Apple Pest Report: Friday, August 10, 2007
Vol. 15 No. 17
Flyspeck
and sooty blotch
The
two primary factors in successful flyspeck control are the amount of rain in
late August and September, and the final fungicide spray date and material. You can’t predict the weather that
far in advance, but you can make an educated guess about how late the last
fungicide application should be in order to sufficiently minimize the risk of
flyspeck and sooty blotch appearing before harvest, or soon after harvest in
storage.
Using
weather forecast data available as of Friday, August 10, if you have cultivars
that won’t be harvested until October 8 or later (risk probably doesn’t
increase with later harvest than October 8 because falling temperatures after
September slow down flyspeck growth), the earliest “safe” final
fungicide application date would be with Topsin M + half-dose captan, or a
strobilurin, on August 23.
In
a low risk block (see http://pronewengland.org/allmodels/FlyspeckBackground.htm
for definition of a low-risk flyspeck block) that date can be pushed back to August
15.
If
you are using a fungicide less effective against flyspeck (e.g. captan at
full-dose but applied without Topsin M), the latest safe application dates are only
a day or two later, but your protection is more susceptible to being cut short
if above normal amounts of rain fall.
So
picking the date for the final fungicide application is a trade-off between
cost (if a later date requires an extra application) and needing to put the
sprayer away for things like making money harvesting apples versus spraying
late enough to have confidence that late season rain won’t allow flyspeck
to reduce crop value.
So
like so many decisions, it’s a gamble. You can increase the odds in your favor
by monitoring the situation and being able to respond if changing conditions
call for action. In this case,
watch late summer and early September rain and leaf wetness hour accumulations. If your coverage is washed off more than
30 days before harvest and it looks like wet weather during the weeks prior to
harvest will provide a total of 220-270 leaf wetness hours (especially in
blocks with any history of past flyspeck problems), then an additional
fungicide application on trees at risk can be a very profitable investment that
prevents extensive losses to flyspeck.
The
fungicide depletion and flyspeck development estimates at http://pronewengland.org/AllModels/MEmodel/RADARME-Monmouth.htm#FLYSPECK
can help you keep track of
the situation.
Flyspeck
and fire blight are like the tortoise and the hare of apple diseases. Fire blight blossom infection risk develops
extremely rapidly, a few hours difference in application timing or a few degrees
change in temperature can make a big difference. When it is on the horizon, fire blight blossom
infection risk requires close attention, but for a limited time during
bloom.
By
contrast, Flyspeck risk develops slowly over weeks, but it just keeps chugging. It isn’t a problem in most years
for most blocks, but when it does occur it can be extensive. There is a lot we don’t know about
this disease, but we know enough that it really should not be a surprise when
it does occur because the conditions that lead to a bad flyspeck outbreak are noticeable
if you are paying attention. It’s
only when you ignore it that it can catch you and bite.
Including
calcium chloride in late summer applications, in addition to the primary benefits
for fruit hardness and preventing calcium deficiency disorders like bitter pit and
cork spot, also helps to prevent flyspeck and sooty blotch.
Here is an
excerpt from a recent Scaffolds newsletter
article by Dr. David Rosenberger of particular interest to organic growers. The date table below the article also
gives testimony that half-dose captan plus Topsin M is an excellent combination
to prevent flyspeck and sooty blotch.
Note that the final application date in this trial was August 31, and that
flyspeck pressure (as indicated by 100% infestation of unsprayed fruit) was
extreme. Also note that the “captan
alone” treatment was at half-dose each application.
“In a 2006 field trial, we
evaluated liquid lime-sulfur (LLS) as an option for summer disease control in
organic orchards. As indicated in the table footnote, the last fungicide
spray was applied 31 August, and protection from that spray was depleted by 14
September, due to accumulation of more than two inches of rainfall. From
14 September until harvest on 3 October, fruit were exposed to 181 hr of
accumulated wetting, and that, combined with some spray gaps earlier during
summer, brought the total flyspeck incubation period to 276 hr of accumulated
wetting by 3 October. That total is slightly more than the 270 hr of wetting
that usually allows appearance of the first flyspeck lesions on unprotected
fruit.
