, however, phloem cells become filled with the X-disease phytoplasma and leafhoppers feeding on these trees can readily acquire the organisms and later transmit them to orchard trees.
Last week, frosty conditions were forecast across many regions of NY. Minimum temperatures collected by the Network for Environment and Weather Awareness (NEWA) from weather stations in the apple growing regions in New York is shown in the table below.
You can access this information organized in text files on the NEWA web site at http://newa.nysaes.cornell.edu/. Click on the Monthly Summary link on the left-hand sidebar and then click on the month of interest for the weather station location.
To keep up on accumulating degree days, try the Degree Day Calculator at http://www.nysaes.cornell.edu/ipm/specware/newa/. Or find out about apple insect phenology models and associated IPM decisions with the Apple Pest Degree Day Calculator at http://www.nysaes.cornell.edu/ipm/specware/newa/appledd.php.
Apple pest model information is organized on the NEWA Apple Home Page at http://newa.nysaes.cornell.edu/apple_home.htm.
If this is your first time visiting NEWA, enter your name and password to login and fill out a brief questionnaire so the NYS IPM Program can continue to improve this kind of information delivery.
LORSBAN 75G - Gowan Co. has received an amended registration for Lorsban 75WG (EPA Reg. No. 62719-301-10163) in New York State that extends the period of its use on apple through petal fall; it was previously labeled only up to bloom. This change means that it can now be used as an alternative to other commonly used petal fall materials against such pests as plum curculio, European apple sawfly, codling moth, and oriental fruit moth, as well as some additional pests listed on its label that might not be controlled by other OPs, including obliquebanded leafroller and rosy apple aphid. This label also lists trunk sprays for many borer species in apple, up to 28 days before harvest.
To minimize confusion, it will help to understand that this change results from an amended definition in the Directions for Use section of the label that defines "petal fall" as being part (i.e., the end) of the "bloom" period. This should make it a bit less puzzling to read the part that 'post-bloom application is prohibited', although it is still somewhat counter-intuitive, like many other aspects of the Lorsban label. Also, although a maximum of 2 applications per year are allowed, there is a limit of 2 lb a.i. chlorpyrifos per season, irrespective of formulation. If a single foliar spray is made at or prior to petal fall, then only 1 subsequent apple trunk application can be made in the same year. The REI is 96 hrs.
KANEMITE 15SC - This is a new miticide from Arysta (EPA Reg. No. 66330-38), now registered in NYS for control of European red mite and twospotted spider mite in apples and pears. The a.i., acequinocyl, represents new chemistry and a novel mode of action, against which no resistance has yet been demonstrated in mite populations. It has activity against all life stages and is recommended for use against threshold populations, normally those occurring in summer. Harvey Reissig has tested this miticide for several years and found it to be a good material with adequate residual activity, and useful as a rotation product in mite resitance management programs. Two applications per season are allowed, with an REI of 12 hours, and a 14-day PHI; it is nominally safe to predatory mites.
ZEAL 72WP - Zeal Miticide, which was a granular formulation, is being stopped from production due to cost issues. "Zeal Miticide1" (EPA Reg. No. 59639-138) is the same product, but a different formulation (wettable powder), which Valent is using as a replacement product. According to their registration manager, Valent is trying to make this transition as seamless as possible. I haven't seen any current data on its relative efficacy, but will provide any that may be forthcoming.
MITE-E-OIL - This is a new horticultural mineral oil registered by Helena (EPA Reg. No. 5905-302) for delayed dormant and summer use in all tree fruits against all major mite pests. It is a highly paraffinic oil with a minimum unsulfonated residue (UR) rating of 96-98%, which should make it generally safe for foliar use in most cases (with the standard cautions against combinations with any sulfur-containing fungicides).