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2022, Issue 2

Cool and Wet

The weather over the past week has been rainy. This wet weather causes leaf wetness on cantaloupe and watermelon. However, leaf wetness is only part of what is needed for disease development on these 2 crops. The three diseases that MELCAST was developed to manage (Alternaria leaf blight, anthracnose and gummy stem blight) require leaf wetness at the appropriate temperatures. For the most part, the wet weather we have had over the past week has been at times when the temperatures are too cool for disease development. 

The column on the right of the table below shows the estimated spray interval based on a week of data. Only Merom Station and Oaktown in the cantaloupe (muskmelon) table show any estimated intervals less than 14 days. It is significant that the only MELCAST sites with less than 14-day intervals are in the cantaloupe table. The cantaloupe model requires cooler temperatures than the watermelon model since the former takes into account the cooler temperatures required for Alternaria leaf blight (which affects cantaloupe more than watermelon). Although none of the watermelon sites show MELCAST values less than 14, there has been some accumulation of MELCAST values. For example, the Oaktown site accumulated 6 values from 5-18 to 5-19. However, all the watermelon sites show 14 days based on the last 7 days of data. Remember to base your MELCAST calculations on the last date sprayed on your field(s).

Little disease has been observed on any cucurbits in the field to date. However, striped cucumber beetles have been observed in southern Indiana. An article by Laura Ingwell and myself that discuses cucumber beetle management was published in the last issue of the Vegetable Crops Hotline and can be found here. An excerpt from this article can be found below:

The take-home message? In areas with high beetle pressure, cucumbers and cantaloupe may require pesticide applications to prevent the transmission of bacterial wilt. A systemic compound applied at the low rate is a good choice. Pumpkins and watermelon, which do not become infected with the bacterial wilt, can be protected with a foliar application of a pyrethroid or acetamiprid.

Cantaloupe Slices

Watermelon Slices

EFI Values for
Cantaloupe EFI Watermelon EFI Total Precip High Temp Total GDD Cantaloupe Spray Interval (in days) Watermelon Spray Interval (in days)
05-23 34 (0) 31 (0) 24.11 69 857 14.0 14.0
05-22 34 (1) 31 (1) 24.11 66 846 14.0 14.0
05-21 33 (1) 30 (2) 23.85 84 834 14.0 14.0
05-20 32 (0) 28 (1) 23.24 89 811 14.0 14.0
05-19 32 (3) 27 (5) 22.58 83 784 14.0 14.0
05-18 29 (0) 22 (1) 21.6 76 761 14.0 14.0
05-17 29 (0) 21 (0) 21.09 85 741 14.0 14.0
* GDD and Precip data begins on January 1, 2022
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Department of Botany and Plant Pathology at Purdue University Administration
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