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AgAlerts 2001 From Griggs County
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Issue # 10, August 3, 2001
Several calls to the office concern the
yellow butterflies that are in large numbers throughout the county. These
are alfalfa caterpillar butterflies. They feed on alfalfa and sometimes
can migrate to soybeans. At this time they are mating and laying eggs on
alfalfa or soybeans.
In alfalfa, the caterpillars are often controlled adequately through timely cutting, naturally occurring diseases, and several parasitic wasps; thresholds for treatment are relatively high at 10 larvae per sweep. Another method for assessing the need to treat is counting larvae per plant. Using this approach, the treatment threshold is one caterpillar per two plants. If many diseased or parasitized caterpillars are observed, relative to healthy caterpillars, control may not be warranted.
In soybeans, this caterpillar should be considered along with others when assessing whether treatment thresholds of 20% defoliation during flowering or pod set might be reached. This defoliation level could occur when 4 to 8 larvae per row foot is found.
Click for more information on alfalfa
caterpillar's.
(click on photo to enlarge)
Sunflower beetle, thistle caterpillars and
banded sunflower moth continue to cause problems in sunflower. Monitor
fields for feeding damage. Treatment should be made for sunflower beetle
if 10-15 larvae are found per plant and 25% defoliation has occurred.
Confection growers should monitor for banded sunflower moth and red seed
weevils.
There is also an new insect that might have an impact on seed
quality. Lygus are most noted for being a pest in seed production
of many crops. Their preference for food is meristematic tissue, embryonic
tissue or new growth of any kind. Lygus insert their mouthparts into the
host and start a "pre-digestion pump" to inject saliva and start
digestion, then suck the fluid into the stomach. This is where the injury
originates. The saliva is toxic to plant tissue, helping reduce the plant
fluid into a digestible source. The result in sunflower seeds is the brown
to black spot due to tissue death at that feeding site. There is still
much to learn about lygus and sunflowers in this region. In the mean time,
to minimize the damage which result in a quality reduction, a general approach
to protecting sunflower from Lygus and other seed feeding insects is
recommended. Any grower who is on a program to control red seed weevils
should be able to control Lygus. Currently NDSU Entomologists are
suggesting two treatments are needed to sufficiently protect confection
sunflowers from insect feeding. One application at the onset of pollen
shed followed by a second treatment 7 days later. The same insecticides
used for seed weevil or banded sunflower moth will work for Lygus.
Reports of grasshoppers migrating from newly cut hay fields or CRP into cropland. At this time these fields have not been treated but numbers are up from last year. Monitor fields next to CRP or haylands for damage.
Recent rains have created the perfect environment for mosquito's. The NDSU Extension Entomology department has written an excellent publication to address mosquito life cycles and control measures. This publication can be obtained from any NDSU Extension office or on the NDSU Extension web page. The publication is "Mosquito Management", E-472, December 2000. This publication lists the various biological and chemical controls available to the home owner.
White mold is starting to show up in canola fields around the area. Fields that were treated with a fungicides are showing reduced infection levels. Yield losses will depend on the time and amount of infection. The following pictures show various degrees of infection.
(click on photo's to enlarge)
Please Contact Our Office For Additional Information
E-mail: griggs@ndsuext.nodak.edu
Go to the 2001 AgAlert Index Page