Apple Pest Report: Friday, May 26, 2006
Vol. 14, No. 8
Scab
Rain keeps dancing in and out of the weather forecast for Highmoor Farm for tonight and Saturday. Latest forecast shows only Friday night - early Saturday showers ending before sun rise. If that timing is what actually happens, most of the scab ascospores ready to release will wait for the next daytime rain, which the long-term forecast shows arriving with several days of light rain starting next Wednesday, May 31. That next daytime rain will be the last major, and the last 'significant' primary scab ascospore infection period of the year.
Despite the historically high rain amounts in some locations, the late April - May weather was conducive for maintaining fungicide protection. The results for your efforts are becoming apparent in the form of healthy green uninfected leaves. Unprotected susceptible trees will show increasing level of scab infection between now and June 1 as 1st generation scab lesions from infection periods will have had time to develop. With over 50% of primary scab potential having had time to appear as lesions by Sunday, May 28, this weekend is a good time to start intentional (as opposed to looking around as you in the orchard for other reasons) scouting for scab lesions. Check both the tops and bottoms of fruit cluster leaves. Don't bother looking at the most recently emerged leaves as they probably were not unfolded when the scab infection periods that have had time to appear as lesions occurred.
The 1st generation lesions from primary scab infections can be sparse and hard to find. So to really be sure you need to give them time to go through another cycle to produce 2nd generation lesions before claiming successful scab control. But infections from all but the earliest infection periods will not have had time to begin appearing until about June 5. So while it is time to begin scab scouting, it will be a few more weeks before not finding scab lesions after a thorough check can be considered solid evidence that no significant degree of scab infection was able to take hold.
Procedure and interpretation for Scab inspection
PROCEDURE:
For a through check examine at least 100 fruit clusters or vegetative shoots per block. Select the cluster/shoots from tree at least 10 trees per block. Your sample of fruit clusters and vegetative shoots should come from at least 10 trees per block (i.e. no more than 10 per tree). Checking 5 clusters/shoots per tree on 20 trees is even better. Randomly select clusters and shoots from all areas of the canopy. Problems due to improper spray distribution can be limited to one section of the tree.
Inspecting a block for scab requires looking at a lot of leaves. In order to do that you don't have time to study each leaf, but instead do a quick "photographic flash" of about 15 leaves at a time. You have to look at each cluster twice, once for the upper leaf surface and again for the underside. By looking at about 15 leaves per cluster/shoot on 100 clusters/shoots, you will be checking about 1500 leaves.
Don't try to scout for other pests at the same time. If you need to check for other pests, do it separately from the scab scouting, either as a separate visit or on the same visit but as a separate walk through the block. To check 100 samples per block for scab takes about 30 minutes of walking and focused gazing. It is not a stroll through the orchard, it is work. But it is work worth doing.
A small hand clicker-counter held that leaves your hands free to grab shoots is useful to keep track of the number of shoots and clusters checked. When you find a leaf with one or more scab lesions, put it in your pocket. When the clicker reaches 100, stop and count the number of scabby leaves you have collected.
INTERPRETATION:
It is impossible to devise a threshold number of infected leaves for two reasons. Because of differences in tree size, orchard operation, marketing, cultivar, site characteristics etc., there is a unique context for evaluating the level of scab infection in each orchard. And the relationship between scab lesions appearing shortly after petal fall and the consequences in terms of fruit infection at harvest is not understood well enough to provide a specific, reliable threshold. With that caution in mind, a threshold of 0.5% of leaves infested (i.e. 8 infested leaves out of 1500 leaves checked) has been suggested by pathologists as a reasonable guess at a threshold for suppression treatments.
The Fall Scab Indexing procedure which is part of the Delayed-First-Spray strategy (see page 13 of the 2003-2004 New England Apple Pest Management Guide) is also built around detecting scab infestation of 0.5% of the leaves. Even though it is a tool built for a different purpose, we can use it as an interpretive guideline for June scab lesion scouting.
If you find less than 5 scab-infested leaves per 100 fruit clusters & vegetative shoots, this suggests with a reasonable degree of confidence that protection during primary (ascospore) scab infection periods was adequate.
Conversely, if you find 18 or more scab-infested leaves per 100 clusters and shoots, that can be taken as evidence that lesion suppression is needed. We used to call that ‘eradication’, but that terminology is misleading because you are not able to completely stop spore production on 100% of the lesions.
