Apple Pest Report: Monday, May 22, 2006
Vol. 14, No. 7
Scab
If the rain arrives as forecast on Friday, May 26, then cumulative ascospore release at Highmoor Farm in Monmouth will reach approximately 95%. This is the same day that McIntosh trees are expected to reach 95% petal fall. This would be the year's final major primary scab ascospore infection period at Highmoor Farm. The key words here are "major" and "ascospore".
"major vs.
significant":
While about 95% of the year's total ascospores at
Highmoor Farm are expected to have been released by the end of the May
26 rain, there will continue to be potentially significant
ascospore releases at Highmoor Farm until there is 0.1
inch of daytime rain after Thursday, June 1. While potentially
significant, infection
periods occurring after a May 26 rain would have less relative infection
potential than those that occurred in the previous three weeks of peak scab infection risk.
The actual absolute infection risk in any orchard depends on inoculum level. In an orchard with high scab potential, even a relatively small portion of the season's infection potential can create more infection risk than the year's worst infection period in a "clean" low-scab orchard.
"ascospore
(primary) scab" vs. "conidia (secondary) scab":
Scab has two phases. In the primary phase,
ascospores release from leaves infected with scab the previous year.
It is the primary ascospore phase which will be winding down soon. Any ascospores that successfully infect susceptible unprotected apple
leaf and fruit tissue start producing secondary asexual (cloned) conidial spores
about two weeks later. These conidia fall onto leaf and fruit
tissue in the same or adjoining trees to give rise to even more
conidia-producing infections. Where scab was not controlled in the
primary phase, cycles of secondary scab infection can continue until
leaf drop in the fall. The emphasis of scab management is
preventing primary infections because once these are established,
getting scab under control is more difficult, requires multiple
fungicide applications, and by the time the further spread of scab is
suppressed a considerable portion of the fruit may be damaged.
For orchards that reached McIntosh full bloom later than May 17, the first soaking daytime rain after McIntosh 95% petal fall will likely be the final major scab ascospore release. The final significant release will likely occur with the first daytime rain over 0.1" that arrives six or more days after McIntosh 95% petal fall.
Even after the threat of primary scab infections wanes, it is important to maintain protection until you can verify that early suppression treatments were effective. Less than 10% of the season's primary scab infection potential has had time to appear as lesions yet. But that is about to change. At Highmoor, by May 31 about two thirds of the primary scab potential will have had time to appear as lesions. And the first lesions from second generation scab that has spread by conidia from the earliest infections will have had time to start appearing.
Until at least 95% of the primary scab potential has had time to appear and has been confirmed absent by scouting, it is risky to let fungicide protection lapse on susceptible trees. That won't be until June 5. While the degree of protection is not as high as for primary scab infection periods, at least a moderate degree of protection should be maintained until that verification date. Respray guidelines to help determining the need for renewed coverage during that transitional period are online at http://pronewengland.org/AllModels/MEmodel/me-Monmouth-SecondaryScabSpray.htm
But let's not look too far ahead, most orchards are still in primary scab season for at least the next week.
Blossom End Rot
Technically speaking, blossom end rot is an alternate name for Dry Eye Rot, caused by the same Botrytis fungus that causes Gray mold in storage. The skin around the calyx turns red then light brown. The affected area becomes sunken and the skin often shrinks and separates from surrounding skin. Often the discoloration is only on one side of the calyx. Symptoms of Dry Eye Rot typically develop in late July and August. Affected fruit often drop prematurely. If harvested, about 50% of affected will decay in storage from gray mold. Dry end rot spores are released during bloom from the skin of decayed fruit left in the orchard from last year.
What we often call blossom end rot is really Calyx end rot. The symptoms are similar. A gray-tan sunken area develops around the calyx. By mid-summer a red border forms around the affected area. Infected fruit are prone to premature drop. As fruit approach maturity, a brown leathery rot may progress to cover one third of the fruit surface. Calyx end rot is caused by Sclerotinia sclerotiorum fungus. The best guess is that spores are released from infected weed hosts such as dandelion and wild clover. Spores have been detected from early bloom until 3 weeks after petal fall, but the prime conditions for infection seem to be 2-3 days of wetness and temperatures of 60-77 F around petal fall. Symptoms of calyx end rot begin developing about one month after bloom.