Four applications of LLS at 2 qt and 4 qt, but not at 1 qt, per 100 gal
controlled flyspeck just as well as four sprays of Topsin M plus Captan (the
commercial standard). When LLS at 1 qt/100 gal was applied six times, or
roughly every 10 days rather than every 21 days, it worked nearly as well as
the higher rates of LLS. However, other trials have shown that LLS is not
very effective for controlling summer fruit rots. In fact, high rates of
LLS (e.g., 4 qt/100 gal) applied during summer may injure fruit skin, and that
injury may exacerbate development of black rot and white rot.
We are still uncertain about the best approach for controlling summer diseases
in organic orchards. Based on work completed to date, I suspect that LLS
controls SBFS primarily via post-infection activity rather than via protectant
activity. Thus, LLS applied at 2 qt/100 gal on a 15 to 20-day interval
starting in early July might provide effective control of SBFS, so long as a
final application is made close enough to harvest to prevent development of
SBFS after the last spray.
Low rates of copper fungicides (e.g., 5 oz/100 gal of Cuprofix Ultra 40
Disperss) can also be used during late July and August to prevent summer fruit
rots. However, even low rates of copper may discolor yellow-skinned apple
cultivars. (Copper applications during June and early July will almost
always cause lenticel injuries that appear as black spots on mature
fruit.) We are currently evaluating the feasibility of using tank mixes
of LLS and Cuprofix during August to determine if that combination will provide
better control of both SBFS and summer fruit rots than either product used
alone.
Phosphite fungicides may eventually provide another alternative for summer
disease control. Aliette was the first fungicide in the phosphite
fungicide group and it was used primarily to control Phytophthora
diseases (i.e., root rots). However, the expiration of the Aliette patent
allowed introduction of less expensive generic phosphites and stimulated
exploration of other potential uses. In both 2005 and 2006, Dr. Turner
Sutton in North Carolina conducted field tests that showed excellent control of
sooty blotch and flyspeck where phosphite fungicides were combined with 6 lb/A
of Captan 50W. The same rate of Captan 50W used alone was
ineffective. Several phosphite fungicides were included in a 2006 trial
conducted in the Hudson Valley. A phosphite-Captan combination provided
residual protection during the preharvest interval (31 August to 3 October)
equivalent to that of Pristine, Sovran, and the Topsin-Captan
combination. Phosphite-plus-Captan combinations may prove useful for
controlling SBFS during late summer after product labels are changed to include
these diseases. So far as I have been able to determine, none of the
phosphite fungicides currently have New York State labels that include SBFS or
summer fruit rots on apples.
Final
note: The very best fungicides will prove ineffective for
controlling SBFS if they are not properly applied. Incomplete spray
coverage and control failures can be expected when spraying in the wind,
driving too fast, using low volumes of water per acre (e.g., < 80 gal/A with
conventional nozzles), or attempting to penetrate dense foliage or clustered
fruit. Where SBFS was a problem last year, growers should first evaluate
their spray coverage to ensure that the fungicides are getting to the intended
target. The second most common problem is failure to respray trees during
late August or early September if heavy rains wash off fungicides more than 25
days prior to harvest. Given the fungicides that are currently available,
complete control of SBFS and summer fruit rots is feasible if fungicides are
applied at the right time and under conditions that allow good spray coverage. “
Apple Scab
Scab
control is excellent in IPM Program monitored blocks, with all except one block
having less then 5 active scab lesions per 100 shoots. Scab can reinvigorate as leaves reach
the end of their lifespan and begin to lose natural resistance to scab in
September. But growers have done an
excellent job with scab control this year, and even if there are frequent late
season rains, the risk of reactivated scab outbreaks seems low this year.
