Organic Program Notes
PO Box 1555, Ventura, CA 93002
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Lygus – tarnished plant bug, Lygus sp.
Habitat strip to attract and focus biological control
Alfalfa strip with Daikon radish, mustard (low growing seed), sequence of bean plantings-such as black eyed peas to attract lygus.
Succession plantings every 2 weeks to keep plants available producing seeds in milk stage, which is most attractive for lygus adults to deposit their eggs and feed their primary predator the big-eyed bugs Geocoris spp.
Maintain by cutting older alfalfa, maturing plants as they become less attractive to lygus.
When lygus numbers high, vacuum lygus using 2 stage screen, 16 mesh (threads/inch) (window screen) and 90 mesh. Release the wasps and small insects in the 90 mesh and dispose of insects in 16 mesh, releasing ladybugs and other large predators.
Alternately run chickens through the strip to harvest insects. You can use cages like a chicken tractor, or movable electric fencing to keep chickens in, predators out.
As lygus numbers build in the habitat strip, everything that eats lygus will show up, so you may not need to do anything. Lacewing can be introduced early in the season to increase the number of predators.
Diabrotica – cucumber beetle
Tachinid fly, Celatoria diabrotica, parasite on adult beetles. Plant flowers to attract hover flies and tachinid flies, especially umbels like dill.
Heterorhabditis sp., Hb or Hm or Hi nematodes are parasite on larva in soil known as corn root worm. Larva lives on the roots of warm season grasses.
As you reduce numbers of Diabrotica, the percentage parasitized will probably go up. There are records of over 60 percent parasitism of adult weevils. I find that general predators in alfalfa reduce the populations of larvae in the soil. The adults migrate into the fields from weed in unfarmed areas and when harvesting fields from miles around. These concentrated populations migrate to vegetables when hay is harvested. Alfalfa is a trap for these populations when it is strip cut early in the spring because they are not driven from the alfalfa when solid field cutting is routine. It is a little more trouble but when the process is the paradigm, hay production is increased because the field must be more quickly harvested in order to irrigate the half grown strips. Often an extra cutting of hay results. If you made seed in the fall, and the seed chalcid was under natural biological control, it would be a win—win situation.
OF COURSE AUGMENTATION OF LACEWING AND LADYBUGS FOSTERS BETTER BIOLOGICAL CONTROL AND GUARANTEES THE MAXIMUM BENEFICAL EFFECTS FROM THESE GENERAL PREDATORS!
Larva on leaf, in soil
Collops larvae is predator of Diabrotica larvae (root worms) and alfalfa weevil
Hooded beetle and other Anthicidae larvae are predators of flower thrips and weevils
Theravid or stiletto fly, larva is predator along with
Many species of rove and ground beetles; Staphlinidae and Carabidae.
Heterorhabditis sp. Nematodes parasite on larva
Sheep off (graze with sheep) first cutting, sheep eat larva in top of plant
Look for overwintering weevils under bark of trees near fields. May be able to use Heterorhabditis sp. Nematodes to decrease numbers
My personal experience with biological control of alfalfa seed production is limited to the low desert of California where seed is generally produced early in the season using the second cutting. This is largely chosen to avoid the alfalfa seed chalcid, Bruchophagus roddi (Gussakovsky). This insect is a major pest of seed production but of little importance in hay production. There are several generations and they emerge from the seeds in greater numbers as the season advances.
Making hay and removing the alfalfa stems before the seed enters the milk stage is physical control of this pest.
During our work monitoring the spotted alfalfa aphid, (SAA) and the exotic parasites that were introduced from the middle east, we focused our attention on strip farming alfalfa hay. Every other land was cut and harvested each irrigation cycle. This was a way to keep the parasites active in the participating farmers fields rather than sending them down wind to the next alfalfa when the fields were solid cut.
We vacuum sampled our fields monthly and counted every kind of insect that we found and identified them with their function in the process of making hay. However one of our farmers decided to go deer hunting in the fall and dried up his field to make seed. We continued to monitor the insect populations and discovered that seed chalcid had many primary parasites attacking them and they were not a serious pest or a deterrent to making seed profitably. While the chalcid is extremely difficult to control chemically, it is vulnerable to natural biological control, at least under this one experience. Our farmer explained that he regularly went deer hunting in the fall and this rotation to seed allowed him to do it. Lygus was also not a problem because the strip cutting process enhanced biological control of all alfalfa pests including alfalfa weevil which has benefited from importation and establishment of several species of Bathyplectes and parasites of the adult weevils (Microtonus spp.). A fungus also attacks the weevils when moisture is high.