  |
|
|
If you're in a hurry, here is the bottom line message from this article: Orchards that have not had fungicide coverage renewed since receiving heavy rain August 11-13 are at elevated risk of flyspeck appearing before harvest. In 2003, flyspeck infections seemed to appear out of nowhere and caused unsightly blemishes on a significant percentage of fruit in some orchards. Conditions appear to pose an even greater risk for harvest season 2004. Flyspeck infections appear as dime-sized circles of small black dots. These dots are the reproductive structures of the fungus that causes flyspeck. Unlike scab which penetrates into apple leaf tissue, flyspeck infections exist in the cuticular wax layer of the fruit. While it may be possible to remove light infections by rubbing the apple, doing so is laborious and impractical if many fruit are affected, and is not effective on severely affected fruit. Sooty blotch is caused by several different fungi which produce oily looking dark green or black patchy areas on the fruit. The exact appearance of sooty blotch varies by environmental conditions, and by which fungus is the cause. Of the two diseases, flyspeck is the harder to control. A management approach that prevents flyspeck will also prevent sooty blotch. Flyspeck ascospores begin releasing around Pink, and continue releasing until about four weeks after Petal fall. Those first generation of spores are probably not a major threat because fungicide applications made for scab prevention at that time will also prevent flyspeck infections. However, those ascospore generate infections in alternate host plants (of which there are many, including blackberry and raspberry) growing in the orchard border, or worse yet, in the tree rows. The risk of flyspeck infection increases as the infections caused by first generation ascospores develop to the point where they start producing successive generations of conidial spores through the rest of the summer. While this pattern is similar to the apple scab life cycle, there are key differences that impact flyspeck management. Unlike apple scab, which has a narrow host range (it only survives by attacking apple, crabapple, mountain ash and few other tree species), flyspeck has a much wider host range. It is harbored by many plants growing in an orchard border, including brambles such as blackberry and raspberry. Removing unmanaged border host plants and pushing the border further away from the apple trees will reduce flyspeck infection pressure, but that isn't practical except on a small scale planting. The flyspeck fungus requires relative humidity of 96% or more to germinate and grow. The optimum temperature range for growth is 65 to 79 F. Thus, trees with large thick canopies, those growing in low spots where morning fog persists, or near orchard borders that provide nearby inoculum and also block drying air flow, are at greater risk. Keeping tree canopies open with good winter pruning, and especially summer pruning, is an effective way to reduce the degree of flyspeck infection by up to 50%. Mowing or removing tall weed growth near apple trees, especially brambles growing right in the tree row, should also help. Weather plays a key role. The lack of hot days this summer has kept temperatures consistently in the range favorable for flyspeck. More importantly, the frequent rains and cloudy damp weather has allowed the number of suitable leaf wetness hours to accumulate faster than normal. It takes about 270 hours or leaf wetness for first generation flyspeck colonies to become visible. The presumption is that colonies becoming visible coincides with availability of a new batch of spores that cause increased infection risk. Last year's experience in Maine and elsewhere suggests that the 270 leaf wetness rule also applies to later generations. There was heavy rain on Sept. 4, 2003 that removed fungicide protection. If that had been followed by a normal or dry September, then it is likely that flyspeck would not have developed before fruit were harvested. But wet weather continued and 270 leaf wetness hours accumulated by the last week of September, which coincided with phone calls from growers saying "Yikes, flyspeck has popped up in a big way!". Hudson Valley NY had similar weather, and a similar late September 'outbreak' of flyspeck. Moving ahead to this year, the number of leaf wetness hours per day in July and August has been about 48% above normal. Many locations received enough rain August 11-13 to remove fungicide protection. Apples that do not receive renewed protection are liable to develop visible flyspeck colonies starting around September 7. And there could be more flyspeck inoculum this year. First of all, because 2003 was a high flyspeck year, there should have been abundant overwintered inoculum to start this year's cycle. On top of that, flyspeck development is probably ahead of last year's pace. In 2003, the estimated date for second generation colonies to become visible was August 6. This year that date was July 27. I checked unsprayed border row trees at Highmoor on July 28 and found numerous small light colonies just starting to show. This suggests that there is even more flyspeck potential this September than last year. It was a tough call to consider spraying after the heavy rain