Disease Tolerance of Zucchini and Yellow Squash Varieties

Varieties to Choose for Late Season Production

In 1997 a screening of experimental (not released) summer squash varieties was completed and showed differences in disease levels among the two named varieties used as controls in the trial. These results prompted a 1998 experiment to evaluate common named summer squash varieties to determine disease levels among varieties being grown in New Jersey. Seven zucchini varieties and nine straight neck yellow varieties were chosen for the study. The experiment included three replications with 16 treatments (varieties). Zucchini and yellow varieties were kept separate for evaluation purposes. Varieties were checked for three primary diseases affecting late season summer squash plantings. The three diseases were powdery mildew, Phytophthora crown rot, and viruses. Two additional yellow squash varieties were planted for observation.

On August 11, 1998 summer squash was hand seeded at a spacing of 30” between plants with two seeds per hole at a grower’s field in Swedesboro, New Jersey. Raised beds at a spacing of 5’ centers with drip irrigation and black plastic mulch were used. Command ME (clomazone) and Paraquat (gramoxone) were applied preplant for weed control between rows. Two applications of Thiodan (endosulfan) were applied to control cucumber beetle. No fungicides were applied. Plants were thinned to one plant per hole on August 20 and missing plants were reseeded to establish a 100% stand. Harvests were done weekly to remove fruit from plants to stimulate vegetative growth. The site chosen in 1998 was the exact site used in 1997. The field has been planted for many years in cucurbit and solanaceous crops that were infected with Phytophthora capsici.

A virus rating to record the number of plants per treatment showing virus symptoms on fruit and foliage was done on September 18. Powdery mildew ratings were taken on October 19 using a 0-10 scale (0=no symptoms; 10=severe symptoms). Also on this date, plants were evaluated for incidence of Phytophthora crown rot by counting the number of infected plants per treatment. A final virus rating was also recorded by rating treatments on a scale of 0-5 (0=no symptoms; 5=severe symptoms). See Table 1 and Table 2 for evaluation results.

There were no statistical differences among zucchini varieties for powdery mildew and Phytophthora crown rot levels. However, there were significant differences with respect to virus levels. The varieties ‘Spineless Beauty’ and ‘Zucchini Elite’ showed the highest initial virus symptoms. ‘Spineless Beauty’, ‘Zucchini Elite’, ‘Independence II’, ‘HMX6704’, ‘Tigress’, and ‘Revenue’ showed significantly higher virus symptoms one week after the last harvest. All varieties showed some viral symptoms after harvests were completed. The important factor is the lack of virus symptoms on fruit during the harvest period. The varieties ‘Dividend’, ‘Revenue’, and ‘Tigress’ showed the least virus during the harvest period.

Yellow squash varieties also did not show significant differences with respect to Phytophthora crown rot levels. There were significant differences in powdery mildew levels. The varieties ‘Sunglo’, ‘General Patton’, and ‘PX41092’ exhibited lowest levels of powdery mildew. ‘Superpik’, ‘Multipik’, ‘Monet’, and ‘Seneca Supreme’, showed the highest levels of powdery mildew. Initial virus levels were highest in the varieties ‘Sunglo’ and ‘PX41092’. Therefore, even though these two varieties were semi-tolerant to powdery mildew, they both had high levels of virus at the first harvest, making fruit unmarketable. All other yellow varieties held up well with respect to virus infection during the early harvest period. At the last virus evaluation all varieties exhibited virus symptoms and there were no significant differences between varieties. When considering low powdery mildew levels and low initial virus symptoms, the variety ‘General Patton’ stands out from these results. Additionally, the experimental varieties ‘PX47592’ and ‘PX50592’ were planted for observation only. These two varieties showed no symptoms of powdery mildew during the harvest period and minimal symptoms just before frost. However, these two varieties showed high levels of viral symptoms during the first harvest.

Table 1. Zucchini disease ratings

 Variety

 Seed Company

 Powdery Mildew Level 1

 Phytophthora Crown Rot 2

  Initial Virus Numbers3

 Final Virus Rating4

 Spineless Beauty  Rogers

9.5

0.0

4.0 a

3.7 a

 Revenue  Rogers

9.3

0.0

0.0 b

1.7 abc

 Dividend  Rogers

9.5

0.0

0.0 b

1.0 bc

 Zucchini Elite  Harris Moran

8.5

0.3

5.7 a

3.3 a

 Tigress  Harris Moran

8.7

0.7

0.0 b

2.0 ab

 HMX6704  Harris Moran

8.3

0.0

0.0 b

2.7 a

 Independence II  Asgrow

8.8

0.3

0.0 b

3.3 a

 LSD(0.05)  

NS

NS

*

*

 
1Powdery mildew levels evaluated on a 0-10 scale with 0=no symptoms and I 0=severe symptoms.
2Phytophthora crown rot ratings based on number of plants per 10 plants in a treatment in a replication.
3lnitial virus numbers based on number of plants per 10 plants in a treatment in a replication
4 Final virus rating evaluated on a 0-5 scale with 0=no symptoms and 5=severe symptoms

 

 Table 2. Yellow squash disease ratings.

 Variety

 Seed Company

 Powdery Mildew Level 1

 Phytophthora Crown Rot 2

  Initial Virus Numbers3

 Final Virus Rating4

Multipik  Harris Moran

9.3 a

0.0

0.0 b

3.0

HMX7705  Harris Moran

9.2 b

1.7

0.0 b

0.3

Monet  Harris Moran

9.3 a

2.7

0.3 b

3.7

Fortune  Rogers

9.2 b

0.3

0.0 b

3.0

Sunglo  Rogers

8.3 c

3.0

7.0 a

4.0

General Patton  Asgrow

8.2 c

2.7

0.0 b

3.7

Seneca Supreme  Johnny’s

9.3 a

2.0

0.0 b

3.3

Superpik  Harris Moran

9.5 a

3.0

0.3 b

3.3

PX41092  Seminis

7.0 c

3.7

7.7 a

4.0

 LSD (0.05)  

*

NS

*

NS

 
1Powdery mildew levels evaluated on a 0-10 scale with 0=no symptoms and 1 0=severe symptoms.
2Phytophthora crown rot ratings based on number of plants per 10 plants in a treatment in a replication.
3Initial virus numbers based on number of plants per 10 plants in a treatment in a replication.
4Final virus rating evaluated on a 0-5 scale with 0=no symptoms and 5=severe symptoms.

By:Michelle L. Infante, Agricultural Agent, Rutgers Cooperative Extension of Gloucester County
Stephen A. Johnston, Pathologist, Rutgers Agriculture Research and Extension Center
Stephen A. Garrison,Vegetable Specialist, Rutgers Agriculture Research and Extension Center

Originally published: Proceedings. 1999. New England Vegetable & Berry Growers Conference and Trade Show. Sturbridge, MA.

Reviewed by: T. Jude Boucher, IPM, University of Connecticut. 2012

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