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How to Manage Pests

UC Pest Management Guidelines

| More pests | More crops | About guidelines |

Cucurbits

Anthracnose

Pathogen: Colletotrichum lagenarium

(Reviewed 11/05, updated 6/08)

In this Guideline:

SYMPTOMS

In California, anthracnose is unusual on cucurbit crops other than seedless watermelon. It can cause leaf, fruit, and/or stem lesions. Foliage lesions are tan to brown except on watermelon foliage where they are dark brown to black. Fruit may develop brown to black, sunken, water-soaked spots. Tiny, black fruiting structures, called acervuli, form within the lesion. In wet weather, pink or orange spores ooze from these fruiting bodies.

COMMENTS ON THE DISEASE

The fungus overwinters on cucurbit plant residue in the soil, on volunteer cucurbits, or on cucurbit seed. Disease development is favored by warm, wet weather. This disease is rarely seen in the field and more often occurs on transplants raised in the greenhouse.

MANAGEMENT

There is resistance in some varieties of watermelon and cucumber, but not in seedless watermelon. Control tactics include crop rotation, use of clean seed, and inspection of transplants. Avoid sprinkler irrigation and keep the tops of the beds dry. Fungicides are rarely needed in California but may be required on seedless watermelons at the first sign of disease.

Common name Amount/Acre R.E.I.+ P.H.I.+
(trade name)   (hours) (days)
A. CHLOROTHALONIL
  (Bravo Ultrex, etc.) 1.4–1.8 lb 12 0
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M5)
  COMMENTS: Do not apply more than 19.1 lb/acre/season.
 
B. MANCOZEB
  (Dithane DF) 1–2 lb 24 5
  (Dithane F-45) 0.8–1.6 qt 24 5
  (Dithane M-45) 1–2 lb 24 5
  (Penncozeb) 75DF Label rates 24 5
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M3)
  COMMENTS: Labeled for cucumbers, melons, watermelon, and summer squash only.
 
C. MANEB
  (Maneb 75 DF) 1.5–2 lb 24 5
  (Maneb 80) 1.5–2 lb 24 5
  (Manex) 1.2–1.6 qt 24 5
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M3)
 
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
1 Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions (for more information, see http://www.frac.info/). Fungicides with a different group number are suitable to alternate in a resistance management program. In California, make no more than one application of fungicides with mode of action Group numbers 1, 4, 9, 11, or 17 before rotating to a fungicide with a different mode of action Group number; for fungicides with other Group numbers, make no more than two consecutive applications before rotating to fungicide with a different mode of action Group number.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Cucurbits
UC ANR Publication 3445
Diseases
R. M. Davis, Plant Pathology, UC Davis
T. A. Turini, UC Cooperative Extension, Imperial County
B. J. Aegerter, UC Cooperative Extension, San Joaquin County
W. D. Gubler, Plant Pathology, UC Davis
J. J. Stapleton, UC IPM Program, Kearney Agricultural Center, Parlier

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