Integrated Pest Management (IPM) in Apple Orchards

Fruit growers do their best to assure consumers
their food is grown in ways that are environmentally, socially and economically sustainable. Regular field scouting and weather monitoring
are key to achieving the production goals of conserving soil and water, reducing pesticide
use, and being good, responsible employers. In this short video, you will learn some basic
orchard scouting principles for a common disease – apple scab – and also mite pests and
beneficials. Weather stations provide site-specific data
on temperature, rainfall, relative humidity, leaf wetness, and degree days to alert you
when conditions are favorable for diseases and insect pests. Routine inspection of trees and the use of
pheromone traps to determine thresholds will help you minimize and better time sprays. Penn State is known for its early work on IPM for biological control of European red
mites. European red mite is a major pest of apple
if controlled only with miticides. With 8 to 10 generations per year this pest
can build in numbers very quickly and has historically been able to develop resistance
to many new miticides in only 3 to 5 years. If biological control by predators is conserved, European red mite is a sporadic, minor pest that is relatively easy to control
with only an occasional selective miticide application, and miticide resistance is not
an issue. A quick way of determining mite levels in your orchards is to use a magnifying hand
lens or a headpiece magnifier to determine the percentage of mite-infested leaves. Select 10 trees in the orchard on the most
susceptible variety and count 10 spur leaves from each tree for
the presence or absence of mites. Then use this graph to determine the mite
threshold level. As a general rule in apples, a spray threshold
of only 2.5 mites per leaf exists early season before June. The threshold increases to 5 mites per leaf
from June through mid-July Use a threshold level of 7.5 mites per leaf
through the rest of the season. If the mites per leaf do not reach
these levels, no control action needs to be taken.
Orchards with stable populations of T. pyri never reach these thresholds as long as there
is at least 1 predatory mite for every 10 pest mites per leaf. Our current population of T. pyri probably
came to Pennsylvania on apple bins moved between states or on nursery stock. A program developed by Penn State and funded
by the USDA conservation programs moved T. pyri from known “seed” orchards
to many new grower orchards and over 80% of Pennsylvania apple orchards
have this predator present at some level. Where conserved, T. pyri has reduced the use
of miticides by over 90%, and some growers have not sprayed mite-susceptible varieties
for more than 10 years. Establishment of T. pyri into orchards where
it is absent is relatively simple and can be accomplished in 1 to 2 seasons once “donor”
orchards with abundant T. pyri populations have been identified as a source. Transfers of T. pyri from these orchards can
be successful by physically moving spur leaves in May and June. Transfers after July appear to be less likely
to establish populations. If not controlled, apple scab can cause losses
of 70% or greater where humid, cool weather occurs during the spring months. Losses result
directly from fruit infections, or indirectly from repeated defoliation which can reduce
tree growth and yield. The pathogen generally overwinters in fallen
leaves and fruit on the orchard floor. As a result, orchards are self-infecting. Primary spores develop during the winter and
begin to mature early spring. Around bud break, the first mature spores
will be released from the infected leaves and/or fruit. The length of time required for infection
to occur depends on the number of hours of continuous wetness and the temperature during
the wetting period. Leaf wetness hours can be calculated by either
beginning the count at the time leaves become wet and ending the count when the relative
humidity drops below 90% or by adding consecutive wetting periods (hours) if the leaves are
again wetted with 8 hours from the time relative humidity dropped below 90% For example, if the average temperature is
between 61 to 75 °F, a minimum of 6 hours of leaf wetness is required for spores to
be dispersed. Once the primary spores have established infection on the plant tissue,
in approximately 9 to 10 days symptoms can be observed. At that time, secondary spores called conidia
are being produced and will do so the remainder of the season, being dispersed by rain or
wind on susceptible tissue. Monitor rainfall and duration of wetness closely beginning at green tip since mature spores
begin to be released around this time. Peak mature spore release is around bloom time
through petal fall. Continue to monitor rainfall and duration
of wetness through mid-June as the final mature spores are released during this time. Start monitoring for lesions (spots) around 10 to 14 days after bud break, which is when
the first symptoms can occur if disease conditions are favorable. For each orchard block, follow a “W shape”
pattern within the block when scouting. Evaluate 10 trees by examining 20 leaves on each of
5 limbs per tree and record the number of leaves showing any scab lesions. 1. Begin with the flower bud (spur) leaves where
early infections are most likely to be noticed. 2. Start with observing the undersurface of leaves
since the undersurface of leaves may become spotted before the top surface. Take notice
of early lesions which may be small, light brown-black spots.
3. As scouting continues during early spring, be sure to observe both the topside and underside
of the leaf. Apple scab infection appears as brown velvety lesions, which will become
darker as they age. After fruit have set, in addition to leaf
observations, examine 20 fruit on each tree and record the number showing any scab lesions.
Use this information to better manage scab in the future. It is important to scout and control apple scab early in the season to prevent secondary
infections from becoming established. Even if you have a professional consultant
who monitors your orchard, it is important to become knowledgeable about basic principles
of integrated fruit production. Penn State Extension offers educational programs on current
best management practices in nutrition, pruning, tree training, crop load management, farm
employee health and welfare regulations, food safety practices, and IPM. For a list of courses,
visit Penn State Extension Tree Fruit Production website, and for timely recommendations, sign up for
Penn State Extension Fruit Times.

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