Bacterial Diseases
Bacterial Wilt
ID: Erwinia tracheiphila is the bacterium responsible for bacterial
wilt and replicates only in the xylem; wilt appears initially on leaves and
then on one or more runners on a plant; look for vascular browning in the
xylem by cutting at the grown level (crown of plant) (visible to the naked
eye)
Cultural Practices: Beetles will aggregate on preferred varieties
(due to cucurbitacins levels); this feature makes use of a susceptible variety
as a trap crop.
Chemical Control: Imidacloprid (Admire) is the preferred material
for striped beetle control, but others are registered.
Angular Leaf Spot
ID: Pseudomonas syringae pv. lachrymans Young spots
are water-soaked and older spots may have holes in center; spots are usually
limited by the main veins of leaves; circular water-soaked and then sunken
spots appear on fruit. (both visible to the naked eye)
Cultural Practices: Use pathogen-free seed and rotate out of cucurbits
for 2 years.
Chemical Control: Use copper or a mixture of copper (Group M1)
plus maneb (Group M3); discontinue sprays during extended rain-free
periods.
Oomycete Diseases
Phytophthora Blight
ID: Phytophthora capsici The blight phase starts in lower areas
of fields with saturated soils; yeast-like growth may start on underside of
fruit and spread to topside; (visible with the naked eye).
Cultural Practices: Management is critical; organism survives
in the soil for many seasons; rotate at least 3 years out of susceptible crops
(pepper, tomato, all cucurbits); avoid planting in fields with a history of
standing water; provide adequate drainage by sub-soiling and disking in spray
alleys during the season; provide means for water to exist fields away from
surrounding susceptible crops.
Chemical Control: Acrobat (Group 15) tank mixed with a protectant
fungicide labeled for the cucurbit of interest (chlorothalonil, maneb or mancozeb,
Groups M5 and M3) may provide some suppression of the disease.
Downy Mildew
ID: Pseudoperonospora cubensis Chlorotic spots appear on the
upper leaf surface and purplish or gray spores form on these spots on the
lower leaf surface. (visible with a hand lens)
Cultural Practices: None available; use the downy mildew forecast
web site from the North Carolina State University http://www.ces.ncsu.edu/depts/pp/cucurbit/
to monitor movement.
Chemical Control: Consider using Acrobat (Group 13) tank mixed
with a protectant labeled for the cucurbit of interest (chlorothalonil, maneb
or mancozeb, Groups M5, and M3) and alternated with Ridomil
Gold Bravo or Ridomil Gold Copper (Group 4) or Gavel (Group 22)
(only labeled on C, M SS, W) and use Bravo and maneb in alternate weeks; or
consider Aliette (Group 33) or Phostrol or ProPhyt (Group 33),
combined or alternated with a protectant fungicide.
Fungal Diseases
Powdery Mildew
ID: Podosphaera xanthii (formerly Sphaerotheca fuliginea)
and Erysiphe cichoracearum Produces white powdery colonies on upper
and lower leaf surfaces, on stems and petioles. (visible with the naked eye)
Cultural Practices: Choose PM tolerant varieties for cucurbit of interest
if available.
Chemical Control: Management of chemicals use for control is critical;
refer to Table 1 and make sure to tank mix protectant fungicides
(Group M5, M3, M1 or other chemicals (chlorothalonil, maneb, mancozeb,
copper, oil, sulfur, etc.) with a strobilurin (Group 11); or with demethylation
inhibitors (Group 3) or thiophanate-methyl (Group 1) and follow
alternation protocol. If resistance to Quadris occurs in the area, you
must use a fungicide from different fungicide group.
Gummy Stem Blight and Black Rot
ID: Didymella bryoniae Leaf symptoms are infrequent unless
plants are infected during a wet growing season; lesions if they develop are
circular and may have black pepper-like specks which are pycnidia; pycnidia
also occur on lower stems and on fruit; fruit lesions may be water soaked
and purplish in color before turning black; field infections often appear
as a dry"petrified wood" beige semi-circular lesion with pycnidia.
(visible with naked eye)
Cultural Practices: Use fungicide-treated seed, as organism is seedborne;
rotate two years out of all cucurbits.
Chemical Control: Bravo (Group 5) used alone or combined with
Topsin M (Group 1) will reduce chance for resistance from developing.
White Mold
ID: Sclerotinia sclerotiorum Look for white, cottony growth
on stems and especially fruit; raisin-shaped black sclerotia appear within
this growth. (visible with naked eye)
Cultural Practices: Rotate 3 or more years out of susceptible crops,
choosing crops like sweet corn and grass cover crops.