The diseases are little understood because they are sporadic and usually minor. But where conditions are right for one or both of these fungi, these diseases can reportedly cause significant economic damage.
The wet weather of May 9 - 22 has probably created more risk for southern Maine orchards that were closer to bloom at the start of that period, and closer to petal fall by the end of it. At Highmoor Farm, the last few days of McIntosh bloom, and the bulk of bloom for later blooming cultivars like Honeycrisp and Golden Delicious, will be on dry days Tuesday - Thursday this week.
The Penn State and Cornell guides also differ somewhat in fungicide recommendations. The table below is from Penn State (http://www.cas.psu.edu/docs/CASDEPT/hort/TFPG/tables/table4-9.htm).
The Cornell tree fruit pest guide does not include Blossom end rot in its fungicide ratings, but does recommend the following fungicides where blossom end rot is a concern: captan, Sovran, Flint, and Topsin M in bloom petal fall and first cover sprays. (The Cornell guide also included Scala and Vangard in that list, but those fungicides are not as effective against fruit scab as the others, and are thought to be less effective as temperatures warm.) The Compendium of Apple and Pear Diseases lists Topsin M at bloom through First Cover as a possible control.
|
Efficacy Rating |
|
| Fungicide |
Blossom end rot (Botrytis) |
| Topsin-M | 2 |
| mancozeb | 2 |
| captan | 3 |
| sulfur | 4 |
| Thiram | 4 |
| Ziram | 4 |
| Nova | 5 |
| Procure | 5 |
| Rubigan | 5 |
| Flint | 6 |
| Sovran | 6 |
| Vangard | 6 |
Fire blight - Since I often sound like Chicken Little when it comes to this disease, I take pleasure in saying that it's been too cool during bloom this year for blossom blight infections. Blossom blight is the most serious phase of fire blight. Without blossom blight, you can devote you attention to more immediate concerns.
Insects
and Mites
Old
Friends
I checked European apple sawfly traps at Highmoor Farm on Saturday, May 20. There were only 3 EAS on 12 traps in four different blocks. Thus, a cumulative average of only 0.25 EAS per trap. The threshold for blocks that did not receive an insecticide at Pink is an average of 4-5 per trap. For blocks that did receive an insecticide at Pink, the threshold is an average of 6-9 per trap. The low trap counts I saw were taken before petal fall and so can't be compared directly to the petal fall thresholds. But I can say that the 2006 EAS population at Highmoor is much lower than previous years when we were catching the threshold number of EAS per day by mid-bloom. Even though a trap catch report from Highmoor is of limited applicability to other orchards, it seems safe to say that the stretch of cool wet weather was not conducive to a high degree of EAS infestation this year. Now that I've said that, the little critters will probably swarm as the sky clears Wednesday afternoon and prove me wrong.
Plum curculio egglaying will commence shortly after petal fall. Usually, damage does not appear until fruit are about 7-8mm diameter, i.e. around fruit set, which is expected to be around May 31 this year at Highmoor Farm. If you are still considering petal fall insecticide options, a relatively new material to consider is Calypso. It is of the same class of insecticides as Assail and Actara, but Penn state rates Calypso higher than those two against the combined petal fall threats of plum curculio and European apple sawfly.
The following is from an article on Calypso in the
May 8, 2006 Scaffolds newsletter Dr. Art Agnello, Cornell University:
" The active ingredient, thiacloprid, is another new
neo-nicotinoid insecticide. Calypso possesses both excellent systemic
activity and excellent crop safety. Its mode of action is through
interference with the nicotinergic acetylchloline receptor and controls
pests by both contact and stomach activities. Calypso has a low acute
toxicity to warm-blooded animals; however, it is highly toxic to
marine/estuarine invertebrates. Calypso possesses activity on apples
against aphids (except woolly apple aphid), leafminers, leafhoppers,
mirid bugs, codling moth, oriental fruit moth, plum curculio, apple
maggot, and European apple sawfly. It will also suppress scale insects
(crawler stage). On pears, it is active against pear psylla, aphids,
codling moth, mealybugs, leafminers, and the pear midge. It will also
suppress scale insects on pears. Calypso has a 12-hour restricted entry
interval (REI) and may not be applied less than 30 days before harvest
(PHI = 30 days) on both apples and pears. Do not apply more than 8 fl
oz per acre in a single application and no more than 16 fl oz per acre
per year on either apples or pears. "
Robert Childs, University of Massachusetts, has a good review of the new insecticide chemistries online at http://www.umassgreeninfo.org/fact_sheets/ipmtools/insect_products_05.pdf. The article is written for ornamental plant pest managers, so some of the brand names are unique to that market. But the same materials are registered for apples: e.g. acetamiprid = Assail, thiamethoxam = Actara.
