IPM News
L.P.Berkett, IPM Specialist
June 4, 1998
In This Issue....
"Orchard Radar"
As part of the AIM project, Glen Koehler of the University of Maine Cooperative Extension System has developed "Orchard Radar" that provides insights into many arthropod pests and diseases and has made it available at:
http://pmo.umext.maine.edu/apple/allmodels/RadarIntro.htm.
As Glen writes: " Apple growers have always used weather-based 'rules of thumb' to help in making orchard management decisions. Researchers have quantified many bio-meteorological relationships relevant to orchard pest biology. Orchard Radar is simply a system that uses real-time site-specific weather observations and forecasts as input for these 'rules of thumb' and quantified relationships, and presents the output as web pages.
"The logistical difficulties in collecting and processing weather data on individual grower computers has prevented full use of the available information by orchard decision makers. Only recently have the components in Orchard Radar become practically available (and it still took a lot of work!). SkyBit Inc. delivers the site-specific weather values in a data format that computers can read. Standard computer software and hardware now have the capability to manage these data. The emergence of the World Wide Web provided a path by which a single computer can handle the large volume of weather data for multiple sites, process that data, and deliver the output to growers."
"This is new territory. Grower participation is critically important for continuation and development of the Orchard Radar products. Are there better ways to present the information? Which Orchard Radar products are useful, which are not? Which seem accurate, which do not? "
"The intention in providing Orchard Radar is NOT to have a machine attempting to make orchard management decisions. The intention is to improve the quality and quantity of the information base upon which YOU make decisions. As with any other source of information, you should look at the Radar estimates as one more piece of the puzzle. My hope is that with experience in referring to the Radar products and how they relate to the real world in your orchard, you will find that they are a useful addition to your Management toolbox."
"One novel aspect of the Orchard Radar is being able to interpret the weather forecast in terms of its effect on orchard events. We all know weather forecasting is less than perfect. But the glass is half full not half empty. Beyond about 2-3 days for precipitation, and about 5-6 days for temperature, specific forecast accuracy breaks down. But even beyond those ranges, the trend lines from longer-term forecasts and climatology still provide useful guidance for 'about when' things are likely to happen. The closer one gets to the estimated date and has to make a decision, the more the Orchard Radar estimate is based on observed data and better quality near-term forecast values, and so the accuracy of the estimate improves as the date of the event approaches."
"One of my fears is that some growers will look upon the Radar estimates as "This what is going to happen!" statements. In no way is Orchard Radar intended to reduce reliance on your existing means of arriving at decisions. Over-reliance on this, or any other single tool, can lead to bad consequences. Like any tool (including pesticides), the Orchard Radar products are only good to the degree that they are used properly. "
Check it out !
Disease Management
For most of the state, we are approaching the time when all lesions from primary infections should be present and visible upon thorough orchard examination. If you do have scab in your orchard, a description of treatment options appears on page 15 of the 1998-1999 New England Apple Pest Management Guide. Two full-rate captan applications 5-7 days apart is an effective treatment, especially when the temperature is above 80 F. The question that is always asked at this time of year is: "How long does a scab lesion remain 'active'? " and, unfortunately, there is no precise answer. As a guideline -- consider that lesions are most productive during the first two weeks after they appear; spore production tends to decrease after about 4 weeks. Remember that no 'eradication' effort is ever 100% effective. If you find scab in your orchard now, you will need to continue to carefully monitor your orchard for new lesions throughout the rest of the growing season.
As I mentioned in an earlier newsletter, I would not be surprised to see more powdery mildew 'primary infection sites' developing in Vermont orchards this spring. Primary infection sites are terminals or clusters that develop from buds where the fungus overwintered; the surface of the tissue is whitish and growth is usually stunted. The important issue is whether spores from these sites infected other leaves on the tree and caused disease. A picture of secondary infection can be found on the Internet at:
http://www.caf.wvu.edu/kearneysville/disease_descriptions/disease_images/ab9.jpg
Please note that mildew spores will only infect young, immature tissue. Once the leaves harden off, the threat of secondary infection is gone. At this point in the growing season, we have passed the most effective time to manage the spread of the disease.
So far, I have not heard of any orchards having a problem with fire blight this year -- which is good !! If you do find a few "strikes" in your trees, the following is a description of the "ugly stub" method for removing the strikes before extensive necrosis develops. This method leaves a branch stub at the cut, rather than making a normal cut right at the branch bark union. This allows the natural barriers at the branch bark union to seal off the branch, provides an easily spotted target for winter pruning, and removes visible inoculum sources during the growing season.