One
way to benefit from excellent scab control is to do a scab index in the mid-September
to early October by checking 100 shoots per block. If there are fewer than 5 scab infected
leaves, then the block can be treated as having low inoculum next spring. The first scab spray can be delayed until
the 4th infection period or Pink, whichever comes first, in
confirmed low inoculum blocks. With
the increased concerns about resistance and continued efficacy of
post-infection scab fungicides, there is less room for error in making sure
that protection is in place when significant scab infection periods begin even
in low inoculum orchards. In other
words, using a delayed start puts more pressure on there being good coverage
and adequate dosage from that first application as it will be the only
protection present, there will be no leftover residue from early applications.
Even if you don’t use all of that flexibility
(e.g. if you are going to apply oil at tight cluster you will probably use that
spray trip to apply a scab fungicide also), it can be useful next spring to
know which blocks qualify for a delayed scab strategy and which don’t. The downside of a fall scab index is
that it needs to be done during September-early October when harvest is in full
swing and time is at a premium. But
to index an orchard block of up to 10 acres (otherwise split and treat as separate
blocks) can take as little as 20 minutes.
Actually, if there is no shortage of scab in the block, it can take only
a few minutes. As soon as you find
5 infected leaves, there is no need to check additional shoot terminals. Knowing which areas have high scab is
also useful information to apply in next spring’s spray decisions. Recording your observations in your
spray record book or elsewhere will protect them from the vagaries of memory,
and make them available to review next spring.
Insects and Mites
Apple
maggot (AM) fly trap captures in most
monitored blocks continue to be low.
But a few blocks that are over threshold are way over threshold. Apple maggot is a very block-specific
pest, so unless you have traps in your orchard there isn’t much that can
be said about current damage risk.
After an insecticide
application has worn off (up to 2 inches of rain in the first 10 days, or up to
1.5 inches of rain or 14 days, whichever comes first), clean off traps and
begin counting again towards a threshold of an average of 1 AM per trap on unbaited
traps, or 5 AM per trap on odor-baited traps. Continue monitoring AM until August
31. While early ripening cultivars
are preferred by AM, crop damage problems are also common on the last harvested
cultivars, as they remain exposed to egglaying damage the longest after the
final insecticide application, and remain as the only oviposition target when earlier
cultivars are removed from the orchard.
European red mites and Twospotted
spider mites have not been much of a problem so far this summer, but mite
levels were near threshold in 4 out of 9 blocks checked on Monday and Tuesday,
August 6-7. If needed, Acramite (7
day preharvest interval), Envidor (7 day PHI), Portal (14 day PHI), and
Kanemite (14 day PHI) can provide contact knockdown of a mite infestation. Vendex (14 day PHI) is another option with
a short PHI, but a single application may not stop an over-threshold mite
infestation. Nexter (25 day PHI) or
Zeal (28 day PHI) are also options where their longer preharvest interval will
not interfere with harvest.
Fall webworm nests are making their annual appearance. The best way to deal with them is
pruning out affected branches and destroying the nest.
Apple-and-thorn skeletonizer is only a problem on low-spray or no-spray apple trees,
and in most cases the foliar feeding they do is more offensive to your eyes
than it is to the health of the tree.
There was more than the usual number of calls about first-generation damage
this year, so I would not be surprised if second-generation damage started
appearing in the next couple of weeks.
Second generation codling moth and lesser appleworm flight and egg hatch are underway. These are major pests for organic
growers. A mid-late August application
of Bt or Entrust will reduce the risk of noticeable damage at harvest.
IPM
Program evaluation
Every year, funding agencies ask for impact
information to justify continuing the UMaine Apple IPM Program. Please take a few minutes to respond to
the 9 questions being sent as a separate email.
Please mark your answers and use an email “reply to message”
to send them. Your help in providing
information for the annual report is greatly appreciated.