The next issue of the Apple Pest Report will discuss scouting for European red mite and leafminer.
During and shortly after bloom is the best time to identify blooming wild apple and other rosaceous host trees for pests in woods within 50-100 meters of orchard. If you find alternate host trees, flag them for later removal. Removing alternate hosts in the vicinity of the orchard can significantly reduce pressure from scab, plum curculio, codling moth, apple maggot, roundheaded apple tree borer and other pests that thrive on unmanaged trees.
New Kids in Town?
1. Apple leaf roller
The following is an excerpt from a news release I received
from a friend who now works for USDA-APHIS, the folks that help prevent
and keep an eye on newly introduced pests:
Inspectors should watch for A. xylosteanus larvae in nursery stock originating in Canada. The insect larvae are lepidopteran leafrollers in the family Tortricidae that disfigure host plants by feeding on leaves. A. xylosteanus is highly polyphagous, feeding on numerous plant genera in numerous families. It damages orchard, ornamental, and forest crops, especially oak, maple, ash, elm, linden, dogwood, and fruit plants in the family Rosaceae such as apple and cherry.
A. xylosteanus is a leafroller with little risk for transport with fruit but with high risk of transport with nursery stock. Assuming the pest is restricted to Newfoundland, transport with commercial nursery stock or individuals carrying stock to Maine is the most likely pathway into the United States. If the insect is present on the Canadian mainland, it will move into the United States by natural means since wild and commercial hosts occur throughout North America.
A. xylosteanus is a minor or occasional pest and has at least 17 parasitoids where it is native. Either native or introduced parasitoids might limit populations of and damage by A. xylosteanus; however, one should not assume that if A. xylosteanus is introduced into the United States it will be controlled by parasitoids.
A. xylosteanus is a quarantine pest in the United States and in Australia. Since it is a quarantine pest in areas where it does not yet occur, export of nursery stock from the United States to these areas would be impacted. Since it is of low or no risk of being transported with fruit, export of commodities for consumption is not expected to be greatly impacted.
Maine, the top apple-producing state in New England, is the closest to St. John’s Newfoundland. In commercial orchards, leafrollers are usually minor pests because they are controlled by insecticides used for other pests. Leafroller problems may increase with reduced summer spraying or with development of pesticide resistance. "
For pictures and more
information, see
http://ip30.eti.uva.nl/bis/tortricidae.php?menuentry=soorten&id=197
2, 3, 4.... Winter moth, forest tent caterpillar and friends
Forest tent caterpillar have increased lately in MA and VT, though I don't know if that is true for Maine, but they certainly are present here. Winter Moth is a long-established and significant pest in Nova Scotia that has recently reached high numbers in ornamental plantings in MA and RI. Winter moth have also been found in Maine. If you have high populations of these species you would know by now as they begin feeding as buds open and foliage develops. But keep an eye out now too. There was concern in southern New England that feeding by large larvae could become more apparent as they moved into the post petal fall period. The primary risk is on young low-spray trees.
The University of Massachusetts has two interesting
and informative fact sheets at
http://www.umassgreeninfo.org/fact_sheets/defoliators/caterpillar_update_06.pdf
http://www.umassgreeninfo.org/fact_sheets/defoliators/wm_id_man.html
Weeds
Weed competition in the tree row is most damaging to tree growth and productivity in the prebloom-bloom-early summer period. Postemergence burndown herbicides are more effective and lower end of rate range can be used when weeds are small: <6" for Gramoxone (paraquat), <8" for Rely (glufosinate), < 12" for Roundup (glyphosate).
Spray calibration for small orchards
The sprayer calibration recommendations for commercial orchards are based on amounts of water to spray per acre. That leaves growers whose planting are measured in number of trees instead of acres with inadequate guidance. Some of the information I did find was wrong.
One key point is that old recommendations to convert X weight ounces into Y tablespoons are fallacious. You cannot accurately convert dry weight measures into a volume measure because the newer products have different densities. Doing so could introduce 100% error into the dosage measurements. If you need to weigh small amounts of a dry pesticide, it is worth the investment of a scale to make ounce and gram measurements.
