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Scab
Most scouted orchards are
still showing very little scab. High mid-summer temperatures, natural
resistance in older leaves, and little new foliar growth all combine to hold
scab infections in check where control was established earlier. Where
there are numerous scab lesions, it would be worthwhile to continue protection
(such as captan applications at two week intervals) to protect fruit from
infection until lesions look completely dead (lack of fuzzy appearance
indicating presence of viable conidial spores). Actually, this is
impossible to confirm, but in the real world you can make a reasonable guess at
when lesions are no longer producing conidia.
Flyspeck
photo by Dan Cooley
Our understanding of flyspeck epidemiology is
still a work in progress. However, the best available estimate is that
flyspeck fungus has now had time to begin producing second-generation spores.
This increases the risk of flyspeck infections. Infections that start in
the next month would have adequate time to become visible by harvest as (usually
dime-sized) circular patterns of tiny black dots on apples. Flyspeck
can lead to downgrading of fruit, especially on varieties with large areas of
yellow skin. Thus, the next four weeks may be the most important period of
the year for protection against flyspeck.
Problems with flyspeck are most likely to occur where
there is a high-humidity microclimate. Large trees with thick canopies,
low spots in orchards, areas with wind blocks or poor air drainage, trees
surrounded by tall grass, and fruit on low hanging limbs are all factors that
increase the risk. Proximity to alternate hosts, especially wild raspberry
and other brambles, is another risk factor.
Flyspeck usually is not an important problem because
cultural prevention does much of the work, and fungicide protection at extended
intervals is adequate. The guidelines for flyspeck fungicide intervals are
described on page 88 of the 2003-2004 New England Apple Pest Management Guide.
You can refer to the Orchard Radar Flyspeck tables to
interpret those guidelines in context with this season's rainfall and
accumulation of leaf wetness hours. Research has shown that leaf wetness
hour accumulation can serve as a useful predictor for flyspeck development.
For example, at Highmoor Farm, the last fungicide
application was full-dose captan on June 23. The
Monmouth flyspeck table for captan and other Group B fungicides estimates
that protection from that application wore off around July 14, but that a
follow-up application with a strobilurin fungicide could be delayed until July
22. The table also suggests that if the June 23 application was the final
fungicide of the year, then based on observed and forecast leaf wetness hour
accumulation, flyspeck colonies could appear on apples as early as August 12.
The fungicide respray intervals are based on
observations in Hudson Valley where this disease is more of risk than at
Highmoor. Given their conservative nature, the estimates are not
compelling directives that fungicide coverage has to be renewed by a specific
date or else a flyspeck problem will develop. As guidelines though, they
are useful in making spray timing decisions.
Apple maggot
Apple maggot flies are on the move at Highmoor Farm. Between Thursday July
10 and Monday July 14,
traps in two blocks that have been unsprayed for several years far exceeded the
threshold of 5 flies per odor-baited trap. In two other blocks that are
under conventional IPM management, trap captures average 3 and 3.5 apple maggot
flies per trap during that 4-day period. I expect that by today those
blocks will also have reached threshold. A fifth IPM block averaged 1 AM
per trap during the July 10-14 period.
Each
block is unique with respect to apple maggot infestation pressure. Trap counts
allow delay and reduced number of applications where pressure is low. If
you don't have apple maggot trap data from your orchard, then this is the time
to begin insecticide coverage to protect against apple maggot egglaying, and
also against the various Lepidopteron pest species described below.
The
need for renewing coverage depends on accumulated rainfall and proximity to
harvest. There are apple maggot respray guidelines on the web for July and
August spray dates at the four Orchard Radar sites. (for example:
Monmouth - July spray dates)
Refer
to the New England Apple Pest Management Guide for appropriate insecticide
options, which include Imidan and Avaunt.
Codling
moth and other caterpillars
Every year just as I finish being amazed at the ability
of European apple sawfly to ravage an unprotected apple crop, along comes codling moth
to validate its status as the number one apple insect pest in North America.
Codling moth stings and fruit entries at the calyx and
stem ends have proliferated on unsprayed trees over the past three weeks.
As of today, 1st generation codling moth egg hatch is estimated at about 80%
complete. Organic growers need to continue protection from Bt or Entrust
applications for at least another week. (Codling
moth respray guidelines are online for Monmouth and the other Orchard Radar
sites).
Oriental fruit moth (OFM) and lesser appleworm (LAW) are other caterpillars that
feed inside developing apples. OFM and LAW, along with redbanded
leafrollers that feed on the surface, are beginning second generation moth
flights. Codling moth's other Lepidopteron relative, obliquebanded
leafrollers, are beginning second generation larval feeding at this time.
As with codling moth, OFM, LAW and the leafrollers are not normally a problem
where insecticide applications are made against plum curculio in June, and then
against apple maggot in mid-late July and August.