Chemical Control: For farms with short rotations, consider the biological
product Contans for incorporation into the soil prior to planting.
Fusarium Crown and Fruit Rot
ID: Fusarium solani f. sp. cucurbitae Crown of plant
may be girdled and the dark brown decayed area covered with white or pinkish
colored fungal mycelium; tan or white circular lesions appear on side of fruit
touching the ground. (visible to naked eye)
Cultural Practices: A soilborne fungus that survives in the soil for
at least 2 years; rotation out of cucurbits for 3 years.
Chemical Control: None available
Plectosporium Blight (formerly Microdochium Blight)
ID: Plectosporium tabacinum (previously Fusarium tabacinum)
Light tan lesions that are spindle shaped develop on the underside of the
leaf, which may lead to leaf distortion; spindle shaped lesions also appear
on stems, petioles and fruit stems and also on fruit shoulders, where it appears
a white, tan or silver russeting. (visible to the naked eye)
Cultural Practices: A soilborne pathogen recently introduced into
Massachusetts and Connecticut, which in a moist season can result in considerable
loses for pumpkin and summer squash. The fungus prefers a depth of 2-4
inches; use of a no-till cover crop can reduce disease levels compared to
bare ground culture.
Chemical Control: The protectant fungicide chlorothalonil (Bravo)
(Group M5) should be included in the spray program when fruit begin
to set.
Alternaria Leaf Spot or Blight
ID: Alternaria cucumerina Lesions first appear on the older
crown leaves as circular brown spots; as lesions expand they develop concentric
rings; more common on muskmelon than pumpkin or winter and summer squash.
(visible to the naked eye)
Cultural Practices: Follow a 2-year rotation out of all cucurbits.
Chemical Control: Can be controlled with most protectant fungicides
(Groups M5, M3 and M1) and used in alternation with strobilurins (Group
11) fungicides.
Anthracnose
ID: Colletotrichum orbiculare More likely to occur on muskmelon,
watermelon and cucumber. Appears as tan or brown oval lesions on upper
leaf surface; raised acervuli (often salmon-colored) with hair-like setae
(whiskers); lesions with fruiting bodies will also appear on fruit. (visible
with a hand lens)
Cultural Practices: Use disease-free seed; follow a 2-year rotation
out of cucurbits. Be mindful under moist conditions and high humidity
for 24 hrs.
Chemical Control: Apply Bravo (Group M5) alone or in combination
with Topsin M (Group 1) in alternation with Group 11 fungicides
(Quadris and Cabrio). If resistance to Quadris occurs in the area, you
must use a fungicide from different fungicide group.
Septoria Leaf Spot
ID: Septoria cucurbitacearum Initially appears as very small
water-soaked spots which turn beige or white in color; pycnidia (small black-pepper-like
spots) appear inside the leaf and stem lesions; raised rash-like white spots
also appear on fruit of pumpkin and winter squash. (visible with naked eye
or hand lens)
Cultural Practices: Following a 2-year rotation will eliminate most
disease carryover. Requires cool temperatures and summer rains to spread
to fruit.
Chemical Control: Disease is controlled with a good fungicide program
that includes Bravo (Group M5).
Scab
ID: Cladosporium cucumerinum Young lesions are water soaked
but when older turn tan with a yellow halo and eventually crack and fall out;
fruit lesions vary as cavity or erumpent lesions on fleshy fruit (summer squash)
or sunken dry and corky lesions on hard fruit (pumpkins and winter squash.
(visible to the naked eye)
Cultural Practices: Use disease-free seed; follow a crop rotation
out of cucurbits for 2 years.
Chemical Control: Control is achieved with protectant fungicides like
Bravo (Group M5) and is especially needed during cool and wet springs
and summers.
References
1. Compendium of Cucurbit Diseases. 1996. Ed. T. A. Zitter, D. L. Hopkins,
and C. E. Thomas. APS Press, St. Paul, MN. 87pp.
2. Pumpkin Production Guide. 2003. Ed. D. Riggs, NRAES, Ithaca, NY.
152pp.
3. Vegetable MD online web site: http://vegetablemdonline.ppath.cornell.edu
for selected fact sheets, news articles (ie. Occurrence of Strobilurin Resistance
and Impact on Managing Powdery mildew of Cucurbits), and images.
4. Fungicide Resistance Action Committee site for Fungicide Groups
used in this paper. http://www.frac.info/publications/FRACCODE_sept2002.pdf