If the number of scab-infested leaves per 100 clusters/shoots is between 5 and 18, you can either increase the sample to see if a clear result comes out, or quit sampling and make a judgment call based on your personal and market sensitivity to scab. With early samples, keep in mind that only a portion of the scab pressure has had time to appear. See http://pronewengland.org/AllModels/MEmodel/me-Monmouth-ScabLesionChart.htm for updates on scab lesion appearance.
For a combined 200 cluster/shoot sample, finding less than 12 scab infested leaves indicates adequate control. Finding more than 24 infested leaves indicates need for eradication.
Insects
and Mites
While evidence so far for Highmoor Farm at least is that European apple sawfly
populations are down this year,
it is worth noting that where EAS are at a problematic level, then
insecticidal control is needed within a few days of petal fall to be
fully effective. If you don't have trap catch data of your
own, it is risky to assume that EAS were a no show this year. EAS
can be a serious pest.
Plum curculio is, unfortunately, a more reliable pest. In some years, cool weather and slow fruit growth after petal fall means that it can take up to 9 or 10 days before any egglaying cuts start to appear. I don't think that will be the case this year. The mild temperatures on Thursday-Saturday, followed by highs in the mid-upper 70s, and probably more importantly, nighttime temperatures near 60 combined with high humidity, are the conditions that plum curculio females prefer for their egglaying missions. Fruit that haven't already reached the preferred diameter threshold of about 7-8mm will get there quickly. It all adds up to risk of serious plum curculio damage pressure in the coming week.
Sevin (carbaryl) used as a thinner will provide about a week of protection. Fruit are less rate-sensitive to Sevin than other thinners, so if you are going use Sevin as a thinner, you can increase the rate to the insecticidal rate without undue interference with thinning objectives and with the advantage of more confidence that the application will provide a solid 7 days of protection.
Leafminer mine counts shortly after petal accurately predict the need for control. Finding more than a total 6-20 mines on 40 interior fruit cluster leaves is indication that control is needed. Mines will appear as light colored areas of leave surface on the underside of leaves, usually near the base. "Interior" means near the trunk. Only use fruit cluster leaves for this sampling.
European red mites are now in peak egglaying stage to produce the second generation. The impacts of mite feeding are less obvious to the human eye around petal than late season bronzing, but it is the early season damage that most likely to affects fruit size for this year and bud set for next year. This is an important time to check for mites. If there is a problem it is much easier to control sooner rather than later because once mites lose generational synchronicity (i.e. most are in the same developmental state at the same time) it is more difficult for a single miticide application to stop the momentum of the mite population. Effective petal fall miticide options include Apollo, Savey, Zeal, Agri-Mek and Vendex. Summer oil is also an option but only if you do not plan to use captan within 10 days before or after the oil application.
The mite treatment threshold until June 15 is if more than 30% of middle-aged fruit cluster leaves have living hatched mites present, or if there is more than an average of 1 mite per leaf. If you check 40 leaves and find 5 or fewer with mites, then it is safe to assume you are below threshold. If you find 23 or more infested leaves, you can assume treatment is needed. The Apple Pest Scout Card has charts to help with field sampling. Having the chart in your pocket makes mite scouting a lot easier and efficient.
Got weeds?
2006 Weed Management Twilight Tours
While not targeted to orchard weed problems, you can learn a lot at these sessions that will be applicable to your orchard as well as other crops that you may grow.
Three “weed-walk” twilight tours will be held in June, featuring on-farm research demonstrations being conducted on central Maine organic farms. Each session will be from 6:30 to 8:30 pm. The first tour, at the Peacemeal Farm, will be on Monday June 19th, and will feature weed management strategies for diversified and organic vegetable growers. Two subsequent tours, Monday June 26th and Thursday June 29th, will focus on weed management strategies in cereal and annual forage crops, and should be of interest to dairy farmers with weed control problems in row crops and cereals.
Tours will include discussion of a wide range of ecologically-based weed management strategies including stale seedbeds, pre- and post-emergence cultivation, optimizing crop competition, and fall strategies to encourage weed seed predation and mortality. Bring your weed samples, questions, and hot tips for your friends and neighbors. For more information contact Eric Gallandt (581-2933; gallandt@maine.edu) or Rick Kersbergen (800-287-1426; richardk@umext.maine.edu).
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Monday, June 19th Peacemeal
Farm Directions: If you are coming from the south on the North road, the farm is just over a mile on the right. If you go down a steep hill and pass over a stream you have gone to far. If you are coming from the north on the North Road, the farm is on the left just under two miles. You will see vegetable fields on the left and the farm is on the left at the top of the hill after crossing over a stream.