on September 4, 2003. Given the 2004 situation described above, I suggest that a similar, and more clear cut situation exists this year. High inoculum, accelerated development, and fungicide depleting late season rain. If you made a final application after August 13 with a fungicide effective against flyspeck at proper dose and with good coverage, then the risk of your apples showing flyspeck before October is low. But if your final application was before August 13, the silver lining is that you still have time to renew protection. Sovran or Flint are the best fungicides to prevent flyspeck, and a full dose application will provide protection for about 21 days or 3.5 inches of rain. Sovran and Flint can also reach back to stop growth of infections that have had less than 100 leaf wetness hours since starting. Unfortunately, Sovran has a 30 day preharvest interval, but the PHI for Flint is 14 days. Full dose captan, or Topsin M + half dose captan will protect for about 21 days or 2.5 inches of rain. Topsin M (but not captan) also has reach back activity. A Topsin M + captan or captan-only application has a zero day PHI, but there is the 4-day REI (Restricted Entry Interval) of captan to deal with. Legally, the REI constraint does not apply to non-employees, but trying to explain the fine points of worker protection regulations to pick your own customers is asking for trouble, so you might as well assume that captan also has a 4 day PHI. The flyspeck fungicide respray guidelines for the Orchard Radar sites (e.g. Monmouth, Sanford, Gorham, Old Town) can help you keep track of the date until which you can expect earlier fungicide coverage to prevent flyspeck from being able to accumulate enough leaf wetness hours to develop visible infections. Our understanding of flyspeck biology is not sufficient to create a specific predictive weather- based model, and site characteristics play a large role that is not considered in those estimates. Therefore, the Orchard Radar flyspeck forecast is more of a relative indicator to compare the risk between years than a specific prediction for all locations in the current year.
Here is a 2003-2004 comparison:
2004 If your fungicide protection was removed by heavy rain prior to August 14, there is risk of flyspeck infections becoming visible before harvest for all but the earliest cultivars. For more information, see the Cornell fact sheet on sooty blotch and flyspeck and a recent Cornell newsletter article Scab Maine orchards visited by the Apple IPM program scout that had nagging (in some cases worse) scab levels in late June and early July were finally able to get scab under control. Where scab is hard to find (less than 5 infected leaves per 100 shoots), fungicide protection for flyspeck should be adequate to keep residual scab from increasing in September. If you are still finding more than 18 scab-infected leaves per 100 shoots, captan at two week intervals will is an effective and relatively economical way to deal with those symptoms. But to solve the problem requires examining all the steps in the system you use to protect your trees: timing, dosage, coverage. In the last few weeks of trouble shooting discussions with people fighting scab in backyard plantings, the common cause has been mixing fungicide at dilute rates but only applying a fraction of the dilute amount of water per tree. Home fruit tree all purpose spray dosage is based on the tree being sprayed until run-off, until it is completely soaked. If you are going to spray less water than that, then you have to increase the amount of pesticide per gallon of tank mix by the opposite degree to compensate. For example, if you are only to apply half as much water as it takes to soak the tree, then increase the concentration by 2X. The best way to figure out how much water it takes to soak the tree is take a representative tree, spray it until is can't hold anymore water and any additional water just runs-off. It is OK to use less water than the dilute rate. Commercial growers hardly ever spray at 1X. But if you are going to spray at 2,3 or 4X, then the amount of pesticide per gallon of tankmix has to be increased by a factor of 2,3 or 4 times to compensate. See page 104 of the 2003-2004 New England Apple Pest Management Guide. Cedar apple rust Just as I was wondering why we never get cedar apple rust in Maine, three cases from backyard apple trees came into the Extension Plant Diagnostic Lab in one week. The yellow spots on leaves are striking but do not indicate threat to health of the tree, and can be considered an insignificant oddity on backyard trees. I am not aware of cedar apple rust becoming noticeable in any Maine commercial orchard, but if so, the recommendation would be to include and SI or EBDC fungicide in Pink to Petal fall applications next year. Insects and Mites Apple maggot fly captures at Highmoor Farm have been high this year, and not just in the traditional hot spot. The large number of unsprayed apple trees near Highmoor makes it impossible to translate traps catches there as an indicator for other locations. AM trap catches at the UNH Hort Farm have been up this year. Unless you have monitoring traps indicating otherwise, a final insecticide protection against AM should be made late enough to provide effective protection