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Powdery mildew is an annual problem in fall grown cucurbit crops. Labeled fungicides usually provide acceptable disease control when applied on a 7 to 10-day frequency. But the fungus has developed resistance to several fungicides. 

And that can cause problems.

To address this, several new cultivars of pumpkin and squash with tolerance to powdery mildew were evaluated in recent trials at the Plateau Experiment Station in Crossville, Tennessee. 

In the pumpkin trial, Magic Lantern from Harris Moran, fared well, and is an excellent powdery mildew tolerant pumpkin. One acre of Magic Lantern was grown near the disease tolerant squash trial in 1999, and only a few plants developed mild symptoms of powdery mildew. The acre produced well and the fruit had excellent appearance.

The squash trial evaluated selected Harris Moran squash breeding lines for tolerance to powdery mildew. These were compared to Dixie, a yellow summer crookneck type cultivar from Asgrow Seed Co. Dixie is highly susceptible to powdery mildew. 

Selected lines were Zucchini Elite, 
SSXP 788, SSXP 789, SSXP 793, SSXP 848, SSXP 850 (all Zucchini type), and HMX 9736 (acorn type). 

Crops were grown on land that was used to produce a spring crop of greens collard, kale, mustard, spinach, and turnip. Following harvest, the site was tilled on July 20 with an offset harrow. 

Fertilizer was broadcast at 300 lbs. of 10-10-10 per acre and the site was disked twice. Squash lines were direct seeded on July 21.

Rows were 38 inches apart and 64 ft. long. Hills of 2 plants were spaced 4 ft. apart in the row. The plot was cultivated on August 3. Asana was sprayed at 0.05 lb. Ai/A on August 3 for insect control.

Squash fruit were harvested as they matured to keep the plants in a growing condition. No yields were recorded.

Observations on disease severity were made throughout the season, and disease ratings were made on October 5. Disease ratings were on a scale of 1 to 10 with 1 being no visible disease symptoms and 10 being complete defoliation.

Only three hills of SSXP 850 were produced but all the other squash lines produced a good stand. Mocrodochium blight was not observed on plants of any line.

Powdery mildew was observed about midseason on the leaf petioles of Zucchini Elite and developed on the leaf blades by the end of the season. Dixie and Zucchini Elite were the most susceptible lines, and HMX 9736 was intermediate in susceptibility. Lines SSXP 786, SSXP 788, SSXP 789, SSXP 793, and SSXP 848 developed little or no powdery mildew symptoms.

Plants of line SSXP 850 showed no evidence of downy mildew but there were few plants of this line.

All Zucchini type cultivars produced nice light green fruit. Line HMX 9736 produced attractive dark green acorn shaped fruit. 

Fruit color was highly acceptable for acorn squash.  Fruit size was relatively small and plants were very compact.

The fall season was relatively dry after the trial was planted, and may account for the small plants and fruit.

Most plants of the numbered lines were compact, and plants, especially of SSXP 786, SSXP 788, SSXP 850 had a very distinctive cut leaf pattern.

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