General info........
INSECTS
The insects common to cucurbits are aphids, cucumber beetle,
pickleworm, leafhopper and spider
mites. In addition stem bores and squash bugs often cause substantial
losses. The main insects to be
concerned with are squash bugs and stem borers and three types of
cucumber beetles.
Banded cucumber beetle: light green bug with 3 black stripes
Spotted cucumber beetle: greenish-yellow with 12 irregular black
spots on back
Striped cucumber beetle: these are yellow with 3 black stripes
The adult squash bug is brownish-black, flat backed, 5/8 inch long,
and lays its eggs on the
underside of leaves, usually in rows at a right angle. When the eggs
hatch, brightly colored nymphs
appear which then proceed to feed on the plant sap. Squash bugs can kill
small plants and can cause
leaves to wilt and die.
Squash vine borers can be very destructive. The first symptom to
look for is wilting of the vine. The
squash vine borer is wasp like with copper-green fore wing and
reddish-orange, black abdomens. The
insect over winters in the soil as a larva or pupa. The borer burrows
into a stem, then hollows it out,
leaving a slimy frass. After over wintering it emerges as a moth (wasp
like).
The moth lays eggs on the basal portion of the stem, and in 1 to 2
weeks borers emerge and
penetrate the stem. Control is difficult, but sprays applied during egg
laying and hatching are
recommended.
Pickleworms infect the fruit, stem, and leaves. They are
yellowish-brown on the wings and have
hair-like scales on their abdomen.
Other pests that might be a problem include flea beetles, melon leaf
hopper, leafminer, thrips, and
cutworms. In addition to feeding damage, cucumber beetles spread virus
and bacterial wilt, while leaf
hopper transmits curly top virus.
Sanitation, good cultural practices and crop rotation will all aid
in insect control.
DISEASES
Angular leaf spot Causal organism: Pseudomonas lachrymans Carsner.
The bacteria is a rod with
1-5 polar flagella, forming capsules and green fluorescent pigment in
culture. Circular, smooth,
glistening, transparent, white colonies form on beef peptone agar.
Symptom: The disease appears on leaves, stems, and fruits as small
water soaked spots. On leaves
they enlarge up to about 3 mm in diameter, becoming tan on the upper
surface and gummy or shiny
on the lower surface and assuming an angular shape as the lesion in
delimited by veins. The necrotic
centers of leaf spots may drop out. On stems, petioles and fruits, the
water soaked spots are covered
with a white crusty bacterial exudates. As fruits begin to mature, brown
lesions in the fleshy tissue
beneath the rind develop, and the discoloration continues along the
vascular system which extends to
the seeds.
Bacterial Wilt Causal organism: Erwinia tracheiphila Holland. The
bacteria is a motile rod with 4
to 8 peritrichous flagella. Capsules are formed. Agar colonies are
internally resticulated, small, and
circular, smooth, glistening, white and viscid.
Symptoms: The first signs of wilt usually appear on individual
leaves as dark green patches which
become flaccid in sunny weather. As the disease progresses, more leaves
wilt and eventually an entire
branch is affected. The wilting then becomes permanent, and the leaves
and vines shrivel and die.
Occasionally an exudate on fruit is visible. When wilted stems are
cross-sectioned, the viscid, sticky
bacterial matrix exudes from the bundles and may be drawn out in strands
of 1 inch or more. This
feature is used as a means of diagnosis. Disease over winters in the
bodies of adult cucumber beetles.
Blossom Blight Causal organism: Choanephora cucurbitarum Thaxt. A
member of the family
Choanephoraceae of the Phycomycetes. The fungus produces both conidia
and sporangia spores.
Symptoms: The disease is of importance as a fruit rot of squash and
has been observed on other
cucurbits. The disease starts as a blossom blight. As the blossoms fade
after opening, they are
covered with a white, dense growth of the fungus, consisting chiefly of
immature conidiophores. The
conidial heads develop promptly, becoming purple-black at maturity. The
organism invades young
fruit and causes them to decay and die. In larger fruit a rapid, soft,
watery rot occurs, the tissue
becomes covered with sporgangia. The damage is chiefly on fruit in the
field.
Scab Causal organism: Cladosporium cucumelinum A fungal pathogen.
The mycellum is septate,
branching, hyaline when young turning greenish to black with age.
Conidia are oblong, colored,
mostly continuous, some one-septate.
Symptoms: Appears in midsummer on leaves as small, roughly circular
to angular spots which are
water soaked, brownish and sometimes covered with exudates. Under
continuous high humidity,
sporulation occurs on the surface in the form of an olivacous mold. The
greatest damage is to the
fruit. Early in development of the fruit spot, a gummy brown exudate
appears on the surface, and the
crater-like spot grows, the surface tissue sinks, and the exudates may
dry down in the form of large
brown bead. When the fruits are infected after they reach full size, the
host reacts by corking out the
infected portion and forming a tan, shallow, scab.
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