It has also become
apparent that lack of insecticide protection in late July and August can lead to
a build up of apple pith moth to the point where it is no longer a curiosity but
a major pest.
Imidan or Avaunt will
provide protection against all of these species. For organic growers,
repeated Bt applications should provide fair to good control of Lepidoptera but
will do nothing for apple maggot. Entrust will provide short term apple
maggot control, but is rated lower than Bt against codling moth.
European red mite
populations are still remarkably low this year. The fourth generation is typically the most abundant
generation of the year. Fourth generation nymphs are now visible in the
Sanford area, and will begin hatching over the next week in other Maine
locations.
The recommended treatment threshold for July 15
to August 15 is an average of 5 living hatch mites per leaf, or finding one or
more mites on 76% of middle-aged leaves. A mini-sample of 40 middle-aged
leaves is below threshold if 24 or fewer of those leaves have mites. A 40
leaf sample is over threshold if 38 or more of the leaves have living hatched
mites present. The full set of
mite
sampling threshold tables are online.
Plum Curculio
Plum curculio egglaying continued between July 10-14,
but at a reduced rate, and should be winding up over the next week. This
information is relevant only for organic growers using Surround. Plum
curculio in blocks where growers used insecticide applications at petal fall,
first and/or second cover were killed back then and remain dead to this day! |
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Trunk
Borers
The following
text is excerpted from a recent issue by Art Agnello in Scaffolds, the
Cornell University tree fruit pest newsletter. The full article with
descriptions of all four species is at
http://www.nysaes.cornell.edu/ent/scaffolds/2003/7.7.html#i3
*****************************
The Apple-boring beetles are some of the most difficult
fruit insects to control, owing to their concealment during the majority of
their developmental period. The following information is taken from IPM
Fact Sheet No. I-26, Apple-Boring Beetles:
Although the number of wood-boring beetles attacking fruit trees is
relatively small and their infestations sporadic, four species found in N.Y.
are capable of seriously damaging or killing trees when they do occur.
Taken in order of importance and pest frequency, they are the roundheaded
appletree borer, Saperda candida, flatheaded appletree borer,
Chrysobothris femorata, broad necked root borer, Prionus laticollis,
and tilehorned prionus, Prionus imbricornis. With the exception of
the flatheaded appletree borer, which is a buprestid (metallic wood-boring
beetle), they belong to the cerambycid (long-horned beetle) family, and the
last two are closely related species in the group known as Prionus root
borers. All are native to and widely distributed throughout the U.S. and
southern Canada. They all damage deciduous fruit and shade trees by
tunneling as larvae into the conducting tissue of the lower trunk, crown and
roots, and compound the injury by providing an entryway for destructive
fungi. There is a broad host plant range for each of these pests; plants
attacked by all four species include apple, cherry, peach, and plum, with
the roundheaded and flatheaded borers also occurring in quince, pear,
flowering crabapple, mountain ash, shadbush, cotoneaster and hawthorn. The
flatheaded borer and one or both of the two Prionus species are also serious
pests of numerous other trees, including pecan, hickory, poplar, willow,
chestnut, oak, maple, dogwood, linden, and several shrubs.
Adults
The adult roundheaded appletree borer is an attractive (to
some) beetle about 5/8-1 inch long, olive brown with two longitudinal white
stripes running the length of the body, gray antennae, which are stout,
many-segmented, and approximately body length; its legs are also gray, the
underside of the insect is silvery white, and its entire body is covered
with fine hairs that give it a neat appearance. This species requires 2-3
years to complete its development, depending on location; most (perhaps
two-thirds) occurring in N.Y. probably require 3 years. Beetles emerge
mostly at night through round, pencil-size holes from the bases of infested
trees over a period of 2-3 weeks, usually during mid-June in N.Y., although
they have been noted in the trees as much as a month earlier. After
emerging, the adult feeds on the leaves, twigs and fruit of host plants.
Mating occurs about one week after emergence, and the female lives
approximately 40 days, normally hiding by day and secretively laying eggs,
usually in young healthy trees. The female makes a longitudinal cut in the
bark with her mandibles near the base of the tree, inserting a single egg
between the bark and xylem, and cementing it in place with a gummy
secretion.
Larvae
The roundheaded appletree borer larva, a fleshy, cream-colored,
legless grub, is about 1/8 inch long upon hatching and 1 inch when fully
grown; it actually reaches nearly twice this length during its development,
but a considerable shortening occurs just prior to pupation. It has a dark
brown head and blackish mandibles. The first thoracic segment is broader
than the rest of the body, with a patch of brownish tubercles on the dorsal
(top) surface. The body segments are separated by deep constrictions, and
most have large oval spiracles on either side. This species passes through
six instars during the course of its larval development, moving upward or
downward in the trunk depending on the year and stage of growth, feeding on
the inner bark (or cambium) layer, and widening its tunnels as it feeds.
