How to Manage Pests
UC Pest Management Guidelines
Scientific Name: Therioaphis maculata
(Reviewed 11/06, updated 4/08)
In this Guideline:
The spotted alfalfa aphid is a small, pale yellow or grayish aphid
with four to six rows of spined black spots on its back. Mature females may
either be wingless or have wings with smoky areas along the veins. This aphid
prefers warm weather and is generally found during summer months. In the
Imperial Valley, high populations may continue into fall and winter.
Spotted alfalfa aphids inject a toxin into the plant as they feed.
Severe aphid infestations stunt plants, reduce yield, and may even kill plants.
These aphids also secrete large quantities of honeydew. Plants become very
sticky at relatively low aphid densities, and a black fungus that grows on the
honeydew excreted by the aphid reduces palatability to livestock and lowers the
alfalfa's feed value.
The use of resistant varieties and encouragement of natural enemy
populations help to control spotted alfalfa aphids. Border harvesting or strip
cutting can be important for preserving natural enemies. In the event that host
plant resistance fails or natural enemies do not hold aphid numbers below
economic threshold levels, insecticide treatments may be necessary.
Planting alfalfa varieties resistant to spotted alfalfa aphid has been
the most effective means of controlling aphids in alfalfa. However, biotypes of
spotted alfalfa aphid that are capable of infesting previously resistant
varieties are constantly evolving, and even fields planted to resistant
varieties should be checked frequently. When selecting varieties, consult your
farm advisor for information on varieties suited to your area, or check the current leaflet Winter Survival
Fall Dormancy & Pest Resistance Ratings for Alfalfa Varieties from the National Alfalfa Alliance Web site.
Additionally, a yearly alfalfa variety report can be found at http://alfalfa.ucdavis.edu.
Biological Control (View
photos of natural enemies)
Common reddish lady beetles, including the convergent lady beetle,
attack and consume this aphid. Green lacewings can also be important in
regulating aphids and many other predators including bigeyed bugs (Geocoris spp.), damsel
bugs (Nabis spp.), and syrphid
flies also play a role. An introduced parasite, Trioxys complanatus, has become established on the spotted alfalfa
aphid. Brown aphid mummies attached to leaves and stems of alfalfa plants
indicate the presence of this parasite. Caution should be exercised in treating
for aphids when the parasite is present.
Use border-strip cutting during harvest to help maintain populations of
parasites and predators within the field. (For more details, see BORDER-STRIP HARVESTING.)
Organically Acceptable Methods
The use of resistant varieties and biological and cultural controls are
acceptable to use on an organically certified crop. Organically certified
insecticides such as azadirachtin (Neemix), neem oil (Trilogy), and pyrethrin
(PyGanic) are registered for use on alfalfa to control aphids but studies have
not been conducted in California to determine their effectiveness.
Monitoring and Treatment Decisions
It is important to sample all fields, even
those with resistant varieties, frequently during periods of maximum aphid
activity. Start sampling for spotted alfalfa aphid in June and continue until
fall. To combine monitoring with cowpea aphid see APHID
In addition to monitoring aphid
populations, also take sweep net samples for lady beetles and record all counts
on a monitoring form .
|Time of occurrence
||No. of aphids per stem
||40 aphids per stem*
||20 aphids per stem*
|After last cutting in the fall
||50 to 70 aphids per stem
|Newly seeded alfalfa in lower desert
||20 aphids per stem
*Do not treat if the ratio of lady beetles to aphids is equal to or
exceeds the following:
|No. of lady beetles per sweep
||No. of aphids per stem
|ON STANDING ALFALFA
|1 or more adults
||5 to 10 aphids
|3 or more larvae
|1 or more larvae
|The following materials are listed in order of
usefulness, taking into account efficacy and impact on natural enemies and
honey bees. When choosing a
pesticide, also consider environmental impact. Not all registered pesticides are listed. Always read label of product being used.
|Note: The following materials have not
been tested under California conditions but have been found to be effective in other areas.
||MODE OF ACTION: An organophosphate
(Group 1B)1 insecticide.
||COMMENTS: Do not make more than 4 applications/year or apply
more than once per crop cutting. Do not apply when bees are present. Avoid
drift and tailwater runoff into surface waters. Preharvest interval is 7 days
for cutting and grazing when 0.5 pt/acre used, 14 days for 1 pt/acre, and 21 days for rates above 1 pt/acre.
||MODE OF ACTION: An organophosphate (Group 1B)1
||COMMENTS: Check label to see if product allows only one application
per year or per cutting. Do not apply when bees are present.
UC IPM Pest Management Guidelines:
UC ANR Publication
Insects and Mites
C. G. Summers, Entomology, Kearney Agricultural Center, Parlier
L. D. Godfrey, Entomology, UC Davis
M. Rethwisch, UC Cooperative Extension, Riverside County (Blythe)
D. R. Haviland, UC Cooperative Extension, Kern County
P. B. Goodell, Entomology, Kearney Agricultural Center, Parlier
R. F. Long, UC Cooperative Extension, Yolo County
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