University of Maryland Extension

Frequently Asked Questions

General Questions

Melcast - Watermelon

Melcast – Muskmelon (Cantaloupe)

TOMCAST - Processing tomato disease forecaster


General Questions:

Calendar fungicide applications (every 7, 10 or 14 days) have been the most common method of managing foliar diseases in Maryland for many years. Several weather-based fungicide application models have been developed which are based on environmental conditions which favor pathogen infection and disease development. Use of a weather-based model allows growers to apply fungicides at the time when they are most needed. Several of these models have been tested in the mid-Atlantic region. These models have performed well and resulted in reductions in the number of fungicide applications in both research station and on-farm trials and in grower use.

How does a weather-based model work?

A model is developed by determining the effect of weather (primarily temperature and the duration of leaf wetness) on development of disease. This relationship is used to advise growers on favorability of local weather conditions to disease development. Growers can schedule sprays to coincide with conditions that favor development of disease, and reduce sprays when weather is not favorable.

What models are available at this web site?
  • Melcast Watermelon model
  • Melcast Muskmelon (cantaloupe) model
  • TOMCAST Processing Tomato model
What diseases are forecast?
  • Melcast Watermelon - gummy stem blight and anthracnose
  • Melcast Muskmelon -Alternaria leaf blight
  • TOMCAST -early blight, septoria leaf spot, anthracnose
Have these models been tested in Maryland?

The watermelon and tomato models have been tested extensively in the mid-Atlantic region. The muskmelon model has not yet been tested here. Melcast (the melon forecast system) has been tested on watermelons in Maryland and Delaware. TOMCAST has been used commercially and has been provided to growers in PA and NJ through CES automated phone lines.


Melcast - Watermelon

What diseases does this model help in forecasting?

Gummy Stem Blight and Anthracnose

Are these the only foliar diseases that I need to worry about in my watermelons?

Gummy stem is the most important foliar disease in watermelon. It causes more yield loss in Maryland than other foliar diseases. Anthracnose can cause damage to fruit making it unsalable. Alternaria leaf blight was present on watermelon in some areas of the state in 1999. However damage to foliage was generally not severe enough to cause yield loss. However, you should still scout the field regularly and watch for other serious diseases of watermelon.

What other diseases may occur?

Scheduling fungicide sprays according to Melcast-Watermelon will control diseases in most situations. However, in some years and fields other serious diseases occur. Therefore scout fields being sprayed using the Melcast model. Look for bacterial fruit blotch and downy mildew. If these diseases are present additional disease control measures are warranted (see Extension Bulletin 236).


Melcast – Muskmelon (Cantaloupe)

What diseases does this model help in forecasting?

Alternaria leaf blight

Is this the only foliar disease that I need to worry about in my muskmelons?
  • Melcast should only be used if you have planted a powdery mildew resistant variety such as Athena.
  • Alternaria is the most important disease of muskmelon in our area. However, melons are susceptible to other diseases. You should still scout the field regularly and watch for other serious diseases of muskmelon.
What other diseases may occur?

Scheduling fungicide sprays according to Melcast-Muskmelon will control diseases in most situations. Although generally not as important, gummy stem blight and anthracnose can occur and cause losses. Scout fields and if these diseases are evident, resume a calendar spray program. Downy mildew may occur in mid to late summer. If you observe downy mildew additional disease control measures are warranted (see Extension Bulletin 236).


TOMCAST - Processing tomato disease forecaster

What diseases does this model help in forecasting?

TOMCAST forecasts sprays for early blight, septoria, leaf spot and fruit anthracnose on tomato.

How does TOMCAST work?

It is based on the average temperature during the hours when the foliage is wet. When the temperature is favorable for pathogen growth and the leaves are wet for a period of time, TOMCAST will accumulate DSV’s (disease severity values).

Are these the only foliar diseases I need to worry about?

These three diseases are the primary yield limiting foliar diseases of processing tomato in our area. However, tomatoes are susceptible to other diseases. You should still scout the field regularly and watch for other diseases of tomato.

What other diseases may occur?
  • Scheduling fungicide sprays according to TOMCAST will control foliar diseases of processing tomato in most situations.
  • Late blight (caused by Phytophthora infestans) occurs in some years in our area. If you observe late blight, additional disease control measures are warranted. Refer to Extension Bulletin 236 or additional fungicides for control of late blight may be available through a special exemption from the EPA. Contact a county extension educator for more information.
  • Fruit rot (Pythium or Phytophthora Buckeye Rot) may also be a problem in some fields. If these fruit rots are observed additional fungicide applications are warranted (see Extension Bulletin 236).
Maintained by the IET Department of the College of Agriculture and Natural Resources. © 2017. Web Accessibility