Harvest
weather influences
There are some associations between weather in the
weeks prior to harvest and optimum coloring, risk of preharvest drop, and storage
problems. Risk estimates based on
conditions at Highmoor Farm are updated daily at
http://pronewengland.org/AllModels/MEmodel/me-Monmouth-ChillHour.htm
Dr. Renae Moran and Patti
McManus will be providing information for maturity charts which I will include
in upcoming emails.
Honey
bee situation
Folks who attended the excellent Maine State Pomological Society annual
meeting and orchard tour at Peter and Diane Wallingford’s orchard in July
will remember the interesting discussion of the honeybee situation. Here is some follow-up information from
USDA.
Colony Collapse Disorder Action Plan
Colony Collapse Disorder
(CCD), a significant disappearance of honey bee colonies that may be affecting
bees in more than 22 states, threatens the production of crops dependent on
bees for pollination as well as honey production. Pollination is responsible
for $15 billion in added crop value, particularly for specialty crops such as
nuts, berries, fruits, and vegetables. Of the 2.4 million colonies of bees in
the United States, the almond crop in California alone requires 1.3 million
colonies, and this need is projected to increase significantly over the next
few years. The bee industry is facing difficulty meeting the demand for
pollination in almonds because of bee production shortages in California.
Consequently, growers depend increasingly on beekeepers from other states to
transport honey bee colonies across the country to meet the pollination
demand. If researchers cannot find
a solution to CCD, beekeepers will be unable to meet demand for this and other
crops.
The action plan
coordinates the federal strategy in response to CCD. It has four main
components:
(1) survey and data
collection needs;
(2) analysis of samples
to determine the prevalence of various pests and pathogens, exposure to
pesticides, or other unusual factors;
(3) controlled
experiments to carefully analyze the potential causes of CCD; and
(4) developing new
methods to improve the general health of bees to reduce their susceptibility to
CCD and other disorders.
Current theories about
the cause(s) of CCD include increased losses due to the invasive Varroa mite;
new or emerging diseases, especially mortality by a new Nosema species
(related to the microporidian giardia); and pesticide poisoning (through
exposure to pesticides applied for crop pest control or for in-hive insect or
mite control). In addition to these suspects, perhaps the most highly-suspected
cause of CCD is a potential immune-suppressing stress on bees, caused by one or
a combination of several factors. Stresses may include poor nutrition (due to
apiary overcrowding, pollination of crops with low nutritional value, or pollen
or nectar dearth), drought, and migratory stress brought about by the increased
need to move bees long distances to provide pollination services (which, by
confining bees during transport, or increasing contact among colonies in
different hives, increases the transmission of pathogens). Researchers suspect
that stress could be compromising the immune system of bees, making colonies
more susceptible to disease.
The CCD action plan is
online at http://www.ars.usda.gov/is/br/ccd/ccd_actionplan.pdf
A very handy book
Highmoor Farm’s
supply of the 238-page “Tree
Fruit Field Guide to Insect, Mite and Disease Pests and Natural Enemies of
Eastern North America” has been sold, but Dr. Renae Moran is ordering
20 more copies which will be sold at a bargain price of just over $20 (compared
to $32 + $6 shipping if you buy it online).
It wasn’t until
decades later that I appreciated why my oldest brother used to buy me his
favorite music albums for birthdays/Christmas when I was a kid. That way he knew the music would be in
the house for him to listen to. It was
a win-win situation because I got introduced to some great tunes at a young age
(all you Yardbird fans stand up and cheer!).
Now you can use that
strategy to buy this book for that special someone in your family. Imagine their joy when they realize you’ve
given them 500 full-color pictures of oldies but baddies like apple scab, fire
blight, stink bugs, and obliquebanded leafroller, along with lesser known
classics like pear slug and Fusicoccum constriction canker.
Or you can treat
yourself, you deserve it!
Happy Harvesting,
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