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Strawberry Plasticulture March 3, 2003
Volume 4, No. 10
Strawberry Mites and their Management in Berry Fields: Do I have
Mites!!!!
Dr. Kenneth A. Sorensen
Extension Entomologist
North Carolina State University
Some questions asked about mites with comments.
With the low winter temperatures this year will mites survive?
Yes. Mites are present and exist in Canada, Europe and in areas of the
North in the United States. They can and will survive winter temperatures
well into single digits. They pass the winter as eggs in microhabitats
and as adults who have metabolized nutrients in the fall and converted
them to alcohol (antifreeze). Fluctuating temperatures are more detrimental
to mites and they get “tricked” into converting to spring
too early. This happens with trees and strawberries in those years.
In 2003 things are sitting tight and should break at a proper time.
Do I have mites and how can I be sure?
Assume you have mites! But check plants for mite stages using a 10X
hand lens. You can also use a dissecting microscope. Several county
extension offices have these scopes and can assist you. We looked at
leaves from 5 sites in Rockingham County this week and only found one
mite and several aphids (living and dead). I looked at several leaves
last week at a field in Wake County and only found aphids living.
How do take a sample for mites?
Remove the older leaves laying flat on the plastic. Do not examine new,
unfolding leaves. You can mix the sample with old lower leaves and old
leaves in the middle of the plant. Mites at this time have been confined
to the older leaves contacting the black plastic around the base of
the plant where temperatures are the highest.
How many mites or plants containing mites means I need to do something?
As a rule 5 % of the plants with mites means be prepared to spray. It
is not necessary to count all the mites on a leaf, but rather just presence
or absence of mites is sufficient. Be sure to record the number sampled
with the date.
Should I take samples every week?
Only if you want to stay completely on top of mite development. Sample
and when 5% level is reached monitor the weather and get the sprayer
ready and the miticides out.
Why monitor the weather?
Mites can pass through a complete cycle (adult to adult) in about 7
days at temperatures of 80 and 50 day / night. Warm weather, bright
sun, low wind and no rain are favorable for mite development. The degree
of favorable conditions and the duration will determine how fast mites
will build up.
Why worry about mite build-up?
Once mites are completing cycles within the population you have all
stages overlapping and the effectiveness of miticides and the frequency
of applications and the spray intervals will change and the level of
control will vary and never be complete. Once you have mites and webbing
and damage to the foliage you are behind the 8 ball, the fire is ragging
and the horses are out of the barn! To prevent this from happening with
mites keep weekly records, monitor the weather and spray and pray!
Which miticide is the best?
The one that works. All miticides have their place and you must select
the one that fits your situation at the time. Acramite is the new one
with unique chemistry and has not been used so resistance should not
exist. It also is effective against all mite stages and has good residual
activity. Try it and order early so your dealer has it on hand. Savey
is another new miticide that has ovicide activity. It can only be used
once a year. Then there is AgriMek, Kelthane, Vendex and etc. AgriMek
label indicates two applications. Kelthane is an old miticide that still
works when not over used. Vendex is a selective miticide but it is slow.
Where do I find out how to use a miticide?
The label is the best source of information. For service consult with
County agents, University Specialists, ask your dealer and ask your
neighbor. Your experience counts too. Read spray guides and refer to
handouts from meetings and various newsletters.
Help. I have difficulty in selecting a miticide.
Several factors can influence your decision. Experience, availability,
cost, formulation, safe to the applicator, safety to good mites and
insects, safety to the environment, size of container, shelf life, time
limitations to harvest, re-entry interval, compatibility with other
sprays, pH of my water, class of miticide, mode of action, when used
last in my field, resistance level of mites in my field etc. It is not
easy and simple to select one. But you gather information, integrate
that information and make the best choice at the time.
Best advice for now:
For now the best advice is to check those fields, select the leaves,
and examine for mites. Take leaves from 100 plants in your field. Only
sample until you find 5% of those leaves infested. Once you find 5 leaves
with mites, you know you have mites. Additional counts can indicate
what areas of the field have mites. If you map this out, you could spot
treat in those areas only that have mites. Mites and mite populations
do start in hot spots in the field and you usually know where they are.
Also monitor around edges of fields and even check a few of those broadleaf
winter annual weeds. Keep records. Spray if needed and follow-up with
more samples after 5 days to see how good you did and whether you need
another spray.
We will have more to say about miticides and their application in
the next newsletter.
E. Barclay Poling, Small Fruit Specialist
Campus Box 7609
Kilgore Hall - Office 252
NC State University
Raleigh, North Carolina 27695-7609
919.515.1195
919.515.2505 (fax)
919.418.9687 (mobile)
web site:
http://intra.ces.ncsu.edu/depts/hort/berrydoc/
click HERE
to return to strawberry advisories page
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