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Monday, June 26th Morrison Farm Directions: After turning onto the Atkinson Rd. in Charleston, the farm is just under a mile on the right as you go up the hill. |
Thursday, June 29th Henry Perkins
Farm Directions: After turning onto the Bog Rd. in Albion, the farm is on the right approximately 3/4 of a mile. It will be the first dairy farm you come to. |
Spray calibration
Anytime is a good time to check sprayer calibration. A lot of money passes through those nozzles and even an error of 5-10% adds up to a lot of wasted pesticide or could lead to poor control requiring additional spray trips and pesticide loads, or expensive damage to the crop.
Here are some points that came up in recent conversations with Dr. Andrew Landers, a pesticide application technology specialist at Cornell University, and Jonathan Reinecker, a technical representative for the TeeJet Spraying Systems Company.
* There are different opinions about distribution of spray volume in top half vs. bottom half of an apple tree. Back in the days of 25 feet tall, 400 gallon per acre trees, a standard recommendation was 2/3 of the spray volume in the top half of the tree, 1/3 in the bottom half. And some folks still go by that. With smaller trees these days, some people, say the distribution should be 50:50, and some say 1/3 top, 2/3 bottom. Andrew and Dr. Terrence Robinson are conducting tests this year with thinners to see how volume should be distributed.
* Water sensitive cards don’t show true droplet size, but used throughout canopy they show if spray pattern is equal throughout canopy. Surround makes a good spray pattern marker.
* Typically, airblast sprayer fans turn counter clockwise. Looking from the rear of the sprayer, the right side of an airblast fan is pushing air up, the other side down. This means that nozzles on the right and left sides of the manifold are exposed to greatly different air stream directions. Testing done by Dr. Landers in vineyards found that as a general rule, changes in nozzle orientation can be made to account for these differences in air stream to improve even distribution of spray volume across the canopy. These guidelines developed in vineyard tests, so use caution in applying them to apple trees which can be considerably taller and thicker than grape vines. But as a starting point, the adjustments are interesting and make intuitive sense for apple trees too.
On the "fan blade going up" side of the manifold (typically the right, looking from rear), turn off one or two top nozzles and orient the highest two remaining nozzles to point down 20 degrees from the horizontal. Keep the other nozzles horizontal. On the "fan blades going down" side of the manifold, point all the nozzles at 45% up from the horizontal.
* Ceramic nozzles cost a few dollars more than stainless steel or brass. But they also last 4 - 10 X longer than steel, and 20-50X longer than brass. Brass nozzles are not worth considering because they wear so fast. The cost - benefit ratio for more durable, wear-resistant nozzles is convincing, which makes it surprising that many people skimp when it comes to paying a few dollars more for better nozzles to deliver $400 of pesticide per acre per year.
* When nozzle orifice wear increases flow by more than about 10%, the pattern of droplet distribution also becomes distorted. When you buy nozzles, buy an extra one to keep in brand new condition as a way to check that the other nozzles are still within 10% of rated output.
* A tower sprayer with target sensors gives the best spray pattern and most efficient spray delivery, but at $44,000 each only makes sense for large orchards. For smaller orchards, a retrofit with tower manifold costs about $4000 and might be economically feasible. The horizontal spray direction from a tower gives much better coverage because droplets don’t have to push through foliage by starting from a nozzle located well below the target foliage.
* Turning down PTO speed on an AgTec air shear sprayer to 25% below the recommended rate reduced drift at 80 feet by 75% with no loss in coverage. (see an article on this in the Fall 2004 NY Fruit Quarterly).
* The Cornell Pest Management Guidelines for Commercial Tree-Fruit Production calibration section gives synopsis of Andrew's advice on airblast sprayers. See his web site for additional resources.
Scouting
Co-op
TJ Baldwin has been hired as the apple scout and will begin training next week. I will try to fit in everyone within a reasonable driving radius of Highmoor Farm into the route, though this may mean biweekly instead of weekly visits for some locations. Growers who signed up will receive a call within the next weeks as TJ begins getting familiar with the route and the different orchards.
Congratulations
to Tom and June Gyger for getting Five Fields Farm accepted by Land for Maine's Future Board for farmland conservation in April 2005. I knew Tom had been engaged in the multi-year process, but not seeing Five Fields on the LMF web site last week, did not know the process was complete. That makes four orchards in the program. If you know of others, please let me know.
Sincerely,
Glen
Glen Koehler
Pest Management Office
491 College Avenue
Orono, ME 04473
Voice: 207-581-3882
Email:
gkoehler@umext.maine.edu
Web:
PRONewEngland.org
Fax: 207-581-3881
What we call the secret of happiness is no more a secret than our willingness to choose life. - Leo Buscaglia