Are you seeing bright yellow/orange spots on your leaves or fruit-- particularly on Golden Delicious? They are probably Cedar Apple Rust lesions. This disease is caused by the fungus, Gymnosporangium juniperi-virginanae, which infects eastern red cedar and apple. Spores that infect apple leaves and fruit come from galls produced on cedars. Peak spore release occurs from early pink to full bloom. Given the wet weather we had during bloom, the appearance of this disease in not surprising particularly if you were not using an SI and/or EBDC fungicide during that period. A picture of lesions on leaves is available on the Internet at:
http://www.caf.wvu.edu/kearneysville/disease_descriptions/disease_images/phot2-10.jpg
A picture of what a lesion looks like on fruit can be found at:
http://www.caf.wvu.edu/kearneysville/disease_descriptions/disease_images/phot2-11.jpg
The one good thing about this disease is that it does not spread within the orchard during the growing season. Any spores produced in the lesions only infect eastern red cedar -- so what you see is all that you will have this year.
Hopefully, your pre-bloom or post-bloom management of this pest has been effective. Currently, the cool weather will slow down population growth, but with the return of hot weather, populations can increase quickly. The following chart is based on research conducted in New York. It appeared in the 1998 "March Message" by Dr. Ron Prokopy, et. al., and can be used in making decisions of whether further treatment is necessary.
Time Frame |
Action threshold based on % leaves with motile mites |
June 1 - Jun15 * |
45% |
June 15 - July 1 * |
55% |
July 1 - July 15 ** |
65% |
July 15 - August 15 ** |
80% |
* Take middle-age fruit cluster leaves
** Take middle age leaves from anywhere
To conserve any T.pyri predator mites that might be in your orchard and thus enhance biological control, Pyramite would be the first choice, then Kelthane if miticides are needed. In terms of insecticides, pyrethroids, dimethoate, Carzol, Lannate, and Vydate should be avoided; these are toxic to the predator mite. Also, Lorsban should not be substituted for Guthion or Imidan unless there is a compelling pest control need for doing so.
After visiting some orchards in the state, it appears that most of the Leafminer population (Spotted Tentiform/Apple Blotch Leafminer) is currently in the late tissue-feeding stage or have entered the pupal stage. Because the growing season is farther along than what is considered "usual", sap-feeding mines of the second generation may be present at the end of June. A way to monitor when to start scouting for sap-feeding mines is to use pheromone traps to determine the second flight of the adults. Researchers at Cornell estimate that most of the second generation for the Spotted Tentiform Leafminer will be in the sap-feeding stage at 500-700 degree days (base 43 F) from when second moth flight begins. Keeping track of degree days can be used as a guideline for when to monitor your orchard for sap-feeding mines which is the most effective stage to treat if the number of mines is above threshold levels.
In the Northeast, another leafminer -- the Apple Leafminer [Lyonetia speculella (=prunifoliella)] -- has been causing damage on apple trees. Last summer, Dr. Dick Straub of the Hudson Valley Lab provided the following information in the July 7, 1997 issue of Scaffolds.
"Female moths oviposit in tender new foliage by piercing the undersides of leaves and depositing single eggs inside the leaf tissue. The hatched larvae form serpentine mines, which are visible as wavy brown lines on the tops of leaves. As the larvae grow, they enlarge their mines into brown blotches, within which they consume all of the tissue between the upper and lower epidermis. Unlike other leafminers of apple, L. speculella is characterized by frass (small black pellets) that is constantly expelled on a silken thread from the mine by the feeding larvae. Just prior to pupation, larvae spin cocoons, which are suspended by threads and resemble a hammock. Appleleafminer probably has 4 to 6 generations per year in southeastern New York."
"Moreover, unlike our other leafminers, larval damage is confined to the youngest foliage, particularly terminal leaves of vigorously growing shoots. Root initials or water sprouts that are partially shaded are the preferred sites for feeding and pupation. Severely mined leaves turn brown and die; most such leaves drop off prematurely, thereby decreasing the number of the most photosynthetically active leaves. The potential for damage is greater in young orchards than in mature ones, and vigorous trees usually sustain higher infestations than do less vigorous trees."
"Populations normally do not achieve high abundance or cause critical damage until the beginning of the harvest period of our earliest cultivars. Insecticidal control of larvae or adults at this time may not be a reasonable tactic because of the pre-harvest interval of most materials; and just as importantly, because infestations do not damage fruit or cause premature drop of fruit. Broad-spectrum insecticides typically used in cover sprays (OP's) are unlikely to provide significant control of adults or larvae. The optimum control tactic would be 1 or 2 sprays of either methomyl, oxamyl, endosulfan or a pyrethroid at petal fall or 1st cover. Undoubtedly, imidacloprid at the same timing would also do some good. We consider that sprays are necessary only on non-bearing trees where vigor is essential, or on bearing trees that had high infestations the previous season."
Pictures of this moth, its mines and pupal stage can be viewed at:
http://www.caf.wvu.edu/kearneysville/pest_month/insectfocussept.html
Apple Maggot season will be upon us soon. It is time to make sure your traps are cleaned and ready to be placed in the orchard.
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Where trade names or commercial products are used for identification, no discrimination is intended and no endorsement is implied. Always read the label before using any pesticide. The label is the legal document for the product use. Disregard any information in this newsletter if it is in conflict with the label.