until the end of August. Early ripening cultivars are most at risk from AM egglaying. The following excerpt is from an article by Harvey Reissig and Art Agnello in the July 26 Cornell Scaffolds Newsletter. "Growers and consultants using an AM monitoring program often are concerned about late season catches of flies on traps during September and October in commercial apple orchards. Studies conducted in NY have not shown that there is any need to apply control sprays after the middle of August, even though flies can still be captured on traps after the estimated period of residual effectiveness of the last spray. Apparently, female AM active late in the season in apple orchards do not oviposit in fruit, even though most of them have completely developed eggs in their ovaries." The treatment threshold for European red mites (ERM) and twospotted spider mites (TSSM) from August 15 to August 31 is an average of 7.5 living hatched mites per leaf (don't count dead mites or unhatched eggs), or if more than 83% of middle aged leaves have mites present. Mites were below threshold in all monitored blocks August 9 -13. If mites do exceed threshold, Pyramite is the best rescue option for ERM and Acramite is the best option for TSSM. Leafminers: Leafminer mine counts were near zero in most monitored orchards August 9 - 13, but two blocks had high counts. Because of potential for winter injury causing sensitivity to preharvest drop this year, it seems prudent to use the 'stressed tree' threshold of an average of 1 sap-feeding mine per leaf. If your apple trees exceed this threshold, we are at the tail end of the optimum treatment period. If leafminer control is needed, Assail or Calypso can do the job while also providing protection against apple maggot. Second generation codling moth egg hatch should be well underway in the Sanford area, and just getting started in the Monmouth area. Normally, a mid-August final insecticide application targeting apple maggot fly is adequate to also prevent late season codling moth damage. For organic growers, a series of Bt applications can subdue 2nd generation codling moth. The best timing for beginning Bt applications for codling is August 13 in Sanford, August 25 in Monmouth, and August 28 in Old Town. The preharvest interval for Bt products is typically 0 days, but check the label of any product you use. Second generation white apple leafhopper (WAL) can cause stains on fruit with excreted honeydew, and may contribute to preharvest drop. But these effects are only likely at high densities of greater than 3 WAL per leaf. WAL are more likely to be a problem as a nuisance to pickers. There is no set threshold for picker nuisance. If you find more than 25 WAL per 100 leaves there more nuisance potential later in September. The neonicotinoids (Provado, Assail, Calypso) and pyrethroids (Asana, Danitol, Warrior), and Avaunt are all very effective. But carbaryl that is typically included in all purpose fruit tree spray mix products is also very effective. Even though Imidan is not highly rated against WAL, an Imidan application for AM and codling moth will also help suppress WAL. Weeds Just a reminder that late season glyphosate (Roundup) use is not a good idea, and that some weed cover going into winter helps insulate roots. Other stuff I wrote the following article back in July when it looked like we might finally get some summer heat. That didn't happen and growing degree days (base 50F) are running 4 days behind normal in Sanford, 8 days behind in Monmouth and 12 days behind in Old Town (as the tomatoes in our garden demonstrate). But for future reference at least, here is info on heat stress.
Hot
Weather-Related Injuries
The following heat index chart shows
what it “feels like” and at what temperatures heat stress can occur.
Exposure to full sunshine can increase these considerably.
Behavioral
affects: When blood is being brought to the body surface to be
cooled, less blood goes to the active muscles, the brain, and other
internal organs. As a result, strength declines, fatigue occurs sooner
than it would otherwise, and alertness and mental capacity may be
affected. Workers who must perform delicate or detailed work may find
their accuracy suffering, and others may find their comprehension and
retention of information are lowered. Discomfort can lead to
irritability, anger, and other emotional states which sometimes cause
workers to overlook safety procedures or to divert attention from
hazardous tasks. Physical effects: Physical activity can limit the amount of blood that flows to the skin to release heat. Heat stress can also be intensified by age, weight, fitness, medical condition, and acclimatization to the heat. The worst possible conditions would be a hot, humid, windless day, following a cool spell. Sweating can maintain a stable body temperature if the humidity level is low enough to permit evaporation and if the fluids and salts lost are adequately replaced. An individual who is heat acclimated may perspire almost twice as much as an unacclimatized individual. When the body cannot release heat, it stores it. This raises the core temperature and heart rate putting health at risk. Three common heat disorders, in increasing order of severity, are 1) heat cramps, 2) heat exhaustion, and 3) heat stroke.
