Managing late season grape berry moth
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
With
this hot summer, berry moth development is moving along quite rapidly.
Recent observations of grape clusters have revealed increasing levels of
infestation by grape berry moth larvae, and this reflects infestation
by the second generation that layed eggs during mid-late July. The grape
berry moth degree day model is also predicting the start of egglaying
by the third generation (1,620 GDD) of this pest this week for many
regions of southwest Michigan. This is almost two weeks earlier than
during 2009, but with this warm season, the start of the third
generation at this timing just in advance of veraison suggests that moth
phenology is tracking vine development quite closely. Overall, berry
moth pressure is higher than last year, and management of this pest
during the next month before harvest is critical to ensure that fruit
infestation by insects and the associated diseases are not a problem
facing growers, processors and wineries. With many Niagara vineyards
being harvested after Concords, plantings of this variety will also
require more attention than is typical.
Scouting is critical at this time of the season to identify vineyards
that require protection from grape berry moth through the rest of the
season. Growers with vineyard blocks that have a history of infestation
by this pest should take the time to walk through those blocks and
assess the level of infestation before deciding whether a spray is
required. In vineyards with very low infestation or where early-season
frost damage removed most of the crop, the time and expense of a
pesticide application is not warranted at this time of the season.
Insecticide applications should be limited to vineyard borders where
berry moth pressure is highest, to blocks where infestation is
developing and a crop will be harvested. With regular vineyard scouting,
growers can continue to monitor this pest and make decisions on whether
pest populations warrant insecticide control as we go through August
and into September.
Maintaining control of grape berry moth requires a combination of good
timing, high insecticide activity and excellent cluster coverage. This
update will cover each of these issues.
Timing
The late summer generation of grape berry moth typically starts laying
eggs in the period just before veraison with increasing egglaying
through August and into September. This late-season generation can lead
to infestation of harvested clusters and can expose clusters to fruit
rots, making it important to reduce injury from this generation. Using
crop growth stages provides some adjustment for variation between the
seasons, but we also now have the degree day model at www.enviroweather.msu.edu
to help refine these timings and ensure optimal timings for control
sprays. The model is predicting the start of third generation grape
berry moth this week in southwest Michigan. With fewer degree days up
north, this point in the insect’s development is expected to be reached
by the middle to end of next week. This is the predicted start of the
third generation egglaying, a timing that is appropriate for growth
regulator insecticides such as Intrepid. Growers planning to use a
broad-spectrum insecticide should wait for 100-200 growing degree days
before applying insecticide to ensure that applications target eggs as
they hatch, and so the residual doesn’t decline before egglaying peaks.
Follow-up application may be needed to maintain control in areas with
very high pressure.
In 2010, our degree day accumulations are so far ahead of normal that
there is potential for some late-season activity of grape berry moth (a
partial fourth generation). The risk of this is lessened by the insect
population naturally being triggered by shorter day lengths to enter
diapause, where the larvae develop to a pupa, but do not emerge again as
adults. Instead, they prepare for the cold winter months and drop to
the vineyard floor. During very warm years, some of these larvae may use
the warm conditions to bypass the diapause and attempt a fourth
generation. We will continue monitoring this pest through August and
September to determine whether a fourth generation is possible.
Insecticide activity
When selecting an insecticide, there are many options for berry moth
control. Some of these are selective for this pest, while others will
also provide control of leafhoppers, Japanese beetles and other insects
that can occur at the same time. For details of registered pesticide
options, consult MSU Extension publication E-154.
The selective insecticide Intrepid has shown good effectiveness against
berry moth in small plot and vineyard-scale trials, and we have tested
it in the mid-season timings in July and August at the 12 oz rate and at
8 oz/acre. Although this is more expensive than many standard
insecticides, the product lasts a long time (two to three weeks
depending on the rate) and is resistant to wash-off. This helps make it
an effective tool to use against the high pressure of egglaying by berry
moth seen late in the season, when maintaining control would otherwise
require multiple sprays. This works on the molting system of the moth
larvae and therefore allows biological control to remain active.
However, because it is selective, Intrepid will not control leafhoppers
or beetles. It also has a 30-day PHI, so many growers have been using
this in their programs a month or more before harvest to protect
clusters while they get ready for the harvest activities. Use of
Intrepid has also reduced the number of infested berries and the number
of diseased berries in samples taken at harvest. Intrepid is quite
stable under hot conditions and resistant to wash-off once sprayed
providing good residual control.
There are many broad-spectrum insecticides available for berry moth
control, including a number of pyrethroids that provide inexpensive
control and that have broad insect activity. These provide effective
control of moths, eggs, and larvae of grape berry moths. They have
relatively short residual control in the hotter summer weather when
growers might be spraying for the third generation of grape berry moths.
In our trials with Danitol, Baythroid, and Capture, the lower rates of
these products declined in activity against grape berry moth after nine
days. If using a pyrethroid to control grape berry moth along with
Japanese beetle in the hot sunny conditions of August, using the full
rate will provide the best residual control, but no more than 10-14 days
control should be expected. Despite the temptation to look only at the
price per acre when making decisions, be sure to rotate this class with
other chemical classes to avoid resistance developing. This means that
growers should rotate out of this group of insecticides (Baythroid,
Danitol, Capture, Mustang Max, or any generic pyrethroids) and use an
alternative chemical class the next time an insecticide is used. Sevin
or Imidan (buffered to pH 6) are both in different chemical classes. Be
aware that Imidan now has a 14 day re-entry interval in
grapes. There are also many effective reduced-risk insecticide options.
These include Intrepid that was mentioned earlier, and also Altacor and
Belt that have high activity on moth larvae. Altacor has also
demonstrated activity on Japanese beetles in recent trials this summer,
reducing feeding damage to leaves, and it provides control of grape
berry moths with a 3-4 oz rate with a 14-day pre-harvest interval.
Assail is a neonicotinoid insecticide that has moderate activity on
grape berry moth and will also provide control of leafhoppers and
Japanese beetles.
Coverage
Getting cluster coverage with your spray material is
essential for berry moth control. This is important for getting full
activity from broad-spectrum insecticides and even more important if
applying any of the newer chemistries that must be eaten to be
effective. As the canopy becomes denser after bloom, increase the water
volume and slow down to ensure the pesticide has a chance to contact the
pest. Juice grape canopies have many layers of leaves during the late
summer, making it hard to penetrate to the clusters, but this is
essential if the insecticide is to work against grape berry moth. If the
spray doesn’t hit the cluster, a significant investment of time and
money is being wasted. Spraying every row is another important component
of ensuring that your clusters are well covered.
To illustrate this, our research in a mature Niagara vineyard found that
an airblast sprayer operated at 20 gallons of water per acre gave only
half the control of grape berry moths in August compared with one
running at 50 GPA. We have also seen that vineyards treated using
alternate row spraying at 20-30 gallons of water per acre have poor
control of berry moth, likely due to the spray material not reaching
both sides of the clusters.
One way to test your coverage is to spray water or SURROUND WP kaolin
clay through the sprayer in a test run. Immediately after spraying (with
water) or after the spray has dried (for the kaolin), lift the canopy
of the sprayed and adjacent rows to see where the material hits the
cluster. If there are untreated berries, these are sites where a berry
moth larva could avoid the treatment and survive. These results
emphasize the need to calibrate your sprayer and adjust through the
season to ensure it is getting good cluster coverage, because it can
make a big difference for control.