Biology Reference
In-Depth Information
alyssum, blue flax, campanula, carnation, colum-
bine, coreopsis, cosmos, delphinium, foxglove,
geranium, larkspur, nasturtium, pansy, petunia,
poppy, portulaca, pyrethrum, scabiosa, Shasta
daisy, stock, strawflower, veronica, and zinnia.
In beets there are clearing of veins, leaf curl-
ing, with sharp protuberances from veins on
underside of leaf, increase in number of root-
lets. In tomato, where the disease is called
western yellow blight or tomato yellow, seed-
lings turn yellow and die. Older plants show
twisting and upward rolling of leaflets, stiff
and leathery foliage, with leaf petioles
curling downward; branches and stems are
abnormally erect; the whole plant is dull yel-
low, often with purple veins; roots are killed,
few fruits formed.
In cucurbits, tips of runners bend upward; old
leaves are yellow, tip leaves and stems abnor-
mally deep green. In beans, there is a thickening
and downward curling of first true leaf, which
becomes brittle. The plant stops growing and
may die. Older plants survive until the end of
the season, with puckering and downward curling
at the top of the plant, reduction in size of new
leaves, shortened internodes.
Ornamentals grown near diseased beets are
usually infected. Zinnias have shortened inter-
nodes, chlorotic secondary shoots arising from
leaf axils. Cosmos leaflets are twisted and curled,
petioles bent down. Geranium leaves are chlo-
rotic between veins with protuberances on lower
surface.
The virus is confined to phloem in plants and is
transmitted by the beet leafhopper (
Circulifer
tenellus
). The insects winter on weed hosts, lay-
ing eggs and maturing the first generation there
before migrating in swarms, often hundreds of
miles, to sugar beet fields. When the beets are
plowed out, the hoppers migrate to neighboring
gardens.
Control
Destruction of weed hosts helps some-
what, as does early planting. There are resistant
varieties of sugar beets, none of table beets.
Tomatoes are sometimes protected with tempo-
rary muslin tents. Infected plants must be
destroyed.
Beet Distortion Mosaic Virus
Transmitted probably by a fungus
Polymyxa
betae
; spreads in California.
Beet Latent Virus
A symptomless virus in beets.
Beet Mosaic Potyvirus
On sugar and table beets, spinach. Discrete yel-
lowish lesions, then chlorotic mottling, darkening
of vascular tissue; leaves bend back near the tips,
which sometimes die. Transmission is by pea,
peach, bean, and other aphids.
Beet Ring Mottle
On sugar beet and spinach; stunting, distortion,
mottling; transmission by aphids.
Beet Necrotic Yellow Vein
Tobamovirus
On sugar beet and transmitted by soil-borne fun-
gus
Polymyxa betae
.
Beet Pseudo-Yellows Closterovirus
Yellowing of sugar beet, carrot, spinach,
cucumber, lettuce, and ornamentals; transmission
by greenhouse whitefly.
Beet Savoy
Leaves are dwarfed, curled down, with small
veins thickened; roots have phloem necrosis.
A plant bug (
Piesma cinerea
) is the vector.
