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

2. Neem: Based on a limited number of studies, neem products gave good control of
many aphids (see the neem chapter for a discussion of the different types of neem
products).
3. Summer oils provide some control.
4. Rotenone is recommended in the older literature, but it is no longer registered as an
insecticide.
ASTER LEAFHOPPER (Macrosteles fascifrons)
The aster leafhopper is a greenish tan insect that looks dark from the top. It has six black spots
on the front of its head and is sometimes called the six-spotted leafhopper. This species has
been reported to overwinter as eggs in the north, but the major source is from jet stream
migrations from the southern United States. There can be three to five generations per year.
Aster leafhoppers feed on a wide variety of plants, beginning with early weeds and crops, such
as lettuce, winter grains, and early flowers. Later, they move onto summer crops, including
carrots, celery, and parsnips. When severe, leafhopper feeding distorts leaves, but it does not
cause economic damage in Umbels unless it carries the aster yellows pathogen. Aster yellows
is caused by a mycoplasma-like organism transmitted by leafhoppers, especially the aster
leafhopper (see below for details on the disease). Adults migrating from the south may have
acquired the aster yellow mycoplasma during the previous season. To acquire the mycoplasma,
the leafhopper must feed on an infected plant for at least eight hours; the pathogen must then
incubate in the leafhopper for about three weeks before it can be transmitted to another plant.
A feeding period of eight hours is also required to transmit the disease to a new plant.
Cultural Control:
Managing leafhoppers in carrots and other crops in this family is only important if they are
carrying the aster yellows pathogen. If aster yellows has been a problem in a given area,
managing weeds may be useful. Common weed hosts include thistle, fleabane, wild lettuce,
sow thistle, chicory, wild carrot, galinsoga, dandelion, plantain, and cinquefoil.
Materials Approved for Organic Production:
Spraying for the aster leafhopper should be based on monitoring with sweep nets; however,
monitoring is only important if the pests are known to be carrying the aster yellows pathogen.
There is no a quick and easy way to determine if they are infected. Some states with
commercial production of susceptible crops (e.g., Michigan) monitor for leafhopper numbers
and infectivity levels.
1. Pyrethrum has been shown to control leafhoppers.
2. Surround is labeled for leafhoppers, but has shown mixed results.
PARSLEYWORM (Papilio polyxenes)
The parsley worm is a caterpillar with black and white banding and yellow spots along the
black bands (Photo 9.3). The larva of the black swallowtail butterfly, it is a voracious feeder on
parsley, dill, fennel, and occasionally carrots. It spends the winter as a pupa (chrysalis) attached
to trees, buildings, etc. In mid spring, adults emerge and lay eggs singly on plants in the carrot
family. The caterpillar feeds for about 3 weeks. Since this insect is a valued bit of natural fauna,
and the pest never builds to large numbers, moving it to a non-crop host is the best option for
control.
WEBWORMS
Webworms are more of a problem in the south and west than they are in the Northeast, but
occasionally the garden webworm (Achyra rantalis) or the alfalfa webworm (Loxostege sticticalis)
reaches levels of concern in New York and New England (Photo 9.4). Webworms begin feeding
on the underside of a leaf, and as they get larger, they eat through the leaf, creating large
notches or holes. As their name implies, webworms spin webs among the leaves (Photo 9.5).
Damage from young or small numbers of webworms may go unnoticed, but as the larvae mature,
they can consume leaves rapidly and destroy a whole crop. Webworms overwinter in the
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