Cantaloupe Diseases on Foliage

Anthony P. Keinath

Research and Extension Vegetable Pathologist, Clemson University

Depending on the weather, four foliar diseases can commonly be found on cantaloupe (muskmelon) in South Carolina.  Correctly identifying a disease is the first step in selecting the best control measure.  Symptoms of the diseases and signs of the pathogens are useful in deciding which disease is present on a sample.  Gummy stem blight is the disease found most commonly, but Alternaria leaf blight can be confused with it.  See the first chart below to compare diagnostic symptoms of these two diseases.  Two different mildews, downy mildew and powdery mildew, also affect cantaloupe.  See the middle chart  for symptoms and signs of mildews.  Control measures are presented at the bottom of the page.
 
Gummy stem blight on cantaloupe leaves
Gummy stem blight on cantaloupe stems

 
Alternaria leaf blight on cantaloupe leaves
Downy mildew on cantaloupe leaves

 
Symptom Gummy stem blight Alternaria leaf blight
Size (diameter) of individual leaf spots 1/2 to 1 inch 1/4 to 3/4 inch
Color of leaf spots Brown Yellow (early), then brown with dark rings and yellow haloes
Shape of leaf spots Round, or triangular at leaf edge Round or oval, scattered over the leaf
Vine cankers Bleached or tan sections on main vines None
Stem canker Tan or reddish brown sunken or swollen area at soil line None
Fruit rot Round, sunken spots, especially on Western types Usually none

 
Symptoms and Signs Downy mildew Powdery mildew*
Color of leaf spots (early stage) Yellow or pale green Yellow, pale green, or  a white, powdery mold
Shape of leaf spots (early stage) Irregular or angular Round or angular
Leaf blight 
(late stage)		 Tan or brown dead leaf tissue, looks like “burn” Pale yellow or brown, leaves covered with white, powdery mold
Fungus growth Only on bottom of leaves On bottom and top of leaves
Color of fungus Purple or grayish or white White
*Most hybrid cultivars are resistant to the common race 1 of powdery mildew.
 
 

Controls

Details about fungicides are available in the Southeastern U.S. 2007 Vegetable Crop Handbook.

Gummy stem blight and Alternaria leaf blight usually can be controlled with the protectant fungicides mancozeb, maneb, or chlorothalonil (Echo or Bravo). Because the fungus that causes gummy stem blight has become resistant to strobilurins, use Pristine alternated with protectants if disease is severe. Even though Pristine contains a strobilurin, the combination of two active ingredients controls both strobilurin-sensitive and strobilurin-resistant gummy stem blight fungi.

The strobilurins Amistar, Cabrio, and Pristine, which are both protectant and systemic (eradicant), will control Alternaria leaf blight.  Always rotate a protectant fungicide with a strobilurin.

Rotate out of fields with severe gummy stem blight and Alternaria leaf blight for 2 years.  This will allow the crop residue infested with the disease-causing fungi to decay so they will not carry over in the soil.

Downy mildew is a disease that blows into South Carolina from fields farther south about May 15 each year. To prevent an outbreak of downy mildew, spray chlorothalonil (Echo or Bravo) starting in early May. To see when downy mildew is predicted to arrive in South Carolina, check the Curcurbit Downy Mildew Forecast Homepage. During an epidemic of downy mildew, systemic fungicides will be needed to manage spread. Use Previcur Flex plus a protectant alternated with Tanos plus a protectant to get the best control.

Powdery mildew is not a serious threat to cantaloupe because of resistance to the common race 1 in new hybrid cultivars.  If race 2 powdery mildew is present, apply Quintec alternated with chlorothalonil.

For more information about how to control cantaloupe diseases, contact Dr. Anthony P. Keinath.

This page was created March 27, 2000.  It was last updated May 30, 2007 .

Please report any problems or questions with this webpage to the webmanager.