Pesticide dosages are based on spraying the trees until they are so wet that more water would just run off. This is called the "dilute" amount of water. You can spray use less water than that to carry pesticide to the foliage, but when using a concentrate spray, you have to increase the amount of pesticide per gallon to compensate for the decreased volume of water sprayed. For many pesticides, spraying concentrate allows you to reduce the amount of pesticide by about 25% from the dilute amount. Thus a 5X spray (one fifth the dilute amount) would only require increasing the amount of pesticide per gallon by 4X.
The following table gives estimates of how many gallons of water might be needed to spray trees to run-off (dilute). The best way to use this table is as a guideline and do a test spray on one or two of your own trees to see how much water you have to spray before the entire canopy is saturated. The amounts change through the season because there is a great increase in foliar surface to cover as shoots grow. (But there is also much lower spray capture efficiency early in the season, so the degree of change is not directly related to the change in amount of foliar surface).
If your trees have different dimensions (are not as wide as they are tall for example), then you will want to adjust the amounts from those indicated in the table. But this gives you a reference point to begin your own test measurements.
For example, if you are spraying eight trees that are 12 feet tall and wide at petal fall, then the dilute amount of water for those trees should be in the ball park of 8 x 3.8 quarts which is about 30 quarts, or 7.6 gallons. If the pesticide label had a dose of 1 lb. per 100 gallons dilute, then to treat those trees you would use 7.6/100 x 1 lb. which is .076 lb. One pound is 454 grams, .076 x 454 = 35 grams of pesticide mixed into 7.6 gallons of water.
If want to save time by spraying at 5X, then you put 35 grams of the pesticide into 6 quarts of water (8 * .76 ~ 6). If want to reduce the dosage by 25% because of the concentrate spray, you would reduce the 35 grams to 26 grams.
Estimated amount of water to spray apple trees to run-off.
| Tree height and width |
Early spring (bud break to pink) 0.5 gallons per 1000 cubic feet |
Transition (bloom to fruit set) 0.7 gallons per 1000 cubic feet |
Summer full foliage (fruit set to harvest) 1 gallon per 1000 cubic feet |
| 6 feet | 0.08 (0.34 quart) | 0.12 (0.47 quart) | 0.17 (0.68 quart) |
| 8 feet | 0.2 (0.8 quart) | 0.28 (1.1 quarts) | 0.4 (1.6 quarts) |
| 10 feet | 0.4 (1.6 quarts) | 0.55 (2.2 quarts) | 0.8 (3.1 quarts) |
| 12 feet | 0.7 (2.7 quarts) | 0.95 (3.8 quarts) | 1.4 (5.4 quarts) |
| 14 feet | 1.1 (4.3 quarts) | 1.5 (6.0 quarts) | 2.2 (8.6 quarts) |
| 16 feet | 1.6 (6.4 quarts) | 2.25 (9.0 quarts) | 3.2 (12.9 quarts) |
Estimated amount of water to spray apple trees with a 5X spray.
|
Tree height and width |
Early spring
|
Transition
|
Summer
full foliage |
| 6 feet | 0.017 (0.07 quart) | 0.024 (0.09 quart) | 0.034 (0.14 quart) |
| 8 feet | 0.04 (0.16 quart) | 0.06 (0.23 quarts) | 0.08 (0.32 quarts) |
| 10 feet | 0.08 (0.31 quarts) | 0.11 (0.44 quarts) | 0.16 (0.63 quarts) |
| 12 feet | 0.14 (0.54 quarts) | 0.19 (0.76 quarts) | 0.27 (1.09 quarts) |
| 14 feet | 0.22 (0.86 quarts) | 0.30 (1.21 quarts) | 0.43 (1.72 quarts) |
| 16 feet | 0.32 (1.3 quarts) | 0.45 (1.8 quarts) | 0.64 (2.6 quarts) |
Congratulations
to Jason Davis getting Cayford Apple Orchard accepted by Land for Maine's Future Board for farmland conservation. See http://morningsentinel.mainetoday.com/news/local/2745498.shtml
Other orchards in the program are Lakeside Orchard in Manchester
http://www.state.me.us/spo/lmf/projects/project_detail.php?project=1545 McDougal Orchard in Sanford, and Five Fields Orchard in Bridgton.
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