Resource Guide for Organic Insect and Disease ... - Cornell University

8 Organic Resource Guide
to female activity and cutting off all outer leaves before the winter leaves appear
in late season. Research in Ontario has shown that the use of lightweight floating
row covers can protect developing plants from leek moth damage. In small
plots or gardens, floating row covers work well. In the case of garlic, they should
be placed early in the season. The cover can be kept in place with a variety of
methods, e.g., trench and dirt, sandbags. The cover can be removed during the
day for weeding and then reinstalled before the leek moth flight in the evening
and early morning.
10. With garlic, remove and destroy the leaves and scapes of the garlic after harvest
and before drying, reducing the population of pupae that can be found in the
drying sheds afterwards.
Materials Approved for Organic Production:
Spinosad products have shown efficacy.
While many products are labeled for onions, in some states (like New York), the product label
must also list the pest species. In New York, Cornell was able to obtain special labeling (2ee)
for the use of Bt products and Entrust against leek moth. Field tests in Canada and greenhouse
tests in New York have shown that Entrust has worked well. In a greenhouse test at Cornell,
Bt products were largely ineffective. Because leek moth tends to be in sheltered parts of the
plant, coverage is very important.
CUTWORMS (many species)
Cutworms are occasional pests of onions early in the season. In some years, they cause major
losses, while in other years, there are no losses at all. Cutworms are the larvae of approximately
a dozen different species of night-flying moths. Most species that attack onions overwinter as
partially grown larvae that become active early in the spring when the onions are young and
susceptible. Cutworms hide in the soil during the day and crawl on the surface at night. They
feed and cut off young seedlings at the soil surface.
Cultural Control:
1. Since most species lay their eggs on vegetation in the late summer or fall, keeping
fields clean of weeds and crops in the fall helps. Fall plowing exposes larvae to birds.
Of course, this advice is counter to recommendations to keep soil covered.
2. Alternatively, delayed seeding in the spring can also be effective. Cultivating fields
in the spring, after vegetation has appeared and grown a few inches, can starve
cutworms before the onions are planted. A few shallow cultivations during this
“starving period” can expose cutworms to birds and other predators. Take caution not
to delay planting too long, as onions must be planted fairly early in order to be mature
enough to produce large bulbs when the long day bulb initiation signal is received in
June.
Materials Approved for Organic Production:
1. Entomopathogenic nematodes have shown good efficacy when environmental
conditions are favorable (warm, moist, but not soggy soil). Steinernema carpocapsae
has been shown to be very effective against cutworms, although reports are not
specifically in onion production. Success with nematodes depends on proper
application methods and good environmental conditions (moist soil). Irrigation may
be necessary to keep the soil moist for at least two weeks after application. Be sure to
carefully follow the instructions from the supplier.
2. Baits - Spinosad or Bt will kill the caterpillars, but getting the pest
to consume the insecticide as a foliar application before significant
damage is done is difficult. However, some farmers have reported
good results using these materials in baits. In order to rid the area
of pests, the bait is spread on the ground near the plants or prior to
planting.