Some of the frass produced fills the tunnels, and some is pushed through
openings to the outside, where it accumulates in small piles and has the
appearance of sawdust at the base of the tree. By the end of its third
season of feeding, the larva has bored several inches straight up in the
trunk and constructed a pupal chamber just beneath the bark surface, within
which it passes its final winter.
Damage
The roundheaded appletree borer is considered to be the species of
boring beetle most destructive to fruit trees in N.Y.. Toward the end of
the 1800's it was deemed second in importance only to the codling moth as an
apple pest, and there was some speculation that it might cause the demise of
N.Y.'s apple industry. However, because of the adult's susceptibility to
pesticides applied against other pests in most commercial orchards, it is
found today mainly in abandoned, wild or unsprayed plantings. Trees of all
sizes are attacked, but those from 3-10 years old suffer the most.
Frequently, several larvae may be found in a single tree, which is enough to
completely girdle a young tree. Infested trees have a sickly appearance,
producing sparse, pale-colored foliage. Continued yearly attacks can kill
the tree or weaken so that it is broken off by the wind. Young trees that
have been girdled will often bloom profusely and set a heavy crop of fruit,
and then die in the process of bringing it to maturity.
Management
No single management method has been proven fully effective, and the
most successful efforts involve a combination of preventive and remedial
techniques.
o Cultural Practices: New trees should not be started in areas in
proximity to the borers' wild host plants, especially flowering crabs,
thorns, hawthorns or Amelanchier spp; destruction of any such plants
within 300 yards of the orchard will greatly improve this tactic. Keeping
the base of the trees free from rank growth of weeds, grasses, briars and
shrubs not only makes it easier to detect and remove borers, but also
exposes them to natural enemies such as golden and downy woodpeckers, ants,
and a (small) number of parasitic wasps and flies. Heavily infested trees
that are beyond recovery should be removed and burned before the following
spring to prevent developing borers inside from completing their life
cycle. Keeping trees in a healthy, vigorous condition is one of the best
preventive measures against attack by flatheaded appletree borer, especially
for newly transplanted trees. This is also a (somewhat less effective)
measure for Prionus root borer infestations; disease, drought, mechanical
injury, and poor soil conditions increase tree susceptibility.
o Foliar and Trunk Sprays: The adult population of the roundheaded and
flatheaded appletree borers can be reduced by application of the pesticides
commonly used to control plum curculio and codling moth in N.Y.,
particularly those applied at the beginning and end of June. Sprays of
broad-spectrum insecticides against Prionus borer adults are only partially
effective. However, with the supplemental label for the use of Lorsban 4E
in directed trunk applications against apple-boring beetles, homeowners and
commercial growers alike have a relatively effective option available for
managing the most damaging life stages of these insects. Moreover, the
middle two weeks of July would be an optimal window for this spray
application.
o Oviposition Barriers: In early May, protective coverings of various
materials can be wrapped around the bottom 12-24" of trunks (higher, up to
the level of the branches, for flatheaded appletree borer) to exclude the
female beetles from their preferred oviposition sites. Mosquito netting,
fine mesh hardware cloth, tree wrap, tarpaper, cotton batting, or even
layers of newspaper should be wrapped loosely around the trunk, tied at the
top with twine and covered at the bottom with soil. Barriers should be
removed in September, after all egg-laying activity is finished. An
alternative method is to paint the lower surface of the trunk using white
latex paint; this approach tends to work better on the smooth trunk surfaces
of younger trees, and should be repeated each year, as the paint layer tends
to crack with normal tree growth.
o Surface Deterrents: Additional protection from ovipositing females is
gained by applying a deterrent wash on uninfested trunk surfaces using a
paintbrush; an alkaline mixture of insecticidal soap plus caustic potash
(lye) mixed to the consistency of thick paint is recommended. This should
be applied every 2-4 weeks, depending on rainfall, from late May through
July to deter egg-laying of the roundheaded appletree borer.
o Trap Logs: A large number of flatheaded appletree borer adults can be
trapped out by placing posts or felled logs of almost any kind in the
orchard, either pounded in upright or simply lying on the ground and exposed
to the sun. These can be coated with tanglefoot to catch the beetles, or
else left uncoated until the egg-laying period is past, and then removed to
another site and burned.
o Worming: Destruction of the roundheaded appletree borer by hand is more
labor-intensive, but this can be the most effective measure, depending on
the magnitude of the infestation. During bloom and again in September,
inspect the bark surface for small pinholes with sawdust exuding from them,
checking the lower 24" of the trunk to just below the soil surface. Using a
sturdy knife, cut through the bark at any such points until the burrow is
reached; use caution not to further damage the tree. Insert a stiff wire
that is slightly hooked at the end, to reach and impale the borer if
possible. Soil insecticides and fumigants have shown some promise against
larvae of the Prionus borers, but none that are commercially available are
fully effective. Coarse trunk sprays of Lorsban applied for control of
other borers will provide some efficacy against these species as well.
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