1) Heat Cramps are muscle pains or spasms—usually in the abdomen, arms, or legs. Heat cramps usually affect people who sweat a lot during strenuous activity, which depletes the body’s salt and moisture. The low salt level in the muscles causes painful cramps. Heat cramps may also be a symptom of heat exhaustion.
First Aid: Stop all activity and sit quietly in a cool place.
2) Heat Exhaustion is the body’s response to an excessive loss of the water and salt contained in sweat, resulting in dehydration. Warning Signs. When the rise in skin temperature results in sweating, bodies unaccustomed to heat will often be inefficient at sweat production, producing little and excessively salty sweat. Conversely, the victim may experience heavy sweating. Victims may have headache, and muscle cramps and may become pale; irritable, confused, tired, dizzy; and nauseous. The skin will be moist and clammy, but the body temperature will remain near normal. The victim’s pulse rate will be fast and weak, and breathing will be fast and shallow. If heat exhaustion is untreated it may progress to heat stroke.
First Aid. Get the individual to a cool shaded
area and administer fluids by mouth.
3) Heat Stroke: Heat stroke occurs when the body becomes unable to control its temperature. The body’s temperature rises rapidly, the sweating mechanism fails, and the body is unable to cool down. Body temperature may rise to 106 degrees F or higher within 10-15 minutes. Heat stroke can cause death or permanent disability if emergency treatment is not given. Warning signs vary but may include: An extremely high body temperature (above 103 degrees F, orally); Red, hot, and dry skin; Rapid, strong pulse; Throbbing headache; Dizziness; Nausea; Confusion; or Unconsciousness; First Aid. If you see any of these signs, you may be dealing with a life-threatening emergency. Get the victim to a shady area. Have someone call for immediate medical assistance while you begin cooling the victim rapidly using whatever methods you can. For example, immerse the victim in a tub of cool water; place in a cool shower; spray with cool water from a garden hose; sponge with cool water; or if the humidity is low, wrap the victim in a cool, wet sheet and fan them vigorously. Monitor body temperature and continue cooling efforts until the body temperature drops to 101-102 degrees F. If emergency medical personnel are delayed, call a hospital emergency room for further instructions. Do not give the victim alcohol to drink. ***************************** Pesticide safety equipment increases the risk of heat stress. What happens to heat index ratings when wearing pesticide applicator PPE (personal protective equipment) such as the Tyvek coveralls used for orchard spraying and for scouting blocks during the REI period? Normally, relative humidity on a hot afternoon is around 50 - 70%. Because they block air, heat and moisture exchange, the relative humidity inside water resistant coveralls is about 99%. Even if the head is still free to perspire, this raises the apparent RH for your body's overall cooling system.
Assuming an apparent relative humidity of 90% for a person working in a
water resistant coveralls, at air temperature of 80F or above the heat
index exceeds 90. This means that heat cramps and heat exhaustion
are possible.
At 85 F and above, working in PPE can create a heat index above 105.
This means heat cramps and heat exhaustion not only possible, but
likely, and heat stroke becomes possible.
Sources: Air Force Pamphlet 91-216, 1998. http://afsafety.af.mil/AFSC/RDBMS/Ground/pubs/pam.pdf Heat Stress in Agriculture, USEPA, http://are.berkeley.edu/heat/heat.stress.epa-98.guide.htm Heat Index, Nat. Oceanic and Atmospheric Agency (NOAA), 2003. http://www.crh.noaa.gov/pub/heat.htm Heat Index and Technical Attachment: The Heat Index "Equation",
NOAA, 1990. Thermal Regulation Protective Apparel and Heat Stress The Exogenous Factor, The 50-Degree Company, 2000. http://50degree.com/exogenous.asp
Sincerely,
P ublished and distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914, by the University of Maine Cooperative Extension, the Land Grant University of the state of Maine and the U.S. Department of Agriculture Cooperating. Cooperative Extension and other agencies of the USDA provide equal opportunities in programs and employment.A member of the University of Maine System. Where company or brand names are used, it is for the reader's information. No endorsement is implied nor is any discrimination intended. Always consult product labels for rates, application instructions and safety precautions. Users of these products assume all associated risks.
|
|
Home:
Maine Apple IPM Pr General IPM and Apple industry links
Putting Knowledge to Work with the
People of Maine
A member of the University of Maine System |
gram